Sizing Battery Charger/Inverter

[RandyT]

I’m in the planning stage if replacing a single 12 volt battery with 4, 6 volt in a series-parallel configuration. Each battery is 6 volt and has a 245 AH rating. If my ohms law serves me correctly and the wiring done properly, I will end up with a 12 volt and 490 AH system. The original charger/inverter will not be sufficient to properly maintain the battery bank so I plan to replace it. My question is this, what amp battery charger should be used with a battery bank having a total 490 AH rating? Is there some formula or rule of thumb for determining which size charger to use based on a AH rating?

[diugo]

The answer depends simply on how much 12V energy you use in a typical day---not the size of the battery bank.

Suppose in a typical day you use 120Ah of 12V energy.

If you stay plugged in 24 hours a day, the inverter-charger only has to put out five amperes---since 5A times 24h equals 120Ah.

If your inverter-charger is plugged in only 15 hours a day---because you are on the road the other nine---the charger has to then provide 8 amperes.

Now, suppose your only charging source is a portable generator. If you want to run it only two hours a day, you would need a 60A automotive charger and at least a 1000W generator (60A x 15V / 0.9 efficiency).

[hankpage]

If you already have a three stage 55amp charger/CONVERTER you should be fine with that in the scenarios that diugo gave. Charging from your TV will take time.

[RandyT]

Thanks, that's very helpful!