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Onan Generators Restoring, operating and maintaining vintage Onan generators.

Onan Generators

New Proud Owner of an Onan JC


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  #51  
Old 10-12-2017, 10:20:15 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: New proud owner of a JC

If it has set for awhile, I like to pull plugs and crank engine over till it has oil pressure.
I have lightly loaded (40 amps) a JC off a 20# bottle.
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  #52  
Old 10-12-2017, 10:28:09 PM
JohnnyC JohnnyC is offline
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Default Re: New proud owner of a JC

Quote:
Originally Posted by JT240Z View Post
Didn't remove that cover yet but I did look at it from every opening. Good suggestion to remove and inspect it though. It will be on the list of things to do.

I did remove the generator cover and turned her over using the large nut on the end. Turned it clockwise and felt and heard nothing strange. I could feel all four compression cycles for the four cylinders and each felt pretty much the same.

Suggestions on how to do an initial start? It will take me a while to get her in a position where I can feed her NG. The only propane I have on hand is a few 20lb bottles. Can I just feed it with propane from a 2 stage regulator? I have one that can supply 165k BTU at 11 WC that I used to feed a 6.5K NHM genset. I'm not talking about load testing it. Just getting her started and verifying she produces power.

Technically you didn't loose because I haven't completely removed that cover yet. If you're ever in my area we can share some beers.
Attached is a picture showing the very first time I fired up my 15.0 JC after it was dropped off at my house. Due to the size and resolution of the picture, you may not see the voltage shown on the volt meter and the oil pressure, but you can clearly see 1 BBQ tank of propane and a regulator from my BBQ too. I did not have the demand regulator hooked up for the first firing. The trick is to hook it up as you see, slightly crack open the tank's value until you hear a faint "woosh" sound of the vapor in the carburetor, then toggle the JC to the start position. Once the JC fires over you will need to tweak the propane flow slightly until the motor runs smooth. It may take several times before you get the hang of it. Once the JC is running smoothly, you can check things over such as oil pressure and leaks. You will NOT be able to run a load (anything over 12 amps from my experience) until you hook inline a demand regulator and a second BBQ tank. If you run a load, the tank will most likely freeze up quickly.

OK on the beer. Hopefully someday..

JohnnyC
New Jersey
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  #53  
Old 10-13-2017, 10:54:36 AM
JT240Z JT240Z is offline
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Default Re: New proud owner of a JC

I may have an even a better way of doing the initial startup. As you can see in this pic, I have the demand regulator and the cutoff solenoid already on the unit.


I'm thinking that all I need is the LP tank and a primary/secondary regulator. I do have a new motorhome LP regulator that will take tank pressure down to 11" WC and will supply 165,000 BTU. Wish I had a larger tank than 20lbs but I guess that will have to do for initial startup and checkout. I may be able to wrap the tank with a heat blanket to assist vaporization of the LP. I may be able to borrow a 100lb LP tank from someone if you guys see the need. Since this thing is rather heavy I'd like to be able to test it out before placing it at its final resting place.

On a side note, the generator not only came with the transfer switch but also came with about 200' of #6 stranded wire, two breaker boxes, and a fused 3 phase master switch. Seems like they took everything out that was even remotely connected to the generator. I didn't know the wire came with it until I opened up the transfer switch and found all the wire coiled inside. No wonder it was so darn heavy. Also found all the original Onan manuals for the generator inside. Unfortunately, there was no manual for the transfer switch itself.
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  #54  
Old 10-13-2017, 12:24:37 PM
Mac Sine Mac Sine is offline
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Default Re: New Proud Owner of an Onan JC

You only need the primary regulator (that could be a 2-stage unit) to reduce the tank pressure to the inlet pressure needed at the KN demand regulator. The maximum inlet pressure value should be stamped in the body of the KN regulator.

Tank size relates to the surface area available for vaporization of the liquefied propane back into the gaseous state. As long as there is sufficient vaporization area to maintain the correct gas inlet pressure at the KN regulator, you can maintain a given load on the engine. Put a pressure gauge in your line so that you can monitor the gas inlet pressure at the KN. If the pressure begins to decrease from your initial setting (and the tank is getting cold), then there is insufficient vaporization area to maintain the load on the engine and you will have to decrease load, or add a tank or tanks to your system or use a single larger tank.
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  #55  
Old 10-13-2017, 12:59:38 PM
JT240Z JT240Z is offline
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Default Re: New Proud Owner of an Onan JC

Great! I have several full 20lb tanks that I can cascade together if I need to. The primary regulator is a 2-stage regulator that should be able to supply the KN as long as the tanks stay warm enough. This is only to verify engine runs and the generator provides power. Plan to do a full load test once it's connected to NG. Kind of hard to load up a 15kw generator that's sitting on my trailer in the front yard.
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  #56  
Old 10-13-2017, 02:04:03 PM
len k len k is offline
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Default Re: New proud owner of a JC

A 15JC takes ~ 290K BTU/hr at full load and ~ 120K at no-load. So if your reg can make 160K then it's good enough for ~ no-load testing.

BBQ tank is only good for ~ 50k-75k BTU/hr steady state in summer. So I think it will eventually freeze up even at no load, but I think you'll get at least a few minutes of run time before that happens. ( takes a time for liquid propane to get cold, and thus tank pressure to drop below min reg operating pressure).
Other trick is can flow some warm water over outside of propane tank to help keep it from freezing up.


Obviously since you have the demand reg good to use it, so you won't have to play around with tweaking propane tank valve. Check that reg vents are not plugged, mud wasps.
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  #57  
Old 10-13-2017, 02:50:18 PM
JT240Z JT240Z is offline
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Default Re: New proud owner of a JC

Quote:
Originally Posted by len k View Post
A 15JC takes ~ 290K BTU/hr at full load and ~ 120K at no-load. So if your reg can make 160K then it's good enough for ~ no-load testing.
Are you sure about those numbers? According to the operators manual, it more like 110cf/hr on propane at full load. Natural gas is closer to your numbers at 255cf/hr.
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  #58  
Old 10-13-2017, 03:40:30 PM
len k len k is offline
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Default Re: New proud owner of a JC

I remember others saying on nat gas 15JC at full load consumes ~ 280-290k BTU/hr.
This sounds about right since 15JC FL uses 2.4 gal/hr gasoline, or (2.4 x 125,000) = 300 k BTU/hr gasoline.

If you have Onan numbers use them. I was running ballpark estimates. So I just took nat gas full load number and ratioed it (1/2.4) to NG no-load and ASSUMED propane would require about the same BTU/hr. (on gasoline 15JC is ~ 1gal/hr no-load and 2.4 full load)

Other thing is your chart calls out different units than I am , they are not the same......"cubic feet/hr" VS kBTU/hr

Last edited by len k; 10-13-2017 at 04:04:04 PM.
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  #59  
Old 10-13-2017, 04:57:41 PM
JT240Z JT240Z is offline
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Default Re: New proud owner of a JC

1 cf/h ~= 1000 BTU/h so 110cf/h ~= 110k BTU/h as I understand it. The chart above is straight out the JB JC owners manual.
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  #60  
Old 10-13-2017, 05:37:24 PM
MBB MBB is offline
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Default Re: New Proud Owner of an Onan JC

Here is a little info on the transfer switch.

Options

A001 3 pole Transfer Switch
B001 Nema Cabinet #1
C005 Controls
D003 Door Assembly with Voltmeter
E004 Accessory Control 3 Wire Start
J004 Exerciser Clock 7 Day
K001 2 Amp Battery Charger
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Last edited by MBB; 10-13-2017 at 05:58:20 PM.
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