RE: [Repeater-Builder] Re: 24 vdc to 12 vdc

[Paul Finch]

Ron and All,

EZGO Golf Carts do this all the time with there electric golf carts, they
tie the tail lights and head light if any to the lower two 6 volt set of
batteries.  I admit it is not the best way to go about it but it seems to
work, as Ron said, it depends on the load and in the case of the carts the
duty cycle.

Paul
  

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright
Sent: Saturday, March 29, 2008 5:22 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Re: 24 vdc to 12 vdc

Al,

Your point is well taken and I understood this.  However, for the most part
a rig is not going to be drawing much current, in receive most of the time.
Little affect on the charge/discharge of the lower battery.  This is why in
a previous post I said depends on the load if wanting to connect across the
lower battery.

I think the solution to this topic came from you and others long ago.  Use a
24-12 converter.  They are about the same price as a battery.  However, for
the typical 50 W rig I would have no problem connecting across the bottom
battery.  The batteries get lots more abuse from the vehicle.  A 1 amp draw
99% of the time is little compared to the typical draw from the other stuff.
If drawing the currents you are talking about, again connecting to the lower
battery would be a problem.

73, ron, n9ee/r



>From: Al Wolfe <[EMAIL PROTECTED]>
>Date: 2008/03/29 Sat AM 01:07:34 CDT
>To: Repeater-Builder@yahoogroups.com
>Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc

>
>Ron, et al,
>A corollary of Kirchhoff's law says that all currents are equal in a 
>series circuit and all voltages are equal in a parallel circuit. Tapping a 
>load across the lower battery represents a parallel circuit of the bottom 
>battery and the load (radio) using 12 volts, and this parallel circuit is
in 
>series with the upper battery. If I supply 10 amps from the 24 volt
charging 
>circuit the upper battery receives 10 amps. However, if the load (radio) 
>draws 5 amps the bottom battery can only get the other 5 amps to charge it.

>Hence the application of Kirchhoff's law of currents equal in a series 
>circuit. There is no way for the bottom battery ever to be equally charged 
>with the top battery as the radio has drawn away some of the current from 
>the bottom battery. This current can never be replaced in this 
>configuration.
>
>If the charging current drops to 5 amps then the top battery get 5 amps 
>and the bottom battery gets none. If the charging device is off then the 
>bottom battery continues to supply 5 amps to the load (for a while!)
>
>If this condition continues very long the terminal voltage of the bottom 
>battery will be depressed towards 12 volts or lower but the 24 volt
charging 
>device doesn't know this and will attempt to apply full charging voltage 
>(probably 28 volts or so) to the two seriesed batteries. If the depressed 
>voltage on the bottom battery is down to 12 volts (typical) the top battery

>will get 16 volts, not a healthy situation! It only get worse as the 
>condition continues.
>
>Now there are solutions. One can switch batteries (top with bottom) 
>every few hours but who would actually do this? Or one could put a phantom 
>load across the top battery, something that draws about the same current as

>the radio but this would be rather wasteful of energy and tricky to make 
>work.
>
>Many 12 to 14 volt linear power supply circuits (Astron or ARRL 
>handbook) can be adapted to convert the 24 - 28 volt source down to 12 - 14

>volts just by injecting the +24 volts into the power supply after the main 
>rectifier diodes. But here again the power supply will use up about as much

>power as the load. (Kirchhoff's law again)
>
>If conserving power is important then a switching supply would be in 
>order as some of them are more than 90 % efficient.
>
>73,
>Al, K9SI
>
>>Re: 24 vdc to 12 vdc
>>Posted by: "Ron Wright" [EMAIL PROTECTED] n9eerptr
>>Date: Tue Mar 25, 2008 5:04 am ((PDT))
>
>>Depending on the load connecting across one battery, the one connected to 
>>ground or the lower of the 2 12 batteries, will work.  I >would not do is 
>>load is heavy because I am sure the charging system is for both batteries 
>>and draining one much more than the other >could upset things.
>
>>Kirchhoff's current law says the sum of the currents will be zero. 
>>Kirchhoff's voltage law says sum of voltages will be zero.  Not sure >why 
>>revelant here, but I am sure Kirchhoff had something else to do with 
>>voltage and current sources.  Would like to know.
>
>>73, ron, n9ee/r
>
>>>From: Al Wolfe <[EMAIL PROT

