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Author Topic: air conditioner current  (Read 86636 times)

ku4ns

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air conditioner current
« on: May 14, 2009, 08:25:55 PM »
Has anyone measured the current draw of their 13500 btu air conditioner. I'm looking to see what it actually takes to run the ac with a generator. I would like to buy a small, quiet, and easy to handle generator similar to the Honda 2000 watt or the Yamaha 2400 watt. Both of those are very quiet and light weight, but will they run an ac? I have used a Honda 3000 which worked great but was hard to move around by myself.
I have a 2007 KZ 2450 5th wheel, recent upgrade from a TT.
John

Carl L

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Re: air conditioner current
« Reply #1 on: May 15, 2009, 12:30:19 AM »
Well 13500 BTU/hr translates to 3954 Watts.   Wikipedia's article on airconditioning in the section on portable A/Cs states:  "Modern units run on approximately 1 to 3 ratio i.e., to produce 3 kW of cooling this will use 1 kW of electricity."   So the 13,500 BTU unit will use at least 1300 Watts of power from a generator.   However do remember that you will have other AC loads in the RV -- the microwave being the biggy.
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Gary RV_Wizard

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Re: air conditioner current
« Reply #2 on: May 15, 2009, 05:55:34 AM »
A typical 13,500 btu RV a/c will use 14.5-15A and a high efficiency model about 11.5 amps. That's under full load (compressor running and fan on high).  The tricky part is compressor start-up, when the amp load doubles for a few seconds and gives you a brief 3000-3600 watt load.  If this passes quickly enough most small generator can ignore the overload, but sometimes the breaker will trip or the a/c won't start due to low current.
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tweak

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Re: air conditioner current
« Reply #3 on: May 19, 2009, 01:41:35 PM »
I have a Honda 2000 and keep in mind that they are rated at 1600 watts not 2000. I also have the 13500 btu roof units and will do some tests with the Honda 2000 and post the results here. At this time my only concern would be start up current draw.
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John From Detroit

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Re: air conditioner current
« Reply #4 on: May 19, 2009, 03:00:17 PM »
Interesting fact on the Honda 2,000 watt inverter jobs.. Thanks.

Another fact to consider is where as a A/C may want 1300 watts RUNNING

The starting current on that compressor can astound you
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ku4ns

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Re: air conditioner current
« Reply #5 on: May 19, 2009, 08:27:09 PM »
I'm looking forward to seeing the test results. I have my eye on the Yamaha 2400 watt generator, just because if the little extra wattage.
John

huronwoods

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Re: air conditioner current
« Reply #6 on: May 21, 2009, 01:50:11 PM »
We have a Yamaha 3000 watt inverter generator, rated at 2800 watt continuous, similar to the Honda 3000 watt unit. We run a standard Coleman 13,500 AC roof unit with the generator. On a hot day, when the starting load on the compressor is highest, the generator will start the AC, but it sound as though there is little reserve there during the 1 second it takes to start. As a rule of thumb, the starting amps for an AC compressor, which starts under load, is between 8 and 10 times the running amps. If running amps of the compressor only is 11, then the instantaneous starting current could be as high as 88 amps. This is what the generator must contend with.

I haven't tried running AC with a 2000 watt generator, but I have heard that it is very borderline. It works for some people and not others. Best to stick with a 3000 watt unit, or two 2000 watt units with a parallel cable, available form Honda.
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Marsha/CA

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Re: air conditioner current
« Reply #7 on: May 21, 2009, 06:32:43 PM »
I had a slide in truck camper for several years.  We had a 13500 btu air conditioner put on it and ran it with a Honda i2000 generator.  It did a great job!  I also had a microwave put in the camper and could not run the microwave while the A/C was running.  We loved that little generator and still have it for stuff around the house.  I traveled alone a lot (have horses and went camping with lady friends) and I could lift and move that little generator anywhere.

