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Car Forum / Driving, Maintenance, Tuning / RVs / December 2007Onan 2.5 LP genset
I have an Onan 2.5 genset on propane. It will start but not keep running. If the weather is warm, it will sometimes keep running but in cold weather, forget it! I am suspecting either the control assembly or the voltage regulator rather than the fuel/ignition side. If I hold the start button down, it will keep running until I release the button, then it quits. The low oil switch is OK. There is only 65 hours on the unit. I have the service manual with all the schematics. Does anyone have any ideas? I am desperate but still persevering. Thanks Ron >I have an Onan 2.5 genset on propane. It will start but not keep running. >If [quoted text clipped - 10 lines] > Thanks > Ron May have a little moisture in the propane that is freezing up. DMax >>I have an Onan 2.5 genset on propane. It will start but not keep running. >>If [quoted text clipped - 4 lines] >May have a little moisture in the propane that is freezing up. >DMax DMax, thanks for the reply. The cold weather that seems to cause this is only about 45 degrees F. My sense is that the problem is electrical because of how it quits exactly when the start button is released. When it decides to run, it runs well, will operate the A/C just fine. We carry a Honda now for reliability, but I sure would like to get the Onan to run like it is supposed to. Ron It's the propane that's the problem, I'm pretty sure of it. When you release the start button, it quits. That's the key to the problem. The start button not only turns on the starter motor but it turns on the propane solenoid. Once the motor is running it's supposed to let propane through and when the motor stops the propane stops flowing. The starter switch overrides the relay. I bet you need a new propane relay. But, the best thing you could do is get rid of the propane and convert the Onan to gasoline which is much safer than propane. Propane explosions are a serious threat. Harry Harris >I have an Onan 2.5 genset on propane. It will start but not keep >running. If [quoted text clipped - 11 lines] > Thanks > Ron  SignaturePosted via a free Usenet account from http://www.teranews.com >It's the propane that's the problem, I'm pretty sure of it. When you >release the start button, it quits. That's the key to the problem. The [quoted text clipped - 13 lines] >> Thanks >> Ron Harry, it turns out that the propane solenoid had something stuck in the valve seat so the propane was on all the time, at least some propane was getting through all the time. I was able to get the unit running by disconnecting the ignition enable output (P1-4) but then it won't shut off unless I turn off the propane. So then I disconnected the propane solenoid (didn't need it hooked up because it was stuck open) and reconnected the P1-4 and now it works fine. I got the solenoid working, reconnected it and now everything works. At least it is working on the bench like it has before. As I may have mentioned earlier, it acts up in colder weather. For my next test, I have removed the Control Assembly (A1) and put it in the freezer and will hook it up in the morning to see what happens. Thanks for your help Ron >>But, the >>best thing you could do is get rid of the propane and convert the Onan >>to gasoline which is much safer than propane. Propane explosions are a >>serious threat. I can't believe this Harris guy is still hanging around here and still spouting this ridiculous crap. Good grief. And thank heaven for filters. GB in NC >>>But, the >>>best thing you could do is get rid of the propane and convert the [quoted text clipped - 9 lines] > > GB in NC Ridiculous crap? Well, I never . . . I helped the guy pinpoint the problem and you call it ridiculous crap. I might have saved his life and you call it ridiculous crap. His propane was on all the time and had a small leak. That's not good. It's a good thing I spoke up about what was the matter and it's a good thing I am an expert in propane applications. When I say propane is dangerous I know of which I speak. Take it to the bank. Harry Harris SignaturePosted via a free Usenet account from http://www.teranews.com >>>>But, the >>>>best thing you could do is get rid of the propane and convert the [quoted text clipped - 9 lines] >When I say propane is dangerous I know of which I speak. Take it to the >bank. Harry,I agree that propane is dangerous.....I am a retired firefighter and have seen some devastation. I appreciated your help and I hope you continue to help others. Ron >>>>>But, the >>>>>best thing you could do is get rid of the propane and convert the >>[quoted text clipped - 9 