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RVing message boards => Remodeling your RV => Topic started by: Phrog on July 19, 2017, 06:02:39 PM

Title: Convert from 30 amp service to 50 amp
Post by: Phrog on July 19, 2017, 06:02:39 PM
Have a 1996 holiday rambler with a 30 amp service cable. The RV also has an Onan Marquis 7000 generator that pushes out 50 amps into the RV. When on generator power, I can run both the bedroom A/C and the main A/C simultaneously. When I'm plugged into the 30 amp service I can only run one of the two A/C units. Since the RV appears to be configured for 50 amp service (generator), can I just get an adapter for my 30 amp service cable and run the RV on 50 amps, thus being able to utilize both A/C units simultaneously when plugged in?

I really can't understand why the RV is configured to pump out 50 amps on generator power, but only 30 amps when plugged in; or why it was configured to only be able to use both A/C units on generator power.
Title: Re: Convert from 30 amp service to 50 amp
Post by: John Stephens on July 19, 2017, 07:27:53 PM
No. If it's configured for 30amp, you will have to change both the shore power cord and the wiring from the transfer switch to the main box. You will also have to make sure the transfer switch is designed for 50 amp as well as the main box, and you will have to add a 20 amp breaker to go along with the 30 amp breaker you currently have. You may get lucky and have all this already in place if the genset puts out 50 amps and nothing catches fire. But you'll have to check it all out first. It doesn't make any sense that they would set the coach up for 50 amp service and only give you a 30 amp cable.
Title: Re: Convert from 30 amp service to 50 amp
Post by: Phrog on July 20, 2017, 07:41:00 AM
Gotcha. Thanks
Title: Re: Convert from 30 amp service to 50 amp
Post by: Gary RV_Wizard on July 20, 2017, 08:34:36 AM
Elaborating a bit, the Onan 7000 has a little over 50A available at 120v, but that is NOT equivalent to RV 50A shore service, which is 50A @ 240 but utilized in most RVs as 2x 50A/120v sources for a total of 100A available. We can get into tech details if you like, but your coach is NOT set up for 50A service.

Most likely what you have is two outputs from the Onan, one 30A that provides the same power as the shore cord, plus an additional 20A circuit that feeds direct to the rear a/c through a special switch.  John has already outlined what it takes to convert.

An alternative is to install a second external 20A/120v power cord that you could plug into a shore power outlet when available. That would work essentially the same as the secondary genset circuit and allow both a/c to run.  Many power pedestals have multiple outlets you could plug to, but there are adapters available to draw two power circuits from a single 50A shore power outlet as well.
Title: Re: Convert from 30 amp service to 50 amp
Post by: Phrog on July 20, 2017, 03:18:04 PM
I like the suggestion of a second external 20A circuit for the second A/C. I would assume doing that would be considerably cheaper than attempting to convert the unit to a totally 50A service. I think almost everywhere I've been has a 20A receptacle on the power post. Seems worth looking into.
Title: Re: Convert from 30 amp service to 50 amp
Post by: Gary RV_Wizard on July 21, 2017, 09:10:29 AM
It's usually pretty simple, but the details depend on just how it is now wired. In most cases a simple manual transfer switch and an extra cord is all you need.
Title: Re: Convert from 30 amp service to 50 amp
Post by: NY_Dutch on July 21, 2017, 12:19:37 PM
If your coach has the "Front/Rear" selector switch typically used in this setup, where you can run both A/C's only when the switch is in one position, then the wiring mod needed to run the second A/C from separate 20 amp feed is really pretty simple. All of the wiring mods can be done in the generator junction box where its output wiring connects to the coach wiring. I'll provide more details if the selector switch is the type of setup you have. All that's involved is adding an outlet and a short cord and plug. And a heavy duty extension cord of course.
Title: Re: Convert from 30 amp service to 50 amp
Post by: Gary RV_Wizard on July 21, 2017, 01:44:07 PM
Here is a variation on the "two power cord" solution, using a portable a/c unit.  A similar approach could be used here toi plug into a 50A outlet instead of using the 30+20 outlets

http://www.rvforum.net/SMF_forum/index.php/topic,107061.msg964475/topicseen.html#new (http://www.rvforum.net/SMF_forum/index.php/topic,107061.msg964475/topicseen.html#new)
Title: Re: Convert from 30 amp service to 50 amp
Post by: NY_Dutch on July 21, 2017, 06:21:37 PM
Here's a block diagram of the 30 amp, two A/C setup in our previous coach. The mod for running the second A/C from an external 20 amp outlet is shown between the generator and selector switch. The photo below it is not my mod, but the only difference is that I used 12GA SO cord instead of the Romex shown.
Title: Re: Convert from 30 amp service to 50 amp
Post by: Phrog on July 22, 2017, 09:13:20 AM
Thanks for all the suggestions.

Yes, I have a selector switch. Both A/C's run on gen power when the switch is position 1 and the thermostat is set so both A/C's will work (temp selection). On house power I need to switch between positions 1 & 2 to power the different A/C's.
Title: Re: Convert from 30 amp service to 50 amp
Post by: NY_Dutch on July 22, 2017, 09:50:36 AM
Great! The key to the conversion is to sort out which wires in the generator junction box only feed the A/C that's not powered when the switch is in the #1 position on shorepower. Selectively disconnecting the wires (with the power OFF!) and then firing up the gen to see what doesn't work is all it takes. Disconnecting one of the black wires will lose power to everything in the coach except one A/C, telling you it's the other black wire that you want for the conversion. Repeat the process to isolate the correct white wire. If the wire you select first only cuts off one A/C and nothing else, you're good to go. Now you just need to add an extender box to the junction box, wire a foot or so of 12 GA cord to the black and white pair that go to the A/C, and a 20 amp utility outlet to the pair from the generator, plus a safety ground connection on both. If you use wire nuts for the connections, tape them so they don't vibrate loose. Screw everything down tight, install a suitable cover plate, plug in the short cord to the outlet, and test that everything works just as it did before. If all is ok, then all you need when you want both A/C's on with shorepower is a 12 GA extension cord to plug the short cord into before you plug it into the shorepower utility outlet. Other than the wires being in a relatively tight work space, it's not a difficult conversion if you take your time and think through what you're doing. Oh, and you may find that your A/C's are reversed from the way they're shown in my block diagram. That just changes which one runs on the extension cord.
Title: Re: Convert from 30 amp service to 50 amp
Post by: Phrog on July 22, 2017, 10:14:54 AM
Great info. RV is presently getting some exterior body work done, so I won't be working on this issue for a while. Of course, that's after I get the generator repaired as well.............