Ed, Last month, you asked about the governor on an old Onan genset. I'm sorry I missed that discussion in real time, but here's what I know about my Onan MDJE, 7.5KW, 2-cyl, 19hp, circa 1975 machine. Before I get rolling, I'll note that some folks responded by telling you that the revolutional speed (rpm) of the machine should ***not*** change as load changes, and that is absolutely "correct" in the big picture. However, electrical load changes will result in a varying mechanical load on the driving diesel engine, and that would allow the machine to speed up or slow down ***in the absence*** of a mechanism to compensate for the varying mechanical loading of the driving diesel. You correctly concluded that the compensation mechanism is the machine's governor. The governor "system" is a very elaborate mechanical feedback system. It's goal is to continuously monitor the speed of rotation of the diesel drive engine and simultaneously adjust the throttle linkage to maintain the rated rpm's spec'ed for the alternator end of the genset. For my MDJE, the spec is +/- 26 rpm from no load to full load. The nominal spec for rpm is 1800 for my 4-pole machine. My old machine probably varies more than 26 rpm, due to 35 years of wear on the governor's mechanical components. That said, most electrical appliances will run fine from 56 to 63 AC cycles-per-second (some say Hz), so a no load to full load variation of 100 rpm is not the end of the world. The mechanical governor mechanism is very complex. In the MDJE, integral with - and part of - the cam gear is a slotted conical plate. The plate has slots machined radially around it's diameter; they fan out from the center. Captive within these slots are ball bearings. As the machine's speed of rotation varies, the ball bearings demonstrate centripetal reaction (respond to "centrifugal force"), and they move towards or away from the center of the gear as machine rpm changes. I'm going to skip the mechanical arrangement of the internal parts, as you and I are probably not going to tear the machine apart, so it really doesn't matter. Suffice it to say that the movement of the plate in response to the movement of the ball bearings is transferred to a rotating shaft that emerges from the front cover of the engine, and becomes the origin of the throttle linkage. A firm spring in the linkage causes the ball bearings to "fall inward" as machine speed decreases. Their mass causes them to move outward as the machine speeds up. A spring mechanism is used to "balance" the set point. Below the set point, more throttle; above the set point, less throttle. As you can see, a very delicate arrangement of physical spinning parts and the theory of angular momentum... Attached to the balancing spring is an arm that connects the internal governor components to the throttle arm of the injection pump. The spring's tension is adjusted to "balance" the the revolutional speed (rpm) from no load to full load. The absolute value of rpm (1800 in this case) is adjusted by adjusting the length of the throttle linkage. Achieving a high degree of accuracy of the adjustment requires a high quality mechanical or digital tachometer, or a very accurate frequency meter on the AC output. Most mechanics prefer the tachometer. In addition to the spring's tension and sensitivity adjustment, the throttle linkage has no less than 5 places where it's length can be affected and/or intentionally adjusted. Yecchhh!!! There are only a couple of things that can "screw up" the governor's performance: 1. physical damage to the cam gear or the cone/ball bearing governor plate 2. removal and reinstallation of the injection pump (usually to have it re-sealed) 3. corrosion/binding in the spring or linkage mechanism Generally, unless you've done this before, adjusting the linkage is NOT a user DIY activity. It's tedious, and one adjustment affects all of the others. Better to find a wizened old mechanic who's worked on these monsters and has machine-specific knowledge to do the adjusting. Assuming parts replacement is not required, you're only looking at 1 to 2 hours of labor, depending on what the mechanic encounters as he works. That labor estimate also assumes that you have removed the sound shield (if you have one) and the flywheel safety cover (so the mechanic can attach a piece of reflective tape to the flywheel to run his tachometer) before the mechanic arrives. Of course, you'll have to put that stuff back, too. Finally, once you have the linkage adjusted correctly, spray it with "high temp spray paint. The paint is not primarily to prevent corrosion. It's to provide witness marks in case the linkage ever needs to be removed to facilitate parts replacement in the area of the linkage. Well, so, that's what comes to mind. Hope you find it useful. Jim Peg and Jim Healy aboard Sanctuary Currently at Stuart, FL, heading SW towards Punta Gorda Monk 36 Hull #132 MMSI #367042570 AGLCA #3767 MTOA #3436

We have the same generator and were experiencing the same problem. Before you get to deep into causes have you replaced the fuel filters.We replaced them on ours and the problem went away. A cheap try. On Mon, Nov 14, 2011 at 7:18 PM, Jim Healy <gilwellbear@gmail.com> wrote: > Ed, > > snip > > Last month, you asked about the governor on an old Onan genset. I'm sorry > I missed that discussion in real time, but here's what I know about my Onan > MDJE, 7.5KW, 2-cyl, 19hp, circa 1975 machine. > >

