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JPaTV · 06-04-2018, 09:14 PM

Good evening!

I have a Onan 7500 with 2 Dometic roof ACs. Both ACs work perfectly when plugged to shore power. However, when I start the generator to run the ACs, the breaker on the generator trips. The generator will still keep running, it just wont supply power anymore.

I can use one AC at a time without issue on the generator, but it wont run both of them, and it should - because its plenty of power.

I am going to swap out the old breaker on the generator for a new one to see if that helps, and also I am going to manually stagger the power-up for them to see if I can manage the surge amps from the compressors turning on.

Any thoughts would be awesome. Thanks!

twinboat · 06-05-2018, 04:46 AM

You have 60 amps to play with on that generator. You probably have a 30 amp double breaker.

On shore power you have 50 amps per leg. Not a problem for 2 ACs.

Has anyone re-configured any of the breakers in the main panel ?

If both ACs are on the same leg, they can overload one side of the double breaker, tripping both. Unless you ha e 3 ACs, one should be on each side.

With all power off, including the inverter, you could remove the main breaker box cover and see if you can figure out if the AC breakers are split up..

Hit_the_Rhod · 06-05-2018, 05:18 AM

You might also want to check all of your connections, especially the grounds. Look for loose connections, and/or discolored or corroded wiring. It's possible you might have a bad connection, leading to more resistance, and therefore more load on the breaker.

I also second checking to see if your coach is wired with both AC units on the same outlet leg of the generator

. Dumb to do it that way, but I've seen it and stranger stuff as well on RV's and boats . . .

twinboat · 06-05-2018, 05:53 AM

Quote:

Originally Posted by Hit_the_Rhod

You might also want to check all of your connections, especially the grounds. Look for loose connections, and/or discolored or corroded wiring. It's possible you might have a bad connection, leading to more resistance, and therefore more load on the breaker.

I also second checking to see if your coach is wired with both AC units on the same outlet leg of the generator

. Dumb to do it that way, but I've seen it and stranger stuff as well on RV's and boats . . .

You need to research your theory a bit.

A bad, arching or heating, connection does not lead to more amp draw.

The bad connection is like adding a resistor in series with what your powering. The voltage and amperage will be split between the two.

If you ever electric welded, you would see that the amps are highest when the rod is in full contact with the metal. Once the arc is created, the amps drop off.

Of course, an electric motor that is overworking, will cause a rise in amp draw and that cause heating in the connections, but then the amperage is being disapated as heat.

JPaTV · 06-05-2018, 08:22 AM

Quote:

Originally Posted by twinboat

You have 60 amps to play with on that generator. You probably have a 30 amp double breaker.

On shore power you have 50 amps per leg. Not a problem for 2 ACs.

Has anyone re-configured any of the breakers in the main panel ?

If both ACs are on the same leg, they can overload one side of the double breaker, tripping both. Unless you ha e 3 ACs, one should be on each side.

With all power off, including the inverter, you could remove the main breaker box cover and see if you can figure out if the AC breakers are split up..

Hi Twinboat, thanks for your insight!

In the main panel, there are independent breakers for the ACs - so each one has its own on the main breaker. I'm pretty sure its a standard wiring scheme-- the generator goes to the auto-transfer switch and into the main breaker where it splits off to the ACs and other amenities. I can confirm that in the main breaker, the ACs have their own breakers.

So, the physical breaker on the generator itself is the one that is tripping. I'm wondering if the breaker is old and maybe is tripping on a lesser load. Note: the ACs are trying to fire up at the same time on the generator.

I'm not tripping anything at the main panel, and when I'm plugged into shore, the ACs can come on without issue. So it leads me to believe that maybe the breaker on the generator maybe bad.

I can run either of the ACs on the generator, not both, at the moment. So I'm thinking that if it was a ground issue on either of the ACs, that they would trip the shore power breaker, too.

I keep thinking of the options and keep circling back to it maybe being a worn out breaker on the generator.

If I can run each generator on their 30A breakers without tripping - that would mean that they are running under 24A, given the 80% tripping threshold. Multiply two ACs running at a max of 24A (in order to not trip their respective breakers) - that's a 48A load on the generator. If I have a 60A breaker (I have to see if its a 50 or 60) - 80% of the 60 just barely gives me room for the full load of 48A. So, my theory is, if the breaker is weak and it is tripping before 80% load, this might be my problem.-- I hope it is anyway... it seems like the most straightforward repair!

