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Old 09-16-2020, 09:38 PM   #1
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Running 2ac's on 30amp

Have a 50amp MH, thought could only a single ac unit on 30amps, first time at 30amp hookup and both work. I realize probably can't run much else with both units running however to just cool the MH on a hot day works great. Is this typical or is there anything special maybe on pedestal?
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Old 09-16-2020, 09:59 PM   #2
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I don't think you have any special power supply, but I do think you got lucky and maybe you have a robust pedestal supply that doesn't sag with lots of amps. Any of these will probably make it unworkable:

Low pedestal voltage. Low voltage pulls more current and you are already running at the limit.

Starting both compressors at the same time. The inrush current will probably trip the breaker before they start.

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Old 09-16-2020, 10:27 PM   #3
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Thereís probably more variation in current between different sizes and models of air conditioners, particularly when adjusted for operating temperatures, than there is between 30A breakers (provided breakers are good).

Just saying itís likely more about air conditioner loads than breakers.
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Old 09-16-2020, 10:43 PM   #4
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Originally Posted by mrgscooter View Post
Have a 50amp MH, thought could only a single ac unit on 30amps, first time at 30amp hookup and both work. I realize probably can't run much else with both units running however to just cool the MH on a hot day works great. Is this typical or is there anything special maybe on pedestal?
There is a chance your air conditioners have a soft start built in. This allows 2 ac units to run at one time. If you pull the side panel off the ac unit and see a capacitor you don't have a soft start. I'm going to install them on mine. Its called Micro-Air. https://youtu.be/soP0uZFd0nQ
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Old 09-16-2020, 10:47 PM   #5
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Originally Posted by mrgscooter View Post
Have a 50amp MH, thought could only a single ac unit on 30amps, first time at 30amp hookup and both work. I realize probably can't run much else with both units running however to just cool the MH on a hot day works great. Is this typical or is there anything special maybe on pedestal?


Typical AC will draw about 14A so yes it can work. But they draw much more at start up so if both happen to cycle on at the same time you might trip the pedestal breaker. Isnít a fatal event though. Just try again, one at a time.
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Old 09-16-2020, 10:52 PM   #6
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So what size are your A/Cs? In a factory installed dual A/C installation in a 27B coach they are probably less than 13.5K BTU units so two 11K or 9.2K BTU A/Cs can easily be run on 30 amps.
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Old 09-16-2020, 10:53 PM   #7
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I'd say that you're pretty lucky: congratulations!
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Old 09-16-2020, 11:05 PM   #8
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So what size are your A/Cs? In a factory installed dual A/C installation in a 27B coach they are probably less than 13.5K BTU units so two 11K or 9.2K BTU A/Cs can easily be run on 30 amps.

The newer 29M has 15,000 BTUH standard, and optional dual 13,500 BTUH.

Unless they are running in desert conditions, many models can pull less than 13 Amps each, and some energy efficient ones a lot less. Basically, an A/C can pull less than a microwave, so running two at once isnít that different than running microwave and one A/C simultaneously on 30A service. And thatís extremely common. I donít see the big deal as long as both A/Cs donít start together, or other loads are on at same time.
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Old 09-17-2020, 12:18 AM   #9
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Have a 50amp MH, thought could only a single ac unit on 30amps, first time at 30amp hookup and both work. I realize probably can't run much else with both units running however to just cool the MH on a hot day works great. Is this typical or is there anything special maybe on pedestal?
Nothing special. Any 30 amp will run 2 a/c but NOTHING else.
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Old 09-17-2020, 02:48 AM   #10
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I'd say lucky you. I have had 30 amp pedestals pop when the microwave was used at the same time as 1 air conditioner.
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Old 09-17-2020, 03:31 AM   #11
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I'd say lucky you. I have had 30 amp pedestals pop when the microwave was used at the same time as 1 air conditioner.

Maybe youíre the unlucky one.

Seriously though, we use the microwave extensively and run it for extended periods to heat dinners while the A/C is going full blast, and it hasnít been a problem in our own RV or in numerous rentals weíve traveled in. The only times I recall a problem was when we had A/C, microwave, and wife used hair dryer. That combination trips breaker pretty fast.
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Old 09-17-2020, 12:01 PM   #12
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Chance,
You didn't say what you were plugged into (if at all); or the amperage capacity of the RV that you were in.
(Just trying to make sure. that the comparisons are valid...)
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Old 09-17-2020, 01:24 PM   #13
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Chance,
You didn't say what you were plugged into (if at all); or the amperage capacity of the RV that you were in.
(Just trying to make sure. that the comparisons are valid...)

