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OnanMan, Generator Tech
Category: RV
Satisfied Customers: 255
Experience:  14 years in the Cummins/Onan distributor network, Level 3 certified in RV, Marine and industrial fie
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Generator is a Generac it starts and runs but it shuts off

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Generator is a Generac it starts and runs but it shuts off after 1 minute??????
Hi I am Don, I am assuming the oil level is ok? Also, if the oil is ok do you have a voltmeter so we can check a few things?
Customer: replied 8 years ago.
Oil level is ok i don't think the oil has more than 100hrs on it i can check my records yes i do have a voltmeter as i am a heavy truck journeyman mechanic.
Ok I am an Onan guy but I have seen my share of Generac...I would like to start by removing the wire that goes to the low oil pressure switch.   It is usuallly by the oil filter.   Remove that wire and run the gen and see what happens...Now understand that this is not my job and I will be back on here about 6pm EST USA time..
Customer: replied 8 years ago.
I disconnected the wires at the filter housing ran it runs fine for 40 sec then shuts down same thing. This is a Generac 4.5kw.
If oil level is above the fill mark will it shut it down i will drain a bit to the proper level and try it know.I made sure that a/c was off for it not to start with a load on while running.
Hmm, next I would check to see if it is making electricity when it runs..
Customer: replied 8 years ago.
I changed oil it calls fo 10w30 started it ran for 40 sec shutdown again, from past experience this generator never did make electricity right off the bat. Once started it would run then it would kick ON the electricity it seems that now when i start it it runs until the kick in mode then stalls.
i checked the microwave clock to see if it comes on and it doesn't.
What actually kicks in the generator to come ON???
The operators manual says to check C1 relay where would this be???
Ok, your coach has what is called an automatic transfer switch (ATS). The ATS has a time delay in it to delay going to the generator immediately. This is to assure that the gen has warmed up a little and settles down before putting a load on it. That is a normal delay that you have been seeing. What I need you to do is find the circuit breaker that is on the gen (or where the gen goes to the ATS) and check for electricity during the 40 seconds.
Customer: replied 8 years ago.
Would this be located within the generator area or in the coach itself.
The generator breakers are on the gen, probably behind the control cover. The ATS is on the coach, you can follow the shore power cord and it will take you to it, you would have to remove the cover and on the cover will be a diagram showing you which wires are for the gen.
Customer: replied 8 years ago.
Mosquitos are crazy have them by the 100 have to shuter down tonite were is the cover you are talking about.
The cover is on the ATS, you have to trace your shore power cord to the box (ATS). Remove the cover and it will have a diagram showing which is the generator wires. If you check at the ATS, have someone start the gen while you hold the meter on the black and white wires (1 lead of the meter on black and 1 on the white).
Customer: replied 8 years ago.
The only thing i could find following the shore plug was a junction box located under the stove inside the coach it's a juction box with 2-white wires together in a barret connector and 2-black wires hooked up together in a barret connector haven't found a cover with wirring schematic on it yet.....
I more less know i don't have power coming out of generator because when i start it it runs fine and just before it shuts down it seems like it surges about 3 different times and then shuts down would this mean that it's trying to put out but something is stopping it from putting out.
While i had it running yesterday i checked to see if clock on microwave would come On it never did this tells me that the generator is not putting out power.
Well the microwave may not have time to show anything when the gen shuts down. We need to find the ATS or the breakers on the gen, Have you looked for circuit breakers on the gen? When you find them, try running with the gen breakers off.
Customer: replied 8 years ago.
I turned off both breakers at generator one is a 20amp the other is a 30amp same thing it shuts down
Ok so you know where the breakers are, remove the cover for access to the breakers and using a voltmeter, check to see if you can read at voltage at the breakers.
Customer: replied 8 years ago.
I only have 4 volts at the breakers.
Ok this is why it shuts down, now we need to find the brushes. On the generator end (opposite the engine), find a cover that can be removed. It might be a cover on the very end or towards the end. What we are looking for is a device that has 2 wires going to it that seem to go into the generator it'self.
Customer: replied 8 years ago.
Found the brushes that run on the rotor still have lots of brushes left it seems.
Ok do they ride in and out of the block easy? How does the slip rings look (where the brushes ride)? They should look like polished brass. Can you ohm the slip rings? Put 1 lead on each slip ring and record the ohms, then 1 slip ring to ground.
Customer: replied 8 years ago.
I get about 50 to 180 ohms depending on my connection on the slip rings.
From slip rings to ground 0 wich is ok.
Customer: replied 8 years ago.
Slip rings do have a dark color what could i clean them with fine emery cloth good enough the brushes slide in and out very easily i would say tha they are about 1/2" in size.
Ok I would try to clean the slip rings with a non detergent brillo type pad and take another reading, if the reading is the same then the rotor is bad..
Customer: replied 8 years ago.
What should be the reading on these rotors????? What am i looking for an ideal reading
I would say around 20 ohms.
At least clean it off and try again...
Customer: replied 8 years ago.
ok thanks for now i will continue probably tommorow.
Ok, I will get on when I get off work ok? around 6PM eastern USA
Customer: replied 8 years ago.
sounds good
Ok, talk to you then..
Customer: replied 8 years ago.
I pulled out generator from rv cleaned the slip rings then checked ohms reading i'm at 15.3ohms now
I put it back together then it would not start and stay running cause i had to disconnect fuel line i ended up starting it but i had to dissconnect oil pressure sensor now i'm back to starting it and still only have 4.3 a/c volts at breakers
What's next boss.
Ok see if you get a "field flash" on the brushes when cranking. It is battery voltage. If you have field flash and you already changed the board then it is a volt regulator unless you have a major failure in the stator which is unlikely since you have residual (4V).
Customer: replied 8 years ago.
I didn't change any board??????? I will check to see if i have bat voltage while cranking at the brushes be back in a few minutes
Ok sorry, that was another customer, but it's ok because we will learn something if you have field flash..
Customer: replied 8 years ago.
I have 3-4volts at the brushes while crancking
Be sure you are on the DC scale, sorry I have to ask even if it sounds stupid. You should have battery voltage...12V.
Customer: replied 8 years ago.
I am on the DC scale i'm only getting 3-4 DC volts.
Ok, I would try jumping 12V to the brushes on the wire NOT labeled 0. And see if the gen makes 120V or so..
Customer: replied 8 years ago.
You want me to put 12v directly to the brushes while engine running
is this right.
Yes, and have your ac meter on the breakers to see if you get voltage
Customer: replied 8 years ago.
be back in 2 min
Customer: replied 8 years ago.
i have 75AC volts when i do that i can hear the generator work while this is happening.
It sounds like the engine bogs down?
Customer: replied 8 years ago.
yes is 75ac volts enough tho???
It might be enough but the engine shouldn't bog down unless there is a load, is the breakers off?
Customer: replied 8 years ago.
no the breakers were both on when i did the test
Ok try with them off, the engine shouldn't bog down
Customer: replied 8 years ago.
ok tried the test again all of a sudden i have 138ac volts so i decided to try it i turned on air conditioner in coach it fired up then after 2 minutes i heard the engine change tone but it's working as we speek.

