Re: [RE-wrenches] discharging Rolls batteries

[Hugh]

OK I have been studying the literature list given me by Joel.  I did 
study all of this theory stuff back in the 1970s when I first got 
into this stand-alone windpower stuff, but it was good to go over it 
again, especially with my new enquiry.


I also have three fairly clear personal answers to my question "Is 
there an actual loss of amphours in cold weather or is the battery 
just not so good at delivering?"  The following answers indicate that 
the amphours are still there, but the loss of performance results in 
a loss of voltage that makes the battery appear to be discharged 
prematurely.



At 15:12 -0400 14/1/10, James Surrette wrote:


Regarding temperature effects on capacity, earlier responses are 
spot on as the lower capacity is totally as a result of slower 
reaction times as a result of lower temperatures.  



At 22:58 +1300 16/1/10, Bruce Geddes wrote:
 to use your analogy of the bank, in cold weather the money counters 
operate more slowly and if the temperature rises they return to 
normal speed.  The money is still there, it is just the rate at 
which it comes out that varies.


At 09:46 -0800 16/1/10, Darryl Thayer wrote:

Now for Discharge: .  The amp-hrs are there but the watt-hrs are not.



OK so if the battery is not actually discharged but is operating at a 
lower voltage due to lower temperature, then it seems to make sense 
to use a lower cut-off voltage.  And people who fly their systems by 
the SOC meter alone will not even be aware of the voltage, and will 
not care that it drops below the normal range.  So I think I now have 
the answer I was looking for there.  Low battery threshold voltages 
should be temperature compensated (although in the opposite direction 
to charging 'bulk' or 'absorption' set-points).


I don't know if anyone is in the mood to take this battery study 
further?  I'd like to talk about Peukert's Law next.  It has some 
similarities.


According to Peukert's law (and manufacturers' data bears this out 
well) the capacity of a battery depends on the rate of discharge. 
Everyone who knows anything about batteries knows that the capacity 
is specified at a certain rate whether it be C20 for a 20 hour 
discharge or whatever.  And the capacity at 100 hours (C100) is about 
33% higher than the capacity at the 20 hour rate.  If you look at the 
way this is measured though, it is based on running the battery down 
to a chosen 'discharge limit' voltage.  And I have not heard anything 
from Wrenches nor seen anything in the literature to suggest that the 
battery discharged in 20 hours has actually lost any amphours 
compared to the 100 hours one.  So it appears to me that if you give 
it a rest and then start discharging it again, but now at the 100 
hour rate you could still get another 33% extra capacity.


Well now.  I don't expect to get away with saying that.  But why not? 
I can't find any evidence that it is not true.


That's probably enough for now, if anyone has bothered to read this 
far.  Thanks for any reactions.

--
Hugh Piggott

Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk___
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Re: [RE-wrenches] discharging Rolls batteries

[Joel Davidson]

Re: [RE-wrenches] discharging Rolls batteriesA battery is an open system. Heat 
is lost. 2nd law of themodynamics. See 
http://theory.uwinnipeg.ca/mod_tech/node70.html

  - Original Message - 
  From: Hugh 
  To: RE-wrenches 
  Sent: Saturday, January 16, 2010 5:04 AM
  Subject: Re: [RE-wrenches] discharging Rolls batteries


  Hi Bruce,


  At 22:58 +1300 16/1/10, Bruce Geddes wrote:
in cold weather the money counters operate more slowly and if the 
temperature rises they return to normal speed.  The money is still there,




  Yes but if that is the case then the actual capacity is not affected by 
temperature - just the ability to deliver.  I would like to think it's that 
simple, but in reality I suspect that there is some loss of amphours under 
these conditions.  I am not yet clear about the mechanism, but I suspect that 
there is more to it than just a 'volt-drop' style explanation such as you offer 
below.


  As far as I understand it, there are two losses: one of voltage due to 
internal resistance and chemical 'sluggishness' and another actual loss of 
capacity in amphours ( getting less amphours out of the battery than you put 
in).  I am trying to establish what happens to those missing amphours, and also 
to what extent they actually are missing and to what extent they are just 
rendered inaccessible by the decision to end the discharge at a certain voltage 
which in turn is affected by the previous 'volt-dop' issues.


  If it were really just a case of the bank tellers having cold fingers then it 
would seem reasonable to hammer the battery down to a much lower voltage in the 
confident knowledge that we are still only taking out 50% of the capacity as 
enshrined as 'good practice'.  however if some of the cash has actually got 
lost (where to?) then it is nt legitimate to hit the battery bank for more cash 
in this way.


  I haven't yet heard from any Wrench what actual voltages they would use to 
set the LBCO or the genstart on an Outback (or an SW), but one has told me 
off-list that it's a negotiation with the client.  Fair enough but what are the 
numbers used in the negotiation, and are they temperature dependant?


  Thanks, Joel for the reading matter which I am working on!  I hope to become 
wiser in due course.


  best


  Hugh




  At 17:45 -0800 15/1/10, Joel  Davidson wrote:


Some charge energy is lost in heat and some in coulombic efficiency.
There are educational powerpoints, papers and other information about 
batteries on the internet.
See http://en.wikipedia.org/wiki/Faraday_efficiency
and http://www.mpoweruk.com/soc.htm
and 
http://web.mit.edu/mit_energy/resources/iap/MatSciOfRenewEnergy_Lecture2_Batteries_2006.pdf
and http://ecee.colorado.edu/~ecen4517/materials/Battery.pdf
and 
http://users.ece.utexas.edu/~kwasinski/EE394V_DG_Fall2008_Week5%20part2.ppt#1
and for info about long series strings of batteries see 
http://www.battcon.com/PapersFinal2004/SymonsPaper2004.pdf





  Bruce:
Hi Hugh.

Positive electrode:  PbO2 + 3H +HSO4 + 2e = PbSO4 + 2H2O  (e= electron)

Negative electrode:  Pb + HSO4 = PbSO4 + H +2e

Sorry, I can't insert the superscript symbols to show electrical charge.  
If it is confusing let me know and I will repost this with the charge in 
brackets following the ion.

In cold conditions the ion transfer rate slows so in effect the internal 
resistance of the cell rises.  It simply can't deliver the electrons under 
load.  If the electrons are taken out at a reduced rate then the Vdrop of the 
"internal resistance" is lowered and the cell terminal voltage stays up for 
longer.

So, to use your analogy of the bank, in cold weather the money counters 
operate more slowly and if the temperature rises they return to normal speed.  
The money is still there, it is just the rate at which it comes out that 
varies.  In cold weather the counters simply won't deliver as much before they 
say "my fingers are too cold, that's all you get today!"

Bruce Geddes
PowerOn

  - Original Message -
  From: Hugh
  To: RE-wrenches
      Sent: Saturday, January 16, 2010 12:25 PM
  Subject: Re: [RE-wrenches] discharging Rolls batteries


  hi


  We know that batteries deliver less amphours at low temperature and at 
high currents.  Volts drop quicker.  That's my starting point.  My question 
that I still do not hear an answer to is this:


  If the battery is a bank account and its harder to get the money out in 
cold weather and when you want to get your hands on a lot at once...  Does this 
actually mean that some of the money gets lost?  What happens to it?  Is it 
perhaps available later when the bank warms up or the demand gets less hectic?  
Is there really less money in there or does it just seem like less due to the 
conditions?


  I notice tha

Re: [RE-wrenches] discharging Rolls batteries

[Darryl Thayer]

Hi Hugh I am copying you and wrenches as some of my posts have not shown up.
The way I look at it is:  A charged battery has some number of molecules of 
Ions? each carry 2 electrons.  That is you store of Amp-hours, 6.25x10^18 
electrons make 1 amp-sec.  Now at rest and 25 C the electrons want to excape at 
2.1 volts per cell the voltage times the charge is the energy.  and if you 
charge slowly and discharge slowly one amp hour in should equal 1 amp hour out. 
 If you charge fast the ions cannot line up fastenough to collect their 
electrons and the voltage rises and some of the electrons make H2 and O2, 
causing water loss. You are charging at higher voltage than you will ever get 
out, and wasting both amp-hrs and voltage ie wasting energy. (some electrons 
make H2SO4 and some make H2 and O2) 

Now for Discharge: The way you get amp-hrs is the ions give up theie electrons. 
If the battery is cold the the Ions can not move very fast, and you have to 
force them, by using part of their desire to rid themselves of their electrons 
and the voltage drops.  (Now it also depends upon the distance the Ions have to 
move, so when you first start discharge the voltage is higher and after a while 
the voltage falls do to a lack of Ions near the plates called hysterises) The 
amp-hrs are there but the watt-hrs are not.  The watt-hrs you can get out 
depends upon the voltage and amp-hrs.  The voltage as we see depends upon the 
discharge rate, it also depends upon hysterisis. 

In my solar class I have the students measure hystersis at 25 C and slow rates. 
 

As to your important question can the LVCO be set and what should it be set 
at?. It is to complicated and I think the SOC method should be best.   



