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Onan Generators

Natural gas conversion to propane or gasoline

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Old 01-03-2010, 08:11:29 PM
gerald m gerald m is offline
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Default Natural gas conversion to propane or gasoline

I am thinking of buying a 208-230 volt 12 kw. 3 phase gen with auto start from a local hotel. Please dont ask me why because I dont really need it. It was used for backup power. The gen was set up to run on natural gas , People tell me that there isnt enough Natural gas pressure at a home regulator to make the thing work.Is this true and if so is it hard to convert to propane or gasoline without much time or money? I dont know the size of the engine as I havent went to look at it yet I am dealing with the manager and he dosent seem to know to much about it except what I have told you. I can but this machine for $200.00 dollars it is suppose to be in very nice condition and has been stored inside for a number of years since it was unhooked . Thank-you for your time. Gerald m
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Old 01-03-2010, 08:25:18 PM
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Mikey4026 Mikey4026 is offline
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Default Re: natural gas conversion to propane or gasoline

Are we speaking of a 12JC Onan?
The model, spec and serial numbers would be great.
From memory it needs 260Cuft\hr on natural gas, approx 264,000 BTU at full load. Pressure is not the problem, volume maybe? Your gas company should be able to tell you how much is supplied to the house through the regulator, then subtract what you are already using. A larger regulator may be required. It will require no extra equipment to operate it off of propane vapaor. If it is a 12 lead generator with a 15 or 18 spec code, it is reconnectable for any voltage. Many were also capeable of running gasline, look for a fuel pump or a mixtrure adjusting screw on the bottom of the float bowl.

Last edited by Mikey4026; 01-03-2010 at 09:09:07 PM.
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Old 01-03-2010, 08:50:05 PM
K D Redd K D Redd is offline
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Default Re: natural gas conversion to propane or gasoline

For $200, I would buy it in a heart beat. I gave $100 for a 4CCK ongasoline that needed work. If your lucky it might be a -15 or -18 that is reconnctoble to 120/240V single Phase. RUN, do not walk, to the manager with the 200 in your hand.

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Old 01-03-2010, 10:22:17 PM
Gunny Gunny is offline
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Default Re: natural gas conversion to propane or gasoline

Propane is they way I'd go. Your are going to have to get a tank, size will depend on a lot of factors such as how long yo want it to run, coldest temperature you expecte.

Propane won't go bad like gasoline over time.
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Old 01-03-2010, 11:21:11 PM
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EricWood EricWood is offline
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Default Re: natural gas conversion to propane or gasoline

You may be able to use nat. gas still. Look at the model number of the gas meter. The two or three numbers in the model # usually signify the max. cfh that can flow through it. such as XX450XX, or XX45XX.

You will also need to find out what the gas company's supply pressure after meter is. Often times is either 11" wc, or 2 psi. You'll be all right with 11" wc, but will need to tap in right after the meter somewhere for a dedicated run to the genset.

In application, for example, if you have a 450 cfh meter, and using Mikey's 264 cfh max genset demand, have a 95 cfh furnace, and 20 cfh water heater, max demand would be 379 cfh-- within its capacity, with enough room to likely still run your stove.

If your meter flow is too small; ie, 250 or 350, find out how they would work with you on increasing size of your service.

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Old 01-04-2010, 11:49:25 AM
Dave Edmonds Dave Edmonds is offline
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Default Re: Natural gas conversion to propane or gasoline

I have a 20ES at my house, running on natural gas. Consumption (according to the book) is just over 300,000 btu at full load.
The book says to provide 10-20" water column at the generator. That would have required the gas company to provide a 2-pound meter, and I would have to provide the regulators to get it back down to 7" for the house and 10-20" for the generator. Gas company wanted about $800 to make the change.
Gas company also informed me that existing gas meter (typical for normal residence) is good for 400,000 btu.
Followed Gunny's advice and hooked it up to existing 7" WC service - 1" line - about 10' from meter to generator. Runs just fine up to 15 KW; wouldn't do 20 KW, but found misadjusted throttle linkage not opening throttle fully. Have not load-tested since that problem was solved.
The only potential problem is that the house gas furnace can draw 125,000 btu and generator can draw 300,000, thereby overloading meter/regulator and dropping pressure below 7" (and it DOES - drops to about 5" - I have a gauge at the meter output). However, a bit of conservation can make sure that this condition doesn't occur (don't let the wife dry clothes and cook dinner when the heat is on!).
In other words, I was too cheap to spend a lot of money when there really was no justification to do so. The main thing I had to consider is to make sure there was adequate gas flow to the generator, since the pressure being fed to the unit is "marginal" (according to the book). Hope this helps.
Dave Edmonds
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