This past Spring my Fischer Panda gen set would bog down under load. There were a few issues with the Kubota engine which were corrected and fixed a small part of the problem. A few weeks later when trying to run the upper AC unit which draws about 16 amps when running and about 60 at start up, it would not start. After significant testing and checking with the experts I finally called the Fischer Panda tech department. They suggested a couple of tests which required a meter which would check the frequency (hz) of the power produced under NO load. With that information they said that my problem was the capacitors in the control box. Sure enough one of the six capacitors in the control box had blown it's top off. And another tested bad. I replaced the bad capacitors and sure enough the gen set now produces like a champ. So, if you have any capacitors in your gen set you should check to see that they are functioning properly. That may fix your problem. Paul On 11/14/2011 8:18 PM, Jim Healy wrote: > Ed, > > Last month, you asked about the governor on an old Onan genset. I'm sorry I missed that discussion in real time, but here's what I know about my Onan MDJE, 7.5KW, 2-cyl, 19hp, circa 1975 machine. > > Before I get rolling, I'll note that some folks responded by telling you that the revolutional speed (rpm) of the machine should ***not*** change as load changes, and that is absolutely "correct" in the big picture. However, electrical load changes will result in a varying mechanical load on the driving diesel engine, and that would allow the machine to speed up or slow down ***in the absence*** of a mechanism to compensate for the varying mechanical loading of the driving diesel. You correctly concluded that the compensation mechanism is the machine's governor. > > The governor "system" is a very elaborate mechanical feedback system. It's goal is to continuously monitor the speed of rotation of the diesel drive engine and simultaneously adjust the throttle linkage to maintain the rated rpm's spec'ed for the alternator end of the genset. > > For my MDJE, the spec is +/- 26 rpm from no load to full load. The nominal spec for rpm is 1800 for my 4-pole machine. My old machine probably varies more than 26 rpm, due to 35 years of wear on the governor's mechanical components. That said, most electrical appliances will run fine from 56 to 63 AC cycles-per-second (some say Hz), so a no load to full load variation of 100 rpm is not the end of the world. > > The mechanical governor mechanism is very complex. In the MDJE, integral with - and part of - the cam gear is a slotted conical plate. The plate has slots machined radially around it's diameter; they fan out from the center. Captive within these slots are ball bearings. As the machine's speed of rotation varies, the ball bearings demonstrate centripetal reaction (respond to "centrifugal force"), and they move towards or away from the center of the gear as machine rpm changes. I'm going to skip the mechanical arrangement of the internal parts, as you and I are probably not going to tear the machine apart, so it really doesn't matter. Suffice it to say that the movement of the plate in response to the movement of the ball bearings is transferred to a rotating shaft that emerges from the front cover of the engine, and becomes the origin of the throttle linkage. A firm spring in the linkage causes the ball bearings to "fall inward" as machine speed decreases. Their mass causes them to move outward as the machine speeds up. A spring mechanism is used to "balance" the set point. Below the set point, more throttle; above the set point, less throttle. As you can see, a very delicate arrangement of physical spinning parts and the theory of angular momentum... > > Attached to the balancing spring is an arm that connects the internal governor components to the throttle arm of the injection pump. The spring's tension is adjusted to "balance" the the revolutional speed (rpm) from no load to full load. The absolute value of rpm (1800 in this case) is adjusted by adjusting the length of the throttle linkage. Achieving a high degree of accuracy of the adjustment requires a high quality mechanical or digital tachometer, or a very accurate frequency meter on the AC output. Most mechanics prefer the tachometer. > > In addition to the spring's tension and sensitivity adjustment, the throttle linkage has no less than 5 places where it's length can be affected and/or intentionally adjusted. Yecchhh!!! > > There are only a couple of things that can "screw up" the governor's performance: > 1. physical damage to the cam gear or the cone/ball bearing governor plate > 2. removal and reinstallation of the injection pump (usually to have it re-sealed) > 3. corrosion/binding in the spring or linkage mechanism > > Generally, unless you've done this before, adjusting the linkage is NOT a user DIY activity. It's tedious, and one adjustment affects all of the others. > Better to find a wizened old mechanic who's worked on these monsters and has machine-specific knowledge to do the adjusting. Assuming parts replacement is not required, you're only looking at 1 to 2 hours of labor, depending on what the mechanic encounters as he works. That labor estimate also assumes that you have removed the sound shield (if you have one) and the flywheel safety cover (so the mechanic can attach a piece of reflective tape to the flywheel to run his tachometer) before the mechanic arrives. Of course, you'll have to put that stuff back, too. > > Finally, once you have the linkage adjusted correctly, spray it with "high temp spray paint. The paint is not primarily to prevent corrosion. It's to provide witness marks in case the linkage ever needs to be removed to facilitate parts replacement in the area of the linkage. > > Well, so, that's what comes to mind. Hope you find it useful. > > Jim > > Peg and Jim Healy aboard Sanctuary > Currently at Stuart, FL, heading SW towards Punta Gorda > Monk 36 Hull #132 > MMSI #367042570 > AGLCA #3767 > MTOA #3436 > > > > > _______________________________________________ > http://lists.trawlering.com/mailman/listinfo/trawlers_lists.trawlering.com > > To unsubscribe or modify your subscription options (get password, change email address, etc) go to: http://lists.trawlering.com/mailman/listinfo/trawlers_lists.trawlering.com > Trawlers& Trawlering and T&T are trademarks of Water World > Productions. Unauthorized use is prohibited.