Re: [Repeater-Builder] Re: 24 vdc to 12 vdc

[Ron Wright]

Al,

Your point is well taken and I understood this.  However, for the most part a 
rig is not going to be drawing much current, in receive most of the time.  
Little affect on the charge/discharge of the lower battery.  This is why in a 
previous post I said depends on the load if wanting to connect across the lower 
battery.

I think the solution to this topic came from you and others long ago.  Use a 
24-12 converter.  They are about the same price as a battery.  However, for the 
typical 50 W rig I would have no problem connecting across the bottom battery.  
The batteries get lots more abuse from the vehicle.  A 1 amp draw 99% of the 
time is little compared to the typical draw from the other stuff.  If drawing 
the currents you are talking about, again connecting to the lower battery would 
be a problem.

73, ron, n9ee/r



>From: Al Wolfe <[EMAIL PROTECTED]>
>Date: 2008/03/29 Sat AM 01:07:34 CDT
>To: Repeater-Builder@yahoogroups.com
>Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc

>
>Ron, et al,
>A corollary of Kirchhoff's law says that all currents are equal in a 
>series circuit and all voltages are equal in a parallel circuit. Tapping a 
>load across the lower battery represents a parallel circuit of the bottom 
>battery and the load (radio) using 12 volts, and this parallel circuit is in 
>series with the upper battery. If I supply 10 amps from the 24 volt charging 
>circuit the upper battery receives 10 amps. However, if the load (radio) 
>draws 5 amps the bottom battery can only get the other 5 amps to charge it. 
>Hence the application of Kirchhoff's law of currents equal in a series 
>circuit. There is no way for the bottom battery ever to be equally charged 
>with the top battery as the radio has drawn away some of the current from 
>the bottom battery. This current can never be replaced in this 
>configuration.
>
>If the charging current drops to 5 amps then the top battery get 5 amps 
>and the bottom battery gets none. If the charging device is off then the 
>bottom battery continues to supply 5 amps to the load (for a while!)
>
>If this condition continues very long the terminal voltage of the bottom 
>battery will be depressed towards 12 volts or lower but the 24 volt charging 
>device doesn't know this and will attempt to apply full charging voltage 
>(probably 28 volts or so) to the two seriesed batteries. If the depressed 
>voltage on the bottom battery is down to 12 volts (typical) the top battery 
>will get 16 volts, not a healthy situation! It only get worse as the 
>condition continues.
>
>Now there are solutions. One can switch batteries (top with bottom) 
>every few hours but who would actually do this? Or one could put a phantom 
>load across the top battery, something that draws about the same current as 
>the radio but this would be rather wasteful of energy and tricky to make 
>work.
>
>Many 12 to 14 volt linear power supply circuits (Astron or ARRL 
>handbook) can be adapted to convert the 24 - 28 volt source down to 12 - 14 
>volts just by injecting the +24 volts into the power supply after the main 
>rectifier diodes. But here again the power supply will use up about as much 
>power as the load. (Kirchhoff's law again)
>
>If conserving power is important then a switching supply would be in 
>order as some of them are more than 90 % efficient.
>
>73,
>Al, K9SI
>
>>Re: 24 vdc to 12 vdc
>>Posted by: "Ron Wright" [EMAIL PROTECTED] n9eerptr
>>Date: Tue Mar 25, 2008 5:04 am ((PDT))
>
>>Depending on the load connecting across one battery, the one connected to 
>>ground or the lower of the 2 12 batteries, will work.  I >would not do is 
>>load is heavy because I am sure the charging system is for both batteries 
>>and draining one much more than the other >could upset things.
>
>>Kirchhoff's current law says the sum of the currents will be zero. 
>>Kirchhoff's voltage law says sum of voltages will be zero.  Not sure >why 
>>revelant here, but I am sure Kirchhoff had something else to do with 
>>voltage and current sources.  Would like to know.
>
>>73, ron, n9ee/r
>
>>>From: Al Wolfe <[EMAIL PROTECTED]>
>>>Date: 2008/03/24 Mon PM 04:36:54 CDT
>>>To: Repeater-Builder@yahoogroups.com
>>>Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc
>
>>
>>>>This is a very common issue in aircraft. The most obvious question is
>>>>does your jeep use 2 each 12 volt batteries? If so, simply connect
>>>>your radio across one of 'em.
>>
>>>This is done all the time but is a very, very bad idea. Ever hear of
>>>Kirchhoff's law? Check it out. It's a very quick way to ruin two 
>>>batteries.
>>
>>>Get a real converter. The switching kind are much more efficient than the
>>>linear voltage dropping kind.
>>
>>>Al, K9SI
> 
>
>   
> 


Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.

[Repeater-Builder] Re: 24 vdc to 12 vdc

[Al Wolfe]

Ron, et al,
A corollary of Kirchhoff's law says that all currents are equal in a 
series circuit and all voltages are equal in a parallel circuit. Tapping a 
load across the lower battery represents a parallel circuit of the bottom 
battery and the load (radio) using 12 volts, and this parallel circuit is in 
series with the upper battery. If I supply 10 amps from the 24 volt charging 
circuit the upper battery receives 10 amps. However, if the load (radio) 
draws 5 amps the bottom battery can only get the other 5 amps to charge it. 
Hence the application of Kirchhoff's law of currents equal in a series 
circuit. There is no way for the bottom battery ever to be equally charged 
with the top battery as the radio has drawn away some of the current from 
the bottom battery. This current can never be replaced in this 
configuration.

If the charging current drops to 5 amps then the top battery get 5 amps 
and the bottom battery gets none. If the charging device is off then the 
bottom battery continues to supply 5 amps to the load (for a while!)

If this condition continues very long the terminal voltage of the bottom 
battery will be depressed towards 12 volts or lower but the 24 volt charging 
device doesn't know this and will attempt to apply full charging voltage 
(probably 28 volts or so) to the two seriesed batteries. If the depressed 
voltage on the bottom battery is down to 12 volts (typical) the top battery 
will get 16 volts, not a healthy situation! It only get worse as the 
condition continues.

Now there are solutions. One can switch batteries (top with bottom) 
every few hours but who would actually do this? Or one could put a phantom 
load across the top battery, something that draws about the same current as 
the radio but this would be rather wasteful of energy and tricky to make 
work.

Many 12 to 14 volt linear power supply circuits (Astron or ARRL 
handbook) can be adapted to convert the 24 - 28 volt source down to 12 - 14 
volts just by injecting the +24 volts into the power supply after the main 
rectifier diodes. But here again the power supply will use up about as much 
power as the load. (Kirchhoff's law again)

If conserving power is important then a switching supply would be in 
order as some of them are more than 90 % efficient.

73,
Al, K9SI


>Re: 24 vdc to 12 vdc
>Posted by: "Ron Wright" [EMAIL PROTECTED] n9eerptr
>Date: Tue Mar 25, 2008 5:04 am ((PDT))

>Depending on the load connecting across one battery, the one connected to 
>ground or the lower of the 2 12 batteries, will work.  I >would not do is 
>load is heavy because I am sure the charging system is for both batteries 
>and draining one much more than the other >could upset things.

