volt/amps/watts question.

[BAD ORCA]

I was just mulling over some future electrical work and have been considering multiple chargers for a large battery bank. I suddenly realized or wondered if the 30amp shore power inlet would be capable of running three chargers simultaneously as well as some other loads like appliances etc...

If its 120 volt shore power at 30amps does that means it can provide approximately 3600 watts of useable power?

Three 60 amp chargers would use approximately 2700 watts total. If my math is correct i think im ok but would probably want to keep loads to a minimum while charging.

[Dsanduril]

Short answer:yes.

30A@120V = 300A@12V. With efficiency losses, and charging at 14.x V a 30A shore service could provide ~200A of “12V” charging. Less depending on the “other loads”.

[BAD ORCA]

Great! thanks. looks like i'll be ok so long as i dont add a fourth charger/fifth battery. Looks like that limits me to four Firefly's instead of five if i want to stay on 30 amps.

[Sailmonkey]

Why do you have 1 charger to 1 battery?

[valhalla360]

Originally Posted by Dsanduril

Short answer:yes.

30A@120V = 300A@12V. With efficiency losses, and charging at 14.x V a 30A shore service could provide ~200A of “12V” charging. Less depending on the “other loads”.

Long answer: No

For longer duration loads, a 30amp outlet is only rated for 80%, so you really only have 24amps available or about 2880w. People who push 30amps continuous out of a 30amp outlet tend to burn up the cord ends.

Then you have efficiency losses and other loads that are likely eating up between 400-1000w. (I assume if you are running a boat with plentiful electrical equipment if you are trying to charge at extreme rates).

Then you have what the battery bank can absorb. Particularly, with Lead Acid batteries, there are limits on what they can absorb. Once you hit that limit, throwing more amps at it doesn't speed things up.

[BAD ORCA]

Originally Posted by Sailmonkey

Why do you have 1 charger to 1 battery?

Almost. Im going to have a bank of four Firefly's as my house bank. Their latest tech sheet recommends an occasional restorative charge at .4C. That means i would need to get approximately 180amps of charging into them.

I have a single Sterling 60 Amp charger now so figured i would add two more of them to get to .4C. They are approx. 900 watts each @ 60 amps so 2700'ish watts if all three were on at the same time.

I have a single Firefly now and normally charge it at .3C so, during typical charging of the house bank i would probably only run two of them at once. Running all three at once would only be done two or three times a year at dock so i would be able to not run anything else while doing this restorative charge, that way im not maxing out my 30Amp inlet.