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Old 09-04-2015, 05:16 PM   #1
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Default Series/parallel battery "balancer"

The discussions of the etrek battery wiring brought up the question of balancers in battery banks, and while the way Roadtrek had their "mechanical" balancer wired in would not do much for the 24/12v system they had, it is an interesting idea in a plain Jane 4 X 6v setup, like several of us are working on.

All the balancer Roadtrek uses is a cable(s) between the intermediate connectionS in a series/parallel string. The benefit would be it would put any given two batteries on different series strings at identical voltages, which may help keep certain batteries from mismatching as much.

In a simple 4 battery setup it would look like this.



Checking the voltage in our two pair, neither single battery matches the other in the string, or the other string. I do read .07v between the two connections that would be at the ends of the red line.

I have looked around, and not found any reference on the battery sites to say this is either good or bad. I would be very easy to do for anyone that has all 4 in the same place, if it did any good.

Anybody ever seen anything mentioned about doing this setup?
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Old 09-04-2015, 05:42 PM   #2
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Hmm. Interesting.

There is another pattern, which is probably electrically equivalent (modulus wire losses), but conceptually clearer. That is to remove one of the two vertical wires between the top and bottom banks and instead to connect the negative terminals of the two top batteries. That way it becomes clear that what is happening is that we have two large 12V banks, each made up of two smaller 12V batteries wired in parallel. These two banks are then wired in series to produce 24 volts. The same idea drawn differently can be seen here:

battery series:parallel.jpg

which I found here:

BatteryStuff Articles | Understanding Series and Parallel Battery Configurations

I find it easier to reason about the behavior of the system if done that way.
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Old 09-04-2015, 06:24 PM   #3
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Yep, that sure looks like the equivalent circuit, and is the old standard parallel first , then series, while the one I had from Lifeline was series first, then parallel. I think the only difference would be the ability to match all the cable lengths, which might be an issue. The nice part of just adding the jumper is that is will carry near zero current, so it won't mess up balance of wiring on a system. On a setup like you have, with two batteries in each place, there could be a definite benefit from doing the setup you show, because you would only need the single cable between them.

I am going to be tied up for quite a while here, but when I get ready to do the install in the fall, I probably will just put in a jumper and run a couple of charge cycles to see what happens.

To do it really right, I would probably need to put in the jumper, and then also use 6v battery electronic balancer to balance the two parallel pairs to each other. I think Sterling makes one but don't know how spendy or how much parasitic they would take.
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Old 09-04-2015, 06:29 PM   #4
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When you do your tests it would be cool to put in a shunt and see what kind of current flows.
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Old 09-04-2015, 06:41 PM   #5
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Quote:
Originally Posted by avanti View Post
When you do your tests it would be cool to put in a shunt and see what kind of current flows.
I actually may be able to do that, depending on when I do the test, as I will have an second shunt available once I remove the Trimetric currently in the van. Good idea.
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