NiCd Battery Ah Calculation

This should help...

http://www.openelectrical.org/wiki/index.php?title=Battery_Sizing

2.4V into 48V gives 20.

20 x 3 is 60. => 3 strings of 20 batteries in parallel.

If each battery is 357Ah then the Ah capacity of the 3 strings is 3 x 357Ah = 1071Ah @ 48V.

What happens to the 10 batteries left over?

i get the impression that the capacity of the whole assembly is 357 Ah, so each of 3 hypothetical strings must have a capacity of 119 Ah, which must also be the capacity of a single cell. The problem is that I have never seen and cannot find an NiCD cell with a capacity of more than 2 Ah, so there may be a decimal point problem somewhere, or we should be going to sealed lead-acid batteries.

If only the original poster would say....

I suspect that you have 72 batteries three strings of 24. You only get the 357 Ah if you discharge them to 1V (2 volts for each pair): so that's a total of 1,071 Ah.

Alternatively you may have 4 strings of 18 (still 72 batteries). Fully discharged (down to the 1V/2V level) you'd still have 36V, which seems like a reasonable minimum for equipment spec'd to run on nominal 48V. That would give you 1,428 Ah.

Over 3000 Kg of batteries WOW!

These question can be more of a puzzle than our challenge questions.

Because the OP has mentioned both 2.4V individual battery voltage and 48 volt nominal, and because the 2.4 v is the correct nominal voltage of the Alcad VN357-2 battery, I'm guessing that there must be 20 such batteries per string -- leaving one to wonder where the extra 10 cells go (after paralleling three such strings.)

Putting 3.5 parallel strings in a car would result in castration of the perpetrator. But apparently it is done in the telecom industry.

Or the op's finger slipped, and he typed 70 when he meant 60.

This does not add up in the traditional way.

To keep with the existing terminology, I'll call two cells in series a battery. The whole group of series parallel cells I'll call a pack.

Each battery of two cells in series is 2.4V nominal. Therefore, to make 48V nominal, you would need 20 such batteries in series. Then paralleling these in 3.5 sets would give you 70 batteries, for 1249.5 Ah. Of course, you cannot parallel the last 10 batteries as a series string across any existing 48 volt string. The 10 additional batteries could be added at random to the pack (each in parallel with any 2.4V battery) or first connected in series and paralleled with a 24 volt group.

This never used to be done, but apparently works -- although it would seem to cause problems in keeping the pack balanced. Here's an article.