Can I use a 90 amp 24 volt circuit to operate a 15K BTU A/C with inverter?

belfert · September 30, 2015, 03:27:51 PM

My inverter is fed by a 90 amp 24 volt circuit from the alternator when the bus is on the road. Is that enough to power a 15K BTU air conditioner/heat pump? My inverter is a Prosine 3.0 so it is capable of 3,000 watts. I'm thinking it will be close with the conversion loss.

I'll just use the generator if it won't work.

Lin · September 30, 2015, 04:35:04 PM

To be sure, you would want to find what the start and running amps are on the AC. Your 90 amp circuit at 24v is 2160 watts. That would mean it could run 18 amps of 120v minus the efficiency loss. Say 15 amps for a rough guess. That may be okay for running, but startup may be the issue.

Scott & Heather · September 30, 2015, 08:14:07 PM

If it's the inverter type as you say, my guess is that yes it will work without issues. Is this a roof top or mini split?

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sledhead · October 01, 2015, 04:43:18 AM

how big is your battery bank ?

you should have no problems as your batteries and the engine running will support the start up amps

dave

blue_goose · October 01, 2015, 05:00:26 AM

With the 90 amp X 24 volt you only have 2160 watts input to the inverter. To get full use from the inverter you need to have at least a 150 amp fuse.
Jack

Oonrahnjay · October 01, 2015, 07:32:34 AM

Quote from: Scott Bennett on September 30, 2015, 08:14:07 PMIf it's the inverter type as you say, my guess is that yes it will work without issues. Is this a roof top or mini split?

Scott, I am not 100% clear on it but I think his question is running "a 15K BTU A/C" on power from a Prosine inverter. He doesn't say that the A/C unit is an inverter type so it appears to me that it's not. As other people have noted, what he has seems marginal on a number of counts.

Oonrahnjay · October 01, 2015, 07:52:01 AM

Quote from: belfert on September 30, 2015, 03:27:51 PM
My inverter is fed by a 90 amp 24 volt circuit from the alternator when the bus is on the road. Is that enough to power a 15K BTU air conditioner/heat pump? My inverter is a Prosine 3.0 so it is capable of 3,000 watts. I'm thinking it will be close with the conversion loss.

I'll just use the generator if it won't work.

Brian, what's the manufacturer's stated current draw (probably listed in amps but watts would be better) for the air conditioner in normal run mode and start up? If you can get the manufacturer's specs on a start-up capacitor or similar system (or confirm lack of one), that would probably help, too. It looks to me that you are marginal as things are set up but you could probably do OK with a few small changes. But you can't be sure until you have the exact current requirements for the A/C unit.

TomC · October 01, 2015, 08:52:33 AM

If he has a 50DN alternator, then going down the road, the voltage will be 28.2 volts which works out to be 2538 watts before any losses (90amp circuit). I would go no higher than 80% which gives you 2030 watts. This will be marginal.

When I bought my Trace 2512 inverter (MSW), the inverter had the ability to be stacked with another to create 5,000 watts. I too was thinking about running my A/C going down the road with the inverter since I have a 300amp 50DN that would give me 4230 watts max at 14.1 running volts. Instead of pushing that second inverter on me, the gal that sold me (also the shop owner) asked if I had a good Diesel generator (meaning heavy duty 1,800rpm type). I said yes, a 10kw with 4cylinder Kubota. She said, just run the generator and only use the inverter for intermittant low watt stuff like coffee maker, microwave, heater, water heater, TV, stereo, etc. That's what I did and as result have never had a problem with the inverter in 21 years. Good Luck, TomC

belfert · October 01, 2015, 03:50:57 PM

I have 600+ pounds of batteries fused at 225 amps. The inverter could draw from the battery bank for startup and such. I used an existing circuit that used to be for the air conditioner motors to draw power from the alternator. I could get a lot more than 90 amps from the alternator with proper wiring.

I think I will skip this for now.

bevans6 · October 01, 2015, 04:34:57 PM

I wouldn't skip it, I'd just do it. I would expect that it would work just fine - lots of alternator power backed up by battery bank for surge loads. If the breaker popped, I would - depending on the cable sizes - bypass it. I have 1/0 cable feeding my inverter to power a 15Kbtu air conditioner with no breaker, and it works perfectly. I do have a fuse before the inverter rated appropriately for the cable.

edit: To be clear, the key to my solution is to make sure the cable size is appropriate to the load. The ampacity of the cable has to support the continuous load plus 15%, and the install should be fine.

Brian

bevans6 · October 02, 2015, 04:03:55 AM

On my MCI, that wire that feeds the AC motors is a quite short 1/0 gauge wire (8 feet long or so) which is good for around 150 amps continuous. That is the cable I use to bond my house system with the bus system and run my AC unit on the road. I tapped directly into the bus bar, I did not use the breaker. FWIW

Brian

Oonrahnjay · October 02, 2015, 05:41:59 AM

Quote from: bevans6 on October 02, 2015, 04:03:55 AMOn my MCI, that wire that feeds the AC motors is a quite short 1/0 gauge wire (8 feet long or so) which is good for around 150 amps continuous.

Are your start systems and house system both 24V, Brian (Evans)?

Scott & Heather · October 02, 2015, 07:27:44 AM

Quote from: Oonrahnjay on October 01, 2015, 07:32:34 AM
Scott, I am not 100% clear on it but I think his question is running "a 15K BTU A/C" on power from a Prosine inverter. He doesn't say that the A/C unit is an inverter type so it appears to me that it's not. As other people have noted, what he has seems marginal on a number of counts.

Oops. My bad. Apparently my LASIK surgery wasn't worth the price! Lol

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bevans6 · October 03, 2015, 08:53:26 AM

Quote from: Oonrahnjay on October 02, 2015, 05:41:59 AM
Are your start systems and house system both 24V, Brian (Evans)?

Yep, standard MCI fare. House and bus are both 24 volts. The MC-5C and a multitude of other MCI models have 4/0 cable from the batteries to the engine bay stud. From the engine bay stud is a 1/0 cable to the alternator and a 4/0 cable to the starter motor. From the batteries there is a 1/0 cable to the AC junction box bus bar, which feed the front electrical panel bus bar and the AC fan motors. I just ran a 1/0 cable from the AC junction box bus bar to my battery combiner switch, which itself feeds the inverter and can bridge the house and bus systems together. There is a fuse to the inverter only, nothing else is fused. I use the house batteries as start batteries from time to time, and I don't believe that start batteries should be fused. I only fuse loads.

Brian