--- On Sat, 1/16/10, Hugh  wrote:

> From: Hugh 
> Subject: Re: [RE-wrenches] discharging Rolls batteries
> To: "RE-wrenches" 
> Date: Saturday, January 16, 2010, 7:04 AM
> 
> Re: [RE-wrenches] discharging Rolls
> batteries 
> Hi Bruce,
> 
> 
> At 22:58 +1300 16/1/10, Bruce Geddes wrote:
> in cold
> weather the money counters operate more slowly and if the
> temperature
> rises they return to normal speed.  The money is still
> there,
> 
> 
> 
> 
> Yes but if that is the case then the actual capacity
> is not
> affected by temperature - just the ability to
> deliver.  I would
> like to think it's that simple, but in reality I
> suspect that there is
> some loss of amphours under these conditions.  I am
> not yet clear
> about the mechanism, but I suspect that there is more to it
> than just
> a 'volt-drop' style explanation such as you offer
> below.
> 
> 
> As far as I understand it, there are two losses: one
> of voltage
> due to internal resistance and chemical
> 'sluggishness' and another
> actual loss of capacity in amphours ( getting less amphours
> out of the
> battery than you put in).  I am trying to establish
> what happens
> to those missing amphours, and also to what extent they
> actually are
> missing and to what extent they are just rendered
> inaccessible by the
> decision to end the discharge at a certain voltage which in
> turn is
> affected by the previous 'volt-dop' issues.
> 
> 
> If it were really just a case of the bank tellers
> having cold
> fingers then it would seem reasonable to hammer the battery
> down to a
> much lower voltage in the confident knowledge that we are
> still only
> taking out 50% of the capacity as enshrined as 'good
> practice'. 
> however if some of the cash has actually got lost (where
> to?) then it
> is nt legitimate to hit the battery bank for more cash in
> this
> way.
> 
> 
> I haven't yet heard from any Wrench what actual
> voltages they
> would use to set the LBCO or the genstart on an Outback (or
> an SW),
> but one has told me off-list that it's a negotiation
> with the client. 
> Fair enough but what are the numbers used in the
> negotiation, and are
> they temperature dependant?
> 
> 
> Thanks, Joel for the reading matter which I am working
> on! 
> I hope to become wiser in due course.
> 
> 
> best
> 
> 
> Hugh
> 
> 
> 
> 
> At 17:45 -0800 15/1/10, Joel  Davidson
> wrote:
> 
> 
> Some charge
> energy is lost in heat and some in coulombic
> efficiency.
> There are educational powerpoints,
> papers and
> other information about batteries on the
> internet.
> See http://en.wikipedia.org/wiki/Faraday_efficiency
> 
> and http://www.mpoweruk.com/soc.htm
> and 
> http://web.mit.edu/mit_energy/resources/iap/MatSciOfRenewEnergy_Lecture2_Batteries_2006.pdf
> and http://ecee.colorado.edu/~ecen4517/materials/Battery.pdf
> 
> and 
> http://users.ece.utexas.edu/

Re: [RE-wrenches] discharging Rolls batteries

[Hugh]

Hi Bruce,

At 22:58 +1300 16/1/10, Bruce Geddes wrote:
in cold weather the money counters operate more slowly and if the 
temperature rises they return to normal speed.  The money is still 
there,



Yes but if that is the case then the actual capacity is not affected 
by temperature - just the ability to deliver.  I would like to think 
it's that simple, but in reality I suspect that there is some loss of 
amphours under these conditions.  I am not yet clear about the 
mechanism, but I suspect that there is more to it than just a 
'volt-drop' style explanation such as you offer below.


As far as I understand it, there are two losses: one of voltage due 
to internal resistance and chemical 'sluggishness' and another actual 
loss of capacity in amphours ( getting less amphours out of the 
battery than you put in).  I am trying to establish what happens to 
those missing amphours, and also to what extent they actually are 
missing and to what extent they are just rendered inaccessible by the 
decision to end the discharge at a certain voltage which in turn is 
affected by the previous 'volt-dop' issues.


If it were really just a case of the bank tellers having cold fingers 
then it would seem reasonable to hammer the battery down to a much 
lower voltage in the confident knowledge that we are still only 
taking out 50% of the capacity as enshrined as 'good practice'. 
however if some of the cash has actually got lost (where to?) then it 
is nt legitimate to hit the battery bank for more cash in this way.


I haven't yet heard from any Wrench what actual voltages they would 
use to set the LBCO or the genstart on an Outback (or an SW), but one 
has told me off-list that it's a negotiation with the client.  Fair 
enough but what are the numbers used in the negotiation, and are they 
temperature dependant?


Thanks, Joel for the reading matter which I am working on!  I hope to 
become wiser in due course.


best

Hugh


At 17:45 -0800 15/1/10, Joel  Davidson wrote:


Some charge energy is lost in heat and some in coulombic efficiency.
There are educational powerpoints, papers and other information 
about batteries on the internet.
See 
<http://en.wikipedia.org/wiki/Faraday_efficiency>http://en.wikipedia.org/wiki/Faraday_efficiency

and <http://www.mpoweruk.com/soc.htm>http://www.mpoweruk.com/soc.htm
and 
<http://web.mit.edu/mit_energy/resources/iap/MatSciOfRenewEnergy_Lecture2_Batteries_2006.pdf>http://web.mit.edu/mit_energy/resources/iap/MatSciOfRenewEnergy_Lecture2_Batteries_2006.pdf
and 
<http://ecee.colorado.edu/~ecen4517/materials/Battery.pdf>http://ecee.colorado.edu/~ecen4517/materials/Battery.pdf
and 
<http://users.ece.utexas.edu/~kwasinski/EE394V_DG_Fall2008_Week5%20part2.ppt#1>http://users.ece.utexas.edu/~kwasinski/EE394V_DG_Fall2008_Week5%20part2.ppt#1
and for info about long series strings of batteries see 
<http://www.battcon.com/PapersFinal2004/SymonsPaper2004.pdf>http://www.battcon.com/PapersFinal2004/SymonsPaper2004.pdf






Bruce:

Hi Hugh.

Positive electrode:  PbO2 + 3H +HSO4 + 2e = PbSO4 + 2H2O  (e= electron)

Negative electrode:  Pb + HSO4 = PbSO4 + H +2e

Sorry, I can't insert the superscript symbols to show electrical 
charge.  If it is confusing let me know and I will repost this with 
the charge in brackets following the ion.


In cold conditions the ion transfer rate slows so in effect the 
internal resistance of the cell rises.  It simply can't deliver the 
electrons under load.  If the electrons are taken out at a reduced 
rate then the Vdrop of the "internal resistance" is lowered and the 
cell terminal voltage stays up for longer.


So, to use your analogy of the bank, in cold weather the money 
counters operate more slowly and if the temperature rises they 
return to normal speed.  The money is still there, it is just the 
rate at which it comes out that varies.  In cold weather the 
counters simply won't deliver as much before they say "my fingers 
are too cold, that's all you get today!"


Bruce Geddes
PowerOn

- Original Message -
From: <mailto:h...@scoraigwind.co.uk>Hugh
To: <mailto:re-wrenches@lists.re-wrenches.org>RE-wrenches
Sent: Saturday, January 16, 2010 12:25 PM
Subject: Re: [RE-wrenches] discharging Rolls batteries

hi

We know that batteries deliver less amphours at low temperature and 
at high currents.  Volts drop quicker.  That's my starting point. 
My question that I still do not hear an answer to is this:


If the battery is a bank account and its harder to get the money out 
in cold weather and when you want to get your hands on a lot at 
once...  Does this actually mean that some of the money gets lost? 
What happens to it?  Is it perhaps available later when the bank 
warms up or the demand gets less hectic?  Is there really less money 
in there or does it just seem like less due to the conditions?

Re: [RE-wrenches] discharging Rolls batteries

[Bruce Geddes]

Re: [RE-wrenches] discharging Rolls batteriesHi Hugh.

Positive electrode:  PbO2 + 3H +HSO4 + 2e = PbSO4 + 2H2O  (e= electron)

Negative electrode:  Pb + HSO4 = PbSO4 + H +2e

Sorry, I can't insert the superscript symbols to show electrical charge.  If it 
is confusing let me know and I will repost this with the charge in brackets 
following the ion.

In cold conditions the ion transfer rate slows so in effect the internal 
resistance of the cell rises.  It simply can't deliver the electrons under 
load.  If the electrons are taken out at a reduced rate then the Vdrop of the 
"internal resistance" is lowered and the cell terminal voltage stays up for 
longer.

So, to use your analogy of the bank, in cold weather the money counters operate 
more slowly and if the temperature rises they return to normal speed.  The 
money is still there, it is just the rate at which it comes out that varies.  
In cold weather the counters simply won't deliver as much before they say "my 
fingers are too cold, that's all you get today!"

Bruce Geddes
PowerOn
  - Original Message - 
  From: Hugh 
  To: RE-wrenches 
  Sent: Saturday, January 16, 2010 12:25 PM
  Subject: Re: [RE-wrenches] discharging Rolls batteries


  hi


  We know that batteries deliver less amphours at low temperature and at high 
currents.  Volts drop quicker.  That's my starting point.  My question that I 
still do not hear an answer to is this:


  If the battery is a bank account and its harder to get the money out in cold 
weather and when you want to get your hands on a lot at once...  Does this 
actually mean that some of the money gets lost?  What happens to it?  Is it 
perhaps available later when the bank warms up or the demand gets less hectic?  
Is there really less money in there or does it just seem like less due to the 
conditions?


  I notice that Ah capacity is actually defined as how much Amphours you can 
get out before the battery reaches a certain terminal voltage.  I am wondering 
whether it is the ability to maintain voltage that is the limiting factor 
whereas the chemicals in there can still deliver amphours, given  the right 
temperature and time later.  You can certainly see recovery take place when a 
battery warms up and/or operates on lighter loads.


  One last time what happens to the chemicals (lead and lead oxide) that 
represent Amphours of charge in the battery plates?  For me this is a little 
bit like current of 10 amps entering one end of  a piece of wire and only 9 
amps coming out the other end.  I understand that the volts go down due to 
voltage drop (in this analogy) but loss of current is entirely a different 
matter.


  Thanks for any help with this rather obscure question.


  Hugh


A lead-acid battery is an electro-chemical processor (just like you and 
other living things). When you and your battery are cold or hot, performance 
changes because the chemical process is affected by temperature. Cold equals 
sluggish chemical reaction, reduces the capacity to perform work, and affects 
battery performance linearly. Battery chemistry is well understood. When I get 
some time, I'll google for temperature-based formulas and charts unless someone 
else posts the links first.

  - Original Message -
  From: Hugh
  To: RE-wrenches
  Sent: Friday, January 15, 2010 12:02 AM
  Subject: Re: [RE-wrenches] discharging Rolls batteries


  Hi Jamie,




Remember, as batteries cool actual capacity is reduced, so if 200AH is 
50% @ 25C it is significantly more than 50% @ 5C.   Thus, you are discharging 
more deeply.



  But earlier you put it this way:


  Regarding temperature effects on capacity, earlier responses are spot 
on as the lower capacity is totally as a result of slower reaction times as a 
result of lower temperatures.  



