More Batteries vs. More aH

[theojkett]

Hey Kids,

I have posted a similar question before on this forum, but let's treat this one differently.

If I have (8) 6V 230aH Batteries on my 48Volt system and I want more storage. Meaning if I added eight more of the same batteries a year from now, wired them accordingly, will I have more storage, more aH, both, all of the above, none of the above, waisted my money?

Just trying to understand. Education on this subject does not explain this very well.

Thanks all!!

[Sunking]

OK lets straighten you out.

Battery Capacity = Voltage x Amp Hours = Watt Hours.

So you have 8 units x 6-volts x 230 AH = 11,040 watt hours of capacity.

There are 4 ways you can configure them, 6, 12, 24, or 48 volts:

8P = 6 volts @ 1840 AH = 11,040 watt hours
2S4P = 12 volts @ 920 AH = 11,040 watt hours
4S2P = 24 volts @ 460 AH = 11,040 watt hours
8S = 48 volts @ 230 AH = 11,040 watt hours

No mater how you configure them, you have 11,040 watt hours. Now for the bad news. Rule 1: You never ever want to configure batteries in parallel unless it is absolutely necessary and if you do will severely shorten cycle life. Thus with 8 of your batteries 48 volts is the way to go. Rule 2 never mix old with new batteries under any circumstances.

Series Batteries Rule: Voltage Adds, AH does not add. So 8 x 6-volt 230 AH batteries in series (8S) is 48 volts @ 230 AH
Parallel Batteries Rule: Amp Hours add, voltage does not add. So 8 x 6-volt 230 AH batteries in parallel (8P) is 6 volts @ 1840 AH.
Watt Hour capacity adds regardless of configuration.

Lastly use as high of a battery voltage as possible as this will say you MONEY and gain efficiency. A good rule of thumb is never exceed 800 AH at any given battery voltage. A 80 Amp Controller has the following panel wattage limitations.

1000 watts @ 12 volts
2000 watts @ 24 volts
4000 watts @ 48 volts

This is based on charge rate of C/10 so with 800 AH maximum is 80 amps of charge current.

[theojkett]

Thank you. Best answer I have received on the question.

[Sunking]

you are welcome. Just remember AH does not mean much of anything without a VOLTAGE. Here some simple formulas.

Watts = Voltage x Current

1200 watts = 12 volts x 100 amps
1200 watts = 24 volts x 50 amps
1200 watts = 48 volts x 25 amps
1200 watts = 120 volts x 10 amps

Amps = Watts / Voltage

100 amps = 1200 watts / 12 volts
50 amps = 1200 watts / 24 volts
25 amps = 1200 watts / 48 volt
10 amps = 1200 watts / 120 volts

Volts = Watts / Amps

12 volts = 1200 watts / 100 Amps
24 volts = 1200 watts / 50 Amps
48 volts = 1200 watts / 25 Amps
120 volts = 1200 watts / 10 Amps

Amp Hours = Amps x Hours
Hours = Amp Hours / Amps
Amps = Amp Hours / Hours

Watt Hours = Watts x Hours
Watts = Watt Hours / Hours
Hours = Watt Hours / Watts

It is all very simple grade school algebra if schools still taught algebra.

[Mike90250]

here's a screen shot off a spreadsheet.
But remember - adding new batteries to an old bank, will quickly age the new ones, to match the performance of the older batteries.

BatteryWattHourCapacity.jpg