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Old 02-21-2017, 04:28 PM   #1
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Figuring amp hours for 6 volt bank

The previous owner added six 6-volt batteries as a house bank. Each is 225 amp hrs. So do I have 1350 amp hours or do I divide by 2 since it is wired as a 12 volt system, giving me 675 amp hours.

I am guessing the 675 but am not sure.

Thanks
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Old 02-21-2017, 04:35 PM   #2
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Yes, you have 675 amp hours at 12 volts.

David
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Old 02-22-2017, 01:19 PM   #3
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Quote:
Originally Posted by wwestman View Post
The previous owner added six 6-volt batteries as a house bank. Each is 225 amp hrs. So do I have 1350 amp hours or do I divide by 2 since it is wired as a 12 volt system, giving me 675 amp hours.

I am guessing the 675 but am not sure.

Thanks
The rule of thumb is:

Batteries in series - add voltage together. Amp hours stay the same.
Batteries in parallel - add Amp Hours together. Voltage stays the same.

Your batteries must be set up with 2 batteries in series - 3 times - to yield 3 pairs of 12V. Then these 3 "pairs" of batteries are connected in parallel which keeps the voltage at 12V but "adds" the AH of the 3 pairs together. So it gives the 675 Amp Hours you were guessing.

Ken
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Old 02-22-2017, 03:22 PM   #4
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Don't forget to downrate for peukert effect.
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Old 02-22-2017, 04:51 PM   #5
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Originally Posted by capn_billl View Post
Don't forget to downrate for peukert effect.
Most boat owners are only discharging the house bank at somewhere around 15-30% of the 20 hour rating, as an average discharge load. Boat owners often get slightly more usable capacity, at their average discharge rates, not less.

Only when running items such as an inverter or other loads that exceed the 20 hour discharge rate does your usable Ah capacity shrink. Battery temp can also create slightly more or less usable capacity.

If we assume the 675 Ah bank of batteries are healthy & broken in, and between 70-80F, and can actually deliver the full rated capacity, then any discharge load that is below 33.75A (the 20 hour rate) is going to mean the bank will have more usable capacity than the 20 hour Ah discharge rating.
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