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  1. #1
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    Onan RV QG 5500 amp issue

    We have a 2014 Grand Design Momentum 355TH with a Cummins Onan RV QG 5500 EVAP generator. From everything I have read this generator it is a 50 amp generator. Even the labeling on the outside 'Shore power' says 50 amps and the generator has 2 x 30-amp breakers in it too. I find it odd how after we power on 2 A/C's, refrig, water pump and a couple other things it is around 39 amps but once it gets past 40 amps it acts as if it gets tripped and never reaches 50 amps. So once it is tripped (or overloaded?) now both A/Cs power off and generator goes back to idle and my EMS Control panel goes blank. I checked that both of my 30-amp breakers are just fine. Eventually the 'power' EMS control panel lights up and shows GEN and then after several minutes the other right lights up (W/H, A/C-RR, A/C-FRT, A/C-MID) as if it reset itself. Then I can power up both A/C units again. If I only run the 2 A/C's, have the refrig on Propane and all other main switches off, then it stays consistent around 30 amps and on some hot days it gets up to 35 amps based on what the Power Control system states.
    So is it normal for this generator to not support true 50 amps? Just an FYI, I have done the complete maintenance on this generator such as oil change, oil filter, air filter, Fuel Filter, Fuel Pump, and replaced both 2 spark plugs (with proper gap) plus even did the SeaFoam cleaning of the carb too. I'm scratching my head thinking it should do more then 40 amps or am I thinking incorrectly?

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    Rolling Along LV Naturist's Avatar
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    One thing to remember is that true 50 amp shore power is actually 100 amps; 50 amps on each leg. The genny has 2 x 30 amp breakers making it actually 60 amp available. It's easy to get used to running everything on shore power (100 amps available) and thinking the 50 amps (actually 60 amps) the genny puts out will do the same thing. In your case, I suspect the power management system is shedding loads. I could be wrong about that though...

    John

    Edited to clarify: You indicated you have 3 A/C's. 2 of the A/C's will be on one leg, and the 3rd will be on the other leg. If you are running the 2 that are on 1 leg, say main room and bedroom, that is a large draw against 30 amps available on that leg. try to figure out which 2 A/C's are on the same leg and try using the other one instead, say main room and garage for example. That may help.
    Last edited by LV Naturist; 06-30-2020 at 10:18 PM.
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    After reading some more I did find out that the Cummins Onan RV QG 5500 EVAP will only at the max put out 45.8 Amps even though I have two 30 amp breakers on it.
    In regard to shore power connecting at 50 amps, do you mean at a 50 amp hookup we really get 100 amps? I thought it was 50 amps total and shared between the two paths.

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    A 5500W generator doesn’t supply 50A. 5500W is a little less than 46A. 50A is 6000W.

    Where are you seeing the 50A label?

    Like LV said, if the two air conditioners are running on the same leg, it won’t take much to exceed the rating of that breaker.

    Edit: You answered while I was typing so you are already aware of the 45.8A limit.

    50A RV service is two 50A legs for a total of 100A and 12,000W.
    Last edited by jkwilson; 07-01-2020 at 07:40 AM.
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    Rolling Along LV Naturist's Avatar
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    Quote Originally Posted by JohnTaylorTX View Post
    After reading some more I did find out that the Cummins Onan RV QG 5500 EVAP will only at the max put out 45.8 Amps even though I have two 30 amp breakers on it.
    In regard to shore power connecting at 50 amps, do you mean at a 50 amp hookup we really get 100 amps? I thought it was 50 amps total and shared between the two paths.
    This is correct. If you'll notice on the pedestal, the 50 amp breaker is actually 2 x 50 amp breakers stacked side by side (called a double pole, double throw, or DPDT). This gives you a total of 100 amps available, just remember that each leg (L-1 & L-2) is limited to 50 amps each. As you have found out, the genny is limited in what it can provide not only per leg, but combined. You can probably draw close to 30 amps on one leg, but that limits you on the other leg. Like i said earlier, it's a good idea to get an idea on what appliances and outlets are powered by each leg. This way, you can use some power management techniques (only running this appliance or that at the same time) to better manage what power is available.