  There is an issue here that I need to understand better.  You state that 
a battery has lower capacity in low temperatures.  Suppose you take a fully 
charged, 400 Ah battery and cool it down to -5 degrees C where according to our 
numbers it will only have 80% of its nominal capacity.  You then remove 160 Ah 
(say 10 amps for 16 hours).  It will then be 50% discharged.  Now warm it up 
again to 20 degrees or whatever.  My question is: will you only have 200 
amphours left in it now?  And if so, what happened to the other 40 amphours?  
Does low temperature operation actually lose amphours, or is it just more 
sluggish?  What is the chemical explanation for the lost amphours?


  I understand batteries as a chemical process of converting amphours into 
chemical changes.  I assume that a given amount of electrical charge converts a 
given amount of lead into lead sulphate (and likewise) back again.  I 
understand that cooling will make this process less efficient and thereby 
result in a rise in charging voltage and a drop in discharging voltage.  But 
does a low tem

Re: [RE-wrenches] discharging Rolls batteries

[Joel Davidson]

Re: [RE-wrenches] discharging Rolls batteriesSome charge energy is lost in heat 
and some in coulombic efficiency.
There are educational powerpoints, papers and other information about batteries 
on the internet.
See http://en.wikipedia.org/wiki/Faraday_efficiency
and http://www.mpoweruk.com/soc.htm
and 
http://web.mit.edu/mit_energy/resources/iap/MatSciOfRenewEnergy_Lecture2_Batteries_2006.pdf
and http://ecee.colorado.edu/~ecen4517/materials/Battery.pdf
and 
http://users.ece.utexas.edu/~kwasinski/EE394V_DG_Fall2008_Week5%20part2.ppt#1
and for info about long series strings of batteries see 
http://www.battcon.com/PapersFinal2004/SymonsPaper2004.pdf


  - Original Message - 
  From: Hugh 
  To: RE-wrenches 
  Sent: Friday, January 15, 2010 3:25 PM
  Subject: Re: [RE-wrenches] discharging Rolls batteries


  hi


  We know that batteries deliver less amphours at low temperature and at high 
currents.  Volts drop quicker.  That's my starting point.  My question that I 
still do not hear an answer to is this:


  If the battery is a bank account and its harder to get the money out in cold 
weather and when you want to get your hands on a lot at once...  Does this 
actually mean that some of the money gets lost?  What happens to it?  Is it 
perhaps available later when the bank warms up or the demand gets less hectic?  
Is there really less money in there or does it just seem like less due to the 
conditions?


  I notice that Ah capacity is actually defined as how much Amphours you can 
get out before the battery reaches a certain terminal voltage.  I am wondering 
whether it is the ability to maintain voltage that is the limiting factor 
whereas the chemicals in there can still deliver amphours, given  the right 
temperature and time later.  You can certainly see recovery take place when a 
battery warms up and/or operates on lighter loads.


  One last time what happens to the chemicals (lead and lead oxide) that 
represent Amphours of charge in the battery plates?  For me this is a little 
bit like current of 10 amps entering one end of  a piece of wire and only 9 
amps coming out the other end.  I understand that the volts go down due to 
voltage drop (in this analogy) but loss of current is entirely a different 
matter.


  Thanks for any help with this rather obscure question.

___
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Re: [RE-wrenches] discharging Rolls batteries

[Kent Osterberg]

Hugh,

If my understanding about this is right, the amphours aren't literally
lost when the battery is cold or discharge rate is high.  You would
just have to operate the battery below 1.75 volts to get them.  Not a
situation that is very useful.  But warm them up or lower the discharge
rate and you'll get the full amount.  

Kent Osterberg
Blue Mountain Solar, Inc.



Hugh wrote:

  
  Re: [RE-wrenches] discharging Rolls
batteries
  hi
  
  
  We know that batteries deliver less amphours at low temperature
and at high currents.  Volts drop quicker.  That's my
starting point.  My question that I still do not hear an answer
to is this:
  
  
  If the battery is a bank account and its harder to get the money
out in cold weather and when you want to get your hands on a lot at
once...  Does this actually mean that some of the money gets
lost?  What happens to it?  Is it perhaps available later
when the bank warms up or the demand gets less hectic?  Is there
really less money in there or does it just seem like less due to the
conditions?
  
  
  I notice that Ah capacity is actually defined as how much
Amphours you can get out before the battery reaches a certain terminal
voltage.  I am wondering whether it is the ability to maintain
voltage that is the limiting factor whereas the chemicals in there can
still deliver amphours, given  the right temperature and time
later.  You can certainly see recovery take place when a battery
warms up and/or operates on lighter loads.
  
  
  One last time what happens to the chemicals (lead and lead
oxide)
that represent Amphours of charge in the battery plates?  For me
this is a little bit like current of 10 amps entering one end of 
a piece of wire and only 9 amps coming out the other end.  I
understand that the volts go down due to voltage drop (in this
analogy) but loss of current is entirely a different matter.
  
  
  Thanks for any help with this rather obscure question.
  
  
  Hugh
  
  
  A lead-acid
battery is an electro-chemical processor
(just like you and other living things). When you and your battery are
cold or hot, performance changes because the chemical process is
affected by temperature. Cold equals sluggish chemical
reaction, reduces the capacity to perform work,
and affects battery performance linearly. Battery chemistry
is well understood. When I get some time,
I'll google for temperature-based formulas and charts unless
someone else posts the links first.
- Original Message -
From: Hugh
To: RE-wrenches
Sent: Friday, January 15, 2010 12:02
AM
    Subject: Re: [RE-wrenches] discharging Rolls
batteries


Hi Jamie,

  
  


  Remember, as batteries
cool
actual capacity is reduced, so if 200AH is 50% @ 25C it is
significantly more than 50% @ 5C.   Thus, you are
discharging more deeply.
  



But earlier you put it this way:

  
Regarding
temperature effects on capacity, earlier responses are spot on as the
lower capacity is totally as a result of slower reaction times as a
result of lower temperatures.  

  



There is an issue here that I need to understand
better. 
You state that a battery has lower capacity in low temperatures. 
Suppose you take a fully charged, 400 Ah battery and cool it down to
-5 degrees C where according to our numbers it will only have 80% of
its nominal capacity.  You then remove 160 Ah (say 10 amps for 16
hours).  It will then be 50% discharged.  Now warm it up
again to 20 degrees or whatever.  My question is: will you only
have 200 amphours left in it now?  And if so, what happened to
the other 40 amphours?  Does low temperature operation actually
lose amphours, or is it just more sluggish?  What is the chemical
explanation for the lost amphours?


I understand batteries as a chemical process of
converting
amphours into chemical changes.  I assume that a given amount of
electrical charge converts a given amount of lead into lead sulphate
(and likewise) back again.  I understand that cooling will make
this process less efficient and thereby result in a rise in charging
voltage and a drop in discharging voltage.  But does a low
temperature actually mean that a given amount of lead being converted
to sulphate actually give you less amphours electrically?


(I have similar questions in relation to Peukert's
equation where high discharge rates impact on the amphour capacity. 
The capacity apparently 'recovers' when the discharge rate is
reduced.  To what extent is the capacity actually lost by using
high discharge rates and to what extent is it just a voltage effect
that impacts on the terminal voltage, rather than the actual chemical
state of the battery?)


I hope you can follow my descriptions.
--
Hugh Piggott
  
Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk


  
  
  
  
  
  
  -- 
  
  Hu

Re: [RE-wrenches] discharging Rolls batteries

[Hugh]

hi

We know that batteries deliver less amphours at low temperature and 
at high currents.  Volts drop quicker.  That's my starting point.  My 
question that I still do not hear an answer to is this:


If the battery is a bank account and its harder to get the money out 
in cold weather and when you want to get your hands on a lot at 
once...  Does this actually mean that some of the money gets lost? 
What happens to it?  Is it perhaps available later when the bank 
warms up or the demand gets less hectic?  Is there really less money 
in there or does it just seem like less due to the conditions?


I notice that Ah capacity is actually defined as how much Amphours 
you can get out before the battery reaches a certain terminal 
voltage.  I am wondering whether it is the ability to maintain 
voltage that is the limiting factor whereas the chemicals in there 
can still deliver amphours, given  the right temperature and time 
later.  You can certainly see recovery take place when a battery 
warms up and/or operates on lighter loads.


One last time what happens to the chemicals (lead and lead oxide) 
that represent Amphours of charge in the battery plates?  For me this 
is a little bit like current of 10 amps entering one end of  a piece 
of wire and only 9 amps coming out the other end.  I understand that 
the volts go down due to voltage drop (in this analogy) but loss of 
current is entirely a different matter.


Thanks for any help with this rather obscure question.

Hugh

A lead-acid battery is an electro-chemical processor (just like you 
and other living things). When you and your battery are cold or hot, 
performance changes because the chemical process is affected by 
temperature. Cold equals sluggish chemical reaction, reduces the 
capacity to perform work, and affects battery performance 
linearly. Battery chemistry is well understood. When I get 
some time, I'll google for temperature-based formulas and charts 
unless someone else posts the links first.


- Original Message -
From: <mailto:h...@scoraigwind.co.uk>Hugh
To: <mailto:re-wrenches@lists.re-wrenches.org>RE-wrenches
Sent: Friday, January 15, 2010 12:02 AM
Subject: Re: [RE-wrenches] discharging Rolls batteries

Hi Jamie,



Remember, as batteries cool actual capacity is reduced, so if 200AH 
is 50% @ 25C it is significantly more than 50% @ 5C.   Thus, you are 
discharging more deeply.



But earlier you put it this way:

Regarding temperature effects on capacity, earlier responses are 
spot on as the lower capacity is totally as a result of slower 
reaction times as a result of lower temperatures.  



There is an issue here that I need to understand better.  You state 
that a battery has lower capacity in low temperatures.  Suppose you 
take a fully charged, 400 Ah battery and cool it down to -5 degrees 
C where according to our numbers it will only have 80% of its 
nominal capacity.  You then remove 160 Ah (say 10 amps for 16 
hours).  It will then be 50% discharged.  Now warm it up again to 20 
degrees or whatever.  My question is: will you only have 200 
amphours left in it now?  And if so, what happened to the other 40 
amphours?  Does low temperature operation actually lose amphours, or 
is it just more sluggish?  What is the chemical explanation for the 
lost amphours?


