Re: [EVDL] Reconfigurable Battery Packs

[Ed Blackmond via EV]

> On Oct 23, 2018, at 2:14 PM, Lee Hart via EV  wrote:
> 
> bvgandhi via EV wrote:
>> Hi,
>> 
>> I have lately come across a lot of work done on reconfigurable battery packs
>> which uses the concept of scheduling of battery cells. Instead of oversizing
>> the battery pack with too many cells and adding additional failure modes,
>> reconfiguration works on the idea of using switches and scheduling cells as
>> per power requirement of the vehicle. Does anyone here have any opinion or
>> ideas about this this or has seen previous practical implementations ?
> 
> In general, if you have the cells, then *use* the cells. Otherwise, they are 
> just dead weight.
> 
> All types of batteries have internal resistance. This means they are more 
> efficient at lower currents (more amphours, less voltage drop). Discharging 
> them at higher currents increases the I^2R losses (i.e. less range, more 
> voltage drop). So it is better to always draw power from all the cells, 
> rather than first from some of the cells, then from different cells, etc.
> 
> However, cells have different capacities. If you always draw the same power 
> from every cell, then some will go dead sooner than others. So it makes sense 
> to have some method to distribute the load between the cells according to 
> their ability.
> 
> Many old EVs had reconfigurable battery packs. Their controllers were 
> basically a set of switches that reconnected the pack in various 
> series/parallel combinations to adjust the voltage and thus speed. During the 
> times when cells are in parallel, they are forced to the same voltage, which 
> automatically balances the state of charge between them. The ones at a lower 
> state of charge naturally supplied less current. See the Henney Kilowatt 
> controller at  for an example.

Another way to approach it is to use the switching to build an AC rather than 
DC battery pack.  By switching between different series/parallel combinations 
it is possible to create a multi-level converter. This can create very good 
sign waves without a frequency component at a PWM frequency. Create three 
strings operating 120 degrees out of phase from each other and the battery 
circuit becomes a very nice variable frequency three phase drive. Running the 
strings in phase and synchronized to the utility grid and the battery circuit 
becomes a charger. With sensors monitoring all the cells, they can be switched 
in and out of the circuit keeping all the cells at the same state of charge. 
One circuit integrates the function of battery cell protection, motor drive, 
and charger.

Ed
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Re: [EVDL] Lithium EV battery in colder weather

[Michael Ross via EV]

I believe those cells are LiFePO they are are also at risk from being
stored, fully charged, at temps above 95°F. or charged at temps above 95°F.
I too have ruined LiFePO cells this way.

The paper I read was talking about below freezing of water temps as
problematic, but some cells can take below 0°F temps before encountering
difficulty.

I bet all the car companies have worked out the conditions to be avoided
and manage for good cell life. (Nissan Leaf certainly had to learn about
too high temps and upgrade their management.)  The DIYer has to be more
careful and learn more to avoid costly problems.

You can't broad stroke tar all cells and cell chemistries.  There has been
a lot of learning and improvement in the past decade.

On Tue, Oct 23, 2018 at 7:42 PM Hoegberg via EV  wrote:

> EV  för Robert Bruninga via EV <
> ev@lists.evdl.org>
> den 23 oktober 2018 04:52
> Electric Vehicle Discussion List
> Robert Bruninga
> [EVDL] Lithium EV battery in colder weather
>
>
> > I know that Lithium batteries perform worse at lower temps.  But what
> does
> that mean?
> > Charging, or using? which is worse.
>
>
> The "rule of thumb":
> -Avoid any normal/slow charging below zero degrees in cell temp,
>
> (I dont know what that is in the degrees of freedom-scale, lets call it
> "below freezing")
>
> That rule also apply to deeply frozen laptops, cellphones and so on...
>
> (a sloow trickle charge might be without harm if it is not like
> deep-space-winter-cold standard chemistry cell, just a bit below freezing
> or so. But  I do not know, probably "it depends"..)
>
> Li plating seems real! I think I destroyed a Thundersky, at "only" 0.3C
> charging test at -28'C
>
> *
>
> Discharging cold cells seems "ok" , if you do Low C-rates.
> (May be to run the battery heater for several hours?)
>
> The Thundersky 90Ah cells did perform *extremely* poor in my low temp
> Discharge test.
> Like -BAM- down to my cut off at 1.8 volt, with a very weak load..
>
>
>
> /John
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>

