Generator Invertor sizing

[lawrence_craig]

Hi guys, very quick question,

I have a a 4kVA (3500W) generator. I want to check the sizing of my AC to DC invertor. It is a 12V 40Amp invertor. Is this the correct size or should I rethink it? I couldn't find any material that could help me with this.

Thanks

[smac999]

it would depend more on the size of the battery bank. and the type of batteries. 40a is pretty small and you'll be running the gen a long time to charge batteries with that.

a 3500w gen could power about a 200a charger (but nothing else) but that would only be usefull on bigger battery banks.

you are talking about chargers, not inverters.

[Tillsbury]

Yes, ac to dc is a charger (inverters do the opposite). The size of your charger depends more on the size of your battery bank assuming you're not charging lithium. How many Ah of battery do you have? That will determine the maximum charging current that would be appropriate.

[Dockhead]

Right. For lead acid (non AGM) batteries, you want the charger to be 15% to 20% in amps, as the bank is in nominal AH capacity 20 hour rate. We call that .15C to .2C.



So a 400AH bank would like to have a charger of 60 to 80 amps. Some larger chargers (e.g. Victron) allow you to downrate the charger to get the capacity just right.



You don't want a lot more than 0.2C because charging faster than that can be hard on the batteries.


With lithium or AGM, this does not apply.