Battery bank and inverter sizing

[jgkurz]

Hi all,

I recently installed a new solar panel on my camper that is capable of 9.8amps at full sunlight. The controller is a MPPT type that seems to work well and keep my batteries charged up. I have two new 12v deep cycle Exide batteries that have a combined rating of 322 reserve capacity and 185 Amp Hours @ 20hrs. My inverter is capable of 1500w continuous with 3000w peak. I have no intention of running my ceiling A/C on the inverter but it should work for a short while. The compressor need 8amps and the fan needs 2.5amps so 10.5 amps total. 12v x 11amps is only 132 watts. I can turn my A/C fan on but as soon as I start the compressor the inverter drops saying low voltage. Shouldn't I have enough battery and inverter to run the A/C for a short period?

Thanks!

[2oldman]

jgkurz wrote:
If it was truly 30amp surge wouldn't that trip my 15amp breaker?

No. Breakers are designed to allow some surging before tripping.

I see your amperage question is answered. Better read that inverter manual a little more carefully! 🙂

[beemerphile1]

That wire is nowhere near heavy enough. If you could get the inverter to operate at its capacity those wires would start smoking.

[jgkurz]

smkettner wrote:
That a/c is 10.5 amps at 120 volts. 1260 watts + 10% overhead and some power factor puts you right at the inverter max. Batteries are providing 120 amps and you need 4+ to get any reasonable run time.

BTW what size and length is the 12v wire? 5' of 2/0 would be about my minimum rating.

Ahh. I used the wrong voltage to get my watts. Duh!!! I have 8awg to my inverter plus start-up surge amperage plus not enough batteries seems to be the issue.

[time2roll]

That a/c is 10.5 amps at 120 volts. 1260 watts + 10% overhead and some power factor puts you right at the inverter max. Batteries are providing 120 amps and you need 4+ to get any reasonable run time.

BTW what size and length is the 12v wire? 5' of 2/0 would be about my minimum rating.

[jgkurz]

2oldman wrote:
No. You'll need at LEAST 4 batteries to handle any a/c load, and even then it will be for maybe 15 minutes max.

The startup amps for the compressor are possibly in the 30amp range, meaning 300a from the batteries. That's what your two batteries can't handle.

Thanks for the response.



Wow, I am surprised that the start-up amperage would be nearly triple the regular load but that would explain why I'm having trouble.

If it was truly 30amp surge wouldn't that trip my 15amp breaker?

Also, why would my batteries need to supply 300a for a 30amp load?

[2oldman]

No. You'll need at LEAST 4 batteries to handle any a/c load, and even then it will be for maybe 15 minutes max.

The startup amps for the compressor are possibly in the 30amp range, meaning 300a from the batteries. That's what your two batteries can't handle.