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Gary RV_Wizard

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Re: air conditioner current
« Reply #8 on: May 21, 2009, 07:07:13 PM »
It kind of depends on the overload breaker used in the genset, i.e. how "fast" it trips, and the condition of the a/c itself.  The 8x starting load is much less than 1 second - the average amps for that first second will be more like 2x or even less. If the breaker reacts slowly, the peak will be past before it trips. However, even if the breaker holds, the a/c will choke a bit due to the lack of power for that 1/4 second. If the a/c compressor and electronics are in good shape, it will probably start. If old/worn/weak, it may not.

All that said, the 2000W (peak) is marginal at best and the 2400W is definitely a better choice. The 3000 is the real answer, though.
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Lou Schneider

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Re: air conditioner current
« Reply #9 on: May 22, 2009, 12:05:29 PM »
Don't forget the engine output will be affected by altitude, and as mentioned above, the starting load of the compressor will increase with temperature.

A generator that starts the A/C when you try it on a cool day at sea level may have trouble doing the same on a 100 degree day at a couple of thousand feet altitude.

SkateBoard

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Re: air conditioner current
« Reply #10 on: May 18, 2017, 02:47:48 AM »
I was just searching Google and this thread came up. I have one of those Champion 3,400 watt inverter generators, 3,100 continuous. I have a 15,000 BTU house AC unit coming on Monday and I have a Kill-A-Watt meter and will see how it does. The meter measures the peak watts, running watts and amps. I'll post the results next week.

JackL

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Re: air conditioner current
« Reply #11 on: May 18, 2017, 06:03:22 AM »
The part to think about is the in rush current when it starts.
 I have a new 2016 Forest river travel trailer with a 15,000 BTu A/C, and a residential refrigerator unit and whoever thought that a 30 amp supply would be ok evidently did not have an electrical background.
 After poping the breaker numerous times, I did some calculations and found out that if I had my electric water heater on, and the A/C on and the Refrigerator on every thing would be ok, but if the A/C and the refrigerator clicked on at the same time it way overloaded the 30 Amps, and the breaker would trip.

 I solved the problem by adding a 50 amp panel and supply and changing the A/C unit over to it

Many people don't take into consideration  the in rush current of motors when they are calculating the various loads

Jack l

 

SkateBoard

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Re: air conditioner current
« Reply #12 on: May 18, 2017, 06:27:32 AM »
I read the spec on the unit I'm getting Monday and it draws 1,500 watts total worst case when the compressor initially kicks in. Most AC units have large capacitors inside to take the hit. I will have EXACT figures next week when I plug the unit into my generator along with my Kill-A-Watt meter. I can tell you a Mr. Coffee is 600 right on the money.

Gary RV_Wizard

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Re: air conditioner current
« Reply #13 on: May 18, 2017, 08:11:28 AM »
Quote
I read the spec on the unit I'm getting Monday and it draws 1,500 watts total worst case when the compressor initially kicks in.

Forgive me for being skeptical of that spec, but no a/c over about 8000 btu performs that well. I've measured 25+ amps at compressor start-up on 13,500 btu Colemans. Less than a second at that peak and no more than 2-3 seconds at more than 13A, but well above "1500 watts". However, the peak is short enough that a 20A breaker for the a/c circuit doesn't trip.
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DickHutchings

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Re: air conditioner current
« Reply #14 on: May 18, 2017, 08:11:45 AM »
Got me thinking and I just called my wife and told her to switch the hot water heater back to propane while the AC is running. We're not running on a compressor but only have 30A service at our campground.
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SkateBoard

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Re: air conditioner current
« Reply #15 on: May 18, 2017, 08:30:32 AM »
Forgive me for being skeptical of that spec, but no a/c over about 8000 btu performs that well. I've measured 25+ amps at compressor start-up on 13,500 btu Colemans. Less than a second at that peak and no more than 2-3 seconds at more than 13A, but well above "1500 watts". However, the peak is short enough that a 20A breaker for the a/c circuit doesn't trip.

We shall find out next week. I have the generator, 15k BTU coming in Monday and a Kill-A-Watt meter. Should I video tape it?