    John
    Last edited by LV Naturist; 07-01-2020 at 09:20 AM.
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    Phew.. While I think most of this is right, you can't have a "how many amps" discussion without voltage if you're trying to get to watts.

    The Onan (and just about every other genny out there) is rated in watts. Watts are watts, you don't need to talk about voltage anymore because watts are volts multiplied by amps. 5500 watts could be around 40amps at 110V, around 20 amps at 220V, or around 1 amp at 5500 volts.

    So, clearing that up, a 5500 watt genny often has 2 poles, in a normal genny, they call view it as 220V; much like a 50A circuit you plug into in an RV park has 220V available (not used in the RV though) if you go from L1 to L2. If you want to compare one to the other, a 50A circuit from an RV park has about 12,000 watts available compared to the 5500 watts you have available on a genny. About double, which is why you need a 50A circuit if you're going to run all 3 ACs at once with your batter charger running full tilt and the coffee pot running. You won't be able to do that on a 5500 watt genny, what you will be able to do it run MOST things at the same time, just everything. If you want "everything" you'll need the 12,000 watts or so that a 50A 220 circuit gives you.

    While I said 50A 220, which is what an electrician would call it, our RV actually uses it as 2 50A 120 circuits. This is fine, these circuits are designed for it, but, technically, it is correct, a 50A 220 circuit is really 2 50A 110 circuits. We call it 220 because if you go from circuit 1 to circuit 2, you wind up with 220V. To get 110V, you go from circuit 1 to neutral or circuit 2 to neutral and you get 110. This is "standard" 220 service; it's 4 wires, hot 1, hot 2, ground and neutral. Hot 1 to neutral or hot 2 to neutral will give you 110V at 50A, hot 1 to 2 will give you 220V and hot 1 or 2 to ground will also give you 110V at 50A (but don't do this, there's a reason that ground and neutral aren't the same wire).

    One thing to remember is that true 50 amp shore power is actually 100 amps; 50 amps on each leg.
    No, it's 50A at 220V. That's not 100A service; they are very different. Don't believe me? Open up a power pole, look at the wire sizes. Almost all the time, you'll find 6 gauge wire in there, which is rated for ~50-60A. If it was 100A service, you'd need 2GA wire in there. But 2 poles of 50A aren't 100A, it doesn't work that way. The reason there's so much more power (watts) on a 50A plug compared to a 30 or 20A plug is because it's a 220 line, you have 2 poles in there, both at 50A. So where 30A is about 3500 watts, 50A is close to 12,000 watts.

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    Quote Originally Posted by Overtaxed View Post
    Phew.. While I think most of this is right, you can't have a "how many amps" discussion without voltage if you're trying to get to watts.

    The Onan (and just about every other genny out there) is rated in watts. Watts are watts, you don't need to talk about voltage anymore because watts are volts multiplied by amps. 5500 watts could be around 40amps at 110V, around 20 amps at 220V, or around 1 amp at 5500 volts.

    So, clearing that up, a 5500 watt genny often has 2 poles, in a normal genny, they call view it as 220V; much like a 50A circuit you plug into in an RV park has 220V available (not used in the RV though) if you go from L1 to L2. If you want to compare one to the other, a 50A circuit from an RV park has about 12,000 watts available compared to the 5500 watts you have available on a genny. About double, which is why you need a 50A circuit if you're going to run all 3 ACs at once with your batter charger running full tilt and the coffee pot running. You won't be able to do that on a 5500 watt genny, what you will be able to do it run MOST things at the same time, just everything. If you want "everything" you'll need the 12,000 watts or so that a 50A 220 circuit gives you.

    While I said 50A 220, which is what an electrician would call it, our RV actually uses it as 2 50A 120 circuits. This is fine, these circuits are designed for it, but, technically, it is correct, a 50A 220 circuit is really 2 50A 110 circuits. We call it 220 because if you go from circuit 1 to circuit 2, you wind up with 220V. To get 110V, you go from circuit 1 to neutral or circuit 2 to neutral and you get 110. This is "standard" 220 service; it's 4 wires, hot 1, hot 2, ground and neutral. Hot 1 to neutral or hot 2 to neutral will give you 110V at 50A, hot 1 to 2 will give you 220V and hot 1 or 2 to ground will also give you 110V at 50A (but don't do this, there's a reason that ground and neutral aren't the same wire).



