Troubleshooting a split phase 120/240 inverter

[Livin4us]

Hi again,

Inverter works great on shore power, but we are getting no AC output from the transfer switch to the inverter when we switch to our Onan 5500 generator. We have checked all of our fuses and breakers and everything is in order. So, we are stuck again. We did notice the wiring does not require the input neutral to be connected. Like I said, with shore power it works fine, but we are wondering if the generator needs that neutral. We had a single phase inverter hooked up prior to this and did not have this problem…so any help would be appreciated. I am attaching a diagram of the wiring into the inverter, as well as the wiring of the transfer switch. If we do need that neutral, what would we need to hook it up to? Thank you all again for your help.

 

[Lou Schneider]

Your generator is single phase, 120 volts only. You need to connect the neutral coming from the generator to the neutral input as shown on the terminal strip label. The single hot leg from the generator will go to either L1 or L2 depending on what you want to power in the rig. If you want to power everything from the generator you can jumper L1 to L2 at the generator input.

This will put 120 volts on all 120 volt circuits but be aware you will not see voltage across any 240 volt outlets or appliances when on the generator because L1 and L2 are in phase with each other. You will just have 120 volts from each leg to ground.

 

[Heli_av8tor]

Lou, Isn't it possible to rewire the Onan 5500 internally to provide split phase? Seems I remember that you have done this. I don't know the implications of unbalanced loads if this is done.

 

[Lou Schneider]

Lou, Isn't it possible to rewire the Onan 5500 internally to provide split phase? Seems I remember that you have done this. I don't know the implications of unbalanced loads if this is done.

No, you could do this with the Generac generators that had two windings (20 amp and 30 amp) and two breakers on the output. Swap the polarity of one winding and and you have a 120/240 volt generator. Onan only has a single winding and a single breaker.

 

[NY_Dutch]

Lou, Isn't it possible to rewire the Onan 5500 internally to provide split phase? Seems I remember that you have done this. I don't know the implications of unbalanced loads if this is done.

We don't know which model/rev 5500 the OP has, but my 5500 BGE has two separate windings, each supplying its own 30 amp breaker. Some rev levels bring both legs of both windings out to the controller, and can be rewired for split phase 120/240 by reversing one pair of wires. Other revs have the neutral legs internally tied, with only a single neutral leg brought out. Conversion for those would require major surgery. I've been meaning to see which I have and whether I can make the switch or not. The 4000 BGE on the other hand, has only one 30 amp breaker fed by a single winding.

 

[Livin4us]

Okay…so we have 2 30amp breakers in our Onan. There are 2 hot and 2 neutrals heading into the transfer switch…exact same set up as the shore power. There is 120v per leg (2) on the input side for each (shorepower x2 and generator x2). When we are connected to shorepower we have 2 legs of 120v coming out of our transfer switch into the inverter, but when we disconnect shorepower and run the generator, we have no voltage coming out heading into the inverter.

 

[Lou Schneider]

Do you have 240 volts or 0 volts if you measure from one of the generator hot legs to the other?

 

[8Muddypaws]

Seems logical that the transfer switch might be bad.

 

[Gary RV_Wizard]

Okay…so we have 2 30amp breakers in our Onan. There are 2 hot and 2 neutrals heading into the transfer switch…exact same set up as the shore power. There is 120v per leg (2) on the input side for each (shorepower x2 and generator x2). When we are connected to shorepower we have 2 legs of 120v coming out of our transfer switch into the inverter, but when we disconnect shorepower and run the generator, we have no voltage coming out heading into the inverter.

My guess is that the shore power hot legs are split phase, with the two hots 180 degrees out of phase and thus producing 240v between them. The generator is probably single phase and both hots are the same phase, meaning zero volts between the two of them. Thus Lou's question, and a voltage measurement for each source will determine if is the case.

 

[Livin4us]

Do you have 240 volts or 0 volts if you measure from one of the generator hot legs to the other?

Ok, so we now have 240 output going into the inverter, but no input volts showing on the inverter itself.

When we are connected to shore power, there are 240v showing as A/c input.

 

[Livin4us]

We have 0 volts when touching both, so I now understand. We have to have 240 going into the inverter and the generator only produces 2 single legs, hence single phase. I’m sorry, I am not so good with electrical.

So, can you please explain again how we combine those legs to make it 240v? You said something about a jumper?

 

[Livin4us]

Ok…last question, I understand that we cannot combine the two separate phases to make 240v. So, if we go back to our single phase inverter, can we then jumper the lines so we can utilize both sides of the panel?

 

[Gary RV_Wizard]

We have 0 volts when touching both, so I now understand. We have to have 240 going into the inverter and the generator only produces 2 single legs, hence single phase. I’m sorry, I am not so good with electrical.

So, can you please explain again how we combine those legs to make it 240v? You said something about a jumper?

I don't think you can, but Lou is more knowledgeable on this than I. At best it would involve an internal modification to the generator, not a simple jumper wire somewhere.

 

[Gary RV_Wizard]

Ok…last question, I understand that we cannot combine the two separate phases to make 240v. So, if we go back to our single phase inverter, can we then jumper the lines so we can utilize both sides of the panel?

With a different inverter, i.e. a 120v only model, that should not be a problem.

 

[Livin4us]

Perfect…that is what we are going to do then! Again, thank you all so much for your help! You are a blessing!