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Old 01-15-2012, 09:54 AM   #1
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Will 50 Amps run 3 AC's

I want to add a 3rd air conditioner, the hole/vent is already there as well as the wiring. Here's the thing. i have a 1989 Gulfstream Classic 36' The unit only has 30 amp, But has a 6500 watt onan generator. the rear ac is wired directly to the generator, no switch inside. you can only run the rear ac if the generator is running! very annoying.So i figured i would just wire the rear ac to its own 20 amp plug, that way i could just plug in the rear ac to most campgrounds 20 amp. But if i add a 3rd ac, do i change over to a 50 amp system? I was told that even 50 amp wont run 3 15000 BTU air conditioners. Should i just wire the other 2 Ac's to its own 20 amp plug? So i would have a total of 3 plugs, 1 30 amp and 2 20 amp plugs. I could plug the coach into a 30 amp plug and use a 50 amp plug with a splitter for both 20 amp plugs. Since it seems a lot of campgrounds have both a 30 and a 50 amp plug.Now this 2nd and 3rd air conditioner would only be used in extreme heat, like when im in Vegas during the summer. All 3 would be wired to the generator, which leads to another question.. will a 6500 watt generator run 3 Ac's? And will these plugs be up to code? It seems technically i would be bringing 80 amps into the coach. I have no idea on the legalities.

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Old 01-15-2012, 11:50 AM   #2
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The term 50 amp service is a bit misleading... since it's actually TWO 120v 50amp legs coming into the coach so I would think a properly converted 50 amp rig would handle three AC units.


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Old 01-15-2012, 02:55 PM   #3
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As Rick stated is correct. Be sure 2 units are on one 50 amp leg and the other unit is wired to the other 50 amp power leg. I would also recommend the water heater and microwave be on the single unit leg.
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Old 01-15-2012, 03:29 PM   #4
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I have 3 AC/heat pumps in my rig and they run fine on a conventional 50 amp plug in. They are wired from the factory so that if the clothes dryer is running, only 2 AC's will run at the same time.
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Old 01-15-2012, 04:09 PM   #5
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With a code standard RV 50amp circuit (yes it IS a 240v circuit) and if you load balance the two legs, you can run 3 15kBTU A/Cs AND clothes dryer AND convection oven and plenty more (like elec water heater) all at the same time.

15kBTU A/C will max out at about 16amp ea that's only 48 amps of the 100 amps available on the RV 50amp standard circuit.... Make sure to distrubute the expected loads as evenly as you can across L1 and L2.

An RV 30amp plug is a 120v circuit and thus has only one "leg" and provides only 30amps. Similar to a 20amp 120v circuit thus providing only 20amps.

A standard RV 50amp has 2 50amp 120v "legs" for a total of 100amps at 120v (equivalently 50amps at 240v) because this by code standard is a 240v circuit. The RV 50amp is the exact same outlet used for residential stoves and the like. The 30amp RV outlet is, by code, used ONLY for RV service and no other application and is 120v.

If this does not make sense to you, seek a qualified electrician. (just make sure they don't accidentally wire the RV 30amp plug at 240v "because it looks like it is a 240v" as the RV 30amp is very uniquely and by code ONLY a 120v circuit. It happens regularly.)

A properly sized genset to power a 50amp RV circuit will be >10,000watts (usually 12,500watts)
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Old 01-15-2012, 05:04 PM   #6
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So if 3 ac's require 48 amps then it migbt be possible to run all 3 with a 6500 watt generator? Probably couldnt run anything else but it seems possibel. I talked to an electrician and it appears I would only have to change out the converter box with a single phase 50 amp box, change the poor mans switch box.. I don't have an automatic one but will add one. And of course ill need the actual 50 amp cable. It appears this unit had an optional 50 amp system that could be added. The wires that go to where a 3rd AC can be added are capped off behind the 30 amp converter. Which is actually a 45 amp converter. The generator puts out 52 amps. Doesnt really make sense to me why the manufacturer would only use a 30 amp system when it's wired for more.
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Old 01-15-2012, 06:06 PM   #7
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Ohm's Law: Watts = Volts x Amps.

A 20A 120V circuit provides 2400 watts of power. This is a typical '20A' service for a motorhome.
A 30A 120V circuit provides 3600 watts of power. This is a typical '30A' service for a motorhome.

A 50A 240 circuit provides 12,000 watts of power. This is a typical '50A' service for a motorhome.

Now, an RV air conditioner draws about 12 amps of current at 120V = 1440 watts.

2-AC's draw 2880 watts.

3-AC's therefore will draw 4320 watts of power.

As you can see, a 20A 120V service will supply enough wattage for 1-AC unit.

A 30A 120V service will supply enough wattage for 2-AC units.

A 50A 240V service has plenty of wattage to run 3-AC units. Your generator will have to supply at least 4320 watts of continuous power to run all 3 AC's at once. Mine's a 7500 watt generator.

Simple math.
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Old 01-15-2012, 07:47 PM   #8
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One thing to remember is while a 12,000 -13,000 btu ac will pull 12-13 amps while running it will also need 25 or so amps for 2 secs during startup. The startup amps is what can result in a 50 amp leg shutting down if both AC's on one leg startup at the same time; (25*2)*120=6000 watts total at initial turn ON.

For the 6500 generator, it is divided into a 30 amp (normal RV supply) and a 20 amp rear AC service. It is 50 amps total (6500/120=54 amps) not 50 amps on each side.


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