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Acadia 11-15-2008 08:08 PM

6v wiring
 
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Hi,

Just about to wire in 4 6v golf cart batteries on my boat. I was going to connect each pair in series then in parallel. But as I was flipping through the Calder manual, I found this in his book at around page 22.

Quote:

In a series/parallel setup. It is an excellent practice to cross-connect the positives and negatives on the individual 6v batteries, or 2v cells, (as shown in a picture). This minimizes the differences in the way the batteries work and perform.
I don't have a scanner where I am but I took a picture from another post and did a little msn paint on it to represent the diagram in the Calder book. The blue lines show the cross-connect that are in addition to the normal setup.

Do you connect your batteries this way? Did I read something wrong?

hellosailor 11-15-2008 08:35 PM

I think what he's referring to is a more common setup:

Connect your positive "main" to bank A, connect your negative "main" to bank B. Couple each bank only at the end points--no blue lines that you have drawn.

The purpose of this is so that the "main" wire length is the same to each bank, and the cross-over wire is the same to each bank, once they average at.

If you connected the mains both to "bank a" and then used shorter cables to parallel in "bank b", you would effectively have a longer wire run to bank b than you did to bank a, resulting in unequal draw on the two banks and unequal service.

You could do the same thing (balanced wire lengths) by making a "Y" or using a junction block so that the main wires fed to each bank through equal lengths, but that would actually just add more components and expense.

I'll come back with ASCII art if that doesn't make sense after you've reread it a few times.<G>

GaryHLucas 11-15-2008 08:45 PM

I think he is suggesting what you show if all four batteries are one bank. In that case I think his idea is a good one. However if your four batteries are actually two banks of two batteries to get 12 volts, connected to the boat through a dual battery selector switch, then you would be better off that way. Multiple banks that you select manually gives more reliability and flexibility too. If you accidently kill one bank the other is still in reserve.

sailingdog 11-16-2008 08:34 AM

Yes, but using separate banks reduces the battery bank efficiency. The larger the total bank size relative to the load placed on it, the more usable amp-hours you will get out of it. Two 200 amp-hour battery banks do not give the same usable amount of electricity as a single 400-amp-hour battery bank, given the same loads. This is the same reason batteries have a much lower amp-hour rating at the 5 hour rating versus the 20 hour rating.

Quote:

Originally Posted by GaryHLucas (Post 402536)
I think he is suggesting what you show if all four batteries are one bank. In that case I think his idea is a good one. However if your four batteries are actually two banks of two batteries to get 12 volts, connected to the boat through a dual battery selector switch, then you would be better off that way. Multiple banks that you select manually gives more reliability and flexibility too. If you accidently kill one bank the other is still in reserve.


sailingdog 11-16-2008 08:36 AM

Quote:

Originally Posted by Acadia (Post 402511)
Do you connect your batteries this way? Did I read something wrong?

The main reason to do this is to help ensure the four batteries are loaded evenly and that they are used/charged equally. It is a good idea, but can really complicate your wiring, especially if the batteries are all right next to each other.

Acadia 11-16-2008 11:58 AM

Thanks for the replies.

Yes it will be for one bank. And if it will help I will wire them together this way.

A comment was made regarding wire lenght. How important is this? all my battery connecting wires are within a foot of each other and with #2 wire I figured this would be ok.

Or do we need to be down to inches?

hellosailor 11-16-2008 12:36 PM

How many angels can dance on a pinhead?

Any inequities in the wire length mean unequal draws and unequal service on the banks, but when does that become relevant in the real world?

At .000162 ohms per foot, even when or if you pull 2000 watts for a starter, the difference probably is meaningless. Something like 0.0231 amps for five or ten seconds?

Acadia 11-16-2008 12:43 PM

lol, Thanks


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