lines] >>> >>> GB in NC >>Ridiculous crap? Well, I never . . . I helped the guy pinpoint the >>problem and you call it ridiculous crap. I might have saved his life and [quoted text clipped - 3 lines] >>When I say propane is dangerous I know of which I speak. Take it to the >>bank. >Harry,I agree that propane is dangerous.....I am a retired firefighter and >have seen some devastation. I appreciated your help and I hope you continue >to help others. >Ron And you've never seen any devastation caused by gasoline? GB in NC >>>>>>But, the >>>>>>best thing you could do is get rid of the propane and convert the [quoted text clipped - 25 lines] > > GB in NC Your logic is non-existent, dear. A thinking person doesn't ignore any one dangerous substance just because it's not the ONLY dangerous substance. Ignoring the dangers inherent in propane because gasoline has its own set of dangers is ignorant - just plain stupid to be frank. HH SignaturePosted via a free Usenet account from http://www.teranews.com >>>>>But, the >>>>>best thing you could do is get rid of the propane and convert the [quoted text clipped - 20 lines] > to help others. > Ron You're welcome and I will continue to help as best I can. HH SignaturePosted via a free Usenet account from http://www.teranews.com > Harry, it turns out that the propane solenoid had something stuck in the > valve seat so the propane was on all the time, at least some propane was [quoted text clipped - 13 lines] > Thanks for your help > Ron Ron, It would help quite a bit to know the full model and spec of your genset - Onan does make changes from time to time, so what applies to a spec A unit may be something entirely different by the time you get to spec F or G.. That said, from what you detail above, it appears that your problem is in the generator or controls - if disconnecting the ignition enable line let the genset keep running when immediately before that it wouldn't, then the genset was stopping when the start switch was released because the control module hadn't switched from 'start' mode to 'run' mode. (If the fuel solenoid had been working, it would have closed and shut the genset down - since it wasn't, the engine continued to get fuel, so this fairly definitely points at the control module or the generator). For the control module to switch to 'run' mode, the genset must be generating (and, of course, the module must recognize that it IS generating..). Sequence of operations is like this: Pressing start switch sends 12v from module to start solenoid, fuel solenoid, and voltage regulator field flash, and ungrounds the ignition enable line. Start solenoid closes and passes 12v to starter and to the enrichment solenoid on the regulator, fuel solenoid opens and provides fuel to the regulator, voltage regulator field flash is passed thru the voltage regulator to the brushes/slip rings and thus to the rotating field to establish an intial magnetic field in the generator, and since the ignition enable line is ungrounded, the magneto provides spark as the engine rotates. The engine starts to fire and comes up to speed - as it does so, the rotating field sweeping past the stationary windings produces output in the main windings (T1/T2), the battery charge/control voltage windings (B1/B2), and the quadrature/exciter windings (Q1/Q2). The output of the quadrature windings is fed back to the voltage regulator, which turns it into a higher (than 12v) dc voltage which it feeds to the rotating field. This higher voltage produces a stronger rotating magnetic field, which produces a higher available voltage on the quadrature windings, which the voltage regulator uses to send an even higher dc voltage to the rotating field.......round and round, until the voltage regulator senses that the main windings are at 120v. At this point (which with no load normally corresponds to about 35v dc to the brushes) the voltage regulator stops boosting its output, and varies the dc voltage to the rotating field as needed to maintain 120v output. The quadrature winding will be producing about 145v ac at this point, and the battery charge/control voltage winding will be producing about 22-25v ac (IIRC). The control voltage feeds to the control board (P2-1 and P2-1) and signals it to switch to 'run' mode (actually, when it hits about 19v if I recall correctly). The board switches to run mode, which disconnects the 12v to the starter solenoid (and thus also the 12v to the regulator enrichment solenoid), maintains the 12v to the fuel solenoid, disconnects the 12v field flash to the voltage regulator, and keeps the ignition enable line isolated from ground. The genset will now continue to stay running when the start switch is