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Old 02-27-2013, 07:09 AM   #15
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Trailerking, when did that variable speed Onan become available? Pre 1999 maybe? That is one fine machine.

I pose another question--if the generator runs off a separate tank from the drive engine tank, can one use off road diesel fuel for it, which, here in Florida is cheaper. We have two diesel boats and have off road fuel available.
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Old 02-27-2013, 07:43 AM   #16
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This shouldn't even be a discussion. How can you compare a liquid cooled engine to an air cooled engine? The liquid will be superior in almost all respects other than maybe weight.

And the bigger Onans (twins) run at 1800 rpm. They're quiet, but not when compared to a diesel.

The only way I would go propane is if I didn't think I'd need a genny often. For occasional use the propane would work - though it would be a big factor when valuing the coach?
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Old 02-27-2013, 08:38 AM   #17
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Originally Posted by fighterpilot View Post
Trailerking, when did that variable speed Onan become available? Pre 1999 maybe? That is one fine machine.

I pose another question--if the generator runs off a separate tank from the drive engine tank, can one use off road diesel fuel for it, which, here in Florida is cheaper. We have two diesel boats and have off road fuel available.
I would buy off road diesel every chance I get, no one will ever check your fuel.

Ted.
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Old 02-27-2013, 09:13 AM   #18
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Not too sure when the variable speed became available. Also not sure why they only offer the variable speed on only one model. It would be great if they would incorporate that option on other units. It is quieter and better on fuel than running a constant speed.
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Old 02-27-2013, 01:17 PM   #19
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Absolutely horrible advice to use off road diesel in an on highway vehicle. Unless you have a separate tank for the gen set you are looking at MAJOR MAJOR fines for using off road diesel.

The state board of equalization does spot checks. If you get caught with dyed fuel hang on for a VERY COSTLY ride.

The dye stays in the tank and takes several tanks to use it all up.
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Old 02-27-2013, 02:51 PM   #20
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Absolutely horrible advice to use off road diesel in an on highway vehicle. Unless you have a separate tank for the gen set you are looking at MAJOR MAJOR fines for using off road diesel.

The state board of equalization does spot checks. If you get caught with dyed fuel hang on for a VERY COSTLY ride.

The dye stays in the tank and takes several tanks to use it all up.
I agree, could be MUCH more costly than the amount saved for off-road diesel. I sleep easier following the rules. If you can't afford the fuel, sell the RV.
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Old 02-27-2013, 03:35 PM   #21
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It has been noted that the variable sped Onan diesel generators have better fuel effeciency than constant speed diesel generators. That would be nice, but it ain't so.

The variable speed Onan diesel generators do produce less noise at partial loads than constant speed gen sets, but they do burn more fuel to produce that quiet delight. You have to decide if the extra fuel consumption is worth the price. Below are a few facts and calculations from the PowerTech 7KW constant speed diesel generator and the Onan 8.0 KW diesel gen spec sheets. Both generators use Kubota engines.

PowerTech:
HP: 10.5
Full load
Watts: 7000; GPH: 0.64; Fuel efficiency: 26.64%

50% Load
Watts 3500; GPH: 0.32; Fuel efficiency: 26.64%

Onan:
HP 16.5
Full Load
Watts 8000; GPH: 1.02: Fuel efficiency: 19.1%

50% Load
Watts 4000: GPH: 0.61: Fuel efficiency: 15.97

Notice that as the load on the Onan decreases from full load, its fuel efficiency decreases. Also note that the Onan variable speed has a lower fuel efficiency at full load than the constant speed PowerTech. You can get your first clue about the efficiencies by observing that the Onan uses a16.5 HP engine and the PowerTech uses a 10.5 HP engine to produce almost the same wattage output.

When you consider how the Onan reduces the noise, the increased fuel consumption should not be a surprise. The Onan must first convert its output to 12 volts DC and then invert to 120 VAC at 60 Hertz. Not only that, but it uses two inverters. These conversions of energy exact their own price in fuel effeciency, and that price can be seen in the specifications of the two different technologies.

