Installing Onan in a class C

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shadetreewrench

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Feb 5, 2012
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Hello from a newbie, great forum! I have been here for references many time as a guest, maybe I can get some information.

I have recently purchased a 1989 Mallard 26 foot class C on a Ford E350, as a project for my Father, I currently own a 2007 Rockwood tow behind for myself. Yesterday I found a good used Onan 4.0BGEF genset that is also from a 1989 unit that has been scrapped. The unit runs good and makes power, now I need to install it.

I am in uncharted territory here. None of the units I have ever owned have had one as an installed unit. I am an experienced mechanic and know electrical well, I am absoluety confident I can do the installation, with the proper specifications.

So, here are my questions:
The unit is pre-wired for a generator, has the compartment, (solid box, no vents)  and the circuit box mounted and wired to the converter. I know that a rectangular hole needs to be cut in the floor for the cooling/exhaust vent, where does the intake vent need to be cut in?

There is no under bracing under the box mounted to the chassis. Do i need to fabricate one? Or is the box heavy enough to support the weight.

I want to wire the chassis battery to crank the genset, what gauge wire is used, I would assume 6 ga would be heavy enough.

Of all the people I know, no one has a unit with a similar setup that i can look at, is anyone out there that has this kind of setup ?

Thanks
 
You probably don't have an automatic transfer switch and you will need one, or else you will have to plug in the generator each time you wish to use it. (PIA)  Then it can be wired into the AC side of the electrical system.  You can also dedicate a small battery to the gen. and save some wiring work.  Many generators use a "split head" for 50 amps,, 30 amps on one leg and 20 on another, if you have two roof airs and a 30 amp system in the coach, you can dedicate the 20 amp side to the rear air conditioner and use the 30 amp side to run all else.  .>>>Dan
 
It will need fuel from the gas tank so is there a line there already? If not you will have to tap into the tank. The vent should be in the door and you will need a lot bracing to support it.

I had an Onan 4000BFA in my 1985 RV and it never ran right. I paid to have it fixed about 6 times and fixed it myself a few times. I finally paid to have another one, used, installed for $650. After two months it is now surging and I can't get that solved. I have just bought another RV and one of the things I looked for was that it did not have an Onan. I am probably the only one who feels this way but I won't own an Onan again.
 
utahclaimjumper said:
You probably don't have an automatic transfer switch and you will need one, or else you will have to plug in the generator each time you wish to use it. (PIA)  Then it can be wired into the AC side of the electrical system.  You can also dedicate a small battery to the gen. and save some wiring work.  Many generators use a "split head" for 50 amps,, 30 amps on one leg and 20 on another, if you have two roof airs and a 30 amp system in the coach, you can dedicate the 20 amp side to the rear air conditioner and use the 30 amp side to run all else.  .>>>Dan
Click to expand...

The 4.0KW ONAN will NOT have two outputs of 30/20 amps.  It will have a single 30amp output.  Simply install a 30amp receptacle near your stored power cord (one may be there already) and you won't need a transfer switch, unless it's too difficult to remember to plug the power cord into the outlet when unplugging from shore power.

You will need larger than 6awg wire for the cranking battery lead.  Regular 1/0 or 2/0 battery cable is required.

You will need more than your suggested "rectangular hole" cut in the bottom of the compartment.  The removal of the entire floor (to facilitate the added framing and bracing for the generator) will be required, and will provide all the air flow required by the  generator.  It's too bad the mounting pan and hardware was not salvaged along with the generator.
 
The unit still has the mount pan. It has a ground strap going to the unit and has rubber mounts to the actual generator. So I am gathering I have to cut the entire floor out of the compartment and fabricate a cradle to attach it to chassis, correct? (not two straps bolted to the box) I didnt think they would build the generator compartment 5 sided just to cut the floor out if the generator option was chosen. The coach has an outlet wired into the cord storage compartment wired to the box/breaker at the generator compartment. I have already installed the fuel line to the tank, Ford has a tap already in the pickup assembly just for it.

I guess cutting the floor out makes sense as far as the venting goes, just trying see the way the manufacturer would have made the mount and where it is mounted.

Anybody have any pictures?

Thanks for all your help.
 
Is this a propane genset? That would make the fuel side of the installation easier, I think.

Does the pre-wire include a receptacle for the RV's 30A shore plug? If so, that eliminates the need for a transfer switch - just wire the genset output to the receptacle and plug in when needed.

What is it that is wired to the converter?  I can't think of anything that would require that.

I don't know if 6 ga is enough, but the cranking motor is probably small and the max amp load might be low enough for #6 if the run is short enough, say 12-14 feet total (sum of positive and negative). I'd be more comfortable with 4 ga, though, and 1/0 if the run is all the way from the front to the back.

I agree with Lou on the floor bracing & opening. You may not have to remove all the floor, but the opening is typically large enough for air to circulate up and around the genset and provide both cooling and  combustion air. The two gas chassis coaches we owned were both made that way.
 
I'll bet the RV maker put a solid floor in that ompartment so it could be used for storage if you didn't install a generator.

Usually a generator compartment will have an air intake grille in the compartment door, but I have seen some with a solid door and an air gap between the botton of the door and the generator mounting plate.  Mine is like that, and the heated air is also exhausted underneath the RV, but at the the rear of the compartment, so there is some separation between the two.
 
Lou Schneider said:
I'll bet the RV maker put a solid floor in that ompartment so it could be used for storage if you didn't install a generator.

Usually a generator compartment will have an air intake grille in the compartment door, but I have seen some with a solid door and an air gap between the botton of the door and the generator mounting plate.  Mine is like that, and the heated air is also exhausted underneath the RV, but at the the rear of the compartment, so there is some separation between the two.
Click to expand...

My Bounder does not have a vent in the door.  It does have the entire floor of the compartment removed.  It also has the exhaust exiting at the front of the compartment.

FWIW - It depends on which side of the RV the generator is installed on whether the exhaust can be discharged to the rear of the compartment or not.  All the ONAN generators that I've ever seen have the generator on the right hand end, and the engine exhaust on the left end as you face the control panel.  They may have made some mirror image units, but I've never seen one.
 
None of the three coaches we owned had vented doors - all had the bottom of the compartment open as Just Lou described. But none of the were Class C's either. We did, however, have a trailer that was "generator ready" and it had a louvered door on the compartment and a solid floor.
 
My 1976 Class C was set up for a generator. It had wiring to it from a remote start switch on the dash, battery cable and fuel line. It also had an electrical box in the gen compartment to wire the 120v out from the gen. Inside the coach there were 2 electrical main circuit breakers with a rocker lever on top. As you turned 1 on for shore power the gen 1 was switched off. Switch gen 1 and shore breaker went off. This was from the factory, no need for a transfer switch.
 
As others have suggested, you would definitely want to remove the floor for combustion and cooling air. Our previous coach had an Onan BGE 4kw genset and did have a louvered door as well. You should see a plug in port below the circuit breaker on the right side of the control box on that model. That is where the remote start/hour meter wiring harness plugs in. If you didn't get it with the generator purchase, you could probably shop around for a used one at an rv salvage yard and you would be able to start and stop the genset from inside.
 
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