And BTW, this is with a REAL house AC, not one of those crapola roof units

regval

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Re: air conditioner current
« Reply #16 on: May 18, 2017, 07:35:52 PM »
Has anyone measured the current draw of their 13500 btu air conditioner. I'm looking to see what it actually takes to run the ac with a generator. I would like to buy a small, quiet, and easy to handle generator similar to the Honda 2000 watt or the Yamaha 2400 watt. Both of those are very quiet and light weight, but will they run an ac? I have used a Honda 3000 which worked great but was hard to move around by myself.
I have a 2007 KZ 2450 5th wheel, recent upgrade from a TT.
John

I measured mine with an amp meter that captures peak instant current (start up). The RV AC is a Coleman 13,500 BTU with a LRA (locked rotor amp) rating of 54A. You can usually find this rating on the decal affixed to the AC compressor. So, the start-up current measured was an average of about 40A @ 118VAC.  This equates to a start-up draw of 4720 watts.  Based on that reading, I decided to purchase two Honda 2KW generators (EU2000i), with one of them being a "companion" generator. Linking the two, I have 4000 watts with a peak wattage capability that allows the AC to start without generator overload.
I can run the RV on one generator when the AC is not required. I can manage lifting one of these fueled generator into my truck bed without assistance.

Hope this helps.
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Gary RV_Wizard

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Re: air conditioner current
« Reply #17 on: May 19, 2017, 08:11:22 AM »
Quote
And BTW, this is with a REAL house AC, not one of those crapola roof units

A compressor is a compressor and the laws of physics as applied to electric motors don't change. All electric motors have a starting surge, and a motor that starts under load (any compressor) has an even greater surge.
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SkateBoard

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Re: air conditioner current
« Reply #18 on: May 19, 2017, 12:48:48 PM »
A compressor is a compressor and the laws of physics as applied to electric motors don't change. All electric motors have a starting surge, and a motor that starts under load (any compressor) has an even greater surge.

Yes, the physics do change depending on the compressor. Most are slow start now or with large starting capacitors. Many homes still have the old glass fuses so they must accommodate them.

Many of you ignore the fact that a rooftop unit doesn't even come close to the amount of air volume that comes from a house unit. All those rooftop manufactures are selling a half truth. They advertise xxx CFM but when you actually dig deep that figure is xxx CFM BEFORE the evaporator. What actually blows out if not even close. A home AC measures CFM out the front what you actually feel. NOT before the evaporator.

The LG 15,000 BTU AC I ordered specs say 1,260 watts to run and 11.8 amps. More then enough that a 3,100 Champion can supply.

Either way, I plan to do a test next week and will video tape. I have a series of tests I plan to do.

Full run mode then turn on
Eco mode then turn on
Full mode then turn on then turn on eco mode and see how compressor kicks on and off and how much generator ramps up
I will also be running all these tests with a watt/amp meter attached and record results.

The watt/amp meter also records peak but from what I'm told that surge may only last milliseconds and not be able to be caught by the meter and only with a scope.

Anyways, the proof will be in the video I make so we can put this to rest.

captaindomon

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Re: air conditioner current
« Reply #19 on: May 19, 2017, 01:58:02 PM »
Make sure you check your Kill-A-Watt meter. The standard model is only rated to handle a max of 1850 watts. You don't want to blow out the meter itself ;-)

Gary RV_Wizard

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Re: air conditioner current
« Reply #20 on: May 20, 2017, 09:22:49 AM »
Quote
Yes, the physics do change depending on the compressor. Most are slow start now or with large starting capacitors.


Sure, but that has been true for well over 20 years now, even including RV rooftop a/c. Compressors still start under load and the amp draw is massive, if brief.

Quote
The LG 15,000 BTU AC I ordered specs say 1,260 watts to run and 11.8 amps.

Little different than specs for a typical Dometic or Coleman roof a/c. It will run on a 1600W Honda EU20001. The question here is the locked rotor amps, not the running amps. The start-up load will be closer to the locked rotor amps than the standard running amps.

Will be interesting to see your measurements.
Gary
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SkateBoard

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Re: air conditioner current
« Reply #21 on: May 20, 2017, 11:20:44 AM »
Ya, I'm curious how it goes. I see a lot of people on Youtube that have small generators. They start off in full run mode then back off to ECO mode. That's so the compressor and fan don't start all at once. Once everything is running it's just the compressor kicking on and off. I will try turning the unit to just fan then back to AC when in ECO mode also.

