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Kohler 12 Res Natural Gas Gen OS fault

Birken Vogt

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http://www.kohlerpower.com/onlinecatalog/pdf/tp6196.pdf#57

"Check the magnetic pickup connections. Poor
connections may cause an erratic signal or an
overspeed condition."

Of course then it immediately says:

"An erratic signal causes the
generator set to govern poorly but not shutdown."

If it was in my shop I would carefully set the throttle with my hand, look at it with a scope as far back in the wiring as practical, and if the waveform looked good repair or replace the governor/control board, if it looks bad, fix the problem leading to a bad signal. I might also try hitting the control with a signal generator to simulate the signal and see if it still says overspeed.
 

PowerProTech

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So just to clarify... You attempt a manual run and the unit either goes into an immediate OS or briefly starts, doesn't really come up to speed and goes into OS.

I've seen bad crimps on the pink quick connects for the mpu. Unplug them and tug on each connector.

On the mpu side check for AC output when cranking. Don't worry about the frequency unless the unit has a bad hunt ( ie. broken flywheel teeth)

You can access the mpu by removing the bulkhead or sliding the eng/alt assembly back. If you take everything apart just to clean it then it makes sense to replace it. They usually get pretty rusty and covered with metal filings. I personally wouldn't clean it with emery cloth.
 

Trekrider2001

Registered
It starts does not really come up to speed and then shuts down. MPU= Magnetic pickup Unit? aka speed sensor pickup? The magnet on the flywheel looks rusty. Yes I was thinking that if I do take the whole thing apart, I'll change the unit. But I bought a scope today (thanks to the previous post), got a used Textronix 100 MHz dual trace for $125 locally off of Craigslist. I'll scope the sensor when it stops raining (Seattle). It would be nice to get confirmation that this sensor is faulty before I take it all apart. Also, a brief check on the parts suggests that the unit is about $150... better make sure.
 

Trekrider2001

Registered
Ok, got my scope attached, messed around with it (its been a long time since I used one) finally figured out how to capture and measure. I captured 11 acquisitions at 0 v trigger and it measured the high at 10 mV. Yep. When I doubled checked with an old AAA it gave me a high of 1.2 volts (it was a practically dead bat) so I must have done the measurement right. I'd upload a image of the signal, but this system only allows URL base images to be loaded. Anyway, not much to see, just something that looks like noise and the 10 mv Ch1 High recorded. So this pretty much tells me that the pickup is gone open. Funny thing, I put a AC Multimeter on the same connection I see 4 volts or higher being registered when the unit comes to life for its 1 second run. I wonder why this reading is different. Also, I only disconnected one side of the pair that goes to the pickup as the other connector was very stiff, and my luck with these things is I tend to break such tight connection. I wouldn't think that having one leg to the control board still in the circuit would do anything. What do you think? Should I do another test with both disconnected?
 

Trekrider2001

Registered
New test today. I disconnected both leads from the speed sensor and scoped it. Now I get a big spike, followed quickly by an equivalent spike in the neg direction, then the pattern repeats about 1000 ms later. But this second pulse is much lower. The scope marks the first as 30 mv the second at 10 mv. Interestingly, the unit tries to start just the same, so having the wires connected or not has no effect on what it does when trying to start. Does anybody have a trace of what a good speed sensor is supposed to give out? Also, at 1 s between pluses, we are only at 60 RPM, so a long way from overspeed. Looks like the speed sensor is not giving out enough juice. Do you agree?
 

pegasuspinto

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You're over thinking this waaaaay too far. Measure it with a ohm meter, should be somewhere in the neighborhood of 1000 ohms. Measure the ac volts while cranking, should make the VAC specified in the manual. It's just not complex enough to have any other failure modes. It should be in the neighborhood of several hundred hz because it's measuring the flywheel ring gear teeth.
 

Trekrider2001

Registered
Thanks. ohm meter ready = open (well 12 M ohms). So with the results of the trace and the ohm meter, it looks like the thing is fried. And about over thinking... I'm not thinking... just doing what is suggested by you good folks on this forum. Now comes the fun part, getting the generator apart just to replace this unit. Seems the less complex way is to unbolt the whole unit from the base and move it away from the bulk head at the control board. But I'll need a strong back to help... stay tuned... now to order the speed sensor which will probably take a week.
 

