Battery Bank Wire Size

1L243 wrote:
I built my battery bank four 12 volt deep cycle batteries with 340 amp hours. At the time I had not added the 500 watts of solar and a 2000 watt inverter that I now have.

At the time I used 2 AWG cable between the the batteries which are wired in Parallel. The 2 AWG was a upgrade from the 4 AWG battery cables that it came with.

I'm using 4/0 cable from the inverter to the batteries. I occasionally have a high demand on the battery bank by running the microwave or a drip coffee maker. These events only last for 2 to 5 minutes at a time. When this occurs the battery voltage will drop suddenly as low as 11.8 volts due to the high demand. As soon as the demand is over the voltage recovers almost immediately to it's pre voltage level before the event.

I decided to beef up the battery cables that link the four batteries together with 2/0 cable. I could not find anything that really set the parameters for battery cable size.

I have not had a chance to try it yet but I am curious to see by
increasing the battery cable size to 2/0 if the voltage drop during a high amperage discharge will improve.

Any thoughts.

basicly you have to look at the maximum amprage tht cn be drawn on that line and the distance over what it has to carry that amprage and look up the size on a chart. so a 2000 watt inverter that has say a 3000 watt surge capacity can have a maximum of 250 amps plus a tiny bit for the efficency but that will only ever be momentairly at this level most of the time it will run much less. so at 250 amps on stranded wire for less than 4 feet distance you need 4ga, 4 to 10 feet 2ga, 10 to 19 feet 1/0 ga and 19 to 22 feet 2/0 ga. I like to go one or two sizes larger as a saftey vs. cost factor .

for the battery conection wire I usaly go with the inverter sizing as thats the largest draw that will go through them. the larger you go the less voltage drop but thats only to a point. the only time it will help is if your cables were sized on the small side to start with, but there also is a point of just not being worth it, you could upgrade the cable from a 2/0 to a 4/0 and spend twice the money and only get a 0.001V increase if the 2/0 was already more than good enough, so there also you have to look at charts and there are some that show voltage drop vs wire size also. you might get people thorwing wire sizes at you or just saying do everything in 4/0. the reality is 4/0 isn't cheep and you don't need it for most situations. I used it for the 2 feet between my inverter and bateries like you did but I wouldn't have used it if I had to go 10 feet as I probably wouldn't have been able to aford to do a long run of it, and it gets much harder to work with for pulling and such, but even at 10 feet it is overkill so thats not an issue. but having said all that, if you have it, why not. some people just seam to be able to come across larger wire sizes for free or a screeming deal, if your one of them all the power to you.

just remember building a larger battery bank doesnt change the load at all, just lets you run it longer so it won't affect your wire size requirments adding two more 6V batteries. what would affect it is if you decided to put in a 4000 watt inverter or any apliance that will draw more than 250 amps dc.

Steve