Wazzu
I found your forum while looking for information on my generator it looks like you have a very nice community on gensets here.

I looked through the posts and did not see a post with these issues; if I missed one I am sorry for the trouble.

I recently purchased a used Generac Guardian 12kW, that the previous owner reported had an over speed issue.
PN 0044563
SN 3944196
Hours estimated 125 (no hour meter)
Original Installed December 2005
Fuel Nat Gas
The unit was reconfigured to run of propane for testing and is hooked to a 5 gal cylinder with an 11 inWC regulator.
When I start the generator up it does not make line voltage (only a few volts) it runs briefly and shuts off. The only LED codes are the flashing green and 4 flashing reds, I have not seen the over speed fault code.

I have gone through the trouble shooting process as defined in section 2.3 of the Diagnostic Repair Manual. For Test 4 and Path “B” appears to be the best match.
Wire 2-6 voltage = 95V (>60V)
Wire 11-22 voltage = 3.2V (<60V)
Static Rotor Draw = 0.625A (=0.8A)
Dynamic Rotor Draw = 0.572A (=0.8A)

So I ran Test 7 – Stator Test, all results appear normal except step 22, measure resistance between wires 11 and 33 which is 0.4 ohms (a dead short but there should be no continuity).

I opened the end of the generator to look at the windings; I did not see any sign of shorting or carbon.

Both slip rings had a black build up on them and the resistance was 22 ohms through the brushes. I cleaned the slip rings with Scotchbrite and IPA, and the resistance through the brushes dropped to 18.8 ohms, 18 ohms at the rings (manual says it should be 15.9 ohms for a 12kW).

When the unit was operating I notice an occasional spark coming through the oil cooler fins. I pulled the oil cooler back but I did not see anything in the plenum or on the flywheel, but there were still a couple of sparks that I could see while running during the time that the unit would run before it shut down.

Here are my questions:
1) Is the unit shutting down for an under voltage condition?
2) Based on the troubleshooting tree, it appears that I have shorted primaries on the stator?
3) Since there are no tolerances on the values published in the trouble shooting guide I am assuming my rotor is good at 18 ohms, does anyone have experience with this?
4) The part number in my manual for the stator is 0C7930 it looks like that has been superseded by 0G2822S, is this just a drop in?
5) Do the stator and rotor need to be replaced as a pair or can I just replace the stator?
6) Are occasional sparks in the flywheel area normal?

Thank in advance for any help.
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Peddler
The unit would show a flashing overspeed fault which means no AC output, you may not see this fault if the exerciser is not set. The voltage regulator may be bad but I did not see the results of voltage achieved while putting a fixed 12 volts to the #4 wire which is the rotor. If you AC output goes up to around 90 volts then it is the VR but I do see the excitation voltage as 95 volts which tells me you are getting field excitation. With this the most likely failure would be rotor and stator. Your rotor is probably OK but you have an open in the stator somewhere. The sparks you see are the starter re-engaging because it uses the AC output to tell the unit it is running. Most likely you will have to put on a rotor and stator as they are not sold individually for most units. Good Luck, Peddler
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Wazzu
Peddler;37220 wrote:
The unit would show a flashing overspeed fault which means no AC output, you may not see this fault if the exerciser is not set. The voltage regulator may be bad but I did not see the results of voltage achieved while putting a fixed 12 volts to the #4 wire which is the rotor. If you AC output goes up to around 90 volts then it is the VR but I do see the excitation voltage as 95 volts which tells me you are getting field excitation. With this the most likely failure would be rotor and stator. Your rotor is probably OK but you have an open in the stator somewhere. The sparks you see are the starter re-engaging because it uses the AC output to tell the unit it is running. Most likely you will have to put on a rotor and stator as they are not sold individually for most units. Good Luck, Peddler


Peddler thanks for the response.

You can buy the stator separately for this system PN 0G2822S (was 0C7930), I now have one on order.

The starter re-engaging makes sense, I had not thought about that, I did not hear it but it is pretty loud with the hood up.

-Wade
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Peddler
I think you will find that you can only purchase the stator separately if you have already replaced the rotor and stator previously. That stator 0G2228S only works with the new style rotor. If you are replacing 0C7930 for the first time you need to get the 0G28220SRV which is both the Rotor and Stator. Just to be sure you should check with whomever you ordered the part. Good Luck, Peddler
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Wazzu
Peddler, thanks for the heads up. If the stator and rotor need to be replaced as a unit is there any reason not to go to the 13/15kW set 0G2825ASRV? instead of the 12kW set 0G28220SRV.

-Wade
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Peddler
I never have made that change as the can length is different I think. I think that effects where the generator end support is located in the enclosure. You would have to do some research on that. There really isn't very much difference in power output, not sure it is worth the hassle. Good Luck, Peddler
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