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Old 04-08-2018, 08:56 PM   #1
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Golf cart batteries . . .

Recently the 8D and the 4D on my Gulfstar decided that perhaps they should move on to the next higher plane in life. Meaning that they died. So I replaced them with six 6-volt golf cart batteries (the old geezer cannot lug those 8Ds around these days as well as he used to be able to do!).

I have four of them for the house battery, and two of them for the starter battery. The four are in parallel and series. The two are only in series.

This deals only with the two. Let us call them A and B. A and B have a jumper running from the positive terminal of A to the negative terminal of B. Measuring the voltage between the other two terminals, I get 12+ volts. So the series works OK.

BUT . . . and the question here for Those Who Know . . . between the positive terminal of A and the positive terminal of B, I have six volts (roughly). Why? There should be no voltage difference between them, I would think.

Thanks for any suggestions.

John
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Old 04-08-2018, 09:06 PM   #2
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That is correct. Between the 2 positive posts in a series connection there should be 6 volts.
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Old 04-08-2018, 09:33 PM   #3
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...

This deals only with the two. Let us call them A and B. A and B have a jumper running from the positive terminal of A to the negative terminal of B. Measuring the voltage between the other two terminals, I get 12+ volts. So the series works OK.

BUT . . . and the question here for Those Who Know . . . between the positive terminal of A and the positive terminal of B, I have six volts (roughly). Why? There should be no voltage difference between them, I would think.

Thanks for any suggestions.

John
Jumper A+ to B- so that V=0

V of( A+ to B+ ) = V of (A+ to B-) plus V (B- to B+)
From above A+ to B- = 0V so
V (A+ to B+) = 0 plus V (B- to B+) which by definition is 6V for a 6V batty
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Old 04-08-2018, 09:54 PM   #4
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Yes, the positive of A in this situation is the same as the negative of B because of the jumper cable. So in essence you are measuring from the positive of B to the negative of B, 6 volts.

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Old 04-08-2018, 09:59 PM   #5
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BUT . . . and the question here for Those Who Know . . . between the positive terminal of A and the positive terminal of B, I have six volts (roughly). Why? There should be no voltage difference between them, I would think.
The jumper between A+ and B- means that A+ is at the same potential as B-, so it's tantamount to measuring the voltage difference between B- and B+, which is 6V.

Edit: Too slow.
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Old 04-08-2018, 10:40 PM   #6
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OK. Thanks. I understand now.
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Old 04-09-2018, 06:27 AM   #7
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"and two of them for the starter battery."

This is not ideal,a genuine start batt set like (2) series 31 will hive a faster start in cold weather.

In FL it probably will never matter.
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Old 04-09-2018, 08:17 AM   #8
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"and two of them for the starter battery."

This is not ideal,a genuine start batt set like (2) series 31 will hive a faster start in cold weather.

In FL it probably will never matter.
I tend to agree... If one 6V battery in a single pair fails, you don't have a 12V system. Given 4 or more 6Vs in a bank, that's not difficult to fix, but with only two, maybe not so much.

OTOH, if one 12V G31 out of a pair fails, you still have 12V.

But not only maybe unimportant in FL, it's probably also not difficult to fix (in a diesel boat) with a pair of jumper cables.

FWIW, one of our dual purpose 12V banks is made up of four 6Vs, and it starts that engine just fine. But... if a single 6V in that bank craps out I can fall back to using only a single pair at 12V... and in our case, we also have a parallel switch to momentarily tie in the other bank anyway...

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