I understand batteries as a chemical process of converting amphours 
into chemical changes.  I assume that a given amount of electrical 
charge converts a given amount of lead into lead sulphate (and 
likewise) back again.  I understand that cooling will make this 
process less efficient and thereby result in a rise in charging 
voltage and a drop in discharging voltage.  But does a low 
temperature actually mean that a given amount of lead being 
converted to sulphate actually give you less amphours electrically?


(I have similar questions in relation to Peukert's equation where 
high discharge rates impact on the amphour capacity.  The capacity 
apparently 'recovers' when the discharge rate is reduced.  To what 
extent is the capacity actually lost by using high discharge rates 
and to what extent is it just a voltage effect that impacts on the 
terminal voltage, rather than the actual chemical state of the 
battery?)


I hope you can follow my descriptions.
--
Hugh Piggott

Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk


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Re: [RE-wrenches] discharging Rolls batteries

[Kent Osterberg]

Hugh,

I'll take a try at explaining what is going on with battery temperature 
and high discharge rate issues.  I hope Jamie will clarify, if I've got 
it wrong. 

A battery's capacity is the number of amphours that it will provide from 
full charge down to a terminal voltage of 1.75 vpc.  It isn't literally 
dead at that time -- it isn't chemically exhausted -- chemical reactions 
just aren't happening fast enough to keep the terminal voltage up to 
1.75 vpc.  The rate that chemical reactions happen depends on 
temperature, electrolyte concentration, plate area, and more; so a 
battery's capacity depends on the temperature and rate of discharge.


If a battery is cold, chemical reactions happen slower so the voltage 
drops to 1.75 volts sooner than it would if it were at 25°C.  With a 
rapid discharge, the voltage drops to 1.75 volts with fewer amphours 
removed because the rate of chemical reactions isn't fast enough to keep 
the terminal voltage at 1.75 vpc.


If a battery is discharged at C/20 and 25°C the specific gravity will be 
(about) 1.12 when the terminal voltage gets to 1.75 vpc.  If the battery 
is colder, or if the discharge rate is higher, the specific gravity 
(corrected to 25°C) will be higher at the end of discharge to 1.75 vpc.  
That's because not as many chemical reactions took place before the 
battery couldn't sustain 1.75 vpc.  Since there are still chemical 
reactions that can take place, the battery can sustain a 1.75 vpc 
terminal voltage if it is warmed or the discharge rate is reduced.


Using the Rolls S530 as an example.  The capacity at 25°C is 400 Ah at 
C/20 or 296 Ah at C/6.  For FLA batteries, the capacity changes by 
0.8%/°C (I think that is only true at C/20), so at 0°C and C/20 the 
capacity of the S530 is 320 Ah.  If we discharge it to 1.75 vpc by 
removing 320 Ah at C/20 and 0°C and then warm it back up to 25°C, we 
could remove another 80 Ah before the terminal voltage again drops to 
1.75 vpc.  You could also think of this process in reverse order: remove 
320 Ah at C/20 and 25°C, the voltage will be 1.82 vpc and 80% DOD,  now  
cool the battery to 0°C and the voltage will be 1.75 vpc and 100% DOD.  
Same idea with rapid discharge.  Discharge 296 Ah at 25°C and C/6 rate 
and the terminal voltage will be 1.75 vpc.  Reduce the current to C/20 
and you'll be able to continue discharging the battery to 400 Ah before 
the terminal voltage is 1.75 vpc.


Starting the generator when the battery voltage is 1.96 vpc is about 40% 
DOD (-160 Ah from a 400 Ah S 530 or similar battery) at C/20 and 25°C is 
a good strategy to get good life out of the battery.  If the battery is 
cold or the discharge rate is high, fewer amphours will be removed 
before the generator starts.  At 0°C a 1.96 vpc value should be reached 
at (about) -128 Ah, which is 40% DOD based on the capacity at 0°C.  So a 
voltage based strategy for starting the generator gives (about) the same 
% DOD after temperature correction of the battery capacity. 

Outback's Flexnet DC is the only device that I'm familiar with that can 
start the generator based on the amphours removed from the battery.  It 
is supposed to display SOC and it is programmed with "SOC" values, but 
the battery capacity isn't compensated for temperature or discharge 
rate, so the SOC display is only accurate if the battery is actually at 
25°C with a C/20 discharge.  If the Flexnet DC is programed to start the 
generator at 60% SOC it'll discharge 160 Ah from a 400 Ah battery 
regardless of the temperature or discharge rate.  Just using its SOC 
programming, you wouldn't notice the fact that a battery has less 
capacity when it is cold or discharge rate is high.  In cold conditions 
or with high discharge rates, it'll let the voltage go lower before the 
generator starts.  If it was cold enough, the battery voltage could go 
below 1.75 volts and not start the generator.  Fortunately the Flexnet 
DC can also watch the voltage.


Kent Osterberg
Blue Mountain Solar, Inc.

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Re: [RE-wrenches] discharging Rolls batteries

[Joel Davidson]

Re: [RE-wrenches] discharging Rolls batteriesA lead-acid battery is an 
electro-chemical processor (just like you and other living things). When you 
and your battery are cold or hot, performance changes because the chemical 
process is affected by temperature. Cold equals sluggish chemical reaction, 
reduces the capacity to perform work, and affects battery performance linearly. 
Battery chemistry is well understood. When I get some time, I'll google for 
temperature-based formulas and charts unless someone else posts the links first.
  - Original Message - 
  From: Hugh 
  To: RE-wrenches 
  Sent: Friday, January 15, 2010 12:02 AM
  Subject: Re: [RE-wrenches] discharging Rolls batteries


  Hi Jamie,




Remember, as batteries cool actual capacity is reduced, so if 200AH is 50% 
@ 25C it is significantly more than 50% @ 5C.   Thus, you are discharging more 
deeply.


  But earlier you put it this way:


  Regarding temperature effects on capacity, earlier responses are spot on 
as the lower capacity is totally as a result of slower reaction times as a 
result of lower temperatures.  


  There is an issue here that I need to understand better.  You state that a 
battery has lower capacity in low temperatures.  Suppose you take a fully 
charged, 400 Ah battery and cool it down to -5 degrees C where according to our 
numbers it will only have 80% of its nominal capacity.  You then remove 160 Ah 
(say 10 amps for 16 hours).  It will then be 50% discharged.  Now warm it up 
again to 20 degrees or whatever.  My question is: will you only have 200 
amphours left in it now?  And if so, what happened to the other 40 amphours?  
Does low temperature operation actually lose amphours, or is it just more 
sluggish?  What is the chemical explanation for the lost amphours?


  I understand batteries as a chemical process of converting amphours into 
chemical changes.  I assume that a given amount of electrical charge converts a 
given amount of lead into lead sulphate (and likewise) back again.  I 
understand that cooling will make this process less efficient and thereby 
result in a rise in charging voltage and a drop in discharging voltage.  But 
does a low temperature actually mean that a given amount of lead being 
converted to sulphate actually give you less amphours electrically?


  (I have similar questions in relation to Peukert's equation where high 
discharge rates impact on the amphour capacity.  The capacity apparently 
'recovers' when the discharge rate is reduced.  To what extent is the capacity 
actually lost by using high discharge rates and to what extent is it just a 
voltage effect that impacts on the terminal voltage, rather than the actual 
chemical state of the battery?)


  I hope you can follow my descriptions.
-- 
Hugh Piggott

  Scoraig Wind Electric
  Scotland
  http://www.scoraigwind.co.uk


--


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Re: [RE-wrenches] discharging Rolls batteries

[Darryl Thayer]

Hugh
I find your insite to be correct.  If you take any battery, and it is most 
noticable on slow charge batteries(such as RE and Rolls Solar batteries) if you 
discharge rapidly the voltage will drop much lower than SOC would indicate, if 
you let the battry stand the voltage will recover.  So yes you should be able 
to discharge to a lower voltage and still not be below the safe SOC.  

AS to weather anyone has this possibility Outback should be able to with there 
FnDC, I have discussed this with them, but ...the future.  

A new company Silent Power has also looked at this discharging parameter, and 
... the future.   They say if I can come up with the algorhythm then maybe.  

Thanks for raising this important issue, it is a problem almost every time.  
Darryl

--- On Thu, 1/14/10, Hugh  wrote:

> From: Hugh 
> Subject: Re: [RE-wrenches] discharging Rolls batteries
> To: "RE-wrenches" 
> Date: Thursday, January 14, 2010, 4:35 PM
> 
> Re: [RE-wrenches] discharging Rolls
> batteries 
> Hi Jamie and Dan,
> 
> 
> Thanks for keeping up this thread!  And sorry for
> being
> impatient.
> 
> 
> Now, if the capacity 'loss' is simply due to
> reduced performance,
> is it logical to say that one can push the battery to lower
> voltages
> under low temperature conditions without actually cycling
> it harder or
> reducign its life that way?
> 
> 
> On the question of inverter temperature compensation
> for
> discharge set points, these would surely be adjusted
> downward in low
> temperatures whereas the charging setpoints are adjusted
> upwards. 
> I had never heard of such adjustment to discharge setpoints
> (low
> battery disconnect, genstart, etc).  I would be
> interested to
> know if this type of temperature compensation exists and
> indeed
> whether it is legitimate in terms of sustainable battery
> management.
> 
> 
> Hugh
> 
> 
> 
> 
> Hugh,
> 
> 
> 
> 
> Sorry if you
> found my response limited but have been traveling since
> early this am
> and don't have all information at hand, at the
> moment.
> 
> 
> 
> 
> Regarding
> temperature effects on capacity, earlier responses are spot
> on as the
> lower capacity is totally as a result of slower reaction
> times as a
> result of lower temperatures.  
> 
> 
> 
> 
> Approximate
> Temp effects;
> 
> 
> 
> 
> 40C
> =
> 104%
> 
> 
> 25C
> =
> 100%
> 
> 
> 5
> to 10C =
> 90%
> 
> 
> -5C
> =
> 80%
> 
> 
> -22C =
> 60%
> 
> 
> -- 
>  
> Hugh Piggott
> 
> 
> 
> Scoraig Wind Electric
> 
> Scotland
> 
> http://www.scoraigwind.co.uk
>  
> 
> -Inline Attachment Follows-
> 
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Re: [RE-wrenches] discharging Rolls batteries

[James Surrette]

Hi Hugh, 

You are correct, my comments may have been too simplistic. 

