# lifepo4 8s 280Ar series or parallel?

Registered Users Posts: 4
edited April 7 #1
So I have ordered my lifepo4 8s 280Ar batteries and my plan was to run them in series for a 24v, 280 amp system however, I just watched a youtube video that got me thinking. In the video he arranged the same 8 batteries in series and parallel for a 12v, 560Ar system. Which is best?
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• Super Moderators, Administrators Posts: 31,618 admin
It does not matter in detail... Both 12v @ 560 AH and 24v @ 280 AH store the same amount of energy:
• Power = Voltage * Current
• Power = Voltage * Current * Hours (Time)
• 12 volts * 560 AH = 6,720 Watt*Hours
• 24 volts * 280 AH = 6,720 Watt*Hours
The 12 volt bank will have to supply 2x more current for the same amount of power:
• Power = Voltage * Current
• Current = Power / Current
• 200 Watts / 12 volts = 16.7 Amps
• 200 Watts / 24 volts =  8.3 Amps
So, for the "same amount" of power, you will need 2x heavier wire and 1/2 the length (to keep voltage drop reasonable)--More or less.

If you need 12 VDC power for your devices--12 VDC is fine. If you don't need 24 volts, and are looking at using AC inverter--24 volts (or even 48 volts for a larger battery bank) is usually a better choice (smaller wire, longer distances @ 24 VDC, using a solar charge controller--Both may be rated at 50 amps--But 24 VDC battery bus will "manage" a 2x larger array vs a 12 battery bus)
• 14.5 volts charging * 50 amps = 725 Watt array
• 29.0 volts charging * 50 amps = 1,450 Watt array
Note it may be "more difficult" to find inexpensive BMS for 48 volt systems....

Do paper designs for your system--12 and 24 volt based on your loads and see what the issues are.

Give us you Load Needs, length of wire runs, and Solar/other charging sources--And we can walk you through the process.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 213 ✭✭✭
In the 24v setup, the bms will be attached to each cell. In the 12v setup, each cell is paralleled. You will have one bms lead for every two cells. Troubleshooting cell level problems will be more difficult with the 12v setup as shown. The cell balance function will also not work as well in the 12v setup. You could arrange the 12v system a second way with two 12v strings put in parallel, but then you are looking at two BMSs (unless you go expensive). This setup would give you redundancy.

IMO, unless you need 12v, the 24v single string is more desirable.