This isnít to make an argument that there is something wrong with the Onan. It is just to show that there is a price to pay for making the diesel generator quieter. You pays your money and you takes your choice. Your choice is just as good as that of anyone else. In most cases, you really donít have a choice. Youíve got what the manufacturer put in your coach. Hopefully this can help you get a handle on generator fuel consumption.

Good Luck!
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Old 02-27-2013, 03:48 PM   #22
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We have propane and have no complaints. It's cheaper than diesel and can easily be refilled by mobile propane services which are abundant. I also like not having to worry about carbon monoxide since we have a 1year old child. Also with propane you don't have to worry about diesel fuel going bad if it sits unused.
CAUTION!
Take care of your 1 year old.

Why would you NOT worry about carbon monoxide with an LP generator?
Running a LP generator produces CO..... as burning other fuels in an internal combustion engine.
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Old 02-28-2013, 03:35 PM   #23
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There is not a better RV generator than a QD series Onan. QD=Quiet diesel. It is a inverter type generator that engine speed varies with load like the EU series Honda portables.

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Old 02-28-2013, 06:26 PM   #24
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I'll go diesel. When did they first start putting the QD series in motorhomes? In other words what year models will I have to look for to find one with that in it? Thanks
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Old 02-28-2013, 06:52 PM   #25
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It just boilers down to one thing. If you have a diesel RV, get a diesel generator. If you have a gasoline RV, get a gasoline generator. And if you have, and some will someday a propane or natural gas RV, get a propane or natural gas geny. It's just common sense. My gasoline coach has a gasoline geny and I love it. If I ever get another rig it will be all electric with diesel heat and geny and diesel drive. Only one fuel on board and one tank to fill. I like to keep things simple.
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Old 02-28-2013, 06:59 PM   #26
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I have a fuel tank of 300 gallons- diesel. I can run my 4 cylinder Yanmar diesel for a long time without having to stop and get propane. and with an output of 12,500 watts- camp beside me- I'll plug you in
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Old 02-28-2013, 07:04 PM   #27
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A Genturi Pipe Really helps with the fumes.

Ted.
Unless you or your neighbors have roof vent fans and set them to pull air in!!
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Old 02-28-2013, 07:09 PM   #28
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It has been noted that the variable sped Onan diesel generators have better fuel effeciency than constant speed diesel generators. That would be nice, but it ain't so.
Quote:
Originally Posted by wil01 View Post

The variable speed Onan diesel generators do produce less noise at partial loads than constant speed gen sets, but they do burn more fuel to produce that quiet delight. You have to decide if the extra fuel consumption is worth the price. Below are a few facts and calculations from the PowerTech 7KW constant speed diesel generator and the Onan 8.0 KW diesel gen spec sheets. Both generators use Kubota engines.

PowerTech:
HP: 10.5
Full load
Watts: 7000; GPH: 0.64; Fuel efficiency: 26.64%

50% Load
Watts 3500; GPH: 0.32; Fuel efficiency: 26.64%

Onan:
HP 16.5
Full Load
Watts 8000; GPH: 1.02: Fuel efficiency: 19.1%

50% Load
Watts 4000: GPH: 0.61: Fuel efficiency: 15.97

Notice that as the load on the Onan decreases from full load, its fuel efficiency decreases. Also note that the Onan variable speed has a lower fuel efficiency at full load than the constant speed PowerTech. You can get your first clue about the efficiencies by observing that the Onan uses a16.5 HP engine and the PowerTech uses a 10.5 HP engine to produce almost the same wattage output.

When you consider how the Onan reduces the noise, the increased fuel consumption should not be a surprise. The Onan must first convert its output to 12 volts DC and then invert to 120 VAC at 60 Hertz. Not only that, but it uses two inverters. These conversions of energy exact their own price in fuel effeciency, and that price can be seen in the specifications of the two different technologies.

This isnít to make an argument that there is something wrong with the Onan. It is just to show that there is a price to pay for making the diesel generator quieter. You pays your money and you takes your choice. Your choice is just as good as that of anyone else. In most cases, you really donít have a choice. Youíve got what the manufacturer put in your coach. Hopefully this can help you get a handle on generator fuel consumption.

Good Luck!
Our PowerTech 8.0 uses an 18 hp 3 cyl Kubota engine, at full load it uses .71 gph running at a constant 1,800 rpm.
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