    No, it's 50A at 220V. That's not 100A service; they are very different. Don't believe me? Open up a power pole, look at the wire sizes. Almost all the time, you'll find 6 gauge wire in there, which is rated for ~50-60A. If it was 100A service, you'd need 2GA wire in there. But 2 poles of 50A aren't 100A, it doesn't work that way. The reason there's so much more power (watts) on a 50A plug compared to a 30 or 20A plug is because it's a 220 line, you have 2 poles in there, both at 50A. So where 30A is about 3500 watts, 50A is close to 12,000 watts.
    I believe you understand it, but your explanation is confusing. On an AC circuit Volts times Amps is Volt-Amps, though for mostly resistive loads Volt-Amps and Watts are very close. Using that assumption, 12,000W is 50A at 240V, but at 120V it is 100A. A 50A 120/240V circuit provides 100A total on the two 50A 120V circuits. The wires only have to carry 50A because that is the most any of them will ever carry.

    The neat trick about a 120/240V system is that the neutral doesn’t have to carry that 100A load because the two 120V Legs are 180 degrees out of phase. That means that when the load is the same on each leg, the average neutral current is 0A. Worst case, with one leg fully loaded and nothing on the other, the neutral current is 50A. 50A on L1 plus 50A on L2 gives you 100A for use in the RV.
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    Quote Originally Posted by jkwilson View Post
    I believe you understand it, but your explanation is confusing. On an AC circuit Volts times Amps is Volt-Amps, though for mostly resistive loads Volt-Amps and Watts are very close. Using that assumption, 12,000W is 50A at 240V, but at 120V it is 100A. A 50A 120/240V circuit provides 100A total on the two 50A 120V circuits. The wires only have to carry 50A because that is the most any of them will ever carry.

    The neat trick about a 120/240V system is that the neutral doesn’t have to carry that 100A load because the two 120V Legs are 180 degrees out of phase. That means that when the load is the same on each leg, the average neutral current is 0A. Worst case, with one leg fully loaded and nothing on the other, the neutral current is 50A. 50A on L1 plus 50A on L2 gives you 100A for use in the RV.
    Well, the reason I weighed in on this is because, if you ask an electrician to run you a 50A 120 or a 100A 120 or any of the other variations here, you're going to get the wrong thing. What you want for a 5er is a 50A NEMA 14-50R. Just hand that to an electrician and he'll wire it correctly. If you're wiring it yourself, you need 4 wires in the box, L1 and L2 coming off different phases of your breaker box, if you measure voltage from L1 to L2, you will get 220. You also need a neutral and a ground wire. IIRC, I ran 6 or 4 gauge for everything. And no, don't get 2 50A 110 breakers, you want a standard 220 50A breaker for your box.

    The reason I weigh in on this topic, I spent hours trying to figure out what was "special" about an RV outlet. Everyone kept saying "It's not a 220, if you hook it up to 220, you'll burn up your RV". It's a massive amount of misinformation out there. Here's a great example:

    https://www.rvtalk.net/how-to-wire-a-50-amp-rv-plug/
    Also, you should not hook a 50-amp plug into a 220-volt receptacle.
    Now this guide actually does correctly tell you how to wire it and then, later in the article says:

    After wiring the 50A service, you have to test it before plugging the RV for the first time. Use a voltmeter for this purpose. Attach its one probe to a hot receiver and another probe to the neutral receiver. The reading should be 110 volts. The reading will be 220 volts if you connect the probes to two hot receivers.
    So, don't hook up an RV to 220, but if you test the outlet you just installed, you'll get 220?!

    And you'll hear people talking about "burning up your RV" if you do it wrong. Yeah, if you run L1 to the neutral and L2 to L1, you'll burn up your RV, because you'll be sending 220 down a line designed for 110. But, if you know anything about electric, you know there's always 110 at a 220 outlet, just go from either blade to ground, you'll get 110. So article like this does nobody any favors.