-- 
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Re: [EVDL] Lithium EV battery in colder weather

[Hoegberg via EV]

EV  för Robert Bruninga via EV 
den 23 oktober 2018 04:52
Electric Vehicle Discussion List
Robert Bruninga
[EVDL] Lithium EV battery in colder weather


> I know that Lithium batteries perform worse at lower temps.  But what does
that mean?
> Charging, or using? which is worse.


The "rule of thumb":
-Avoid any normal/slow charging below zero degrees in cell temp,

(I dont know what that is in the degrees of freedom-scale, lets call it "below 
freezing")

That rule also apply to deeply frozen laptops, cellphones and so on...

(a sloow trickle charge might be without harm if it is not like 
deep-space-winter-cold standard chemistry cell, just a bit below freezing or 
so. But  I do not know, probably "it depends"..)

Li plating seems real! I think I destroyed a Thundersky, at "only" 0.3C 
charging test at -28'C

*

Discharging cold cells seems "ok" , if you do Low C-rates.
(May be to run the battery heater for several hours?)

The Thundersky 90Ah cells did perform *extremely* poor in my low temp Discharge 
test.
Like -BAM- down to my cut off at 1.8 volt, with a very weak load..



/John
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Re: [EVDL] Lithium EV battery in colder weather

[Hoegberg via EV]

EV  för Robert Bruninga via EV 
den 23 oktober 2018 04:52
Electric Vehicle Discussion List
Robert Bruninga
[EVDL] Lithium EV battery in colder weather

> I know that Lithium batteries perform worse at lower temps.  But what does
that mean?
> Charging, or using? which is worse.

In general, semifast/fastCharging (or any charging at all below about zero 
degrees seems to be the killer,

look up: the "Li-plating" problem in cold cells at fast charging


/John


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Re: [EVDL] EVLN: The physics of slapping solar panels on cars

[Peri Hartman via EV]

The Stella is an impressive car. I did read the specs, though not 
carefully. The fault is my assumption that climbing, say, 1000m would 
take too much energy. In fact, the climbing by itself probably would 
take between 1 and 2kwh. That leaves plenty. Wow !

Peri

-- Original Message --
From: "Lawrence Rhodes via EV" 
To: "ev@lists.evdl.org" 
Cc: "Lawrence Rhodes" 
Sent: 23-Oct-18 10:03:07 AM
Subject: Re: [EVDL] EVLN: The physics of slapping solar panels on cars

Peri I doubt you have completely looked at the specs of the Stella 
cars.  They have huge trunks and are touted as "Family Cars" basically 
a small SUV.  They use a 15kw battery which without solar has a 400 
mile range.  So they would charge quickly just on Chademo or CCS.  Just 
because a car is solar doesn't mean you have to only use solar.  Ad to 
that it simply has a very long range and is good for everything  but 
towing.  I think a dead deer would fit in the trunk. It is certainly 
the perfect mad max vehicle for when there is no gas.  This vehicle 
will still be able to go 400 miles after every 10 hours in the sun and 
be able to go 45 mph infinitely while the sun shines. The first Stella 
easily made it up the coast on Route 1 and 101  LA to San Francisco up 
and down all those hills.Lawrence Rhodes



Message: 3
Date: Sun, 21 Oct 2018 22:33:59 +
From: "Peri Hartman" 
To: "Electric Vehicle Discussion List" 
Subject: Re: [EVDL] EVLN: The physics of slapping solar panels on cars
Message-ID: 
Content-Type: text/plain; format=flowed; charset=utf-8


What I mean is I (or you or the huddling masses...) want something that
works for a 15 mile solo commute, works to take the family out to
dinner, works to go skiing (hiking, fishing, hunting, ...) for the day,
and works to go out of town for the weekend. I think the Stella might 
be

able to do the first two, for a large percentage of people. The latter
two? I doubt it.