released. Once the genset is in 'run' mode, it will stop if: The low oil switch closes (this directly grounds the ignition enable line, external to the control module) or The genset stops generating (this removes the control voltage input which is keeping it in run mode) or The local -or- remote stop switch is pressed (this grounds the ignition enable line in the module). If the problem happens again, the first thing to do is to hook up a meter to see what voltage the genset is producing - if it's making 120v and not switching to run mode, verify the B1/B2 voltage at the control board. If THAT is ok, then the control module is the problem. If it's NOT making 120v, then further troubleshooting is needed - could be no field flash from module to voltage regulator, bad voltage regulator, poor connection from voltage regulator to brushes/slip rings/field windings, poor connection from quadrature windings to voltage regulator, etc. Alan >> Harry, it turns out that the propane solenoid had something stuck in the >> valve seat so the propane was on all the time, at least some propane was [quoted text clipped - 72 lines] > >Alan Alan, here is some more info for you; this unit is a Spec F, has 65 hours on it and is about 6 yrs old. I put the Control Assembly (A1) into the freezer over night in an attempt to isolate any problems connected with cold temperatures in regarding this assembly but today the genset works fine (on the bench). The B voltage at P2-1 and P2-2 is 17.4 VAC. The main output is 124 VAC. The fuel solenoid voltage at P1-1 is 10.1 VDC while cranking and the field flash voltage at P2-3 is 10.5 VDC while the unit is cranking. Voltage at P2-3 while running (with no load) is 3.4VAC....the manual says that this should be 0 VDC; I don't know if this is relevant??? Here is one more item that may be relevant. The diaphragm in the regulator does not lay flat...it seems to be raised on one side so that the disk in the center is on an angle, not perpendicular to the pushrod on the primer. The end of the primer pushrod has a hair clip on it that is about 3/4 inch long. This means that when the pushrod rotates, as it does due to vibration etc, the end of the hair clip contacts the disc on the diaphragm at wildly different locations due to the angle. This means that as the pushrod rotates, as it does all the time due to vibration, it is impossible to get a consistent setting on the primer. When you push the primer in and rotate the metal disc, you can get anywhere from full flow to no flow. I replaced the long hair clip with a very short piece of bent wire so that only the very end of the primer pushrod contacts the center of the diaphragm and now I can get a more consistent adjustment. With this history in mind, it is possible that this has been at least one of my problems encountered in trying to get the unit to start...either way too rich or way too lean on startup. You know how it goes...often there is more than just one problem happening at the same time. So at the moment, the genset is running fine, at least on the bench. It has worked fine on the bench before, particularly after the last 2 times it has been to Cummins/Onan for repair. When I get it out into the mountains here in Western Canada in the winter, then it acts up. Before I put it back into the rig, I am seriously thinking of taking it up to the ski hill and leaving it in the snow overnight to see if it starts in the morning. Alan, thanks so much for your detailed reply on the problems with this unit. I may not be problem free just yet so you may hear from me again if you have the patience. Ron >Alan, here is some more info for you; this unit is a Spec F, has 65 hours on >it and is about 6 yrs old. 10.5 hours a year? Wow. Less than an hour a month.... GB in NC >>> Harry, it turns out that the propane solenoid had something stuck in the >>> valve seat so the propane was on all the time, at least some propane was [quoted text clipped - 153 lines] > the patience. > Ron I have the patience - if you do a search at groups.google.com, some of the generator repairs I've provided advice on have taken months what with one thing and another. The voltages you've measured look ok (I was working from memory on the B1/B2 voltage, so go with what you measured). Now that you have the voltages, you'll have to catch it the next time it has problems - what you find then will point in the direction of the problem. Your problems with the regulator diaphragm and enrichment pushrod could cause starting problems - but once it does start and run, wouldn't have anything to do with it continuing to run when you release the switch. However, what I HAVE seen as a regular problem (around here, at least) is