Electrical Engineers? Power Questions..

[Nuge]

I own a 1982 Sportscoach CrossCountry (32' SB) which I believe was made by Coachmen. After reading a few threads about 30 Amp to 50 Amp conversions I started going over my paperwork and am a bit confused by some of the numbers found there. I have an on-board Onan 6.5 NH generator rated for 54.2 Amps @ 120 v and 27.1 Amps @ 240 v. (4 wire reconnectible) My converter (with charger board) Is a BW (Magnetec) 6345 rated at 45 Amps @ 12 vdc with 3 amp charge, (Input 6.8A @ 120 vac) yet the plug SPLICED to the end of my cord is only a 30A plug. I have 2 air conditioners but the rear A/C unit only works off of the generator which is mounted right under the rear bedroom! I presently run a 3c/10 Ga. extension cord to run that rear A/C and an electric heater in the winter and have been entertaining the idea of installing that second cord permanently with hard wired outlets for those rear accessories. We mainly use the RV as a cabin on a little river property we own and only exercise the generator for maintenance purposes and have been thinking of taking it out to use as a back-up generator at home and re-installing it when we want to actually go on the road. It seems strange that both A/C units work of off of the generator but NOT shore power. I'm a multi-craft industrial electrician with experience ranging from component level electronic troubleshooting and repair up to working on 13.8 KV substation switch-gear but have only had the RV for 2 years and am NO engineer. I know my converter is a single phase unit and figured if I did try to run 2 phase 240 into the coach I'd have to be concerned about balancing the load. This IS an OLD RV and I don't know if it's worth changing out the power center/converter as opposed to just running an extra line to get by until I retire and upgrade to a newer unit. Any thoughts or suggestions would be deeply appreciated.

[RJay]

Nuge,
If you have a 3-wire supply line from your generator then you can run 54 amps from the generator which is enough capacity to run two A/C's. If you only have a 30 amp shore supply, that is not enough for two A/C's. If you want to change the shore cable to a 50 amp 4 wire service you would only have to wire up the second live leg to the wire going to the rear A/C. If you don't have a automatic transfer switch in your coach one should be added so you can run the rear A/C from both shore power and the generator.

[Dr4Film]

They didn't start wiring normal RV coaches with 50 amp service until much later, not sure exactly what year. My 1992 Airstream Landyacht was a 30 amp service however the generators that were installed usually would provide enough wattage to run both A/C's, that was very typical too.

To completely redo the wiring inside the coach to handle a 50 amp service is way too costly to reap the benefits and even get a return on your investment. It's also a very BIG job to tackle. You have to basically separate one side of the coach for 120 volt AC Leg 1 and the other side of the coach for 120 volt AC Leg 2. One A/C would be wired to each leg, L-1 and L-2. You would also have to upgrade the Inverter/Converter.

It is far more cost effective to just install another 30 amp shore power cord to a receptacle and have that service only supply one of the A/C's and maybe a few other items depending on your needs. You would need to purchase a 30 amp extension and a 50 to 30 amp dog-bone to use the 50 amp receptacle for the additional service wire.

Dr4Film ----- Richard.

[Nuge]

There is a relay in the converter that changes state between an AC supply or house batteries. The AC source is determined by what the plug is connected to. (Shore outlet or internal generator outlet) There must be a separate control that tells the system whether I'm on Shore power or running the generator. My shore power is my own to wire any way I might need, but I WILL keep to the standards used in campgrounds to prevent issues when we do travel or sell our unit. We're trying to stay away from running the generator because it's under our bedroom and quite noisy

[frankdamp]

Just thinking aloud, not actually looking stuff up (I'm a Mech/Aero engineer!), but would it not be possible to build a splitter "dog-bone" that would turn a standard RV 4-wire 50A, 120v supply into a pair of 25A (nominal) with 30A connectors then put a second 30A circuit in the MH to supply the second a/c unit?

Maybe that's Richard's suggestion and I didn't quite get it.

[RJay]

Frank,
Not only is it possible but I believe you can buy them at camping world.

[RustyJC]

RV split phase 50 amp 120/240 VAC service provides two (2) 50 amp legs for a total ampacity of 100 amps or (100 amps x 120 volts =) 12,000 watts.

If you split it, you will have 2 each 50 amp legs, not 2 each 25 amp legs.

Rusty

[Nuge]

So, obviously the splice was just to replace a bad plug since my coach was NOT wired for 240 @ 50 amps. I've already got a 30 Amp outlet wired in at my power pole (And a couple standard outlets) and was aware enough NOT to wire it with 240. It seems funny that the generator puts out 54 Amps and the converter is a 45 Amp unit but the shore power is only designed to provide only 30 Amps. I think the extra cord hard wired to the rear A/C and an outlet in front for a heater is the way to go. (We use two 1500 W heaters for heating in the winter to cut down on trips to fill the on-board propane tank) I was just hoping for an easier way considering the capacities of the generator and converter. I'd still like to know how the system knows if I'm running the generator or shore power???

[RJay]

I think the generator is hard wired to the rear A/C and separate from the rest of the coaches electrical system. The shore power never sees the rear A/C.

[Nuge]

That's possible. The AC print I have is 2 years newer than my MH and shows an A/C selector switch that doesn't exist in my unit...I'll probably have to hard wire the new feed through the generator breaker box located at the gen. compartment.

[mrschwarz]

I had an 81 Foretravel and it was 50 amps. There's a couple of ways you can go. The easiest would be to install a 20 amp socket and plug for the second air conditioner. Wire the socket to the generator and the plug to the second air conditioner. When running down the road, plug into the socket. When parked, plug into a 20 amp circuit.

The other alternative is to convert to 50 amps. This is not quite so easy, but if you have the right equipment and the knowledge to do it, it can be done.

[RJay]

Nuge,
The rear A/C probably has a breaker in the main breaker panel and you can pick it up from there.

[Nuge]

mrschwarz - The rear A/C is already hardwired to the gen set, but the gen set is right under the bed and we're trying to get away from that for our mostly parked use.

RJay - Actually, this unit has a small, two breaker box in the gen set compartment; one for the rear A/C and the other for all other circuits and the front A/C I believe. My prints are incomplete and some are newer than the coach but helpful. I DO have an owners Manual but it doesn't have prints, just operational instructions and some basic maintenance info.

[RJay]

Sorry Nuge, I forgot you had a vintage RV.