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Old 06-08-2013, 11:27 AM   #1
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How do 3+ A/C's work?

I work on mostly trailers, but also do MH work. Just no motor/trans type stuff.
But my question, is how do you get 3 or more A/C units to work on the big coaches?
I know that 50A 240VAC is required for two A/C's, but what about more. Multiple 50A connections?
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Old 06-08-2013, 11:38 AM   #2
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Most 50A MH's are 120V with 2 50A 120V lines coming in the same cord with a total available 100 AMP to run the AC's

And they are probably hook up to a energy management system that can shut any AC off when too many amps are used.

My 30 AMP MH only has 2 AC's but both can be ran the same time with the EMS.
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Old 06-08-2013, 11:41 AM   #3
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I understand there are two 50A/120VAC lines to make a total of 100A/240VAC supply. I know that an A/C has a 20A breaker max, and you need to have only one A/C unit on a supply leg to even out the load.

But what you're saying is not all 3 or more A/Cs will run at the same time?
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Old 06-08-2013, 11:45 AM   #4
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Originally Posted by jesilvas View Post
I work on mostly trailers, but also do MH work. Just no motor/trans type stuff.
But my question, is how do you get 3 or more A/C units to work on the big coaches?
I know that 50A 240VAC is required for two A/C's, but what about more. Multiple 50A connections?
3 A/C units run fine on 50 amp since 50 amp double pole provides 100 amps total on 2 separate legs. There can be a problem with the generator. Up to the Onan 8KW genset a 240 vac output was not available so 3 A/C's would be close to capacity. That's why you see the 10 and 12.5 KW gensets which are true 240 vac output.
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Old 06-08-2013, 11:48 AM   #5
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We have three roof ACs and they work fine on 50-Amp shore power or our 10kW generator. They come in handy in Las Vegas when it's 120 degrees outside!
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Old 06-08-2013, 12:00 PM   #6
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3 A/C units run fine on 50 amp since 50 amp double pole provides 100 amps total on 2 separate legs.
Ok so basically one of your legs is near max with 40A worth of A/Cs on it. Then maybe converter and that's it?
Then the other leg only has 20A of A/C, and whatever else you want. Wash/dry, refr, outlets.
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Old 06-08-2013, 12:26 PM   #7
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All I can tell you that we run whatever we want on a 50 Amp comnnection. In our previous coach, we had 30-Amp service, and it ran two ACs just fine.
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Old 06-08-2013, 12:38 PM   #8
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I understand there are two 50A/120VAC lines to make a total of 100A/240VAC supply. I know that an A/C has a 20A breaker max, and you need to have only one A/C unit on a supply leg to even out the load.

But what you're saying is not all 3 or more A/Cs will run at the same time?
Each leg (just like household wiring) is 120VAC. The only way to read 240 (just like household wiring) is to use a DVOM and place each lead (+ and -) on both input wires. At no time is both legs connected together to add up to 240 (same as household wiring). It would be 120VAC with total capacity of 100 amps.
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Old 06-08-2013, 12:51 PM   #9
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All I can tell you that we run whatever we want on a 50 Amp comnnection. In our previous coach, we had 30-Amp service, and it ran two ACs just fine.
You had the EMS or whatever so that makes sense.

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Each leg (just like household wiring) is 120VAC. The only way to read 240 (just like household wiring) is to use a DVOM and place each lead (+ and -) on both input wires. At no time is both legs connected together to add up to 240 (same as household wiring). It would be 120VAC with total capacity of 100 amps.
I know it's not 240V, but it is. I understand nothing actually uses 240V. It's two phase, three wire service. That all makes clear sense.
I'm just wondering how, or if, you can run three or more A/Cs at once.
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Old 06-08-2013, 12:52 PM   #10
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Each leg (just like household wiring) is 120VAC. The only way to read 240 (just like household wiring) is to use a DVOM and place each lead (+ and -) on both input wires. At no time is both legs connected together to add up to 240 (same as household wiring). It would be 120VAC with total capacity of 100 amps.
Except for certain 220/240 VAC devices like electric ranges, some baseboard heating, some pool pump motors, etc.
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Old 06-08-2013, 12:56 PM   #11
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Except for certain 220/240 VAC devices like electric ranges, some baseboard heating, some pool pump motors, etc.
They just take in 2 legs of 120VAC. They are not combined together though for a single input because the sine waves do not match exactly. If I remember correctly, the wires are connected on each end of the load.
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Old 06-08-2013, 01:01 PM   #12
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You had the EMS or whatever so that makes sense.
No EMS, just straight 30 Amps. 30 Amps will run two ACs just fine.

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I'm just wondering how, or if, you can run three or more A/Cs at once.
There's no "if" to it, we run three ACs a lot of the time, and we run the inverter/charger, and the water heater, and the washer/dryer, and the refrigerator, and the freezer in the basement, and the computer, and the TVs, and the DVD. All at the same time if we so wish.
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Old 06-08-2013, 01:05 PM   #13
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Ok so basically one of your legs is near max with 40A worth of A/Cs on it. Then maybe converter and that's it?
Then the other leg only has 20A of A/C, and whatever else you want. Wash/dry, refr, outlets.
I just checked our current electric status. It's a very humid 90 degrees outside. We have 2 of our 3 airs running along with the washer/dryer and a couple of TVs. The Instahot is on and the electric element for the AquaHot is also on. I'm sure there are some other small current draws. We are using 48 amps, 19 on one leg and 29 on the other. My 3rd A/C is set up on a shared circuit with the washer/dryer. The W/D has priority. If the 3rd A/C is running and we turn on the W/D then the A/C will turn off. We rarely run the 3rd A/C unless we want to cool down rapidly.
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Old 06-08-2013, 01:10 PM   #14
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I just checked our current electric status. It's a very humid 90 degrees outside. We have 2 of our 3 airs running along with the washer/dryer and a couple of TVs. The Instahot is on and the electric element for the AquaHot is also on. I'm sure there are some other small current draws. We are using 48 amps, 19 on one leg and 29 on the other. My 3rd A/C is set up on a shared circuit with the washer/dryer. The W/D has priority. If the 3rd A/C is running and we turn on the W/D then the A/C will turn off. We rarely run the 3rd A/C unless we want to cool down rapidly.
So an EMS type system is how yours is controlled?

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No EMS, just straight 30 Amps. 30 Amps will run two ACs just fine.
Hmmmm, interesting. Never seen where single phase 30A runs two A/Cs fine.

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There's no "if" to it, we run three ACs a lot of the time, and we run the inverter/charger, and the water heater, and the washer/dryer, and the refrigerator, and the freezer in the basement, and the computer, and the TVs, and the DVD. All at the same time if we so wish.
Ok, so how? 20+20 is 40A on one leg. Then the WH is a 15A, that's 55A, that's no go. Wash/dry is either 15A or 20A. That's 55A or 60A. Most outlet circuits are 15A. So that can work one the other leg but what about the leg with 40A of A/Cs already?
I'm not saying you're lying, but I do not see how you can run EVERYTHING at once without tripping your main 50A's.

Is there anyone with a big Prevost conversion with 5 airs? I've seen em before, just not from anyone on here?
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