Now, for going out of town, it wouldn't be too hard to make 
arrangements

to easily pick up a rental. The other case gets harder. You have a lot
of elevation gain, meaning you'll need a pretty hefty battery since
solar isn't going to be anywhere near adequate.



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Re: [EVDL] Reconfigurable Battery Packs

[Lee Hart via EV]

bvgandhi via EV wrote:

Hi,

I have lately come across a lot of work done on reconfigurable battery packs
which uses the concept of scheduling of battery cells. Instead of oversizing
the battery pack with too many cells and adding additional failure modes,
reconfiguration works on the idea of using switches and scheduling cells as
per power requirement of the vehicle. Does anyone here have any opinion or
ideas about this this or has seen previous practical implementations ?


In general, if you have the cells, then *use* the cells. Otherwise, they 
are just dead weight.


All types of batteries have internal resistance. This means they are 
more efficient at lower currents (more amphours, less voltage drop). 
Discharging them at higher currents increases the I^2R losses (i.e. less 
range, more voltage drop). So it is better to always draw power from all 
the cells, rather than first from some of the cells, then from different 
cells, etc.


However, cells have different capacities. If you always draw the same 
power from every cell, then some will go dead sooner than others. So it 
makes sense to have some method to distribute the load between the cells 
according to their ability.


Many old EVs had reconfigurable battery packs. Their controllers were 
basically a set of switches that reconnected the pack in various 
series/parallel combinations to adjust the voltage and thus speed. 
During the times when cells are in parallel, they are forced to the same 
voltage, which automatically balances the state of charge between them. 
The ones at a lower state of charge naturally supplied less current. See 
the Henney Kilowatt controller at 
 for an example.


--
Obsolete (Ob-so-LETE). Adjective. 1. Something that is simple,
reliable, straightforward, readily available, easy to use, and
affordable. 2. Not what the salesman wants you to buy.
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Lithium EV battery in colder weather

[Lee Hart via EV]

Jay Summet via EV wrote:

Note that using a battery (both charging and discharging) will heat the
battery because of the waste heat loss inherent in the inefficiencies of
the charging/discharging process.


That's true. But the efficiency of good EV cells is high (95% or more) 
that very little waste heat is generated. And, the pack is so heavy that 
this heat does not change the pack temperature very much. It's likely to 
be 10 deg.F or less.


Charge efficiency is worst when the pack is nearly full. The older 
lead-acid or nickel-based chemistries could generate more heat because 
they were routinely overcharged for balancing. But that's a bad idea 
with lithium chemistries -- overcharging is avoided because it 
dramatically shortens life!



QuickCharging / Supercharging will heat up the battery faster/more than
a regular L2 charger or trickle charger.


Yes. The faster the charge, the less efficient it is and the more waste 
heat will be generated.


--
Obsolete (Ob-so-LETE). Adjective. 1. Something that is simple,
reliable, straightforward, readily available, easy to use, and
affordable. 2. Not what the salesman wants you to buy.
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Reconfigurable Battery Packs

[EVDL Administrator via EV]

On 23 Oct 2018 at 13:13, bvgandhi via EV wrote:

> I don't think weight is a factor here. I think the idea is to have a battery
> health conscious system to improve longevity and reliability of usage, and to
> have sufficient rest periods for batteries to recover discharge capacity. I
> think battery swap is mainly an alternative to fast charging. 

If the idea is to have batteries of differing capacity for different vehicle 
missions and trips, and perhaps for the EV user to pay according to 
momentary need, that's probably a decent idea.  

Not exactly original, though.  It's been discussed here many times before, 
and no doubt in other forums.  

