Dayton 4lm38b with generac rotor/stator no power output

mjr46 · Sat Jan 25, 2020 6:59 pm

tbonini wrote: ↑
Sat Jan 25, 2020 6:18 pm
I guess that your Gen is different from mine because I don't remember being able to see the slip rings until I removed the rear bearing carrier and then they were fully exposed. To clean mine I sprayed them with electrical contact cleaner and then removed any stubborn spots with crocus cloth. If you can see yours, what do they look like? They should be copper colored and somewhat shiny. If they are copper colored and dull they are probably ok but if they are black like mine were, then they need to be cleaned.

they're a little dirty with some streak lines....definitely not totally shiny/copper colored....i will clean them but i'm skeptical that this is all that is wrong.

Birken Vogt · Sat Jan 25, 2020 7:07 pm

Ohm across each brush/slip ring interface, rotate the engine to several different positions and check again. Should be near zero ohms but you may see as much as a couple ohms in the real world. Best to drill down to an actual problem before throwing parts at it.

Sat Jan 25, 2020 8:16 pm

mjr46 wrote: ↑
Sat Jan 25, 2020 6:59 pm

tbonini wrote: ↑
Sat Jan 25, 2020 6:18 pm
I guess that your Gen is different from mine because I don't remember being able to see the slip rings until I removed the rear bearing carrier and then they were fully exposed. To clean mine I sprayed them with electrical contact cleaner and then removed any stubborn spots with crocus cloth. If you can see yours, what do they look like? They should be copper colored and somewhat shiny. If they are copper colored and dull they are probably ok but if they are black like mine were, then they need to be cleaned.
they're a little dirty with some streak lines....definitely not totally shiny/copper colored....i will clean them but i'm skeptical that this is all that is wrong.

It may not be the ONLY problem, but 4X the proper resistance will cause the field not to energize during cranking and create the issues you are describing.

Troubleshooting is taking 1 step at a time and working your way out. Heading multiple directions all at once is expensive and usually ends in failure...

Rotor resistance on these units should be around 9-12 ohms with a good rotor and clean rings.

mjr46 · Sat Jan 25, 2020 9:31 pm

Chris wrote: ↑
Sat Jan 25, 2020 8:16 pm

mjr46 wrote: ↑
Sat Jan 25, 2020 6:59 pm

tbonini wrote: ↑
Sat Jan 25, 2020 6:18 pm
I guess that your Gen is different from mine because I don't remember being able to see the slip rings until I removed the rear bearing carrier and then they were fully exposed. To clean mine I sprayed them with electrical contact cleaner and then removed any stubborn spots with crocus cloth. If you can see yours, what do they look like? They should be copper colored and somewhat shiny. If they are copper colored and dull they are probably ok but if they are black like mine were, then they need to be cleaned.
they're a little dirty with some streak lines....definitely not totally shiny/copper colored....i will clean them but i'm skeptical that this is all that is wrong.
It may not be the ONLY problem, but 4X the proper resistance will cause the field not to energize during cranking and create the issues you are describing.

Troubleshooting is taking 1 step at a time and working your way out. Heading multiple directions all at once is expensive and usually ends in failure...

Rotor resistance on these units should be around 9-12 ohms with a good rotor and clean rings.

i know all about trobleshooting, i'm an auto tech and do such every day, which is why i haven't bought any parts yet i want to verify what and where the issue is......i just don't work on generators which is why i 'm here and need your guys help to guide me in for the landing as i don't have any manuals nor tons of working knowledge on these systems but i can understand testing with a multimeter, as i do elec troubleshooting on cars everyday of the week. i know with your guys help and knowledge of the specs on these units that i can hone/narrow the problem down......i really appreciate the help!!! it's my moms generator and i have to travel down the road a few miles each time i get a new test from you guys, so it's not as simple as walking out my front door so it may take me some time....tomorrow i plan to clean the slip rings and redo the resistance test as wife just got home with my car and i now have my auto-ranging blue point dvom back!!! :)

mjr46 · Sun Jan 26, 2020 12:18 pm

Okay guys......just tested the 3-4 pin -rotor resistance with my good dvom 45-50 ohms of resistance so with 400 grit sand paper i polished the slip rings while motor was running and then cleaned the brushes.......i now have 9.8-10 ohms of resistance....so guess the slip rings were very dirty.......however i still have the same issue...no voltage output.....and when i hear the chirp i see the voltage regulator is lit but appears kinda dim.......i've been reading that excessive slip ring resistance can overload/work the AVR and thus short it out....???? anyway where do i go from here???

Mon Jan 27, 2020 8:57 am

I would like to stop and take a moment to make sure everyone knows how dangerous cleaning the slip rings with the motor running can be! Please do NOT use that method...

It sounds like your main problem has been cleaned up. I would test to see if you can manually excite the field be taking a jumper wire which runs from the battery positive terminal and when the unit first starts up, briefly jumping it to the 4 wire terminal. This should manually excite the rotor and if the AVR takes off and starts producing normal power, we know that you have a field excitation issue. DO NOT leave the 12V connected for more than a second when the unit is running...

mjr46 · Mon Jan 27, 2020 12:09 pm

yes I know it wasn't the best way/safest, but was the quickest and if it helps the piece of sand paper was affixed to a wooden chop stick.........not like I was going to put my hand anywhere near that puppy..lol I will do the test you described and report back this evening.....thank you so much for the help Chris!!!

mjr46 · Mon Jan 27, 2020 6:27 pm

Chris wrote: ↑
Mon Jan 27, 2020 8:57 am
I would like to stop and take a moment to make sure everyone knows how dangerous cleaning the slip rings with the motor running can be! Please do NOT use that method...

It sounds like your main problem has been cleaned up. I would test to see if you can manually excite the field be taking a jumper wire which runs from the battery positive terminal and when the unit first starts up, briefly jumping it to the 4 wire terminal. This should manually excite the rotor and if the AVR takes off and starts producing normal power, we know that you have a field excitation issue. DO NOT leave the 12V connected for more than a second when the unit is running...

just did the test.......no go......makes a decent spark when i touch it to it briefly....and continues to not output......what next??

Mon Jan 27, 2020 7:01 pm

Next logical step would be to remove the 4 wire from the AVR completely and energize it with 12V while the unit is running, but this time leave the 12V on it. During that, measure AC voltage on the output at the breaker and also on the 2 and 6 wires (together, one lead on 2, the other on 6) and see what you get....

mjr46 · Mon Jan 27, 2020 7:08 pm

Chris wrote: ↑
Mon Jan 27, 2020 7:01 pm
Next logical step would be to remove the 4 wire from the AVR completely and energize it with 12V while the unit is running, but this time leave the 12V on it. During that, measure AC voltage on the output at the breaker and also on the 2 and 6 wires (together, one lead on 2, the other on 6) and see what you get....

all right..give me about 30 min and i'll do that... thanks!!! do i disconnect the 2 and 6 from the avr or just measure it while still connected to avr?