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LIKE2BUILD's avatar
LIKE2BUILD
Explorer
Jul 26, 2016

Portable Generator for 50 amp service

I'm preparing to purchase a 5th wheel that has a 50 amp service. We'll be taking a dry-camping trip in August and I need to get a portable generator that will work. For my dry camping we'll mostly be using the A/C, water pump, and a lights. I can keep the fridge and hot water heater on gas operation.

I've had a 30A TT for many years and I've not dealt with 50A systems. Pardon the ignorance but please help me clear up a few things.
1) Does the 50A work on 240volt or 120volt?
2) If 240volt, is it 25A per hot leg?

To get a full 50A service I believe I would need a 6000 Watt generator (50A x 120V= 6000W). Generac has a 6500W (8000W startup) generator that is within my budget. The kicker is to get 6500W it uses the 240V plug that supplies 27.1A to each hot leg.

Will that generator work?

I just want to be sure I don't get burned buying something undersized. Previously I had a Generac GP3250 for my 30A service TT. I thought it was fine since 3250W would give me 27A. It wasn't until after it failed to run my A/C that I realized it was rated for 27A total and delivered 13.5A per leg of the 240V plug and only 13.5A to the 120V outlets. On a cool day that was okay, but in the hot Tennessee sun the A/C kept tripping the breaker each time it tried to kick in.

When not using the generator for dry camping I'll keep it around to backfeed my house in the event of a power outage.

Thanks,
KJ

18 Replies

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  • SoundGuy's avatar
    SoundGuy
    Explorer
    Jul 26, 2016
    LIKE2BUILD wrote:
    To get a full 50A service I believe I would need a 6000 Watt generator (50A x 120V= 6000W).


    Incorrect. As already explained so-called "50 amp RV service" is actually 50 amps across each of two legs for a total service of 100 amps or 12,000 watts. For "full" 50 amp service you'd therefore want a 12K genset minimum ... that's a whopper of a "portable" generator. :E

    I have to ask though ... since you're intending to tow a 5th which will effectively eliminate the possibility of carrying such a large "portable" genset in the back of the truck where are you planning to carry it? A genset this large would be really heavy so moving it at any time would be a real chore.

    Also, you certainly don't want to simply "backfeed" your house with this genset and possibly kill someone unaware that your house service is hot when it otherwise wouldn't be when normal service has failed. :E If this is your consideration you need to install it with a proper transfer switch that will prevent such catastrophes. ;)
  • LIKE2BUILD's avatar
    LIKE2BUILD
    Explorer
    Jul 26, 2016
    LIKE2BUILD wrote:
    DrewE wrote:
    A 4 kW or so generator wired for 120V (so 120V at 35+ amps) would serve you just fine when running one air conditioner with a decent cushion to spare. The key here is that it's 120V, so you aren't limited to half power per leg. .....

    That was my GOTCHA on the previous generator. It was rated for 3250W running, but I didn't see until later that wattage was divided between each leg of the 240V. So, my actual max available amperage on 120V was 13.5A which caused my A/C to bog and eventually kick out the breaker on the genny.

    The GP6500 info says it supplies 27.1A per leg of the 240V plug. Surely that's enough, right?

    KJ
  • LIKE2BUILD's avatar
    LIKE2BUILD
    Explorer
    Jul 26, 2016
    DrewE wrote:
    A 4 kW or so generator wired for 120V (so 120V at 35+ amps) would serve you just fine when running one air conditioner with a decent cushion to spare. The key here is that it's 120V, so you aren't limited to half power per leg. .....

    That was my GOTCHA on the previous generator. It was rated for 3250W running, but I didn't see until later that wattage was divided between each leg of the 240V. So, my actual max available amperage on 120V was 13.5A which caused my A/C to bog and eventually kick out the breaker on the genny.

    KJ
  • LIKE2BUILD's avatar
    LIKE2BUILD
    Explorer
    Jul 26, 2016
    2oldman wrote:

    RV 50a wiring diagrams

    That is helpful. So a total of 12,000W can be delivered to the breaker panel.

    The Generac GP6500 has a NEMA L14-30R 240V plug.

    The 5er we're going to purchase has a single A/C unit. Given the explanation from that web site, it seems the 6500W genny might work:
    "In the case of the rest of the 50 amp RV's, 250 volts is still supplied to the coach just like your home electrical service but typically one side of the line is used for all the 125 volt appliances except the rear AC and the other side is used for the rear AC only."

    Thoughts?

    KJ
  • DrewE's avatar
    DrewE
    Explorer II
    Jul 26, 2016
    50A RV supply is 50A 120/240V supply, 50A on each leg, or 12 kW total power. It's exactly the same configuration as a standard household electric range (with a four-wire connection, as opposed to the old 3 wire connections that are in some existing buildings).

    Your generator should be sized based on the maximum load you need to support at any given time rather than based on the ratings of the RV input power. For a 30A RV, these are often pretty close to being equal; but for most 50A RVs, the electrical needs are well under the electrical supply limits.

    A 4 kW or so generator wired for 120V (so 120V at 35+ amps) would serve you just fine when running one air conditioner with a decent cushion to spare. The key here is that it's 120V, so you aren't limited to half power per leg. A standard 30A to 50A RV adapter would presumably be needed; this simply connects the one hot from the 30A supply to both of the hots on the 50A supply, so the full generator output is available to start the air conditioner. A somewhat smaller generator could suffice, too, though I can't really say exactly where the cutoff would be.

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