>Kirchhoff's current law says the sum of the currents will be zero. 
>Kirchhoff's voltage law says sum of voltages will be zero.  Not sure >why 
>revelant here, but I am sure Kirchhoff had something else to do with 
>voltage and current sources.  Would like to know.

>73, ron, n9ee/r




>>From: Al Wolfe <[EMAIL PROTECTED]>
>>Date: 2008/03/24 Mon PM 04:36:54 CDT
>>To: Repeater-Builder@yahoogroups.com
>>Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc

>
>>>This is a very common issue in aircraft. The most obvious question is
>>>does your jeep use 2 each 12 volt batteries? If so, simply connect
>>>your radio across one of 'em.
>
>>This is done all the time but is a very, very bad idea. Ever hear of
>>Kirchhoff's law? Check it out. It's a very quick way to ruin two 
>>batteries.
>
>>Get a real converter. The switching kind are much more efficient than the
>>linear voltage dropping kind.
>
>>Al, K9SI
 

Re: [Repeater-Builder] Re: 24 vdc to 12 vdc

[Mike Morris WA6ILQ]

At 12:07 PM 03/25/08, you wrote:
>At 09:56 3/25/2008, Steve S. Bosshard (NU5D) wrote:
> >Anyhow, without a fuse, the reverse protection diode or transorb in the
> >radio tries to short and shunt the reverse current from the radio.
>
>So you are saying it is in parallel (and reverse direction), not
>series (in forward direction)?

Parallel wired reverse protection diodes are standard design procedure.
Have been for years.  They gut away from series diodes in the 1980s...
and for a good reason.

I saw this years ago on a Midland 220 mobile that was rated at 10w.
At 13.8-14v (the average automobile the output was 12-13w or so.
with a voltage drop of only 7 tenths of a volt (the average drop across
a series diode) the output power was 8 to 9 w.
Modern radios with power bricks don't show that as much, but
you get the idea.

But a series diode still isn't going to save you in the dual battery
situation with the starter motor sucking 300 (or so) amps and
putting inductive spikes back on the line.

Mike

Re: [Repeater-Builder] Re: 24 vdc to 12 vdc

[Dave Gomberg]

At 09:56 3/25/2008, Steve S. Bosshard (NU5D) wrote:
>Anyhow, without a fuse, the reverse protection diode or transorb in the
>radio tries to short and shunt the reverse current from the radio.

So you are saying it is in parallel (and reverse direction), not 
series (in forward direction)?



-- 
Dave Gomberg, San Francisco   NE5EE gomberg1 at wcf dot com
All addresses, phones, etc. at http://www.wcf.com/ham/info.html
- 

Re: [Repeater-Builder] Re: 24 vdc to 12 vdc

[Dave Gomberg]

At 09:56 3/25/2008, Steve S. Bosshard (NU5D) wrote:
>Anyhow, without a fuse, the reverse protection diode or transorb in the
>radio tries to short and shunt the reverse current from the radio.

So you are saying it is in parallel (and reverse direction), not 
series (in forward direction)?



-- 
Dave Gomberg, San Francisco   NE5EE gomberg1 at wcf dot com
All addresses, phones, etc. at http://www.wcf.com/ham/info.html
- 

Re: [Repeater-Builder] Re: 24 vdc to 12 vdc

[Steve S. Bosshard (NU5D)]

This assumes that the installer did not fuse the + lead to the radio.  
Normally a 25 to 35 watt radio has a 15 amp fuse but you might be 
surprised how many times the power cable has been cut and no fuse.  
Anyhow, without a fuse, the reverse protection diode or transorb in the 
radio tries to short and shunt the reverse current from the radio.  Most 
of these can handle about 20 amps for a few seconds before the smoke 
gets out.  Then the reverse protection diode is essentially gone and 
next in line us usually the audio power amp, and RF PA.  While the radio 
tries to act like a short (for a few brief moments during cranking with 
the first battery dead the starter will draw hundreds of amps (or try 
to) thru the radio and protection diode.  This doesn't continue very 
long at all.  If the radio is properly fused, then the diode may short 
and blow the fuse, but without a fuse, the radio gets blown.