Always 30-Amp at campground pedestals all over the country. We’ve also successfully powered the microwave and A/C simultaneously from Onan 4,000-Watt gasoline generators on various motorhomes. The generator has a much easier time if you start the A/C first, let it run a few minutes, then start using microwave as needed. Start-up current can be a lot of load on generator, but a breaker doesn’t have the same mechanical limitations of a generator.

The key here is to consider that all air conditioners and cooling conditions are not the same and will load a 30-Amp breaker differently. The newest air conditioners can have higher Energy Efficiency Ratio (EER) which means they will use less power and therefore current to deliver the same 13,500 BTU/hour of cooling. Also, air conditioners require more power and current when it's warmer inside and or outside. Cooling in 90 F weather requires much less power and current than in 105 F weather. Likewise, it takes more power when it’s 90 F inside motorhome than when it’s 80 F inside.

I’m not saying it’s not possible or even likely to trip a 30-Amp breaker under right conditions when trying to power “two” A/Cs, but just because some can’t, it doesn’t mean others will have similar problems.

The Devil is in the details. And let’s not forget that various manufacturers are installing dual 11,000 BTU/hr Power Saver air conditioners in mid-size motorhomes with 30-Amp and 4,000-Watt generators. Also, the difference between 11,000 and 13,500 BTU/hr Power Savers is not that great.
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Old 09-17-2020, 01:35 PM   #14
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Thanks: just had to check..
But now i have to wonder how microwave and air conditioner power usages may differ...
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Old 09-17-2020, 01:43 PM   #15
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30amp service is not always '30amps' maximum, as breakers are not 'exact' is how they react to HEAT(amps) flowing thru them - some will react quicker, such as when the breaker is old, overused, weak, etc, making the RV owner think they have somehow 'used' too much power - the reality is that there is no 'exact' same reaction because there are too many variables.
Yes, your own appliances will determine how 'much' amperage you draw at any given moment, and microwaves are not all of the 'same' amperage draw variety - some are 900watts, while other larger ones are 1100watts, etc. How 'long' you have that appliance operating comes into play. The outside 'ambient' temperature also plays a factor, a BIG factor in very hot weather, where the wires, especially those shore power cords exposed to sunshine, can certainly cause a breaker to trip sooner than 'normal'.

There are a lot of factors when it comes to RV power, but yes, you can easily run two 13.5kw a/c units at the same time on 'only' 30amp power, IF the breaker is new or reacting correctly, and IF you are also aware of your other large draws, such as electric water heaters, microwaves, and even the Converter/Battery Charger.
Power is power, there is no 'you can't do this, you can't do that' answer = in many cases you may be able to successfully do what you wish, while the next stop may not be so kind. It's the nature of the 'mobile' environment and the many various 'electrical' power sources and devices we use along the way.
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Old 09-17-2020, 02:00 PM   #16
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Old 09-17-2020, 02:33 PM   #17
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Maybe youíre the unlucky one.

Seriously though, we use the microwave extensively and run it for extended periods to heat dinners while the A/C is going full blast, and it hasnít been a problem in our own RV or in numerous rentals weíve traveled in. The only times I recall a problem was when we had A/C, microwave, and wife used hair dryer. That combination trips breaker pretty fast.
Yeah, A/C and MW should easily be doable.

Rule of thumb is 2 major appliances at a time in a 30 amp RV.

Lotsa people forget about the silent third major appliance - the water heater on electric - that would break the camel's back.
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Old 09-17-2020, 02:45 PM   #18
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Also lots of time people have the water heater running on electricity and forget that it can use 6A or so.
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Old 09-17-2020, 03:00 PM   #19
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Thanks: just had to check..
But now i have to wonder how microwave and air conditioner power usages may differ...

For what itís worth, air conditioners have improved in efficiency far more than microwaves as far as I can tell, so relative power usage has changed over the years.

When I tested my Class C, both the 13,500 A/C and microwave pulled around 13+ Amps (more or less). Thatís around 1,500 Watts each.

Microwaves today still require around 1.5 Watts of electric power for each Watt of cooking power rating, so a typical 1,000-Watt microwave uses around 1,500 Watts of power.

Older air conditioners, particularly 15,000 BTU/hour sizes, often required close to 2,000 Watts and even more in desert conditions. Those large and inefficient units plus a microwave could easily trip 30A on a hot day. Itís simple math.

By comparison, modern air conditioners, particularly the 13,500 BTU/hr size, can be more efficient than years ago and require much less power; and much less than many microwaves.

Attached is claimed efficiency specs for 13,500 Power Saver. Two of those on a 30A service leaves plenty of spare capacity for smaller loads.
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Old 09-17-2020, 03:22 PM   #20
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P.S. ó Itís kind of sad that manufacturers keep installing low-efficiency air conditioners just to save a little on initial costs ó all driven by the price-point wars. Not only would it help owners, it would help reduce load on campgrounds also.
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