Generator mounting question

[Kirwin]

I am researching semi-permanently mounting an Onan 12. 5 KW Quiet Diesel in the bed of my pickup. From the Onan web site, the cooling air is discharged straight down. I don't want to cut a hole in the bed of the truck, so does anyone have any ideas on how I could accomplish this? Has anyone done it? Can I some how redirect the hot cooling air straight up? I know that an engine this size can put out a lot of heat so I need to be careful as you wouldn't want to direct the air such that it would be recycled back through the generator or pulled back into the radiator supply air. I haven't actually seen one of these generators running so I don't know how the air flow is directed. Any thoughts? Thanks Ken Irwin

 

[Kirwin]

Certainly I'm not the first one to do this.

Some one must have mounted a generator in the bed of their truck before.

 

[muddyduck]

kirwin, i would post it over on irv2.com or rv.net, both rv forums that you have to register for and i bet you would get some answers on your question. I have been thinking about doing the same thing sometime in the near future, but for now thinking only. I have not even picked out the generator to use, the only thing i know for sure is it will be diesel. Hope this gives you another idea. . gp

 

[B.G. Smith]

I have a 4kw and a 5kw Onan, the fan volute on both are bolted on and can be rotated to discharge down, up or to either side. bg

 

[Kirwin]

Irv2

I did post over there it the boon docking forum. So far not much response. I will try to see if the fan discharge is redirectable on the Onan Quiet Diesels. Ken Irwin

 

[Kirwin]

Stopped by Cummins today

They have an installation template and installation instructions that they are getting for me. Unfortunately all cooling air suctions and discharges are on the underside of the generator and are not redirectable according to the Cummins salesman and a specification drawing of the commercial model of this generator. I'm not sure how much room the generator needs under it to prevent restricting the air flow for cooling but I'm hoping that the installation template will specify the minimum clearances for air flow. By the way they want $10,200 for it. Ken Irwin

 

[Newt]

Kirwin Onan shows RV & Marine versions of Quiet Diesel's. Have you checked the Marine? I can see blowing down in a motor home, not in a boat>

 

[Kirwin]

Marine Gensets

I looked at the marine version and it has a wet/dry exhaust and a cooling water circuit. Don't think that would work.

They do make a commercial version but it uses that same enclosure as the RV set as far as we can tell just painted a different color and rated at slightly less due to a different standard. Its the same generator and engine according to the spec sheets. Ken Irwin

 

[Texas Diesel]

This may help.



I thinkink you can get a reverse flow fan for Onan Generators. That would direct the hot air straight up.

 

[Kirwin]

Progress so far

I continue to research and layout how this would work. I received a full scale drawing from Cummins on Friday that gives all the layout information for the underside of the generator enclosure. The cooling air inlet is 12" X 18" and the hot air exhaust is about 6" X 12". I made a cardboard template from the drawing to try to obtain the best mounting location and orientation in the bed of the truck. With the front 28" of the bed taken up by the Transfer-Flow, I wanted to mount it on the drivers side length wise. The generator is 24" X 41" thus it would have to mount inboard of the fender well inside the bed. This will result in an interference issue with the service door on the generator if it were turned such that the hot air exits aft in the truck bed. I believe this is the only acceptable location for hot air discharge as forward air flow would result in heating of the Transfer-Flow fuel tank.

If I move it to the passengers side of the bed length wise it will be turned the correct arrangement for hot air discharge aft but, that will put 800 lbs over the right rear tires. This combined with crown of the road may make the truck lean to much while traveling down the road.

If I put it in the center across the bed just aft of the Transfer-Flow, there will only be 3. 5" clearance between the inner fenders and the side of the generator for longer items to extend past the generator in the bed. The bed is just over 70" with the Transfer-Flow so the effective bed length would be about 46"!!

My other issue I haven't resolved in where to direct the return fuel from the generator that cools the injection pump. If I tee it into the supply line from the Transfer-Flow which would be the easiest way, however, I create a closed loop for the cooling fuel. So I think I have to direct it back to the Transfer-Flow via a separate path.

I am also looking at mounting it on a bed plate so as to increase the clearance under the generator to improve cooling air flow as I don't want to put a 12" X 18" hole in the bed of my truck. This would also facilitate removal for maintenance or to use it in a fixed location for a period of time.

Anyone got any ideas on how best to answer these questions? Thanks Ken Irwin

 

[Newt]

One thought on the return line. If tee'd into the supply line, it wouldn't be a complete closed loop. It would be dilluted by the fuel necessary to run the generator. That'd be a judgement call

 

[Kirwin]

I agree

Thanks for the reply Newt. I had thought of that, but the spec sheet says 1. 2 GPH at full load and 0. 1 gal GPH at no load. So I was thinking that most of the fuel would be recircing a low load when the cooling return flow would be needed most. If the pump is running at full flow I would think that through flow would remove the required heat, but I don't know that for a fact. I could also use a cooler mounted in series with the return flow to remove the heat such as Dodge is using on the power steering pumps on our trucks but I'd like to keep the set up as simple as possible. I might not need any more cooling than to route the fuel back through a piece of pipe in the cooling air inlet stream in the generator. What do you think? Ken Irwin

 

[Newt]

A cooler sounds good. Ford also uses one on the Ford Ranger power steering that would be about right.