Steve

Dave Gomberg wrote:
> At 05:22 3/25/2008, Steve S. Bosshard (NU5D) wrote:
>   
>> any protection diodes - 10 amp protection diode against 400 amp starter
>> current - no contest.
>> 
>
> Steve, this confuses the dickens out of me.   I now understand the 
> reverse polarity part, but won't the protection diode be reverse 
> direction, and therefore the only relevant stat is the reverse 
> voltage, 12v, and therefore presumably within ratings?
>
> I don't see what the current has to do with it because the diode will 
> be non-conducting.   The current rating is only for the conducting 
> direction, right?  (with one battery dead, the other battery will cause
> reverse current thru the first battery during cranking and at that time the 
> protection diode will be briefly conducting).
>
>
>
>   

-- 
/Subscribe to dstar_digital/

Powered by groups.yahoo.com 

Re: [Repeater-Builder] Re: 24 vdc to 12 vdc

[Dave Gomberg]

At 05:22 3/25/2008, Steve S. Bosshard (NU5D) wrote:
>any protection diodes - 10 amp protection diode against 400 amp starter
>current - no contest.

Steve, this confuses the dickens out of me.   I now understand the 
reverse polarity part, but won't the protection diode be reverse 
direction, and therefore the only relevant stat is the reverse 
voltage, 12v, and therefore presumably within ratings?

I don't see what the current has to do with it because the diode will 
be non-conducting.   The current rating is only for the conducting 
direction, right?



-- 
Dave Gomberg, San Francisco   NE5EE gomberg1 at wcf dot com
All addresses, phones, etc. at http://www.wcf.com/ham/info.html
- 

Re: [Repeater-Builder] Re: 24 vdc to 12 vdc

[Steve S. Bosshard (NU5D)]

I have installed land mobile stuff in Gov Surplus fire equipment, (right 
next to Fort Hood) and 24 volt Forestry Service and 24 V street 
sweeping  equipment over the years.  I will NOT install any equipment 
across one battery in a 24 V string. 

Take it somewhere else and let them do it.  I will not.

Without exception, from a RaVo street sweeper to a 2.25 ton truck, the 
driver will forget and leave the equipment turned on that is across the 
one battery resulting in that one battery going dead. 

Now picture this.  2 batteries in a string.  One dead, one hot and 
healthy.  Just for sake of discussion. lets say the radio / siren, stuff 
is across the bottom battery.  Neg to GND, Positive to the Radio / Siren 
stuff AND the Negative of the second battery.  Positive of the second 
battery to the starter solenoid, etc.

As long as both batteries are charged this works GREAT.  When the bottom 
battery is dead, and the top battery is OK, and the driver hits the Cole 
Hersey Switch and tries to crank the engine it is just as though the 
first battery was no longer there.  Remember that the Positive of the 
bottom battery (now dead) is connected to the Negative if the second 
battery, thru the starter motor and back to ground.

This effectively does 2 things.  1 - reverse polarity is applied to the 
dead battery and whatever equipment is hooked to it.  2 - The cranking 
current will be in excess of 400 amps.

The fuse in the Neg side of the radio most likely won't make any 
difference because the case of the radio is tied to the chassis of the 
vehicle - ground.  The fuse in the positive side (if present) may save 
the radio, but most often, the audio PA and RF PA are history as well as 
any protection diodes - 10 amp protection diode against 400 amp starter 
current - no contest.

So, spring for the Astron or NewMar or whatever  DC-DC converter - I 
like the fully isolated if possible or else I would encourage anyone to 
stay away from the one battery connection.  Forklifts are even worse.  
Remember it is just a matter of time before stuff gets smoked...

Steve NU5D
School of Hard Knocks...

