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Old 01-26-2022, 05:34 PM   #1
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Onan 5500: Replacing 20A and 30A breaker with single 50A?

I apologize if this has been asked before, but I've searched and come up with nothing.

I have an RV with standard 50A service, no 240v appliances inside. I boondock a lot, and have an Onan 5500 generator with both a 20A and 30A circuit.

The wiring for the generator is both confusing, and annoying. My Ninja Foodi is a high power electrical appliance; it's on the 20A circuit. My power converter and Foodi together will trip the 20A breaker. I swap the outlet/circuit that my power converter is on if I am going to use the microwave or the Foodi.

From what I have read, the generator is capable of ~45A, and it's internally split into two circuits. Why? Why not have a single 40/50A breaker, wired up similarly to a 30A to 50A dogbone?

Can I replace the pair of circuit breakers inside my generator with a single 50A one, with the appropriate gauge cable to my breaker panel?

I've attached to diagrams, one for the current setup and one for my desired setup.

(Another reason I want to do this is for future power system upgrades - I have 2.4kWh of LiFePO4 now, and a small inverter that powers my residential fridge. I'm planning to upgrade to a Victron MultiPlus, with everything going through that. Life would be easier if the generator was on a single 110v circuit...)
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Old 01-26-2022, 05:58 PM   #2
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Your generator is capable of 45 amp output@120 volts.

You can use 2, 25 amp breakers in place of the 20 and 30, but you loose 5 amps on one leg.


Don't confuse 120/240, 50 amp service . It can supply over 3 times the energy ( 100 amps ) of your 5500 generator.
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Old 01-26-2022, 06:24 PM   #3
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I believe your 5500 watt generator has 2 separate windings of 120v each.

each winding has its own neutral and one winding maybe smaller than the other thus the two different size breakers designed to protect the windings of the generator from overloads.

Do not believe these 2 separate windings can be connected together and protected by a single 50A CB'

Check with Onan before you do anything
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Old 01-26-2022, 07:07 PM   #4
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There are few different sub models of the 5500. They have the same specs but are configured with different circuit breakers. Some are configured with 1 30 and 1 20 amp, others are configured with 2 30 amp. With what you are looking for I would simply swap out the 20 amp for a 30 amp breaker. You will still have a max of 45.8 amp available shared between the two legs.

Here is the Onan spec sheet.

Edit to add.
Swapping the 20 for 30 amp breaker will not require any wiring changes to the transfer switch. Using a single 50 amp breaker will require upgrading the wiring. Doing so will not cause any issues with the genny as both breakers are paralleled on the genny side.

Attaced is the genny output wiring diagram from the Onan service manual and also the parts list for the breakers.
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Old 01-26-2022, 11:48 PM   #5
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Originally Posted by Steve-W View Post
Swapping the 20 for 30 amp breaker will not require any wiring changes to the transfer switch. Using a single 50 amp breaker will require upgrading the wiring. Doing so will not cause any issues with the genny as both breakers are paralleled on the genny side.

Attaced is the genny output wiring diagram from the Onan service manual and also the parts list for the breakers.
Thanks for the diagram - that's what I suspected but I couldn't find anything for sure. I know I can examine the generator itself, but I don't want to start taking panels apart if there are other reasons I can't do what I want.

Actually - couldn't I just use the two existing wires from the generator to the automatic transfer switch in parallel? Replace the 20A and 30A with one 50A, bond them there, and bond them at the transfer switch side?

I will most likely do what you suggested initially, and just replace the 20A with a 30A since that's easier for now. I'll do more comprehensive rewiring later.

I'm still wondering *why* they do it like this, it seems very odd to me. I just want to make sure there's no benefit to the current setup that I'm missing.

I've thought a bit more about my next upgrade for spring time. I've attached a diagram of what I'm thinking about doing. The Victron MultiPlus can be told how much electrical power is available, so if I was on the generator it would know to lower its charging power if the power draw of the RV was getting too high, and it can even boost the power if needed.

The AIMS power converter has a mechanical control for adjusting charging current - so I would just leave it set for max. If I was on a particularly low power hookup like a single 15A, then I would probably sometimes get into a position where the AIMS was providing power to the Victron for the Victron to invert to power the AC appliances. Not the most efficient configuration but not a frequent one.

I know that this design wouldn't give me as much power capability as I'd get if I had full 240v/50A wired into my breaker panel like I do now. But, the only time I see myself needed that much power is if I am on a 50A hookup and need to run more than three space heaters. I don't think that's going to be a common setup, but I can unplug the AIMS and replace it with a space heater to get four, which is probably enough.
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Old 01-27-2022, 12:11 AM   #6
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On the original posting 'Bhima' asked a question:
> From what I have read, the generator is capable of ~45A,
> and it's internally split into two circuits. Why? Why not
> have a single 40/50A breaker, wired up similarly to a
> 30A to 50A dogbone?

Because that's what the RV builder ordered.

I have the same arrangement on an Onan 6.5kw unit. My RV has a 30 amp wiring configuration off the larger winding. The smaller winding was originally wired to the second air conditioner. I rewired the air conditioner and added a 20 amp plug to it, and a matching 20 amp outlet to the generator winding. When I park I can plug the 30 amp cord into the pedestal just like everyone else, AND I can plug a 20 amp extension cord into the duplex outlet on the pedestal and plug the second air conditioner into that cord.