 

[Kirwin]

Progress so far No 2

Well I will be ordering the Onan generator on Monday. At the last minute the local Cummins/Onan dealer showed me a 20 Kw unit (actually rated at 17. 5 Kw continuous) that I had to consider, but based primarily on fuel consumption, I have decided to stay with the Onan 12. 5 Kw RV Quiet Diesel. The unit that Cummins Atlantic showed me on Thursday uses a Kubota 4 cylinder diesel which uses . 97 GPH of fuel at 1/2 load which would be 8,750 Watts according to their brochure. The Onan 12. 5 Kw RV set uses a 3 cylinder Kubota diesel that uses . 48 GPH at 1/2 load which would be 6,250 Watts. The two engines are identical except for the larger generator has 4 cylinders and the smaller one has 3 cylinders. Additionally the RV set has a rubber mounted under carriage to minimize transmission of vibration to the chassis. The other unit just uses Z strips of metal. The Onan cooling air inlet and outlet are both under the generator. This will require that I cut holes in the bed of the truck to provide the cooling air supply and discharge. One hole is 12" X 18' on the inlet side and 7" X 12" on the discharge side.



Alternatively I could raise the generator 6" off the floor of the truck and only duct the hot air and exhaust through the floor. The disadvantage of this is that 1) it makes the generator 6 inches higher (center of gravity concern) and 2) I wouldn't be able to run the generator with a cap (which I currently don't have) as the cooling air supply would be from the air inside the back of the truck. I do not want to discharge both the hot and cold air into the 6 inches under the generator as I would be concerned about recirculation of the hot air causing overheating of the generator. Obviously I cold duct the hot air and direct it aft in the truck box but his this would probably not prevent all hot air recirculation.



The 20Kw generator draws cooling air from the bottom but discharges air out through several places most of which exits out the end of the generator and thus does not lend itself to the enclosed space if I were to install a cap on the truck.



Based on these reasons and my thoughts that the 12. 5 Kw will run my whole house with no problem I have decided to get the Onan 12. 5 Kw Quiet Diesel. have I missed anything here? Still looking for some fuel quick disconnects that wouldn't leak and would be sealed while disconnected. Thanks Ken Irwin

 

[abdiver]

Do you really need 12. 5Kw wouldn't a smaller unit work you don't have to run everything at the same time. As I recall gensets are not mean't to run a real low demand or at max output gensets like to run between 15% to 80% of rated output.



Check with manufacture



my 2cents - Bill

 

[Kirwin]

Why 12.5 kw?

I don't need it for the RV, but for standby power for the house I think I will need it. My current generator is a 25 Hp, 13. 5 Kw, Kohler powered, Gillette Generator that works very well but at about 1 GPH it uses a lot of fuel. And the noise, noise ,noise!!!! So I'm converting to diesel! They don't go up much in price to increase in size when your looking at one large enough to run your house. Ken Irwin

 

[abdiver]

Ken What am I missing, If this Genset is for your house WHY mount in your truck?



I have a MultiQuip 15Kw Genset for my home I built a 12x16 building which will also house my water system and a place to store some of my nice tools and a place for me and my buddies to sit around and have a cocktail or two. Wife is happy to have us guys away from HER house.



I am sure y

 

[Kirwin]

Purpose for my generator setup.

I am trying to find a best of both worlds solution to my standby power needs, and I want to be able to run the A/C in the travel trailer to cool it while on the road on those very hot days. After I stop in the evening with trailer sealed up all day, the temperature will be 95+. I thought that if I started the A/C 4 hours before stopping for the day maybe the trailer would be bearable a little earlier in the evening. Additionally I want a diesel powered generator such that the Transfer-Flow in the bed of the truck can be the fuel source. Propane generators are OK but at . 8 GPH fuel consumption they would quickly use all the propane onboard the trailer. With 100 gallons of diesel in the Transfer-Flow I could boondock a long time before I would need to return to civilization for fuel. Thus I thought the Onan generator would be the best compromise. They are QUIET! They are fuel efficient. And I think the 12. 5 Kw is big enough to run the house. After hurricane Hugo in Charleston and Ivan here in Portsmouth it was difficult to find fuel for the first several days after the storm passed. With a 100 gallons in the Transfer-Flow, I can last 200 hours or about 8 days before I would need fuel. As far as low load conditions, the generator would be at 25% load at 3,125 Watts which is about 12 Amps. This minimum load would be present if I were supplying either the A/C in the travel trailer or supplying the normal hotel loads in the house, so I don't think that long term low load conditions will be a problem. Thanks for the reply. I want to think this thing through thoroughly before I buy the generator. Ken Irwin

 

[emarsh]

be sure to check with the manufacturer about derating for altitude- we have a 12K ONAN nat gas unit for home backup and it had to be derated for nat gas instead of LP gas PLUS another 1kw for 3,000 TF elevation. This makes it an efective 10. 5 KW rating!

 

[OTRPU]

I had the same idea a few years back, and had a whoppin deal on a refurb Onan, decided against doing it when I found out I'd have to cut the bed of the truck for service and such. I decided for me it just wasn't practical. Ended up having a rack welded on rear of 5er to carry the genny on.



Cheers,

Steve J