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An Onan JB Performance Question


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  #21  
Old 08-06-2017, 12:16:52 PM
len k len k is offline
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Default Re: A JB Performance Question

I was thinking about engine sputter ( not firing / missing ) when cold starting. Possibly water (steam) in exhaust condenses on cold spark plug and shorts it out (no spark). Then when next charge(s) of air comes in it drys it out and it sparks again. After engine and plug are hot no more condensation. Just a theory

We have an old spark plug tester that applies high voltage (model T buzz box), can vary pressure ( 150 psi), and has a window to see spark. On old slightly carboned plugs spark is intermittent or non-existent at higher pressures. Condensation on plug should mimic carbon as far as conductivity.

---------------

Leon .......my comments about purging demand reg and hose to carb were to be done with engine off.

Just for test purposes to eliminate that variable, Not a bad idea to purge your whole gas line from house to gen if gen has not been used for ~ 6 months. I know so much air will diffuse into a valve closed off nat gas line in ~ 6-12 months, that the vapor will not ignite, not so sure about a 100 ft line open to gas supply at the house

Last edited by len k; 08-06-2017 at 01:11:39 PM.
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  #22  
Old 08-06-2017, 12:36:41 PM
JohnnyC JohnnyC is offline
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Default Re: A JB Performance Question

Quote:
Originally Posted by MBB View Post
Leon even the Transfer switches have a time delay for the motor to warm up. See attached.
That is true, sort of..... The LT II series transfer switches have optional time delay relays for:

Transfer - allows the generator set stabilize before application of load
Retransfer - allows the utility to stabilize before retransfer of the load
Stop - maintains availability of the generator for immediate reconnection in the event that the utility fails shortly after retransfer. Allows gradual generator set cool down by running unloaded.

My LT II switch has only the Retransfer and Stop time delay relays. All the other relays in the switch are regular non-timed relays and react instantaneously - or at least that is what it seems like. If there is any fixed delay, then it is only a second or two and that is not long enough for a transfer function under heavy load with a genset cold started especially on gasoline.

I attached a picture below with the relays marked. I hope to get a time delay relay for the Transfer function.

The LT III ATS by default have a fixed 3 second delayed Start, 3 second delayed Transfer, 5 minute Stop, and 5 minute Retransfer under their "Package A Control". Package B Control offers adjustable time delays.

JohnnyC
New Jersey
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  #23  
Old 08-06-2017, 12:54:26 PM
JohnnyC JohnnyC is offline
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Default Re: A JB Performance Question

Leon and everyone, I ran the tests mentioned earlier and have it on video on my cell phone. To recap the tests - 1) Cold start with load 2) Warmed up JB and cycling about 6 kw on and off while focusing on amps, and hz as well as sound of the JB running. Testing work well. At the moment the video is in raw files on my cell. I got to run to Home Depot for paint to finish my house painting a.s.a.p. Rain coming late this evening. I will process the videos later today, post to YouTube and provide a link. Leon, once you view the videos I'm sure you will be surprised.

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  #24  
Old 08-06-2017, 12:59:04 PM
len k len k is offline
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Default Re: A JB Performance Question

Leon..... I'ld open up starter and do some maintenance. My 7NHM will sometimes not engage and just spin. Does it more in cold weather than warm. Plastic stater gear assembly
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  #25  
Old 08-06-2017, 12:59:11 PM
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Default Re: A JB Performance Question

Quote:
Originally Posted by armandh View Post
problem overview

cold air is more dense than warm air
thus the start up mix is lean
So, I've been thinking about that. It's hands-down the case for a gasoline carb.

But it's a different situation with a gaseous carb. Simply put, when the ambient air is cold and dense, so is the fuel gas. Both the fuel gas and the air follow the basic fundamental gas laws in pretty much the same way. I think this is why gaseous carbs don't need a choke.
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Old 08-06-2017, 12:59:15 PM
MBB MBB is offline
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Default Re: A JB Performance Question

My point is that motors cars, etc. Should be warmed up first before applying loads as more wear occurs. Newer choke assemblies fuel injection make choking less noticeable however older vehicles specifically when these units were built were not as sophisticated and cars required more of a warm up time. This I would say also applies to generator motors. Probably less so with natural gas but I still would be hesitant about loading to full load without the motor being warmed up.
Just my opinion.
Mike
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  #27  
Old 08-06-2017, 01:12:32 PM
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Default Re: A JB Performance Question

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Originally Posted by Leon N. View Post
...I would be willing to bet there are not many operational JB's out there today that meet this requirement, especially if operating of natural gas which has a much lower heat content than either propane or gasoline. Onan says to derate 20% on NG...
Could be, but mine does. Keep in mind that 'Full Load' as defined by Onan, on a nat gas-fueled JB is 6500W. This was covered in post 28 here:

https://www.smokstak.com/forum/showthread.php?t=145667

My set absolutely recovers in 2s or less at 6500 W.

NL 61 Hz, 233V
6.5 kW 57 Hz, 225V
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  #28  
Old 08-06-2017, 02:21:27 PM
Leon N. Leon N. is offline
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Default Re: A JB Performance Question

The Onan certified performance was demonstrated I am sure with a warmed up engine and running on either gasoline or propane, not NG for sure.

Bottom line, do it any way you want but document the results. My set gets used monthly. The gas line is 120 feet of 1 inch black iron pipe. If I had to do it over again I would use inch and 0ne-half piping. But once again, the set works fine once it has been running for a few minutes. That carb popping is random and does not always occur. Maybe another hint that points to the regulator is even if warmed up and operating within spec, dropping a 4Kw load abruptly does sometimes briefly introduce some carb popping until it settles down. My governor maybe a bit too sensitive, but why is the performance somewhat ragged during the warm-up and not after it has been running for awhile? Has anyone else seen this type of behavior?
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  #29  
Old 08-06-2017, 02:49:09 PM
len k len k is offline
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Default Re: A JB Performance Question

If diaphragm has a crack in it then it may randomly allow air to enter for a leaner mix.
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Old 08-06-2017, 04:21:22 PM
JohnnyC JohnnyC is offline
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Default Re: A JB Performance Question

Leon, here is a video of today's tests as discussed earlier.

https://www.youtube.com/watch?v=UKFm...ature=youtu.be

JohnnyC
New Jersey
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