Battery swapping instead of fast charging has also been much discussed.  As 
with anything, there are pros and cons.  I'm not going to try to list them 
all; see the archive for those discussions.  

http://evdl.org/archive/

Variable battery size has been implemented on a coarse and somewhat less 
efficient scale with battery trailers.  When you need more range, you pull a 
trailer full of batteries.  One example is the "Solectria Super Force" that 
Team New England ran in 2 or 3 Tour de Sol events in the early 2000s.  

https://www.priusonline.com/10-ev-general/10672-tds-report-49-team-profile-
solectria-super-force.html

https://v.gd/M8sizS

Photo:

https://i.postimg.cc/B6MBBsvB/olaf-bleck-superforce-web.png

OTOH, if you're talking about switching cells in and out of a battery 
dynamically, I don't think that's an efficient use of resources.  A high 
capacity battery used lightly will last longer, so I can't see that you're 
really gain anything.  Build it and prove me wrong. :-)

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: [EVDL] Reconfigurable Battery Packs

[Jay Summet via EV]

I suppose if you are making a battery using non-matched cells that may 
be useful, but it seems like it would be easier, cheaper, and more 
reliable to just use closely matched cells and then have a standard BMS 
system on each set of parallel cells.


Jay

On 10/23/18 2:13 PM, bvgandhi via EV wrote:

I don't think weight is a factor here. I think the idea is to have a battery
health conscious system to improve longevity and reliability of usage, and
to have sufficient rest periods for batteries to recover discharge capacity.
I think battery swap is mainly an alternative to fast charging.

--
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Re: [EVDL] Reconfigurable Battery Packs

[bvgandhi via EV]

I don't think weight is a factor here. I think the idea is to have a battery
health conscious system to improve longevity and reliability of usage, and
to have sufficient rest periods for batteries to recover discharge capacity.
I think battery swap is mainly an alternative to fast charging. 

--
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Re: [EVDL] Reconfigurable Battery Packs

[Jay Summet via EV]

On 10/23/18 1:11 PM, bvgandhi via EV wrote:

Hi,

I have lately come across a lot of work done on reconfigurable battery packs
which uses the concept of scheduling of battery cells. Instead of oversizing
the battery pack with too many cells and adding additional failure modes,
reconfiguration works on the idea of using switches and scheduling cells as
per power requirement of the vehicle. Does anyone here have any opinion or
ideas about this this or has seen previous practical implementations ?


Unless you can REMOVE some of the cells when you don't need them so you 
are not carrying around the weight, I see no benefit to switching cells 
in or out of a circuit (but keeping them in the vehicle). I think it 
would be better to use all of the cells you have (to reduce the total 
amp draw / heat buildup / cycle count on any particular cell).


If you can remove sections of the pack, reducing the weight you are 
carrying around for short trips may have some benefits, but I see the 
major benefit there as a battery swapping "fast charging" ability.


(Or easy battery replacement/upgrades over time.)

Jay
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Re: [EVDL] The physics of slapping solar panels on cars

[Lawrence Rhodes via EV]

Below is old thinking.  You must engineer the solar panels to the size and 
weight of the vehicle.  Lets say Stella cars have a 1000 pound weight.  15kw 
powers them 300 miles. They charge in 10 hours and can go 40 mph infinitely. 
They must have a 1.5kw solar panel. Lets just take an old ULTRAVAN.  It is 3000 
pounds.  Put a 3kw solar panel on it and a Leaf drivetrain and you have 
something that can go 50 to 80  miles depending on speed every 10 hours. Don't 
forget the panels will power the vehicle in real time. Just do the math and 
engineering and your have something. Or you can keep converting 2 ton vehicles 
and say it can't be done. My 4kw electric trike should have a 400watt or bigger 
solar panel.   Lawrence Rhodes



From: Robert Bruninga 
To: Electric Vehicle Discussion List 
Subject: Re: [EVDL] EVLN: The physics of slapping solar panels on cars
    (charging while parked)
Message-ID: <0ebd61c4f49143077046bb2df564a...@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"

ALL EV's are predominantly charged while parked.  Solar panels on EV's are
not for propulsion power but for battery charging during the 8 to 16 hour
solar day while parked in the sun, not just the 30 minutes the car is in
use.  This is for those without a dedicated charger at home.

Bob


-Original Message-
From: EV  On Behalf Of Alan Arrison via EV
Sent: Sunday, October 21, 2018 7:26 PM
To: ev@lists.evdl.org
Cc: Alan Arrison 
Subject: Re: [EVDL] EVLN: The physics of slapping solar panels on cars

The numbers don't add up for solar panels on automobiles, never have, never
will.

