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Old 29-10-2022, 08:18   #1
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Question about running a heating / air conditioning system through an inverter

I have a 16,000 btu heating a/c system that runs on 120v shore power. I can't find the exact specs on its power use, because it's not in the manual. And the web site doesn't help because the company currently sells a newer model which is similar but not exactly the same. The best estimate I can find is that it requires about 1300 watts to run, and about 3600 watts to start up.

I also have a 2000 watt generator. It can run everything else fine. But it can't start up the heater/Air Con unit. If I try, even with everything else turned off, it sputters, but doesn't get going.

But I have batteries that can crank an engine, so they should be able to handle it, right? If I'm doing my math correctly, they should have plenty of power to do so.

So if I used an inverter that can handle 3600 watts, , then 3600 watts 12 volts = 300 Amps required. Is that correct?

And since I have 4xAGM house batteries, each of them with 550 cold crank amps, that should be plenty of power to crank it and get it going right? Or am I factoring something wrong?

I'm not worried about draining the batteries, because I'll run the generator to charge the batteries while the heater/aircon system is running.
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Old 29-10-2022, 12:34   #2
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Re: Question about running a heating / air conditioning system through an inverter

You want an inverter that can boost like a victron multiplus. It would only need to make up the difference. So a 2000w would probably work.
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Old 29-10-2022, 12:41   #3
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Re: Question about running a heating / air conditioning system through an inverter

Try starting genny - start a/c fan only - wait a minute and start AC
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Old 29-10-2022, 13:14   #4
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Re: Question about running a heating / air conditioning system through an inverter

Your power draw estimates are close. To give you a feel, our 9000 BTU units draw about 800 to 900 Watts when running. So your estimate of close to, but not quite double that is close.

Your batteries can handle the boost to get the unit started, but... there is of course quite a bit more hardware needed. A inverter/charger with a "Power Assist" feature is required. They are not small, or cheap, and the installation is not trivial.

How much the actual instantaneous start up power is required is a function of how sophisticated the controller on your unit is. Do not forget you actually have THREE motors to start. The compressor, the fan and the water pump. A properly designed marine AirCon controller will stagger the start of these units. You probably will not be surprised to hear that not all units are designed correctly.

An alternative that MIGHT work (you are really pushing it with a tiny generator) is to add a proper soft start to the system. Micro-Air makes some good ones, but you will need to do some research to be sure that what you get will work with your very limited generator. So some searches on this forum, there have been a lot of thread about people working iwth these tiny gensets to run AC units and what works and what struggles.
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