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Onan generator 240/120 rewire?


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Old 03-20-2008, 11:14 AM
randymark randymark is offline
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Default Onan generator 240/120 rewire?

Hi, i am new to this site and whole internet thing, But find it very usefull. I am removing 4.0 kw 120 v kohler genset from my motorhome and am installing onan commercial 6.5 kw 240/120v. generator, model#6.5nhdfbil. should i only use one leg of output? will i only get 1/2 of rated amps?will it damage generator? main question, can i rewire generator to produce only 120v? or should i use 240 to 120 transformer? how big? where to find one cheap? m/home has 1 standard size roof air.Thanks for any help you can provide.
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Old 03-20-2008, 01:29 PM
David W. David W. is offline
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Default Re: Onan generator 240/120 rewire?

Randymark,
I just happened to check in before anyone else, and can answer part of your question. Somebody smarter than me will be by shortly to finish the job.

For now, you should certainly be able to re-wire your ONAN output to one circuit of 120V only and get the benefit of your Genset's full output, versus using two circuits and only having half the output on either circuit. That assumes you don't need to power any 240 Volt devices in the motorhome.

You may be able to find a wiring schematic beneath a removable panel somewhere, but essentially, you should have four leads (M1, M2, M3, M4) and your method of connecting them will determine the output voltage and amperage of the output.

My shortcoming is that I can't tell you exactly how they should be connected, but somebody will be here soon.

David W.
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Old 03-20-2008, 01:29 PM
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Talking Re: Onan generator 240/120 rewire?

What is the COMPLETE Model & Serial Number of your Onan ? It makes a difference.
I suspect that your Genend can be rewired for 120 Vac from 120/240 Vac. You should
look on the Inside of the Connection Box Cover , for the Wiring Diagram for the Output
Connections. This will give you the exact connection scheme for your Genset. YES,
if you only use ONE Leg of your 120/240 Vac Output, you can only draw 1/2 the rated
Kw from the Genset. A transformer could be used to balance all your 120 Vac loads
across both legs of your 120/240 Vac wired Genset. If you go that way, it should be
rated for the Maximum Load, you can apply from your Motorhome. I generate all my
own Power, and I have both 120 Vac, and 240 Vac Loads. I choose to generate my
power at 240 Vac, and then Transform that power for my 120 Vac loads, in order to
not have to worry about Balancing the 120 Vac Loads between the 2 Legs of 120 Vac,
in a 120/240 Vac System. Makes for much better Generation Efficiency.
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Last edited by BTPost; 03-20-2008 at 01:50 PM.
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Old 03-20-2008, 05:24 PM
randymark randymark is offline
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Default Re: Onan generator 240/120 rewire?

its a model#6.5ndfbil ser#G973704328 commercial 6500w. there is no schematic on inside of control panel
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Old 03-20-2008, 05:27 PM
Fatboy Fatboy is offline
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Default Re: Onan generator 240/120 rewire?

I have to assume that your RV is wired for 30a power. If it is a 50a system then it would be a no-brainer. All RV's operate on 110 volts whether they are plugged into a 30 or 50 amp receptacle.

The 50a RV circuit follows the two line/neutral/ground system as residential housing and therefore is a 220 volt system. A
30a RV system uses a line/neutral/ground connection and does indeed supply only 110 volts.

Depending on the location of the circuit breaker panel in the motorhome it may be easy enough to upgrade the panel to a 50a system feed it with 240 volt from the generator (or shore power) and balance the load at the panel.

This is usually done when someone wants a second airconditioner installed which requires a 50a system for simultaneous use.

The 4,000w generator is the correct size for a 30a RV system and upgrading to a 6,500w is a little overkill and probably a waste of fuel plus extra weight.
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Old 03-21-2008, 08:57 AM
randymark randymark is offline
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Default Re: Onan generator 240/120 rewire?

the kohler 4.0kw was done and i got the onan for free, with 340 hours on it. the problem with changing the panel in m/home to 50 amps two leg is what to do with it when plugged into 120v? I am hoping to just rewire generater.
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Old 03-22-2008, 10:11 PM
Fatboy Fatboy is offline
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Default Re: Onan generator 240/120 rewire?

They make a 30 to 50 amp adapter (dogbone), I have to use one on my 50 amp 5th wheel for plugging into a 30 amp box.
Like most RVers I know, I also have a number of different adapters for all occasions. The 50 amp upgrade would only involve a breaker box, a 50a main breaker, and a 50a shore power cable and plug.

To connect the generator into the system, terminate the output with a 50a receptacle mounted in the generator compartment.

That way you can plug the shore power plug into a receptacle on a power pole or into the receptacle fed by the generator.

Some RV manufacturers call this "Generator Ready", "Gen Prep Package", or "Wired for Generator". It's a cheap way of doing things and other than a few vents and an enclosed box, that's about it.
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Old 03-23-2008, 08:58 AM
Mikisan Mikisan is offline
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Default Re: Onan generator 240/120 rewire?

Hi everyone I'm new to this site and I think it's great. Now about the question at hand. I have a 50A fifth wheel and I have allways used a portable Genset for power when dry docking. My home made gen cord just jumpers the 110v output of the Gen to both "legs" of the 220v cord so I can get the full rated output of the Generator. My fiver also came "Gen Ready", There's a two leg, push button breaker box in the Gen compartment. I'll hook both of these to the 110v output of my Gen. as there are no 220v loads in the Trailer. There's an automatic transfer switch in the trailer allready so I don't have to worry about a direct220v short when connected to a 220v shore receptacle. I the afore mentioned 6.5K comm. Genny isn't a portable, as that is very dangerous to try to use in a compartment,, Heat, fumes, fire, etc. I hope some of this is helpfull. Happy Easter to all.
Mike
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Old 03-23-2008, 01:18 PM
randymark randymark is offline
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Default Re: Onan generator 240/120 rewire?

Thanks for your input, this onan is designed to go into a compartment, i have already installed it and is a very clean installation.I wired in a 240 outlet and ran one leg from there to existing panel, I think will put in 50 amp panel and use one leg for roof a/c only with maybe a exterior outlet and replace shore power cord with 240 type and use adapters as suggested, sounds expensive,still,would rather just rewire the generator if possible.anyone know how?
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