This has been proven time and time again.

There is no way it gets even 20 miles per kWh under anything but perfect
conditions and slow speeds.

And the energy from the panels again is under perfect conditions.

It is so light because it has almost no crash protection.

Al
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Re: [EVDL] Lithium EV battery in colder weather

[Jay Summet via EV]

On 10/23/18 11:21 AM, Lee Hart via EV wrote:

If capacity and performance in cold weather are important, that means 
providing some way to insulate and heat the battery to keep it up to 
operating temperature.


Note that using a battery (both charging and discharging) will heat the 
battery because of the waste heat loss inherent in the inefficiencies of 
the charging/discharging process.


So you can charge your battery right before you leave in the morning to 
heat it up a bit, and then discharging it on the drive to work will add 
more heat. The real question is how long is it parked without being used 
and how fast does it drop in temperature. (This is where the insulation 
comes in)


QuickCharging / Supercharging will heat up the battery faster/more than 
a regular L2 charger or trickle charger.


Jay
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[EVDL] Reconfigurable Battery Packs

[bvgandhi via EV]

Hi,

I have lately come across a lot of work done on reconfigurable battery packs
which uses the concept of scheduling of battery cells. Instead of oversizing
the battery pack with too many cells and adding additional failure modes,
reconfiguration works on the idea of using switches and scheduling cells as
per power requirement of the vehicle. Does anyone here have any opinion or
ideas about this this or has seen previous practical implementations ?

 

--
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Re: [EVDL] EVLN: The physics of slapping solar panels on cars

[Lawrence Rhodes via EV]

Peri I doubt you have completely looked at the specs of the Stella cars.  They 
have huge trunks and are touted as "Family Cars" basically a small SUV.  They 
use a 15kw battery which without solar has a 400 mile range.  So they would 
charge quickly just on Chademo or CCS.  Just because a car is solar doesn't 
mean you have to only use solar.  Ad to that it simply has a very long range 
and is good for everything  but towing.  I think a dead deer would fit in the 
trunk. It is certainly the perfect mad max vehicle for when there is no gas.  
This vehicle will still be able to go 400 miles after every 10 hours in the sun 
and be able to go 45 mph infinitely while the sun shines. The first Stella 
easily made it up the coast on Route 1 and 101  LA to San Francisco up and down 
all those hills.    Lawrence Rhodes


Message: 3
Date: Sun, 21 Oct 2018 22:33:59 +
From: "Peri Hartman" 
To: "Electric Vehicle Discussion List" 
Subject: Re: [EVDL] EVLN: The physics of slapping solar panels on cars
Message-ID: 
Content-Type: text/plain; format=flowed; charset=utf-8


What I mean is I (or you or the huddling masses...) want something that 
works for a 15 mile solo commute, works to take the family out to 
dinner, works to go skiing (hiking, fishing, hunting, ...) for the day, 
and works to go out of town for the weekend. I think the Stella might be 
able to do the first two, for a large percentage of people. The latter 
two? I doubt it.

Now, for going out of town, it wouldn't be too hard to make arrangements 
to easily pick up a rental. The other case gets harder. You have a lot 
of elevation gain, meaning you'll need a pretty hefty battery since 
solar isn't going to be anywhere near adequate.


   
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Re: [EVDL] Lithium EV battery in colder weather

[Lee Hart via EV]

Robert Bruninga via EV wrote:

I know that Lithium batteries perform worse at lower temps.  But what does
that mean? Charging, or using? which is worse. Does cold prevent the battery
from accepting a given capacity, or does cold prevent one from using a given
capacity that is already in the battery?


Batteries are "cold blooded". Cold temperatures slow the chemical 
reaction rates and increase the internal resistance, making both 
charging and discharging more difficult. The capacity is still there; 
you just can't use it without the cell voltage going out of spec.


But the exact amount of performance loss varies. There are many 
variations of lithium cells, and each is affected differently by 
temperature.


If capacity and performance in cold weather are important, that means 
providing some way to insulate and heat the battery to keep it up to 
operating temperature.

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affordable. 2. Not what the salesman wants you to buy.
--
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