How does this work does it charge some type of capacitor then it kicks on again when voltage is low i am not sure how it does it's cycle.

So far so good
Why all of a sudden my oil pressure sensor must be unplugged now for it to keep running, it was ok a couple of days ago when you told me to unplug it.

Still running let's keep our fingers crossed....
Ok you may have another problem with the oil switch, if you believe all is well then you need a voltage regulator, my concern was the engine bogging down but the breakers were on so it may have been the load. Let it run, if it doesn't smoke (I think it would have by now) then you need a volt regulator.
Customer: replied 8 years ago.
i just shut it off and tried it again it would not produce any ac voltage so i put 12 volts back on the wires then i saw smoke there is blue wires that come out of a black box that started to melt.????
Is this the voltage regulator??????
is it like a 3 X 3 square?
Customer: replied 8 years ago.
yes it has several spade type connections and i think a little red light and it looks like it could be adjustable with a phillips screw driver.
Yes I believe that is it, see the regulator takes AC from the gen and turns it to DC for the field through a diode or rectifier and I bet that part was went bad and when you put DC on the field it backfed through (the bad) diode. Check for DC on the brushes while cranking, if 0 then definitely a bad regulator.
Customer: replied 8 years ago.
OK so by suppling 12v straight to the brushes by doing this i was doing what the regulator was suppose to be doing wright?????
Customer: replied 8 years ago.
i checked no dc volts at brushes now 0.
Are parts still readilly available for these models.
We have a cummins dealer here that services Onans i guess they could probably get me a regulator.
I believe they are still available, there should be a part number on it. I work for Cummins and we can get generac parts.
Customer: replied 8 years ago.
OK thanks alot Don i will get the part and will keep you posted on the results again thanks for the great help.
Ok I will be here after work..
Ok real quick, if you get the new part (which we know you need anyway) and it still doesn't work, turn off the genset. And I mean put the new part in, have the AC voltmeter in place and start it..If no AC out put, shut the generator down and we go from there..I just hate to see you lose a good part. I am 99% sure that is your problem but there is always that 1% that bites me in the you know what!
Customer: replied 7 years ago.

Hey bud sorry for taking soooooooooo long it was a challenge to find a dealer and get service.

Replaced voltage regulator.Works fine now.

The only thing is not sure if i should adjust a/c output cause conv microwave is weak but yet when we plug in to electrical site microwave works fine???

Gen works cause air conditioning works fine

Ok, see if the microwave works ok all by itself without anything else on. It may be that the microwave is overloading the gen.
Customer: replied 7 years ago.

Everything is off microwave is weak.

The previous owner replaced the original one with a microwave that is called a convexion microwave oven,i guess this one might draw more than the original one??

It might be, does the engine on the gen sound like it slows down any?
Customer: replied 7 years ago.
The gen only lugs down with air conditioner not so much for microwave.
You might need to check the amp draw on the gen when microwave comes on
Customer: replied 7 years ago.
RV is at campground i will not be able to check this out until next week,will keep in touch.
This has gone towards another question that needs to be asked, you don't have to accept this but please go to the forum and ask another question, thanks for choosing Just Answer! Happy motoring...
OnanMan and other RV Specialists are ready to help you
Customer: replied 7 years ago.

I appreciate all of the technical info you gave me, sure is nice to talk to people who know what they are talking about.


Thank you all the best.......

Thank you! and thanks for the accept, it is very much appreciated