Bank of Battery in serie, and why not in serie+//

Re: Bank of Battery in serie, and why not in serie+//

Jacques,

There's a simple way to solve this problem. After battery #12, run batteries #13 through #24 in another row back towards battery #1. You can then hook your equal-length main battery cables to batteries #1 and #24. It would be something like the lower right drawing below, but with 24 batteries for 48 V.



The battery bank capacity (Ah) will be the same as the rating for any one battery. Wired in series, battery voltages add up, but the capacity spec (Ah) doesn't change.

HTH,
Jim / crewzer

Re: Bank of Battery in serie, and why not in serie+//

Jacques,

For your planned 48 V configuration, you have no choice but to connect your twenty-four 2 V batteries in series. From an electrical perspective, there is no parallel connection option. Accordingly, there’s no alternative to the “long” series connection of the 24 batteries. It’ll be essentially the same physical distance if the batteries are lined up in a long single row or if they’re “folded back” in the middle to form two short rows.

Your concern about the resistance of the long battery bank is valid. I’d suggest using short, heavy (~4mm x ~25 mm cross-section) copper bars instead of wire-and-lug cables to connect between the batteries. This approach should minimize the total electrical resistance and improve the reliability of the 23 inter-battery connections.

The advantage of the “folded back” solution (the lower right drawing) is that the battery cables can be connected at the same end of the battery bank and the total battery cable length [(+) cable length and (-) cable length together] will be as short as possible.

STC stands for Standard Test Conditions. It’s a laboratory test that, in part, is supposed to simulate irradiation of 1,000 W /m2, a PV cell temperature of 25 C and wind speed of 1 m/sec. Most manufacturers' power specifications are based on STC.

CEC stands for the California Energy Commission, and PTC stands for PVUSA Test Conditions. The PTC specification is based on 20 C ambient temperature. This generally means the PV cell temperature would be ~65 C, so the PV voltage would be lower than realized under STC conditions. Since the PTC spec better predicts real-world operating characteristic, the CEC uses their numbers for baselining PV module performance.

HTH,
Jim / crewzer