JPaTV · 06-05-2018, 08:31 AM

Quote:

Originally Posted by Hit_the_Rhod

You might also want to check all of your connections, especially the grounds. Look for loose connections, and/or discolored or corroded wiring. It's possible you might have a bad connection, leading to more resistance, and therefore more load on the breaker.

I also second checking to see if your coach is wired with both AC units on the same outlet leg of the generator

. Dumb to do it that way, but I've seen it and stranger stuff as well on RV's and boats . . .

Hey HTR!
I'm sitting here thinking -- I'm thinking the generator puts out a single leg-- but its a 220V. So, the ACs could very easily be put on the same leg either by accident, or for some other reason. So if its on a common leg, it could very well be the issue-- Im gonna look into that, most definitely. Thank you for the brain-jog!

JPaTV · 06-05-2018, 12:48 PM

Have a look at the diagrams I put together. I'm thinking based on whats been said that possibly the two AC units are on the same leg, and that would be cause for tripping the main Geni breaker. This of course, would require 50A main breakers on the circuit panel. If they are 30A main breakers, they should trip well before the geni breaker needs to.

THoughts?

twinboat · 06-05-2018, 01:13 PM

Quote:

Originally Posted by JPaTV

Have a look at the diagrams I put together. I'm thinking based on whats been said that possibly the two AC units are on the same leg, and that would be cause for tripping the main Geni breaker. This of course, would require 50A main breakers on the circuit panel. If they are 30A main breakers, they should trip well before the geni breaker needs to.

THoughts?

It should be wired as in picture #1.

JPaTV · 06-05-2018, 01:28 PM

Quote:

Originally Posted by twinboat

It should be wired as in picture #1.

I'm going to check later today - the more I think this out, the more it seems that two ACs could be wired onto one leg. I should have 2 50A main breakers in my main box, right? My rig is serviced from 50A shore power, so it would seem 50A would be appropriate. I'll have to check later. I hope its simple. It would be nice to have them both working during boondocking.

Thanks!

twinboat · 06-05-2018, 01:28 PM

It could be a failing generator breaker but I would think that if failing, it would trip due to heating after a few minutes of carrying the load. If it trips quickly, I'd think it is sensing an overload.

Checking the AC breaker placement is free, changing the breaker isn't. Its worth a look.

JPaTV · 06-05-2018, 02:04 PM

Quote:

Originally Posted by twinboat

It could be a failing generator breaker but I would think that if failing, it would trip due to heating after a few minutes of carrying the load. If it trips quickly, I'd think it is sensing an overload.

Checking the AC breaker placement is free, changing the breaker isn't. Its worth a look.

Yes, most definitely- I'm going to check that out today. I really appreciate your help!

Old Scout · 06-05-2018, 02:18 PM

.....suspect you will find the AC's are on separate legs....What I would do is check to see what other 120v appliances are on while trying to run the two AC's. Remember you only have 30-35 amps on each leg of the genset vs 50 amps per leg on shore power; so one AC and maybe a water heater, or the battery charger and one or two other draws could push you over the limit for a single leg on the genset. The breaker on the genset is a single throw, double pole, so its hard to tell which leg is tripping the breaker....

JPaTV · 06-05-2018, 03:14 PM

Quote:

Originally Posted by Old Scout

.....suspect you will find the AC's are on separate legs....What I would do is check to see what other 120v appliances are on while trying to run the two AC's. Remember you only have 30-35 amps on each leg of the genset vs 50 amps per leg on shore power; so one AC and maybe a water heater, or the battery charger and one or two other draws could push you over the limit for a single leg on the genset. The breaker on the genset is a single throw, double pole, so its hard to tell which leg is tripping the breaker....

Thanks for the insight Scout! I'll try shutting off as much as I can to see if I can manually lessen the load. Theoretically I should be able to run both ACs if I manage the power consumption effectively, though.

Thanks again!

Davidrvr · 06-05-2018, 04:39 PM

Is this something that is a new problem or you just bought the coach? Maybe the draw is too much for the breakers as they are old ? Maybe the capacitor on the ac needs changed. It might be straining to start .. maybe the compressors are working to hard and pop the breakers? Try watching the loads with each ac and then again with both ac