How do 3+ A/C's work?

[Steve Ownby]

[QUOTE="jesilvas;1597301"]

So an EMS type system is how yours is controlled?

I don't have a full EMS system, just that one circuit. It's true, you can run two A/C's on 30 amp but very little else.

[jamesrxx951]

Originally Posted by jesilvas

So an EMS type system is how yours is controlled?



Hmmmm, interesting. Never seen where single phase 30A runs two A/Cs fine.



?

mine seems to. However, the control panel has the energy management feature. Havent tested on real hot days yet but should find out this summer. These newer A/Cs seems to pull less current than older ones. Start up is likely where all the current needs are. I will have to measure running current on mine now that you have me thinking.

[jesilvas]

Like I said earlier, I deal with trailers and house stuff on MHs, but don't get into the very complicated elec. systems a lot. I just know that on any trailer that is 50A, it can run two A/Cs and 30A can run one. On the MHs I've dealt with, same thing.
So I'm trying to learn.

[Peralko]

Originally Posted by jesilvas

So an EMS type system is how yours is controlled?



Hmmmm, interesting. Never seen where single phase 30A runs two A/Cs fine.



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?

Power comes in to a 120-volt distibution panel with two 50-Amp breakers that connects to distribution circuits. There is no EMS involved.

[bruceisla]

Originally Posted by jamesrxx951

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.

220(240) 60hz uses the 2 opposite phase legs without the neutral ... different from the 220/50 hertz European. That's why the VOM reads 240 (ish) when you measure from leg to leg in the USA (and Canada) ... the meter is not using the neutral. On an electric range, the neutral is present for the portion of the range that uses 120 (for instance, the clock). Otherwise, you don't need the neutral wire (like for a 240 baseboard heater). This is also the reason you need to be careful about using a Range Cord (the wire) as an extension in an RV ... the neutral could be lighter gauge because it's only used for the clock.

Would 230 volts 50 Hz appliances work on 240 volts 60 Hz

[bruceisla]

Originally Posted by jesilvas

So an EMS type system is how yours is controlled?



Hmmmm, interesting. Never seen where single phase 30A runs two A/Cs fine.



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?

Well ... the 40 is probably more like 26 amps with 2 - 13500 A/Cs. Startup is higher but both units don't come on simultaneously ... and startup is VERY brief and the delay in the breaker doesn't even see it.

[FlyingDiver]

Originally Posted by jesilvas

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?

It's 50amps at 240V (50 amp each leg), which is the same as 100amps at 120V.

AC units take 15-20 amps each, so about 50-60amps@120V if all three are running. Which is well within the 100 amp max. Two of the units will be on the same leg, so that leg will be pulling more amps. Best to try not to have any other heavy load (like a large inverter) on the same leg.

[bruceisla]

Originally Posted by FlyingDiver

It's 50amps at 240V (50 amp each leg), which is the same as 100amps at 120V.

Well ... sort of ... it's actually like 2 - 50a out-of-phase 120vac services for a total available 100a. (as opposed to a single 100a 120vac service).

[mcmills]

Unsatisfied with two A/Cs in the hot Texas summer, we had the dealer drop an extra unit in one of the roof vent openings in the dining area. They ran an extra circuit to the electrical panel. Using shore power or genset, we can run all three A/Cs at once, but we rarely do, keeping the bedroom unit off unless occupied. Works fine.

Mike M.
'06 Phaeton 40 QDH
'09 HHR Toad

[Steve Ownby]

Originally Posted by bruceisla

Well ... sort of ... it's actually like 2 - 50a out-of-phase 120vac services for a total available 100a. (as opposed to a single 100a 120vac service).

This is exactly the way 240 vac works in the US. if you look in any home breaker box you will lyrically see 15/20 amp single pole breakers and Double pole for everything larger. The double pole breakers provide 2 legs of 120 at 180 degrees out of phase. If you test across these legs you have 240 vac. If you test either leg to neutral or ground you have 120. If you have a 50 amp coach with a built in load shedding device commonly called an EMS, it determines the size of your shore hook up by checking for 240 across the two energized legs. If the power pedestal is mis wired and the 2 legs are in phase the EMS assumes 30 amp power because there is zero current across those two legs. I've never seen a 100 amp single pole breaker but I guess they could exist.

Many people make the mistake of thinking that RV power pedestals are somehow special in their wiring set up. They are actually industry standard residential configuration. The horror stores you hear come from mis wiring or hooking up to a circuit that was dedicated to a special use. Some welders are wired with a plug that looks like an RV 30 amp but is really 2 legs of 120 vac with a ground and no neutral. Will fry everything. Some older range circuits were similar.