Trekrider2001

Registered
Hi, just a final note to close this thread out. I got the replacement speed sensor and installed it and the generator now works! Thanks everybody for the contributions of ideas and guidance. I also like to say to Kohler... could you have made this generator harder to service? my God, if there is a way to makes things hard you sure found it. The speed sensor is easy enough to replace, once you lift the whole unit off its mounts and clear it from the wall to allow removal of the fan shroud. There was a discussion above about removing the wall at the fan end or unbolting the unit from its motor mounts. I did the latter so I did not have to mess with the gas lines and control cables. FYI, when I measured the new speed sensor it gave me 1.56 ohms. The failed one measured open (well multiple Mohms) so that is a simple test before you have to spend the time to take the unit apart. Thanks again everybody!
 

zaphod

Registered
I have a similar problem with my 12RES. Would it be possible to mount a new MPU on the inspection plate under the oil cooler? It's not used in timing, just rev counting. Anyone done this? I move sensors around on car engines all the time. Any ideas?
Cheers,
Zaphod
 

Zephyr7

Registered
You need a suitable mounting location for the mag pickup where it can “see” gear teeth to count. It’s not always possible to retrofit an alternate mounting location since it needs to see teeth, and it needs a very small clearance to those teeth.

I’m curious, why would you want to move the sensor?

Bill
 

zaphod

Registered
Because its wuch a PIA to get to. I live on an island in Maine most of the winter the Generator is under the snow. If I can move it to the top or side I can service it myself. I’ve done this with automotive sensors who location made repair difficult. I suspect the location is to make repair a dealer job.
Cheers, Zaphod
 

drumfield

Registered
Last Subscription Date
12/20/2018
I also like to say to Kohler... could you have made this generator harder to service?
Haven't you figured it out yet? The ultimate goal of design engineers is to make it as difficult as possible for service techs. So where does that leave us? :shrug:
 

Zephyr7

Registered
Because its wuch a PIA to get to. I live on an island in Maine most of the winter the Generator is under the snow. If I can move it to the top or side I can service it myself. I’ve done this with automotive sensors who location made repair difficult. I suspect the location is to make repair a dealer job.
Cheers, Zaphod
If there is already a mag pickup on the unit, see if there are any other holes it will fit in around the perimeter of the housing the existing sensor is mounted on. Sometimes there are alternate mounting locations or locations for backup sensors. I’m not sure if this applies to the little residential units though, I’m more familiar with the big diesels I get to play with at work.

I don’t think you should try drilling and tapping a new hole anywhere. I don’t see how you could do this in the field with sufficient precision. I’d recommend just leaving the sensor where it is if you are unable to find a preexisting alternate mounting location.

Bill
 

Birken Vogt

Email NOT Working
MPU sensors are added to larger units all the time with just a drill and tap but I can't remember if a 12RES has any good spot for it, but I do know it is no fun to change one.
 

zaphod

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MPU sensors are added to larger units all the time with just a drill and tap but I can't remember if a 12RES has any good spot for it, but I do know it is no fun to change one.
I’m going to poke around the starter motor and look inside at the inspection plate. Hopefully I can drill, tap, or JB weld something in place. I’ll leave the old sensor where it is. Let you know. Cheers,
 

zaphod

Registered
I cut away a bit of the flywheel shroud under the oil cooler and fitted anFord
Crankshaft sensor with the aid of a 1/2 in ID Delran plumbing fitting clamped to the cover plate. I shimmed it using a piece of he sensor box 048” works well. Cost $21.95
Woohoo!
 

Trekrider2001

Registered
I just wanted to post a update. I was having some trouble with the generator running the weekly test. I have Flight Systems control board in the transfer switch. They suggested some spikes are coming in on the pair of starting control wires. I twisted these together in a fairly tight twist and routed the pair in a way to stay away from the power lines. The generator now reliably runs its test and started and operated during a six hour power outage yesterday. But I have another strange issue, but I'll start a new thread for that.
 
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