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Old 18-03-2018, 07:20   #1
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Charging dilemma

Iíve got 4 6-volt 200amp batteries set up as 2 12-volt units tied together for a total of 400 amps. One battery has failed and will not hold a charge. Iíve taken that battery off-line and want to connect the good battery to one of the other two, pos to pos, neg to neg. what will happen when I go to charge? Will they be balanced? Iím in the Bahamas and canít get a replacement battery
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Old 18-03-2018, 07:31   #2
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Re: Charging dilemma

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Originally Posted by meridian28 View Post
Iíve got 4 6-volt 200amp batteries set up as 2 12-volt units tied together for a total of 400 amps. One battery has failed and will not hold a charge. Iíve taken that battery off-line and want to connect the good battery to one of the other two, pos to pos, neg to neg. what will happen when I go to charge? Will they be balanced? Iím in the Bahamas and canít get a replacement battery
The pair linked together will take a lot more time to charge than the single 6v it is in series with, so it will always be behind in voltage when charging and the single battery will see much higher charge voltages, tearing it up. Your charger will not know and see that the whole bank is low on voltage and will keep charging, overcharging the single battery and under-charging the double one continuously.

The single battery is still limited in the AH it has so adding that 3rd battery on half the series circuit is not going to bump your overall bank AH much at all. If you try and utilize that tiny bit of extra AH its going to draw that single way down below the optimal 50% level before the double battery gets even close.

You will be better off just using two batteries.
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Old 18-03-2018, 11:54   #3
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Re: Charging dilemma

What he said.

It will accomplish absolutely nothing to keep using that "third" battery. The twelve-volt pair need to be replaced as a pair. Simply buying one new battery to replace the failed one will be waste of money, unless that "third" battery is nearly new, i.e. comes up to maybe 12.5 volts when charged and after the float is off.
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Old 18-03-2018, 13:11   #4
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Re: Charging dilemma

don't do it. remove both. leave 2.

it won't help you anways. you'd still only have 200 AMP HOURS total. (not amps) because you can't drop the single one below the size of one battery
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Old 18-03-2018, 13:15   #5
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Re: Charging dilemma

Where are you in the Bahamas? Have you checked around? Lots of golf carts out here, Iíd be surprised if you couldnít get batteries for them.
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Old 18-03-2018, 14:30   #6
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Re: Charging dilemma

Effectively, your two batteries in parallel can be thought of as a single 400Ah 6V battery. So you are in effect combining one 200Ah 6V battery and one 400Ah battery in series.

It is not good to combine different Ah batteries series!

The problem is that the battery charging controls will operate based on the average battery voltage and the two batteries will have very different voltages because their capacities are different. The 200 AH battery will become fully charged long before the larger one. The combined voltage will rise, but by the time the controller turns off the charging sources, the 200 AH battery will be overcharged. Meanwhile, the 400 AH battery will not get fully charged. When the bank is being discharged, the 200 AH battery will go flat and its voltage will fall well before the 400 AH battery.
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