However, one other key point we are missing is discharge rate. 

Note your comment, 400AH battery discharged at 10a for 16 (or 20) hours = 50% 
DOD, which is probably not the case. 

Use our S-530, which is 400AH @ the 20hr rate 
(http://www.surrette.com/pdf/pdf_surrette/s530.pdf), meaning it can support a 
20a load for 20 hours (2.1VPC - 1.75VPC).  However, if the current is lowered 
to 10A it can support this load for nearly 50hrs.  This difference is as a 
result of the battery's ability to better utilize the available active material 
(Lead Oxide) during a slower discharge.  Deep cycle products prefer smaller 
loads for longer periods.  Once the loads increase, the reaction time is too 
long to support and available capacity plummets, ie, S-530 = 144AH @ 1hr.   So, 
place a 72A load on an S-530 for 30 mins and you've discharged 50%.  The 
preamble I've just written is similar to the temperature effect as it is the 
result of timeliness of converting lead oxide to lead sulfate. 

Take an S-530, cool to -5C and now the capacity drops by 20% as a result of the 
inability to convert at low temps.  You are correct, the expansion and 
contraction associated with converting lead oxide to lead sulfate (on the 
positive) is not occurring at the same value (20% less) but you are pushing the 
batteries at "a temp adjusted" higher discharge rate.  Thus, the battery cannot 
support the similar current load for as long a period and voltage drops.  SG 
values rise as temperature drops, so like for like SOC values will be different 
if using a hydrometer at -5c & 20C. 

Jamie

>>> Hugh  1/15/2010 4:02 AM >>>

Hi Jamie, 






 


Remember, as batteries cool actual capacity is reduced, so if 200AH is 50% @ 
25C it is significantly more than 50% @ 5C.   Thus, you are discharging more 
deeply.  



But earlier you put it this way: 







Regarding temperature effects on capacity, earlier responses are spot on as the 
lower capacity is totally as a result of slower reaction times as a result of 
lower temperatures. 



There is an issue here that I need to understand better.  You state that a 
battery has lower capacity in low temperatures.  Suppose you take a fully 
charged, 400 Ah battery and cool it down to -5 degrees C where according to our 
numbers it will only have 80% of its nominal capacity.  You then remove 160 Ah 
(say 10 amps for 16 hours).  It will then be 50% discharged.  Now warm it up 
again to 20 degrees or whatever.  My question is: will you only have 200 
amphours left in it now?  And if so, what happened to the other 40 amphours?  
Does low temperature operation actually lose amphours, or is it just more 
sluggish?  What is the chemical explanation for the lost amphours? 



I understand batteries as a chemical process of converting amphours into 
chemical changes.  I assume that a given amount of electrical charge converts a 
given amount of lead into lead sulphate (and likewise) back again.  I 
understand that cooling will make this process less efficient and thereby 
result in a rise in charging voltage and a drop in discharging voltage.  But 
does a low temperature actually mean that a given amount of lead being 
converted to sulphate actually give you less amphours electrically? 



(I have similar questions in relation to Peukert's equation where high 
discharge rates impact on the amphour capacity.  The capacity apparently 
'recovers' when the discharge rate is reduced.  To what extent is the capacity 
actually lost by using high discharge rates and to what extent is it just a 
voltage effect that impacts on the terminal voltage, rather than the actual 
chemical state of the battery?) 



I hope you can follow my descriptions. 


-- 

Hugh Piggott

Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk 


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Re: [RE-wrenches] discharging Rolls batteries

[Hugh]

Hi Jamie,



Remember, as batteries cool actual capacity is reduced, so if 200AH 
is 50% @ 25C it is significantly more than 50% @ 5C.   Thus, you are 
discharging more deeply.


But earlier you put it this way:

Regarding temperature effects on capacity, earlier responses are 
spot on as the lower capacity is totally as a result of slower 
reaction times as a result of lower temperatures.  


There is an issue here that I need to understand better.  You state 
that a battery has lower capacity in low temperatures.  Suppose you 
take a fully charged, 400 Ah battery and cool it down to -5 degrees C 
where according to our numbers it will only have 80% of its nominal 
capacity.  You then remove 160 Ah (say 10 amps for 16 hours).  It 
will then be 50% discharged.  Now warm it up again to 20 degrees or 
whatever.  My question is: will you only have 200 amphours left in it 
now?  And if so, what happened to the other 40 amphours?  Does low 
temperature operation actually lose amphours, or is it just more 
sluggish?  What is the chemical explanation for the lost amphours?


I understand batteries as a chemical process of converting amphours 
into chemical changes.  I assume that a given amount of electrical 
charge converts a given amount of lead into lead sulphate (and 
likewise) back again.  I understand that cooling will make this 
process less efficient and thereby result in a rise in charging 
voltage and a drop in discharging voltage.  But does a low 
temperature actually mean that a given amount of lead being converted 
to sulphate actually give you less amphours electrically?


(I have similar questions in relation to Peukert's equation where 
high discharge rates impact on the amphour capacity.  The capacity 
apparently 'recovers' when the discharge rate is reduced.  To what 
extent is the capacity actually lost by using high discharge rates 
and to what extent is it just a voltage effect that impacts on the 
terminal voltage, rather than the actual chemical state of the 
battery?)


I hope you can follow my descriptions.
--
Hugh Piggott

Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk___
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Re: [RE-wrenches] discharging Rolls batteries

[James Surrette]

Hi Hugh, 

Based on your earlier number - regardless of temp effects - you were only 
removing ~25% of capacity.  You will need to lower your low voltage cut off to 
improve performance.   

Remember, as batteries cool actual capacity is reduced, so if 200AH is 50% @ 
25C it is significantly more than 50% @ 5C.   Thus, you are discharging more 
deeply.  However, batteries produce heat during recharge and discharge. 

Hope this is of some use. 

Jamie 

>>> Hugh  1/14/2010 6:35 PM >>>

Hi Jamie and Dan, 



Thanks for keeping up this thread!  And sorry for being impatient. 



Now, if the capacity 'loss' is simply due to reduced performance, is it logical 
to say that one can push the battery to lower voltages under low temperature 
conditions without actually cycling it harder or reducign its life that way? 



On the question of inverter temperature compensation for discharge set points, 
these would surely be adjusted downward in low temperatures whereas the 
charging setpoints are adjusted upwards.  I had never heard of such adjustment 
to discharge setpoints (low battery disconnect, genstart, etc).  I would be 
interested to know if this type of temperature compensation exists and indeed 
whether it is legitimate in terms of sustainable battery management. 



Hugh 






 


Hugh,
 



 


Sorry if you found my response limited but have been traveling since early this 
am and don't have all information at hand, at the moment.
 



 


Regarding temperature effects on capacity, earlier responses are spot on as the 
lower capacity is totally as a result of slower reaction times as a result of 
lower temperatures.  
 



 


Approximate Temp effects;
 



 


40C = 104%
 


25C = 100%
 


5 to 10C = 90%
 


-5C = 80%
 


-22C = 60%  




-- 

Hugh Piggott

Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk 


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Re: [RE-wrenches] discharging Rolls batteries

[Hugh]

Hi Jamie and Dan,

Thanks for keeping up this thread!  And sorry for being impatient.

Now, if the capacity 'loss' is simply due to reduced performance, is 
it logical to say that one can push the battery to lower voltages 
under low temperature conditions without actually cycling it harder 
or reducign its life that way?


On the question of inverter temperature compensation for discharge 
set points, these would surely be adjusted downward in low 
temperatures whereas the charging setpoints are adjusted upwards.  I 
had never heard of such adjustment to discharge setpoints (low 
battery disconnect, genstart, etc).  I would be interested to know if 
this type of temperature compensation exists and indeed whether it is 
legitimate in terms of sustainable battery management.


Hugh



Hugh,


Sorry if you found my response limited but have been traveling since 
early this am and don't have all information at hand, at the moment.



Regarding temperature effects on capacity, earlier responses are 
spot on as the lower capacity is totally as a result of slower 
reaction times as a result of lower temperatures.  



Approximate Temp effects;


40C = 104%

25C = 100%

5 to 10C = 90%

-5C = 80%

-22C = 60%


--
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Scoraig Wind Electric
Scotland
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Re: [RE-wrenches] discharging Rolls batteries

[Bruce Geddes]

Re: [RE-wrenches] discharging Rolls batteries
  I wonder why there is no temperature compensation on low battery voltage 
settings like there is on charging set points.  Do I just have to use the 
generator much more?

I may be wrong but my understanding of the Outback gear is that the temperature 
compensation is "global".  The V display on the Mate will show temp compensated 
volts and I am of the understanding that this flows through to all parameters 
set in the FX.  Perhaps an Outback rep can clarify this important point?

Bruce Geddes
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Re: [RE-wrenches] discharging Rolls batteries

[James Surrette]

Hi Dan, 

Good point. 

A quick chart on freezing temperatures vs SG; 

Specific Gravity 

(cor. to 80° F/26° C)Freezing Temp 
1.280 -92° F (-69° C) 
1.265-72.3° F (-57° C) 
1.250-62° F (-52° C) 
1.200-16° F (-27° C) 
1.150+5° F (-15° C) 
1.100+19° F (-7.2° C) 

Regards, 

Jamie

>>>  1/14/2010 10:56 AM >>>

More important than loss of capacity at low temps, (at least in my
world), is the fact that battery freeze points rise considerably -- with
a reduced State of charge... So you get a sort of double whammy... not
only do you get less capacity, but they freeze easier.




Dan Brown
President
Foxfire Energy Corp.
Renewable Energy Systems
(802)-483-2564
www.Foxfire-Energy.com
NABCEP #092907-44




 Original Message ----
Subject: Re: [RE-wrenches] discharging Rolls batteries
From: Hugh 
Date: Wed, January 13, 2010 5:47 pm
To: RE-wrenches 

#wmMessage blockquote, #wmMessage dl, #wmMessage ul, #wmMessage ol,
#wmMessage li { padding-top: 0 ; padding-bottom: 0 } 
Hi Jamie, 



Thanks for the very quick response! 



