13500 A/C on 2000 watt inverter?

do you have the model number and specs for the A/C unit
my old roof top a/c's draw about 12~13 amps at 115v

thats 120amps into the inverter, not counting efficiency loss
round that off to 130amps load

unless he has a really good, ambulance/firetruck grade alternator it is NOT going to work

also the LRA "lock rotor amps" for my a/c compressor is 54 amps
to reach that with an inverter means a 540amp input surge

he needs a smaller a/c, and a bigger inverter, and better alternator
run the smaller a/c full blast, NOT cycling on off, the restart cycle on a hot a/c is a real deal breaker for him

the inverter should be 'old school' with a big transformer in it
the transformer/inductor provides a surge ability for starting motors that you can't get with small light weight cheapo "chopper circuit" inverters
even if its pure sine wave, to start motors you need surge capacity

I'm not surprised. That AC size will pull right around 2000 watts when the compressor kicks in, some a little more, some a little less. Sounds like his is a little more. Being right at the cusp, so to speak, is why sometimes folks can get a 13,500 btu AC to work on a 2,000 watt power supply, and sometimes they can't.

Running an AC off a battery in any case is a bad idea because the total power load is so high. Much better is to use a generator, and I'd recommend at least a 2,500 watt one at that as a minimum, with 3,000 watt even better.

Halmfamily wrote:


Yes, he said they run it all day. He also said he is running the heaviest wire he could locate. I told him he would need 4 6 volt batteries and a charger at night as the alternator cannot keep up.

The 4 6 volt may work if the AC is run intermittently and the batteries hit a charging station a few times through the day.

But if there's a 400-700 amp hour daily deficit from continuous duty and no recharges, he'll need even greater battery capacity, maybe 8 or 10- 6 volts.

tpi wrote:
I'll leave it to the experts whether this idea has any chance at all. But off the top it probably suffers from
1. Inadequate inverter.
2. Possible inadequate wiring between batteries and inverter
3. Inadequately sized batteries in amp hour capacity
4. Inadequate alternator capacity

Is this roof air to be counted on for continuous duty during the day?

Yes, he said they run it all day. He also said he is running the heaviest wire he could locate. I told him he would need 4 6 volt batteries and a charger at night as the alternator cannot keep up.

Yes that would be a huge load on the alternator, and probably would wear it out quickly.

Do they have any idea how many amps they would be drawing at 12 volts DC to run the A/C unit? Just the fan motor is probably drawing over 50 amps at 12 volts!

Is it a pure sine wave inverter? If MSW or some sort of pure modified sine wave, then it will not handle the high torque loads of the compressor motor.

I would suggest something like the Pure Sine Wave Trace 2500 watt with a 5,000 watt surge capacity. That will require #000 wire from the inverter to the pair of batteries (4 golf cart batteries would be my recommendation) and #4 wire from the alternator +12 terminal to the + 12 volt terminal on the inverter.

That way the inverter can draw 400+ amps from the battery, and 100 or so from the alternator while starting the compressor, and can draw just 50 - 75 amps from the batteries while the engine is running and the compressor is on, while also getting 100+ amps from the alternator.

You might also consider a Outback inverter in the 3000 watt range, with a 6,000+ watt surge rating.

SolarOnSale.com or SunElec.com might have one of the larger pure sine wave inverters.

When my buddy had his MCI bus conversion, he found that his Trace 12 volt 4000 watt inverter struggled with his 13,500 Btu A/C unit. While the 24 volt inverter worked much better, and less amperage. He has a 300 amp 12 volt alternator and 100 amp 24 volt alternator, so either one is rated at plenty of power to run the A/C unit. His 8V92 engine is much larger than your minivan (at about 1,600 pounds for just the engine) it is 756 cubic inches!

Good luck,

Fred.

I'll leave it to the experts whether this idea has any chance at all. But off the top it probably suffers from
1. Inadequate inverter.
2. Possible inadequate wiring between batteries and inverter
3. Inadequately sized batteries in amp hour capacity
4. Inadequate alternator capacity

Is this roof air to be counted on for continuous duty during the day?