the rubber vent hose that runs from the regulator to outside air. Insects seem to be attracted to the propane odorant, crawl up inside the hose, and die - eventually plugging the hose. With the vent mostly or completely plugged, the diaphragm can't respond to the small vacuum signal from the carburetor to allow fuel to flow. Just to eliminate one possibility, while you have the genset out, pull the hose off and run a stiff piece of wire thru it, see what (if anything) you find inside... Alan >>>> Harry, it turns out that the propane solenoid had something stuck in the >>>> valve seat so the propane was on all the time, at least some propane was [quoted text clipped - 24 lines] > >Alan Alan, on this one, the vent hose runs from the regulator to the carb, at least that is the hose that I think you are referring to. The manual calls this a balance hose and it needs to be a specific length, 23 to 25 inches. I replaced the hose, which was too short, with one the right length and the motor smoothed out a lot. It doesn't look like there is a way for insects to get into this hose. Again, your advice is much appreciated. Standby for a success story when I get this thing to work in cold weather. Ron > Alan, on this one, the vent hose runs from the regulator to the carb, at > least that is the hose that I think you are referring to. The manual calls [quoted text clipped - 7 lines] > get this thing to work in cold weather. > Ron Sorry, Ron - I was thinking of the KY (4KW) Microlite when I wrote that. You are correct on the configuration that you have. If all else fails, you could move to Florida? <g> Alan >> Alan, on this one, the vent hose runs from the regulator to the carb, at >> least that is the hose that I think you are referring to. The manual calls [quoted text clipped - 7 lines] > >Alan Hello Alan; Here is the latest....in the cold weather it starts but fails to keep running as before. If I disconnect the positive wire to the propane solenoid and power the solenoid separately, plus disconnect the P2-4 ignition enable output, it will start and keep running (but won't shut off). Under these conditions, the generator is not putting out any 120v power. After the unit warms up and I reconnect everything, it will start and keep running and produce power. I am going back to your detailed explanation in an earlier posting where you say that if it is not producing 120v there are other problems to look at. I need to first find out if there is good B voltage and go from there. Does this sound like the right way to proceed? Florida is looking very good right now! Ron Hello again, Alan. Right now it is snowing which is somewhat unusual for us here on the west coast so Florida does sound very good. With this cold weather, I got my enthusiasm back up for solving this genset problem and went thru all your notes and my shop manual and figured that it had to be the voltage regulator so today I tried pointing a heat gun at the regulator on low for about 10 minutes to warm it up and the genset started right up and ran beautifully. Prior to that it would not run unless I went through all the steps described in earlier posts to you. I am going to order a new voltage regulator on line and try that. Sound good? Ron >> Alan, on this one, the vent hose runs from the regulator to the carb, at >> least that is the hose that I think you are referring to. The manual calls [quoted text clipped - 7 lines] > >Alan Alan, I mentioned to you that I was going order a new voltage regulator which I did. I got it from ASAP in Pennsylvania. I works fine except that the 120V output has a bad "flicker" to it. The original regulator does not do this. I am afraid that the flickering current will damage the circuitry in the RV appliances like the fridge, microwave, furnace etc. not to mention any computer stuff. I am trying to get some tech support from ASAP to see if they can solve this part of the problem. Cheers Ron >> Alan, on this one, the vent hose runs from the regulator to the carb, at >> least that is the hose that I think you are referring to. The manual calls [quoted text clipped - 7 lines] > >Alan >> Harry, it turns out that the propane solenoid had something stuck in the >> valve seat so the propane was on all the time, at least some propane was [quoted text clipped - 72 lines] > >Alan Alan, one more thing, I have disconnected the oil switch in the past in order to eliminate this as a potential problem and have had no success. Also, I realize that propane regulators are sensitive to altitude, but I don't think that altitude has a bearing on flash voltages etc. Just another unrelated potential aspect to this topic.
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