[jamesrxx951]

Originally Posted by Steve Ownby

This is exactly the way 240 vac works in the US. if you look in any home breaker box you will lyrically see 15/20 amp single pole breakers and Double pole for everything larger. The double pole breakers provide 2 legs of 120 at 180 degrees out of phase. If you test across these legs you have 240 vac. If you test either leg to neutral or ground you have 120. If you have a 50 amp coach with a built in load shedding device commonly called an EMS, it determines the size of your shore hook up by checking for 240 across the two energized legs. If the power pedestal is mis wired and the 2 legs are in phase the EMS assumes 30 amp power because there is zero current across those two legs. I've never seen a 100 amp single pole breaker but I guess they could exist.

Many people make the mistake of thinking that RV power pedestals are somehow special in their wiring set up. They are actually industry standard residential configuration. The horror stores you hear come from mis wiring or hooking up to a circuit that was dedicated to a special use. Some welders are wired with a plug that looks like an RV 30 amp but is really 2 legs of 120 vac with a ground and no neutral. Will fry everything. Some older range circuits were similar.

Unless im misunderstanding you, the only way you are going to use 240 in a home or in a motorhome is if you have an appliance that will take in both legs (one of each phase) and use it (aka a stove). A 240 home stove will use each leg at each end of the element. Since the current is alternating + and -, each leg provides the ground when the phase is -. A motorhome with a 50 amp service plug is no more than 2 smaller wires that feeds it power. You could actually just have one large single wire rated for 100 amps (actually needs a neutral also). Unless a motorhome has an appliance that truly needs both legs the service is still 120 in but capable of 240 appliances.

[bruceisla]

Originally Posted by Steve Ownby

This is exactly the way 240 vac works in the US. if you look in any home breaker box you will lyrically see 15/20 amp single pole breakers and Double pole for everything larger. The double pole breakers provide 2 legs of 120 at 180 degrees out of phase. If you test across these legs you have 240 vac. If you test either leg to neutral or ground you have 120. If you have a 50 amp coach with a built in load shedding device commonly called an EMS, it determines the size of your shore hook up by checking for 240 across the two energized legs. If the power pedestal is mis wired and the 2 legs are in phase the EMS assumes 30 amp power because there is zero current across those two legs. I've never seen a 100 amp single pole breaker but I guess they could exist.

Many people make the mistake of thinking that RV power pedestals are somehow special in their wiring set up. They are actually industry standard residential configuration. The horror stores you hear come from mis wiring or hooking up to a circuit that was dedicated to a special use. Some welders are wired with a plug that looks like an RV 30 amp but is really 2 legs of 120 vac with a ground and no neutral. Will fry everything. Some older range circuits were similar.

yes indeed ... it's not magic!

You can get a big ol' single 100a breaker but I have not personally seen one either .... a bit pricey!

Shop Square D QO 100-Amp Single-Pole Circuit Breaker at Lowes.com

[Steve Ownby]

Originally Posted by jamesrxx951

Unless im misunderstanding you, the only way you are going to use 240 in a home or in a motorhome is if you have an appliance that will take in both legs (one of each phase) and use it (aka a stove). A 240 home stove will use each leg at each end of the element. Since the current is alternating + and -, each leg provides the ground when the phase is -. A motorhome with a 50 amp service plug is no more than 2 smaller wires that feeds it power. You could actually just have one large single wire rated for 100 amps (actually needs a neutral also). Unless a motorhome has an appliance that truly needs both legs the service is still 120 in but capable of 240 appliances.

You are correct. A few coaches with stackable washer/dryers have used the 240 capability and a very few all electric coaches may use it for the range top but it's rare. For most 50 amp coaches they have two legs of 50 amp power at 120. By adopting this standard which uses readily available residential components it does insure that any competent electrician will understand the system. As far as the end user is concerned the 120 vac power in a coach is just like their house.

[bruceisla]

Originally Posted by jamesrxx951

Unless im misunderstanding you, the only way you are going to use 240 in a home or in a motorhome is if you have an appliance that will take in both legs (one of each phase) and use it (aka a stove). A 240 home stove will use each leg at each end of the element. Since the current is alternating + and -, each leg provides the ground when the phase is -. A motorhome with a 50 amp service plug is no more than 2 smaller wires that feeds it power. You could actually just have one large single wire rated for 100 amps (actually needs a neutral also). Unless a motorhome has an appliance that truly needs both legs the service is still 120 in but capable of 240 appliances.

The service is 240/120 ... just like a house.

No .... in your ending scenario, you would need a source (the entire park and pedestal), and cord, and the entire motorhome wired in a non-standard configuration of single-pole 100a 120vac. Wire size would be huge and costly.