    You will see 220V outlets in households for powering up dryers and cookers. Don’t confuse the 14-50R with them. The 220V outlets are ‘common’ type where two 110V sources work together to produce 220 volts for 240V appliances. On the other hand, a 14-50R is an ‘uncommon’ outlet that delivers electricity equal to two 110V sources.
    A 14-50R provides 220 just fine, I use them in my shop for things my table saw (which is a 220 device). A 14-50R is just a regular 220 outlet with a neutral and a ground. That's it, nothing magical. The only thing that's at all unique about them compared to other types of 220 is that they a neutral as well as a ground. But I'm not sure how you could hook an RV up to any 220 outlet that's wired correctly and "burn up your RV". I suppose if you built your own adapter and left the neutral floating? IDK, maybe there is some way to do it, but if you correctly wire a 220 plug, I'm pretty confident that the worst you'd get is "no power" because there's no return line on the circuit. To get 220, you need to have the return line (ground/neutral) bonded to a L1 or L2. If anyone is curious, take a volt meter to a RV outlet, stick one end in the ground and then touch all the blades. The most you'll get it 110V. The only way to get 220 is to cross the 2 phases.

    Let's say you take a standard 220 outlet, like a 6-50. That's a 50A, 220 ONLY plug. There''s no neutral in there, just 2 hots and a ground. Now, let's further say, you're bound and determined to make your 4 connector plug fit into the 3 connector outlet of a 6-50 and somehow make it work. So long as you run L1 to blade one and L2 to blade 2 on the 6-50, your either going to get 1 of two things happening. No power at all in the RV (because there's no neutral) or it's going to work fine in the RV, but not up to code (you'd be using the ground as your neutral).

    I guess maybe some people out there wired their RV plugs with L1 on blade 1 and L2 on the neutral line, that would "burn things up" because you'd be sending 220 in the rig on the wrong lines. But if you correctly wire a 14-50R, you will NOT burn up the RV. And when you go to Lowes, don't tell them you want a "110V 14-50R plug" because they do not exist, they are all 220V outlets that can safely provide both 110 and 220V because of the neutral line in them.

    Sorry, I spent so much time on this when I was wiring in the beginning, everyone kept saying "make sure you don't wire it up 220" and stuff like that and "you'll burn the RV down if you send it 220". Well, you ARE sending the RV 220 anytime you're on a 50A circuit and there's no way to wire a 14-50R that doesn't "wire it up for 220".


    TMI: (Incidentally,, while this is already WAY too much for most people, there actually IS a way to do it. You could send L1 and L2 from the same pole in the breaker box. This is what I thought they might be talking about when they said "don't send 220" and I looked, it's doable, but I couldn't find any way to meet code doing it because the breakers need to be bonded together).
    Last edited by Overtaxed; 08-01-2020 at 05:29 PM.

  9. #9
    Site Sponsor gbkims's Avatar
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    Quote Originally Posted by jkwilson View Post
    The neat trick about a 120/240V system is that the neutral doesn’t have to carry that 100A load because the two 120V Legs are 180 degrees out of phase.
    Since talking about 120/240V power & Onan generators, I was wondering if someone knows if the Onan 5500 generators produce split phase 120/240VAC with windings 180° out of phase.
    I thought I'd read the Onan's 120V outputs were in phase depending on how they're wired.

    I don't have an Onan, just wanted to understand 50A RV service along with EMS, ATS, Onboard Generator wiring.
    Attached Thumbnails Attached Thumbnails RV 50A 120-240V Wiring w Onan 5500.pdf  
    Last edited by gbkims; 08-03-2020 at 08:32 AM.
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    Quote Originally Posted by gbkims View Post
    Since talking about 120/240V power & Onan generators, I was wondering if someone knows if the Onan 5500 generators produce split phase 120/240VAC with windings 180° out of phase.
    I thought I'd read the Onan's 120V outputs were in phase.

    I don't have an Onan, just wanted to understand 50A RV service along with EMS, ATS, Onboard Generator wiring.
    If the 120 legs were in phase, you wouldn’t get 240. The two sides of the transformer are 180 degrees out of phase. You center tap to create the neutral, which is in the middle so is 120V from each leg.

    50A RV service is the same as household service.
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