I note that the temp compensation slope for charging is more like a
curve.  It would be great to have a few more data points on this curve
to match it against the linear compensation programmed into a Tristar
controller. 



But I guess there is some leeway anyway?  My personal 48-V household
battery is rather large (2 x S530 in parallel) and the max charge rate
is low (around 20-30 amps).  Would that be a reason to set a higher
charging voltage maybe, or does it not make a difference? 



As far as the disconnect point, I now have one data point for 50%
discharge: 1.93V at C/20 and 25 degrees C.  Again it would be great to
have a whole family of curves to work from in this area.  Most of the
systems I work on have batteries that are sized for several days usage
rather than 20 hours.  I don't really like to see the LBCO setpoint as
low as 46.3 volts. 



Capacity is reduced at low temperatures.  Now does this mean that there
really is less energy in the battery, so that if I take out 50% of this
reduced capacity I will only end up with a 50% state of charge once it
has warmed, or is this just a performance hit that reduces the voltage
and makes the battery capacity appear to be less?  Will the battery
actually have less amphours to deliver, or will it just be delivering at
a lower voltage?  My point is to ask whether it is legitimate to push
the battery to a lower voltage in cold weather on the assumption that it
is not really running that low, but just sluggish with cold? 



I hope you don't mind all the questions.  I hope the others find the
answers interesting too! 



In an ideal world we could control our end-of-discharge based on
amphours measured, but I have no faith in the calibration of such
devices after a few partial charge swings up and down over period of
days.  So the reality is that we rely on inverter LBCO settings or rules
of thumb such as "never let the voltage drop below 47" to ensure that
the batteries do not get abused. 



Best wishes 



Hugh 




 


Hi Hugh & Wrenches,
 



 


Regarding the charge voltages you sited, you've got the gist.
 



 


As battery temperature drops, you need to increase the charge voltage
to properly charge and, conversely, as temperatures rise, voltage needs
to be decreased to reduce the risk of overcharging.
 



 


I believe the range we site to accommodate for temperature is (in C);
 



 


0-16C: 2.5VPC
 


17-27C: 2.4VPC
 


28-40C: 2.36VPC
 



 


These are your max bulk / absorb voltage settings.
 



 


Regarding a low voltage disconnect, there is a significant difference
between on load and at rest voltages at 50% SOC.
 



 


Below is a table of a cell being discharged at a known constant load
(C/20) over time at 25C;
 




 


SOCVPC
 


100%   2.1
 


75% 2.01
 


50% 1.93
 


25%1.84
 


0%  1.75
 



 


Please note, this is for a cell(s) under constant load and at 25C.  If
the load increased, you would see lower voltages more quickly, 
Moreover, once the load is removed, resting voltages will increase
dramatically, i.e. 1.75VPC on load will equal ~1.95VPC at rest.  If you
were using 2.0VPC (on load) as your cut off, you would only have been
able to discharge ~25% - which does not include capacity reduction due
to temps <25C...and I know they are lower than that here!
 



 


Hope this is of some assistance.
 



 


Regards,
 



 


Jamie
 





 



James Surrette

Surrette Battery Co. Ltd
1 Station Rd.
Springhill, NS, CAN
B0M 1X0

Direct: 902.597.4027
Fax: 902.597.8447




>>> Hugh  1/13/2010 2:26 PM >>>
 


Hi wrenches,
 



 


I have been selling and using a few sets of Rolls 4000 series S530
 


batteries lately.
 



 


I have downloaded the Solar Battery manual from www.rollsbattery.com
 



 


It's very interesting.  At 17 degrees C you need to charge at 14.

Re: [RE-wrenches] discharging Rolls batteries

[James Surrette]

Hugh, 

Sorry if you found my response limited but have been traveling since early this 
am and don't have all information at hand, at the moment. 

Regarding temperature effects on capacity, earlier responses are spot on as the 
lower capacity is totally as a result of slower reaction times as a result of 
lower temperatures.   

Approximate Temp effects; 

40C = 104% 
25C = 100% 
5 to 10C = 90% 
-5C = 80% 
-22C = 60%
 
If you need more immediate responses, always feel free forward your questions 
to supp...@surrette.com, supp...@rollsbattery.com (both go to Serge) or 
p...@barden-uk.com (Technical Manager for Rolls Europe). 

Hope this helps, 

Jamie 

>>> Hugh  1/14/2010 12:49 PM >>>

Thanks, Bruce, 



I have lived with batteries for thirty years so I do know some of the basic 
things but for most of that time I used secondhand batteries.  The last couple 
of years using expensive new ones I find that they often perform less well.  I 
would like to tap into the enormous experience of this forum to calibrate some 
of my assumptions. 



I got a nice speedy and informative reply to my first post but when I asked too 
many questions in the second one it produced a lot less information.  Maybe I 
need to go straight to Rolls tech support for discharge curves at lower 
temperatures and lower currents. 



I do have one more question for any wrench who programs 'genstart' voltages on 
Outbacks and the like.  At what battery volts do you start the generator for a 
system with a large battery and small loads, in the winter? 



I would habitually use about 23.5 or 47 volts as a discharge limit voltage 
(time delayed).  However I am finding that from full charge at a temperature 
around 5 degrees C, I am getting under 25% of the battery capacity using this 
rule.  I this what I have to accept?  Is the capacity that much reduced by 
temperature?  Will I reduce the life expectancy and invalidate the warranty if 
I discharge it to 23/46 volts instead? 



I wonder why there is no temperature compensation on low battery voltage 
settings like there is on charging set points.  Do I just have to use the 
generator much more? 



There I go asking too many questions again.  I do have a few more that I will 
save for now.  Thanks for any more comments. 



best wishes 



Hugh 




  


Hi Hugh, When discussing battery characteristics with a chemist at my supplier 
years ago I was told the capacity at 0 deg c is around 50% of that at 25 deg c 
because the ion transfer rate within the cell is slowed by the low temperature. 
 This "loss" of capacity is recovered once the battery warms again.  The same 
reason why a fully charged cranking battery in a car can fail to turn the motor 
in cold weather.  Ion rate is so low it simply can't deliver enough current to 
the starter motor.  


   


So, the answer to the second part of your question is yes.  


   


A good thread with lots of useful background into how batteries really operate. 
 


   


Bruce Geddes  


PowerOn (at the other end of the world)  


   



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Hugh Piggott

Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk 


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Re: [RE-wrenches] discharging Rolls batteries

[Hugh]

Thanks, Bruce,

I have lived with batteries for thirty years so I do know some of the 
basic things but for most of that time I used secondhand batteries. 
The last couple of years using expensive new ones I find that they 
often perform less well.  I would like to tap into the enormous 
experience of this forum to calibrate some of my assumptions.


I got a nice speedy and informative reply to my first post but when I 
asked too many questions in the second one it produced a lot less 
information.  Maybe I need to go straight to Rolls tech support for 
discharge curves at lower temperatures and lower currents.


I do have one more question for any wrench who programs 'genstart' 
voltages on Outbacks and the like.  At what battery volts do you 
start the generator for a system with a large battery and small 
loads, in the winter?


I would habitually use about 23.5 or 47 volts as a discharge limit 
voltage (time delayed).  However I am finding that from full charge 
at a temperature around 5 degrees C, I am getting under 25% of the 
battery capacity using this rule.  I this what I have to accept?  Is 
the capacity that much reduced by temperature?  Will I reduce the 
life expectancy and invalidate the warranty if I discharge it to 
23/46 volts instead?


I wonder why there is no temperature compensation on low battery 
voltage settings like there is on charging set points.  Do I just 
have to use the generator much more?


There I go asking too many questions again.  I do have a few more 
that I will save for now.  Thanks for any more comments.


best wishes

Hugh


Hi Hugh, When discussing battery characteristics with a chemist at 
my supplier years ago I was told the capacity at 0 deg c is around 
50% of that at 25 deg c because the ion transfer rate within the 
cell is slowed by the low temperature.  This "loss" of capacity is 
recovered once the battery warms again.  The same reason why a fully 
charged cranking battery in a car can fail to turn the motor in cold 
weather.  Ion rate is so low it simply can't deliver enough current 
to the starter motor.


So, the answer to the second part of your question is yes.

A good thread with lots of useful background into how batteries 
really operate.


Bruce Geddes
PowerOn (at the other end of the world)


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--
Hugh Piggott

Scoraig Wind Electric
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Re: [RE-wrenches] discharging Rolls batteries

[dan]

More important than loss of capacity at low temps, (at least in my world), is the fact that battery freeze points rise considerably -- with a reduced State of charge... So you get a sort of double whammy... not only do you get less capacity, but they freeze easier.Dan BrownPresidentFoxfire Energy Corp.Renewable Energy Systems(802)-483-2564www.Foxfire-Energy.comNABCEP #092907-44


 Original Message 
Subject: Re: [RE-wrenches] discharging Rolls batteries
From: Hugh 
Date: Wed, January 13, 2010 5:47 pm
To: RE-wrenches 

