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Author Topic: Can one RV air conditioner be run off of an inverter?  (Read 734 times)

dpickard

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Can one RV air conditioner be run off of an inverter?
« on: February 29, 2016, 11:37:12 PM »
 I know this question may seem silly to some.  I was wondering if one RV air conditioner could be powered by my inverter?
Gil and Dianne
Piedmont area NC
2007 Allegro Bus 40 QDP

Kevin Means

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Re: Can one RV air conditioner be run off of an inverter?
« Reply #1 on: February 29, 2016, 11:56:51 PM »
Some inverters and battery-banks have enough capacity to power a typical RV roof AC unit, but when the  AC unit's compressor kicks on, it momentarily draws a lot of power (amps) and most inverters would shut down. As a practical matter, it doesn't make a lot of sense to run a 1300 or 1500 BTU AC unit off the batteries, because the batteries would be drawn down so quickly that you'd have to plug into shorepower, or fire up the genset anyway to recharge them - in short order.

I saw an add last year for a 2015 Newmar Mountainaire that had 18 house-batteries (from the factory). I was told that it was an option that would enable you to run an AC unit off the batteries. I don't know how popular that option was, or if it's even available anymore. Mountainaires aren't used much for boondocking.

Kev
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dpickard

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Re: Can one RV air conditioner be run off of an inverter?
« Reply #2 on: March 01, 2016, 06:43:05 AM »
Thanks Kev. Very informative answer. Always  wondered about that but was too chicken to try it, LOL. I've  learned something today!  You are always wonderful to help. Thanks again.
Gil and Dianne
Piedmont area NC
2007 Allegro Bus 40 QDP

John From Detroit

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Re: Can one RV air conditioner be run off of an inverter?
« Reply #3 on: March 01, 2016, 07:11:07 AM »
Just watched a video where the V-Bloggers did exactly that.

First: They had 960 watts of solar panel
700 Amp Hours of LiON batteries (EXPENSIVE)
3,000 watt inverter
and the A/C was small (only drew about 9 amps A/C, not 13 like most do)

It worked, but it woudl NOT have worked overnight,m they would have ran out of battery.. (They did it on a very sunny day).

And they still got a Fault flash on the inverter... But not enough to shut it down.
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workerdrone

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Re: Can one RV air conditioner be run off of an inverter?
« Reply #4 on: March 01, 2016, 08:40:08 AM »
It can be done but it's currently VERY unusual as somewhat covered above.

Inefficient standard AC units plus usually limited battery capacity plus usually limited inverter surge and continuous capabilities.

I would actually be more interested in an inverter upgrade that would allow my large battery bank and inverter to assist either a small generator or an otherwise inadequate shore power connection to keep AC running - so I could have a very small, very quiet generator that I only unpack and run when boon docking and really want AC, or maybe I'm dry camping in someone's yard but I can run a long extension cord to a standard residential outlet.
« Last Edit: March 01, 2016, 08:41:46 AM by workerdrone »
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sadixon49

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Re: Can one RV air conditioner be run off of an inverter?
« Reply #5 on: March 01, 2016, 12:02:33 PM »
Most people have no idea of how much current it takes to start a motor.  I read comments here, and at other forums where people say it takes "2 to 3 times" the running current to start a motor. The true number is much closer to 6 to 10 times running current to start, and that's for a good 3 phase motor which has the best starting torque and the lowest starting current. Single phase motors go up from there, they are harder to start, and take longer to get up to speed. Compressor and fan motors are the worst. They usually start under load, unless some form of unloader is included, not likely in the low cost units we see. Air conditioners handle this by using a simple time delay, which in theory, should mean that the compressor won't start until the pressure has equalized across the system. If you have a peak reading ammeter you might be surprised at what you find.
steve
2017 Jayco Redhawk 26XD
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Gary RV_Wizard

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Re: Can one RV air conditioner be run off of an inverter?
« Reply #6 on: March 01, 2016, 04:11:46 PM »
sadixon49 is technically right, but the peak observed on a typical multimeter or onboad ammeter would still probably be about 2x-3x. An oscilloscope would show more, if measuring the true peak, but it goes by so fast nothing in a typical RV or residential circuit has time to react to it. For an RV a/c compressor, the peak lasts about 1 second (maybe 1.5 or even 2), and the value seen on a display or inexpensive VOM will be an average over something like 0.25 seconds.

The inverter sees this peak as well, and tries to draw the DC amps needed to sustain it. If the a/c draws 30A/120v during start-up (mine is measured at 28-33A, depending on line voltage), then the inverter attempts to pull about 310-360A from the battery bank. That much current draw sends the battery voltage plummeting, usually far enough to cause the inverter to trip out on a low voltage fault. With a big enough battery bank, however, the voltage may stay within an acceptable range. "Big enough" is probably upwards of 800AH, but it depends on temperature, cable sizes, battery condition, etc. as well as the actual battery rating.  Even after the start-up surge (which occurs every time the compressor cycles on), the continuous amp draw is on the order of 130+ amps. which probably requires a battery bank rated for something like 4x-5x that, even to provide power for just an hour.

There is a lot of "Kentucky windage" and assumptions in the above estimates, but it gives an idea of what it takes to start and run an a/c compressor on an inverter.
Gary
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