How many batteries?

**noidios** · 12-10-2007, 10:15 AM

Hello all. I've done a lot of searching to try and find my answer, but I'd had no luck. Here's the deal:

I need to run an inverter to power a 120v piece of equipment that draws 15 amps for 30 minutes at a time. Can you tell me how many deep cycle batteries (isolated) this will require?

Can you also tell me how many amps of battery power this setup would draw so I can get a better idea of how far behind the alternator would be in charging the batteries if I decided to leave the vehicle running?

Thanks.

**JC-S60** · 12-10-2007, 10:39 AM

Originally Posted by noidios

Hello all. I've done a lot of searching to try and find my answer, but I'd had no luck. Here's the deal:

I need to run an inverter to power a 120v piece of equipment that draws 15 amps for 30 minutes at a time. Can you tell me how many deep cycle batteries (isolated) this will require?

Can you also tell me how many amps of battery power this setup would draw so I can get a better idea of how far behind the alternator would be in charging the batteries if I decided to leave the vehicle running?

Thanks.

15A for 30 minutes = 7,5Ah

Is these 15A the power that the inverter draws or the power that the 120V device draws?
If it's the latter, 120V * 15A = 1800W. Using a 100% efficient inverter, that would mean 1800W / 12V = 150A. During 30 minutes, that's 75Ah.

You need to find a battery/batteries that have 2 properties: they can handle a continious power draw of 15A or 150A (depending on the above) and they have at least 7,5 or 75Ah of capacity.

Count in the efficiency of the inverter and a reserve for your batteries too.

Good luck,
Joachim