  Hi Jamie,  Thanks for the very quick response!  I note that the temp compensation slope for charging is more like a curve.  It would be great to have a few more data points on this curve to match it against the linear compensation programmed into a Tristar controller.   But I guess there is some leeway anyway?  My personal 48-V household battery is rather large (2 x S530 in parallel) and the max charge rate is low (around 20-30 amps).  Would that be a reason to set a higher charging voltage maybe, or does it not make a difference?  As far as the disconnect point, I now have one data point for 50% discharge: 1.93V at C/20 and 25 degrees C.  Again it would be great to have a whole family of curves to work from in this area.  Most of the systems I work on have batteries that are sized for several days usage rather than 20 hours.  I don't really like to see the LBCO setpoint as low as 46.3 volts.  Capacity is reduced at low temperatures.  Now does this mean that there really is less energy in the battery, so that if I take out 50% of this reduced capacity I will only end up with a 50% state of charge once it has warmed, or is this just a performance hit that reduces the voltage and makes the battery capacity appear to be less?  Will the battery actually have less amphours to deliver, or will it just be delivering at a lower voltage?  My point is to ask whether it is legitimate to push the battery to a lower voltage in cold weather on the assumption that it is not really running that low, but just sluggish with cold?  I hope you don't mind all the questions.  I hope the others find the answers interesting too!  In an ideal world we could control our end-of-discharge based on amphours measured, but I have no faith in the calibration of such devices after a few partial charge swings up and down over period of days.  So the reality is that we rely on inverter LBCO settings or rules of thumb such as "never let the voltage drop below 47" to ensure that the batteries do not get abused.  Best wishes  Hugh  Hi Hugh & Wrenches,   Regarding the charge voltages you sited, you've got the gist.   As battery temperature drops, you need to increase the charge voltage to properly charge and, conversely, as temperatures rise, voltage needs to be decreased to reduce the risk of overcharging.   I believe the range we site to accommodate for temperature is (in C);   0-16C: 2.5VPC  17-27C: 2.4VPC  28-40C: 2.36VPC   These are your max bulk / absorb voltage settings.   Regarding a low voltage disconnect, there is a significant difference between on load and at rest voltages at 50% SOC.   Below is a table of a cell being discharged at a known constant load (C/20) over time at 25C; SOC    VPC  100%   2.1  75% 2.01  50% 1.93  25%    1.84  0%  1.75   Please note, this is for a cell(s) under constant load and at 25C.  If the load increased, you would see lower voltages more quickly,  Moreover, once the load is removed, resting voltages will increase dramatically, i.e. 1.75VPC on load will equal ~1.95VPC at rest.  If you were using 2.0VPC (on load) as your cut off, you would only have been able to discharge ~25% - which does not include capacity reduction due to temps <25C...and I know they are lower than that here!   Hope this is of some assistance.   Regards,   Jamie   James Surrette  Surrette Battery Co. Ltd 1 Station Rd. Springhill, NS, CAN B0M 1X0  Direct: 902.597.4027 Fax: 902.597.8447 >>> Hugh  1/13/2010 2:26 PM >>>  Hi wrenches,   I have been selling and using a few sets of Rolls 4000 series S530  batteries lately.   I have downloaded the Solar Battery manual from www.rollsbattery.com   It's very interesting.  At 17 degrees C you need to charge at 14.4  volts.  At 16 degrees it's 15 volts.  Hmm, Ok I get the idea.  I am  certainly learning to compensate my temperatures this winter.   I did a search in the document for the word 'discharge'.  I am  cutting off at just below nominal voltage and starting my generator.  I do not get much capacity.  A customer has suggested that a lot of  the discharge capacity is to be had at 11.5 volts (he has a 12v  system obviously).  Hmm.  Sounds a bit harsh.  But what voltage  should I be considering to be 50% discharged, and time to start the  genny?  And in a hard frost, the same voltage?   No mention of discharge in the solar battery manual.

Re: [RE-wrenches] discharging Rolls batteries

[Bruce Geddes]

Re: [RE-wrenches] discharging Rolls batteries
  Capacity is reduced at low temperatures.  Now does this mean that there 
really is less energy in the battery, so that if I take out 50% of this reduced 
capacity I will only end up with a 50% state of charge once it has warmed, or 
is this just a performance hit that reduces the voltage and makes the battery 
capacity appear to be less?  Will the battery actually have less amphours to 
deliver, or will it just be delivering at a lower voltage?  My point is to ask 
whether it is legitimate to push the battery to a lower voltage in cold weather 
on the assumption that it is not really running that low, but just sluggish 
with cold?
Hi Hugh, When discussing battery characteristics with a chemist at my supplier 
years ago I was told the capacity at 0 deg c is around 50% of that at 25 deg c 
because the ion transfer rate within the cell is slowed by the low temperature. 
 This "loss" of capacity is recovered once the battery warms again.  The same 
reason why a fully charged cranking battery in a car can fail to turn the motor 
in cold weather.  Ion rate is so low it simply can't deliver enough current to 
the starter motor.

So, the answer to the second part of your question is yes.

A good thread with lots of useful background into how batteries really operate.

Bruce Geddes
PowerOn (at the other end of the world)
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Re: [RE-wrenches] discharging Rolls batteries

[Hugh]

Hi Jamie,

Thanks for the very quick response!

I note that the temp compensation slope for charging is more like a 
curve.  It would be great to have a few more data points on this 
curve to match it against the linear compensation programmed into a 
Tristar controller.


But I guess there is some leeway anyway?  My personal 48-V household 
battery is rather large (2 x S530 in parallel) and the max charge 
rate is low (around 20-30 amps).  Would that be a reason to set a 
higher charging voltage maybe, or does it not make a difference?


As far as the disconnect point, I now have one data point for 50% 
discharge: 1.93V at C/20 and 25 degrees C.  Again it would be great 
to have a whole family of curves to work from in this area.  Most of 
the systems I work on have batteries that are sized for several days 
usage rather than 20 hours.  I don't really like to see the LBCO 
setpoint as low as 46.3 volts.


Capacity is reduced at low temperatures.  Now does this mean that 
there really is less energy in the battery, so that if I take out 50% 
of this reduced capacity I will only end up with a 50% state of 
charge once it has warmed, or is this just a performance hit that 
reduces the voltage and makes the battery capacity appear to be less? 
Will the battery actually have less amphours to deliver, or will it 
just be delivering at a lower voltage?  My point is to ask whether it 
is legitimate to push the battery to a lower voltage in cold weather 
on the assumption that it is not really running that low, but just 
sluggish with cold?


I hope you don't mind all the questions.  I hope the others find the 
answers interesting too!


In an ideal world we could control our end-of-discharge based on 
amphours measured, but I have no faith in the calibration of such 
devices after a few partial charge swings up and down over period of 
days.  So the reality is that we rely on inverter LBCO settings or 
rules of thumb such as "never let the voltage drop below 47" to 
ensure that the batteries do not get abused.


Best wishes

Hugh


Hi Hugh & Wrenches,


Regarding the charge voltages you sited, you've got the gist.


As battery temperature drops, you need to increase the charge 
voltage to properly charge and, conversely, as temperatures rise, 
voltage needs to be decreased to reduce the risk of overcharging.



I believe the range we site to accommodate for temperature is (in C);


0-16C: 2.5VPC

17-27C: 2.4VPC

28-40C: 2.36VPC


These are your max bulk / absorb voltage settings.


Regarding a low voltage disconnect, there is a significant 
difference between on load and at rest voltages at 50% SOC.



Below is a table of a cell being discharged at a known constant load 
(C/20) over time at 25C;




SOCVPC

100%   2.1

75% 2.01

50% 1.93

25%1.84

0%  1.75


Please note, this is for a cell(s) under constant load and at 25C. 
If the load increased, you would see lower voltages more quickly, 
Moreover, once the load is removed, resting voltages will increase 
dramatically, i.e. 1.75VPC on load will equal ~1.95VPC at rest.  If 
you were using 2.0VPC (on load) as your cut off, you would only have 
been able to discharge ~25% - which does not include capacity 
reduction due to temps <25C...and I know they are lower than 
that here!



Hope this is of some assistance.


Regards,


Jamie





James Surrette

Surrette Battery Co. Ltd
1 Station Rd.
Springhill, NS, CAN
B0M 1X0

Direct: 902.597.4027
Fax: 902.597.8447





 Hugh  1/13/2010 2:26 PM >>>


Hi wrenches,


I have been selling and using a few sets of Rolls 4000 series S530

batteries lately.


I have downloaded the Solar Battery manual from 
www.rollsbattery.com



It's very interesting.  At 17 degrees C you need to charge at 14.4

volts.  At 16 degrees it's 15 volts.  Hmm, Ok I get the idea.  I am

certainly learning to compensate my temperatures this winter.


I did a search in the document for the word 'discharge'.  I am

cutting off at just below nominal voltage and starting my generator.

I do not get much capacity.  A customer has suggested that a lot of

the discharge capacity is to be had at 11.5 volts (he has a 12v

system obviously).  Hmm.  Sounds a bit harsh.  But what voltage

should I be considering to be 50% discharged, and time to start the

genny?  And in a hard frost, the same voltage?


No mention of discharge in the solar battery manual.  Any ideas anyone?


Please don't tell me to buy an amphour meter (or worse still to sell

them).  Those things are way too confusing to calibrate.   I can tell

you that I am not getting many amphours out of my batteries in these

low temperatures before the voltage per cell drops below 2.


What do I tell my customers about the end-of-discharge voltage for

sustainable cycling of their Rolls batteries?  And is it temp

compensated?


thanks

--

Hugh Piggott


Scoraig Wind Electric

Scotland

http://www.

Re: [RE-wrenches] discharging Rolls batteries

[James Surrette]

Hi Chris, 

Fairly similar across the range. 

Regards, 

Jamie

>>> "Chris Worcester"  1/13/2010 4:14 PM >>>

Hi Jamie, 
How do these values correlate to the larger Rolls batteries? We have a
number of the 2-KS-33’s out there along with other various sized large
Rolls battery banks. 
   

Sincerely,

Chris Worcester 
Solar Wind Works
NABCEP Certified PV Installer
Phone: 530-582-4503
Fax: 530-582-4603
www.solarwindworks.com
ch...@solarwindworks.com
"Proven Energy Solutions" 

   

From:re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of James
Surrette
Sent: Wednesday, January 13, 2010 11:43 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] discharging Rolls batteries 

  
Hi Hugh & Wrenches, 
  
Regarding the charge voltages you sited, you've got the gist. 
  
As battery temperature drops, you need to increase the charge voltage
to properly charge and, conversely, as temperatures rise, voltage needs
to be decreased to reduce the risk of overcharging. 
  
I believe the range we site to accommodate for temperature is (in C); 
  
0-16C: 2.5VPC 
17-27C: 2.4VPC 
28-40C: 2.36VPC 
  
These are your max bulk / absorb voltage settings. 
  
Regarding a low voltage disconnect, there is a significant difference
between on load and at rest voltages at 50% SOC. 
  
