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Question on Balanced Wiring of Battery Banks, Off-Grid Syst.

PostPosted: Thu Mar 31, 2011 5:12 am
by jpf1030
Howdy All,
In one of my prep subscriptions was a posting which I have posted below. It discusses balanced wiring for your battery bank for your off-grid power system. I had not heard about doing this before. Anyone with better knowledge of balancing wiring for a batter bank is welcome and encouraged to post a reply. Thanks...jpf
The easy way is to use a reverse return. With reverse return the length
of cable for each series string in the bank is equal. To do reverse
return assemble the battery bank. Feed the positive near one corner of
the bank and the negative catty-corner of the positive feed.

feed + ---[ ]---[ ]---
| |
---[ ]---[ ]---
| |
---[ ]---[ ]---
| |
---[ ]---[ ]--- Feed -


On 3/26/2011 11:29 PM, sheldon wrote:
> The only solution I see is to bring the cables from each pair to some sort of stud panel (brass, bronze?) where the bolts are spaced equi-distant from the other. The cable going to the distribution block would be in the middle of the battery connections. This should help keep the voltage drops of the interconnecting cable to a minimum, and balance should be closer to optimal.

Re: Question on Balanced Wiring of Battery Banks, Off-Grid S

PostPosted: Thu Mar 31, 2011 9:22 am
by wesurvive
One should remember the difference in a series and the difference in Parallel connections.

If not everyone knows, here is a simple diagram of each to give you an idea of how to do it.

Now for Parallel you will get more Amps, but voltage stays the same.
Putting batteries in Series will give you more voltage and no Amp increase.

If you have a 12 volt setup, you can use this to get more amps by putting the batteries in Parallel.


If you need 24 volts, you will want to hook two 12 volt in series, or four 6 volts in series to get 24 volts. The Amps will not change. Here is an example of batteries in a series. In this case it is set up for 36 volts in the diagram.


Now to figure Watts you use (P = E X i) , which is (Watts = Voltage X Amp hours) to get total Watts. I used a little (i) instead of a capital (I) because capital looks like a 1.
Watts is the total, volts is the voltage or total Voltage of the batteries and current is Ah or Amp Hours. Or if in Parallel total Ah or Amp Hours and voltage of one battery.
You get the same answer of Watts either way.

If you had three 12 volt 200 Ah batteries in parallel you would get:
12v × 600 A = 72,000 Watts

If you had the same batteries in series you get:
36v × 200 A = 72,000 Watts

Series = More voltage
Parallel = More Amps

To figure out how long your batteries will last here is a Peukert Calculator to help.
Just fill in the blanks and get a round estimate. Take in account for any longer cables and minus the 4 amps for a large Inverter. The Peukert number is going to be between 1.1 for good discharging batteries and 1.3 for less quality batteries. So I always figure in 1.2 to be a little more reasonable. Standard automotive batteries or used batteries I would use 1.3.

Hope that helps those who are new to this.

Re: Question on Balanced Wiring of Battery Banks, Off-Grid S

PostPosted: Thu Mar 31, 2011 2:44 pm
by jpf1030
Hey WeSurvive,
Thanks for posting the additional info which will be a good reference for people. However, you did not address the question of balancing the wiring, that is in regard to a distribution bar for more equal cable lengths to balance voltage drops among them. Did you have any thoughts on that dialogue in the posting that I had inserted with my question? Thanks...jpf