Ron Wright wrote:
> Depending on the load connecting across one battery, the one connected to 
> ground or the lower of the 2 12 batteries, will work.  I would not do is load 
> is heavy because I am sure the charging system is for both batteries and 
> draining one much more than the other could upset things.
>   

RE: [Repeater-Builder] Re: 24 vdc to 12 vdc

[John Barrett]

The practical effect is that the charge on the two batteries will be
imbalanced, and should the charger ever get the more charge battery fully
charged, the under charged battery will fool the charger into thinking the
pair is not fully charged, resulting the in the fully charged battery being
overcharged, and if not quickly damaged, then at least dramatically reduced
in lifetime.

 

Some sort of converter is required to keep the load balanced across both
batteries, and therefore the charge on the batteries balanced.. whether it
be Xantrex or Astron. either will do the job and protect your batteries.

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright
Sent: Tuesday, March 25, 2008 6:04 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Re: 24 vdc to 12 vdc

 

Depending on the load connecting across one battery, the one connected to
ground or the lower of the 2 12 batteries, will work. I would not do is load
is heavy because I am sure the charging system is for both batteries and
draining one much more than the other could upset things.

Kirchhoff's current law says the sum of the currents will be zero.
Kirchhoff's voltage law says sum of voltages will be zero. Not sure why
revelant here, but I am sure Kirchhoff had something else to do with voltage
and current sources. Would like to know.

73, ron, n9ee/r

>From: Al Wolfe <[EMAIL PROTECTED] <mailto:k9si%40arrl.net> >
>Date: 2008/03/24 Mon PM 04:36:54 CDT
>To: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com>
yahoogroups.com
>Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc

> 
>>This is a very common issue in aircraft. The most obvious question is
>>does your jeep use 2 each 12 volt batteries? If so, simply connect
>>your radio across one of 'em.
>
>This is done all the time but is a very, very bad idea. Ever hear of 
>Kirchhoff's law? Check it out. It's a very quick way to ruin two batteries.
>
>Get a real converter. The switching kind are much more efficient than the 
>linear voltage dropping kind.
>
>Al, K9SI
> 
>
> 

Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.

 

Re: [Repeater-Builder] Re: 24 vdc to 12 vdc

[Ron Wright]

Depending on the load connecting across one battery, the one connected to 
ground or the lower of the 2 12 batteries, will work.  I would not do is load 
is heavy because I am sure the charging system is for both batteries and 
draining one much more than the other could upset things.

Kirchhoff's current law says the sum of the currents will be zero.  Kirchhoff's 
voltage law says sum of voltages will be zero.  Not sure why revelant here, but 
I am sure Kirchhoff had something else to do with voltage and current sources.  
Would like to know.

73, ron, n9ee/r




>From: Al Wolfe <[EMAIL PROTECTED]>
>Date: 2008/03/24 Mon PM 04:36:54 CDT
>To: Repeater-Builder@yahoogroups.com
>Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc

>
>>This is a very common issue in aircraft. The most obvious question is
>>does your jeep use 2 each 12 volt batteries? If so, simply connect
>>your radio across one of 'em.
>
>This is done all the time but is a very, very bad idea. Ever hear of 
>Kirchhoff's law? Check it out. It's a very quick way to ruin two batteries.
>
>Get a real converter. The switching kind are much more efficient than the 
>linear voltage dropping kind.
>
>Al, K9SI
> 
>
>   
> 


Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.

[Repeater-Builder] Re: 24 vdc to 12 vdc

[Al Wolfe]

>This is a very common issue in aircraft. The most obvious question is
>does your jeep use 2 each 12 volt batteries? If so, simply connect
>your radio across one of 'em.

This is done all the time but is a very, very bad idea. Ever hear of 
Kirchhoff's law? Check it out. It's a very quick way to ruin two batteries.

Get a real converter. The switching kind are much more efficient than the 
linear voltage dropping kind.

Al, K9SI