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Acadia · 15-11-2008, 16:44

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 forum and did a little msn paint on it to represent the diagram in the Calder book. The blue lines represent the cross-connect that are in addition to the normal settup.

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

AnchorageGuy · 15-11-2008, 16:50

Acadia, We have had two banks of four 6volts each for many years but did not have them connected this way. Not real sure what the advantage to this is.

Acadia · 15-11-2008, 16:54

It's supposed to "Minimize the differences in the way in which the batteries work and perform"????

Not more info than that from the book. Was just curious if anyone had them connected that way.

Thanks Chuck

**David M** · 15-11-2008, 19:05

The only thing I figure is it would equalize the voltage across each battery in case one battery had a little more internal resistance than another. But I don't see how this would make any difference in how well your electrical system functions. It might also be a backup of sorts in case one of your battery terminals starts to take on some resistance. In a sense the terminal with more resistance would not create more resistance for the battery behind it. There would be path for the current to go around the bad terminal. I think its insurance in case you get a bad cable, a bad terminal...or a bad battery. I'm just guessing though.

**GordMay** · 16-11-2008, 01:41

I'll have a look at Calder's advice later today; but I cannot think what he's getting at.
The third figure represents the proper series-parallel battery connection.

donradcliffe · 16-11-2008, 07:01

I am looking at an older Calder book (p15) and it does not show your added blue wires. You must not be reading Calder right, because even if you wanted to cross-connect the batteries at the 6V level it would only take one of your two blue wires to accomplish that. IMHO there are some cons for the cross connection (dealing with troubleshooting battery problems and the failure of single battery cells) and I wouldn't do it.

noreault · 16-11-2008, 07:28

Positive to Positive is in parallel and leaves he voltage the same and doubles the capacity.

Positive to negative is in series and leaves the capacity the same and doubles the voltage.

So the choice depends on what you want to accomplish. If you are powering a 12 volt circuit, you need to connect in series.

AnchorageGuy · 16-11-2008, 07:45

Quote:

Originally Posted by noreault

Positive to Positive is in parallel and leaves he voltage the same and doubles the capacity.

Positive to negative is in series and leaves the capacity the same and doubles the voltage.

So the choice depends on what you want to accomplish. If you are powering a 12 volt circuit, you need to connect in series.

I don't think this has ever been in question since he is setting these up for his 12volt system. The question became whether the pairs should be cross connected.

DeepFrz · 16-11-2008, 09:11

Page 22 of Caulder's book, 3rd edition does show cross connections in a series/parallel battery bank.

The caption does state that it will "minimize differences in the way in which the batteries work and perform".

Not sure that I agree, especially considering the added complexity.

Acadia · 16-11-2008, 09:36

Gord; that third figure is how I was intending on wiring them together

deepfrz; That is the edition I am refering to. Page 22

I have taken the best picture I could with my phone from Calder's book. Had to MSN paint it again because the resolution was not good.

It must of been added to his newer edition because donrad didn't seem to find it in his older copy.

Calder seem to think this in an "excellent practice" so I might just give it a try. But at the same time, the standard connection seems to work fine for most of you.

Pelagic · 16-11-2008, 09:53

I contacted Victron in Holland with this exact question when I replaced my house bank earlier this year with a much larger 24v capacity using 8 x 12v in series/parallel.

They advised that what was more important was that the cable lengths to the Heavy Duty terminals (HD Studs) be of proper size and matched as closely as possible in length for the 4 sets of 24v and that it was not necessary to cross connect because of modern adaptive charging techniques.

Here is what I ended up doing and as you can see, I am only 0.130m in length difference between Port and Stbd.

**David M** · 16-11-2008, 10:02

How does cable length make a difference for such a small difference? Does 0.1M (10cm) make any perceptible difference in resistance?

btrayfors · 16-11-2008, 10:05

Cable length is important: keep 'em as short as possible.

Also, cable size is critical: be sure to use at least 1/0 size cable for interconnections.

And, needless to say by now, clean, tight, professional crimp connections are also critical. Don't skimp here.

Personally, I'd not bother with "cross connections"....an unnecessary complication, especially if you've done the interconnections properly.

Bill

**David M** · 16-11-2008, 10:10

I understand the importance of cable length. I was wondering about the importance of cable length difference for Pelagic's charging system. Apparently something needs to be balanced. In addition to that, one tenth of a meter matters. So that's what has me curious. I'm hoping that Pelagic will fill us in with more details.