One thing I'm curious about. I have a 3,000 Xantrex pure sine wave inverter that is yet to be installed. I also have 4 deep cycle marine batteries. It's not installed yet. The AC will ONLY be run when on shore power or the generator running. Never off the batteries. I'm wondering if the Xantrex will kick in some juice if the generator bogs down during startup.

I'm betting the generator does fine.

Lou Schneider

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Re: air conditioner current
« Reply #22 on: May 20, 2017, 12:31:52 PM »
Be sure to record the ambient temperature during your test.  Resting system pressure and the compressor current both increase when it's hot outside.

It would be a real bummer to have a generator that can start the A/C when it's in the 60s outside but not be able to do the same when the temperature is in the 90s or above.

SkateBoard

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Re: air conditioner current
« Reply #23 on: May 20, 2017, 01:05:29 PM »
Even their web site says it will run it. I really don't see a problem. The one I bought is a new model. 3,100 continuous and 3,400 surge

beaverfever

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Re: air conditioner current
« Reply #24 on: May 24, 2017, 03:42:10 PM »
 having sold and repaired electric motors for approximately 20  years i can tell you the inrush current is  5 to 7 times name plate amps on start up

SkateBoard

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Re: air conditioner current
« Reply #25 on: May 24, 2017, 09:09:47 PM »
having sold and repaired electric motors for approximately 20  years i can tell you the inrush current is  5 to 7 times name plate amps on start up

So, you're saying it won't work? 5 to 7 would be 60 to 84 amps or 6,400 to 8,960 watts.

Gary RV_Wizard

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Re: air conditioner current
« Reply #26 on: May 25, 2017, 08:50:29 AM »
You can't really evaluate inrush current without considering time.  For maybe 1/1000th of a second the current is huge, but by 1/60th of a second the amperage has fallen to 5x or less.  A lab grade oscilloscope would capture the higher values, but by the time consumer grade ammeters can respond, the amps are probably 3x or less. Within 2 seconds, it is down to the "running" amps.

The point here is that the reaction time of the overload circuitry (or breaker or fuse) is what determines if the genset works or not for this application. Most 3 kw gensets respond slowly enough that a instantaneous  3600 watts (30A) is not a problem, but its hard to be sure until a particular load is applied to that specific genset.  I would not expect problems with your combination, but it is still conceivable that there could be one.
Gary
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Wireman134

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Re: air conditioner current
« Reply #27 on: May 25, 2017, 08:04:24 PM »
Inrush current is 5-6X FLA on A/C motors
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Jason389

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Re: air conditioner current
« Reply #28 on: June 06, 2017, 10:37:24 PM »
Quote
One thing I'm curious about. I have a 3,000 Xantrex pure sine wave inverter that is yet to be installed. I also have 4 deep cycle marine batteries. It's not installed yet. The AC will ONLY be run when on shore power or the generator running. Never off the batteries. I'm wondering if the Xantrex will kick in some juice if the generator bogs down during startup.

I'm betting the generator does fine.

You CANNOT run the generator and the inverter at the same time. Sparks will fly, campers will burn down, children will cry. When on generator DISCONNECT the inverter and vice versa. If you do run them at the same time, be sure to video it and have 911 pre dialed. 
« Last Edit: June 06, 2017, 10:46:49 PM by Lou Schneider »

kdbgoat

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Re: air conditioner current
« Reply #29 on: June 07, 2017, 05:47:39 AM »
You CANNOT run the generator and the inverter at the same time. Sparks will fly, campers will burn down, children will cry. When on generator DISCONNECT the inverter and vice versa. If you do run them at the same time, be sure to video it and have 911 pre dialed. 

Not true. Many inverters, including a Xantrex Freedom 3000 have an automatic transfer switch to run the inverter loads off of "normal" AC, whether from shore power or generator, then switch to inverting power from the batteries when AC is not provided to the RV.
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