Not that the above will help you in your situation, but the background info may help you and others as to the WHY.

I still have plans on doing a partial rewire to my RV, and end up with a 50 amp shore power cord and a larger breaker panel... and one side of the RV on one hot circuit of the 50A and the other side of the RV on the other hot
circuit.

Mike
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Old 01-27-2022, 05:39 AM   #7
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Quote:
Originally Posted by Bhima View Post
Thanks for the diagram - that's what I suspected but I couldn't find anything for sure. I know I can examine the generator itself, but I don't want to start taking panels apart if there are other reasons I can't do what I want.

Actually - couldn't I just use the two existing wires from the generator to the automatic transfer switch in parallel? Replace the 20A and 30A with one 50A, bond them there, and bond them at the transfer switch side?

I will most likely do what you suggested initially, and just replace the 20A with a 30A since that's easier for now. I'll do more comprehensive rewiring later.

I'm still wondering *why* they do it like this, it seems very odd to me. I just want to make sure there's no benefit to the current setup that I'm missing.

I've thought a bit more about my next upgrade for spring time. I've attached a diagram of what I'm thinking about doing. The Victron MultiPlus can be told how much electrical power is available, so if I was on the generator it would know to lower its charging power if the power draw of the RV was getting too high, and it can even boost the power if needed.

The AIMS power converter has a mechanical control for adjusting charging current - so I would just leave it set for max. If I was on a particularly low power hookup like a single 15A, then I would probably sometimes get into a position where the AIMS was providing power to the Victron for the Victron to invert to power the AC appliances. Not the most efficient configuration but not a frequent one.

I know that this design wouldn't give me as much power capability as I'd get if I had full 240v/50A wired into my breaker panel like I do now. But, the only time I see myself needed that much power is if I am on a 50A hookup and need to run more than three space heaters. I don't think that's going to be a common setup, but I can unplug the AIMS and replace it with a space heater to get four, which is probably enough.
Going to a single 50 amp breaker and connecting the two hot lines will work., you will need to also jump the two connection points in the transfer switch as well. Swapping the 20 amp breaker will be a simpler mod and accomplish the same thing. My coach geny has 2 30 amp breakers. It is also wired with a genny sub panel which feeds everything but A/C's & water heater. I also have a power management system which when on genny will shed various loads to keep current draw to 45 amps max. it does the same at 30 amps when on 30 amp service.
The Victron Multiplus has a version (Victron Energy Multi Plus 12/3000/120-50 120V) that is set up with 2 120v 50 amp passthrough lines as well. You could wire that in between the shore cord and transfer switch.
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Old 01-27-2022, 10:47 AM   #8
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Safety First

I recommend you do not install a 50 amp breaker unless you understand how all these systems work together.

There is a generator, a transfer switch, and two leg house wiring. Best advice in almost all cases is to not increase breaker size. Everything needs to be reconsidered in order to raise the breaker size.

50 amp circuits require 8 or 6 gauge wire. Transfer switches also have limits. Down stream breaker boxes need reconsidering.

Even raising the 20 amp breaker to 25 amps means all downstream devices need to be re-evaluated. Increasing 5 amps is not much and you may or may not get away with it. Increasing by 30 amps is a serious situation.

Wiring codes were primarily developed because people were injured or killed. Do you feel lucky?
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Old 01-30-2022, 08:27 AM   #9
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One thing you could do is wire the 2 generator outputs together at the transfer switch and have them both feed both legs.

This is the way I have my QQ7000 wired. I did this because all my power goes through my Victron MultiplusII and it only uses the L1 leg for single phase sources, so my reasons were different, but the solution is the same. If you do this there is no need to change any breakers. For my 7kw generator this limits my output to 6kw(50 amps) but for a 5500 with 45 amps output there are no disadvantages that I know of.

Before rewiring I called Onan technical support to verify this was kosher with my generator. That plus reports from others in a Victron group made me comfortable with this solution. I'm not sure why the RV manufacturers don't wire the QG 5500s like this from the factory.
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Old 01-30-2022, 12:30 PM   #10
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IMO, I don't think that replacing a 20 amp breaker with a 25 amp is a wise idea. If the 20 amp winding fails due to over current load, what would that cost? Probably a serious amount.
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Old 01-30-2022, 12:46 PM   #11
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IMO, I don't think that replacing a 20 amp breaker with a 25 amp is a wise idea. If the 20 amp winding fails due to over current load, what would that cost? Probably a serious amount.
Which is one of the reasons it is better to connect the two legs together at the transfer switch after the generator circuit breakers

I believe some qg5500 have two 25 amp breakers so the OPS generator windings may not be semetric, but by keeping same circuit breakers in place both sets of windings will be properly protected.
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Old 01-30-2022, 01:23 PM   #12
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You don't want a breaker rated more then the generator output potential.

If it's built to output 45 amps and you set in a 50 amp breaker, it will overheat the windings before the breaker will trip.

So now you need 2 23 amp breakers.

Leave the Gen breakers as is and tie the outputs of them together.
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