Below is a table of a cell being discharged at a known constant load
(C/20) over time at 25C; 
  
SOCVPC 
100%   2.1 
75% 2.01 
50% 1.93 
25%1.84 
0%  1.75 
  
Please note, this is for a cell(s) under constant load and at 25C.  If
the load increased, you would see lower voltages more quickly, 
Moreover, once the load is removed, resting voltages will increase
dramatically, i.e. 1.75VPC on load will equal ~1.95VPC at rest.  If you
were using 2.0VPC (on load) as your cut off, you would only have been
able to discharge ~25% - which does not include capacity reduction due
to temps <25C...and I know they are lower than that here! 
  
Hope this is of some assistance. 
  
Regards, 
  
Jamie 




James Surrette

Surrette Battery Co. Ltd
1 Station Rd.
Springhill, NS, CAN
B0M 1X0

Direct: 902.597.4027
Fax: 902.597.8447




>>> Hugh  1/13/2010 2:26 PM >>> 
Hi wrenches, 
  
I have been selling and using a few sets of Rolls 4000 series S530 
batteries lately. 
  
I have downloaded the Solar Battery manual from www.rollsbattery.com 
  
It's very interesting.  At 17 degrees C you need to charge at 14.4 
volts.  At 16 degrees it's 15 volts.  Hmm, Ok I get the idea.  I am 
certainly learning to compensate my temperatures this winter. 
  
I did a search in the document for the word 'discharge'.  I am 
cutting off at just below nominal voltage and starting my generator. 
I do not get much capacity.  A customer has suggested that a lot of 
the discharge capacity is to be had at 11.5 volts (he has a 12v 
system obviously).  Hmm.  Sounds a bit harsh.  But what voltage 
should I be considering to be 50% discharged, and time to start the 
genny?  And in a hard frost, the same voltage? 
  
No mention of discharge in the solar battery manual.  Any ideas anyone?

  
Please don't tell me to buy an amphour meter (or worse still to sell 
them).  Those things are way too confusing to calibrate.   I can tell 
you that I am not getting many amphours out of my batteries in these 
low temperatures before the voltage per cell drops below 2. 
  
What do I tell my customers about the end-of-discharge voltage for 
sustainable cycling of their Rolls batteries?  And is it temp 
compensated? 
  
thanks 
-- 
Hugh Piggott 
  
Scoraig Wind Electric 
Scotland 
http://www.scoraigwind.co.uk 
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Re: [RE-wrenches] discharging Rolls batteries

[Chris Worcester]

Hi Jamie,

How do these values correlate to the larger Rolls batteries? We have a
number of the 2-KS-33's out there along with other various sized large Rolls
battery banks.

 

Sincerely,

Chris Worcester

Solar Wind Works
NABCEP Certified PV Installer
Phone: 530-582-4503
Fax: 530-582-4603
www.solarwindworks.com <http://www.solarwindworks.com/> 
ch...@solarwindworks.com
"Proven Energy Solutions"

 

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of James
Surrette
Sent: Wednesday, January 13, 2010 11:43 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] discharging Rolls batteries

 

Hi Hugh & Wrenches, 

 

Regarding the charge voltages you sited, you've got the gist. 

 

As battery temperature drops, you need to increase the charge voltage to
properly charge and, conversely, as temperatures rise, voltage needs to be
decreased to reduce the risk of overcharging. 

 

I believe the range we site to accommodate for temperature is (in C); 

 

0-16C: 2.5VPC 

17-27C: 2.4VPC 

28-40C: 2.36VPC 

 

These are your max bulk / absorb voltage settings. 

 

Regarding a low voltage disconnect, there is a significant difference
between on load and at rest voltages at 50% SOC. 

 

Below is a table of a cell being discharged at a known constant load (C/20)
over time at 25C; 

 

SOCVPC 

100%   2.1 

75% 2.01 

50% 1.93 

25%1.84 

0%  1.75 

 

Please note, this is for a cell(s) under constant load and at 25C.  If the
load increased, you would see lower voltages more quickly,  Moreover, once
the load is removed, resting voltages will increase dramatically, i.e.
1.75VPC on load will equal ~1.95VPC at rest.  If you were using 2.0VPC (on
load) as your cut off, you would only have been able to discharge ~25% -
which does not include capacity reduction due to temps <25C...and I know
they are lower than that here! 

 

Hope this is of some assistance. 

 

Regards, 

 

Jamie 






James Surrette

Surrette Battery Co. Ltd
1 Station Rd.
Springhill, NS, CAN
B0M 1X0

Direct: 902.597.4027
Fax: 902.597.8447




>>> Hugh  1/13/2010 2:26 PM >>> 

Hi wrenches, 

 

I have been selling and using a few sets of Rolls 4000 series S530 

batteries lately. 

 

I have downloaded the Solar Battery manual from
<http://www.rollsbattery.com> www.rollsbattery.com 

 

It's very interesting.  At 17 degrees C you need to charge at 14.4 

volts.  At 16 degrees it's 15 volts.  Hmm, Ok I get the idea.  I am 

certainly learning to compensate my temperatures this winter. 

 

I did a search in the document for the word 'discharge'.  I am 

cutting off at just below nominal voltage and starting my generator. 

I do not get much capacity.  A customer has suggested that a lot of 

the discharge capacity is to be had at 11.5 volts (he has a 12v 

system obviously).  Hmm.  Sounds a bit harsh.  But what voltage 

should I be considering to be 50% discharged, and time to start the 

genny?  And in a hard frost, the same voltage? 

 

No mention of discharge in the solar battery manual.  Any ideas anyone? 

 

Please don't tell me to buy an amphour meter (or worse still to sell 

them).  Those things are way too confusing to calibrate.   I can tell 

you that I am not getting many amphours out of my batteries in these 

low temperatures before the voltage per cell drops below 2. 

 

What do I tell my customers about the end-of-discharge voltage for 

sustainable cycling of their Rolls batteries?  And is it temp 

compensated? 

 

thanks 

-- 

Hugh Piggott 

 

Scoraig Wind Electric 

Scotland 

 <http://www.scoraigwind.co.uk> http://www.scoraigwind.co.uk 

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Re: [RE-wrenches] discharging Rolls batteries

[James Surrette]

Hi Hugh & Wrenches, 

Regarding the charge voltages you sited, you've got the gist. 

As battery temperature drops, you need to increase the charge voltage to 
properly charge and, conversely, as temperatures rise, voltage needs to be 
decreased to reduce the risk of overcharging. 

I believe the range we site to accommodate for temperature is (in C); 

0-16C: 2.5VPC 
17-27C: 2.4VPC 
28-40C: 2.36VPC 

These are your max bulk / absorb voltage settings. 

Regarding a low voltage disconnect, there is a significant difference between 
on load and at rest voltages at 50% SOC. 

Below is a table of a cell being discharged at a known constant load (C/20) 
over time at 25C; 


SOCVPC 
100%   2.1 
75% 2.01 
50% 1.93 
25%1.84 
0%  1.75 

Please note, this is for a cell(s) under constant load and at 25C.  If the load 
increased, you would see lower voltages more quickly,  Moreover, once the load 
is removed, resting voltages will increase dramatically, i.e. 1.75VPC on load 
will equal ~1.95VPC at rest.  If you were using 2.0VPC (on load) as your cut 
off, you would only have been able to discharge ~25% - which does not include 
capacity reduction due to temps <25C...and I know they are lower than that 
here! 

Hope this is of some assistance. 

Regards, 

Jamie 




James Surrette

Surrette Battery Co. Ltd
1 Station Rd.
Springhill, NS, CAN
B0M 1X0

Direct: 902.597.4027
Fax: 902.597.8447




>>> Hugh  1/13/2010 2:26 PM >>> 
Hi wrenches, 

I have been selling and using a few sets of Rolls 4000 series S530 
batteries lately. 

I have downloaded the Solar Battery manual from www.rollsbattery.com 

It's very interesting.  At 17 degrees C you need to charge at 14.4 
volts.  At 16 degrees it's 15 volts.  Hmm, Ok I get the idea.  I am 
certainly learning to compensate my temperatures this winter. 

I did a search in the document for the word 'discharge'.  I am 
cutting off at just below nominal voltage and starting my generator. 
I do not get much capacity.  A customer has suggested that a lot of 
the discharge capacity is to be had at 11.5 volts (he has a 12v 
system obviously).  Hmm.  Sounds a bit harsh.  But what voltage 
should I be considering to be 50% discharged, and time to start the 
genny?  And in a hard frost, the same voltage? 

No mention of discharge in the solar battery manual.  Any ideas anyone? 

Please don't tell me to buy an amphour meter (or worse still to sell 
them).  Those things are way too confusing to calibrate.   I can tell 
you that I am not getting many amphours out of my batteries in these 
low temperatures before the voltage per cell drops below 2. 

What do I tell my customers about the end-of-discharge voltage for 
sustainable cycling of their Rolls batteries?  And is it temp 
compensated? 

thanks 
-- 
Hugh Piggott 

Scoraig Wind Electric 
Scotland 
http://www.scoraigwind.co.uk 
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[RE-wrenches] discharging Rolls batteries

[Hugh]

Hi wrenches,

I have been selling and using a few sets of Rolls 4000 series S530 
batteries lately.


I have downloaded the Solar Battery manual from www.rollsbattery.com

It's very interesting.  At 17 degrees C you need to charge at 14.4 
volts.  At 16 degrees it's 15 volts.  Hmm, Ok I get the idea.  I am 
certainly learning to compensate my temperatures this winter.


I did a search in the document for the word 'discharge'.  I am 
cutting off at just below nominal voltage and starting my generator. 
I do not get much capacity.  A customer has suggested that a lot of 
the discharge capacity is to be had at 11.5 volts (he has a 12v 
system obviously).  Hmm.  Sounds a bit harsh.  But what voltage 
should I be considering to be 50% discharged, and time to start the 
genny?  And in a hard frost, the same voltage?


No mention of discharge in the solar battery manual.  Any ideas anyone?

Please don't tell me to buy an amphour meter (or worse still to sell 
them).  Those things are way too confusing to calibrate.   I can tell 
you that I am not getting many amphours out of my batteries in these 
low temperatures before the voltage per cell drops below 2.


What do I tell my customers about the end-of-discharge voltage for 
sustainable cycling of their Rolls batteries?  And is it temp 
compensated?


thanks
--
Hugh Piggott

Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk
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