I'm converting a cargo trailer into a camper. Over the weekend, I tried to install an AC unit. The unit that I bought requires 8.8 amperes at 115 volts. My inverter is an 1800 watt trip lite that I have had installed in my truck for several years. I've used the inverter to run power tools, electric kettles, and other high current loads, so I'm pretty sure it works fine, and should support 15 amperes without difficulty. When I try to run my AC unit though, it runs the fan for 3 minutes, the compressor never comes on, and then the inverter shuts down. I monitored my 12 volt supply while doing this, and it never even flickered, 13.5 to 14 volts the whole time (engine running) I took the AC unit into the house to see if it would run from a mains outlet, and it does.So...If there's nothing wrong with the AC unit, nothing wrong with the inverter, and nothing wrong with the low voltage supply to the inverter, what could be the problem?

Run your a/c on shore power or generator (large enough to handle it).

Robert Kesselring wrote:If there's nothing wrong with the AC unit, nothing wrong with the inverter, and nothing wrong with the low voltage supply to the inverter, what could be the problem?The inverter and supply powering it just doesn't have the capacity to deal with the A/C's LRA (Locked Rotor Amp) rating which will be many times it's running amps. As an example it's not uncommon that a typical roof mount 13,500 BTU A/C would have an LRA of 60+ amps even though it's total running amps may be well under 15 smps. Just because you have a smaller A/C doesn't mean it's exempt from this sudden high current demand that is overwhelming your inverter. Equipping the A/C with a Micro-Air Easy Start soft starter kit would likely solve this issue.

SoundGuy wrote:a Micro-Air Easy Start soft starter kit would likely solve this issue.Those things are not cheap!!What I'm finding when I google that looks like about $300. For not a lot more, I could upgrade to a larger inverter.The 1800 watt unit that I have is supposed to support a peak of 3600 watts for starting motors, just like you're talking about. 3600 watts should be about 30 amperes. How much do I need to start a 9 amp motor?Wouldn't a spike in draw cause a momentary dip in the low voltage supply, at least until the inverter cut off. I'm not seeing any dip at all. Even setting my volt meter to record max and min voltage, its, recording a min that's still 13+ volts, and it's watching on millisecond time scales.

Classic case of startup amps being too much.As someone mentioned, it may take 40-60amps to get going and the unit just can't put that out.

Robert Kesselring wrote:SoundGuy wrote:a Micro-Air Easy Start soft starter kit would likely solve this issue.Those things are not cheap!!What I'm finding when I google that looks like about $300. For not a lot more, I could upgrade to a larger inverter.The 1800 watt unit that I have is supposed to support a peak of 3600 watts for starting motors, just like you're talking about. 3600 watts should be about 30 amperes. How much do I need to start a 9 amp motor?Wouldn't a spike in draw cause a momentary dip in the low voltage supply, at least until the inverter cut off. I'm not seeing any dip at all. Even setting my volt meter to record max and min voltage, its, recording a min that's still 13+ volts, and it's watching on millisecond time scales. Even “if” you get an inverter large enough to run the ac, it would require a “very” large battery bank to make a sustained run. I haven’t “crunched” the numbers....but, it would require many typical batteries!

Having problems running AC from inverter. | Good Sam Community

valhalla360
Navigator
Aug 20, 2018
Classic case of startup amps being too much.

As someone mentioned, it may take 40-60amps to get going and the unit just can't put that out.
Robert_Kesselri
Explorer
Aug 20, 2018
SoundGuy wrote:
a Micro-Air Easy Start soft starter kit would likely solve this issue.

Those things are not cheap!!
What I'm finding when I google that looks like about $300. For not a lot more, I could upgrade to a larger inverter.

The 1800 watt unit that I have is supposed to support a peak of 3600 watts for starting motors, just like you're talking about. 3600 watts should be about 30 amperes. How much do I need to start a 9 amp motor?

Wouldn't a spike in draw cause a momentary dip in the low voltage supply, at least until the inverter cut off. I'm not seeing any dip at all. Even setting my volt meter to record max and min voltage, its, recording a min that's still 13+ volts, and it's watching on millisecond time scales.
SoundGuy
Explorer
Aug 20, 2018
Robert Kesselring wrote:
If there's nothing wrong with the AC unit, nothing wrong with the inverter, and nothing wrong with the low voltage supply to the inverter, what could be the problem?

The inverter and supply powering it just doesn't have the capacity to deal with the A/C's LRA (Locked Rotor Amp) rating which will be many times it's running amps. As an example it's not uncommon that a typical roof mount 13,500 BTU A/C would have an LRA of 60+ amps even though it's total running amps may be well under 15 smps. Just because you have a smaller A/C doesn't mean it's exempt from this sudden high current demand that is overwhelming your inverter. Equipping the A/C with a Micro-Air Easy Start soft starter kit would likely solve this issue.
jerseyjim
Explorer
Aug 20, 2018
Run your a/c on shore power or generator (large enough to handle it).

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