Onan 6.5 Will Not Stay Running, Blows Fuse

[87Itasca]

Hi all, have been making progress getting the Onan generator on my Windcruiser running. Put a new carb on it since the old one was shot, and I could not locate a rebuild kit. Had no spark, so today I replaced the points, condenser, wires and plugs. When I hold the start button down, it now starts right up, but will shut off as soon as I let off the start switch. If I keep the switch depressed, it will run for about 5 seconds, then blow the 5A fuse on the circuit board. Then it does nothing until I replace the switch.

The model is a 6.5NHE-1R/26101A, where do I go from here?

I tried disconnecting the oil pressure switch, and then grounding it to the head cooling fins to see if it would make a difference (thinking perhaps the pressure switch was bad) but it made no difference. I did change the oil/filter, and the level is good.

[Rickf1985]

Dave is our generator expert but he has not been on here much lately. I know he has been swamped at work. Look up the manual for that generator and go through the troubleshooting section, I seem to remember hearing about this problem and a solution in the past through that route.

[87Itasca]

Appreciate the heads up on the service manual Rick. I downloaded it, plenty of good info.

I'm surprised there is no mention of troubleshooting the blown 5A fuse though. It only says to replace the fuse if blown. Hopefully Dave won't mind being of some assistance here when he gets the opportunity.

I'm hoping it's just dirty slip rings, or a bad board, vs. a shorted rotor or bad stator

[Rickf1985]

Can't be of much help here, I am great on engines but just as in the dark on generators as everyone else. I have not had time to look at the manuals but is there a troubleshooting tree? Sometimes you have to follow a long winding path on those trees to get to the problem and it is tempting to take shortcuts, you cannot take shortcuts on a trouble tree.

[lemortede]

I can tell you that when I had a similar problem it was a ground issue.
The idle solenoid had a short. Took me some time and observing to find the problem.
Went through a ton of fuses.

[87Itasca]

Hi all,

Stumbled across a great troubleshooting guide here:
http://www.flightsystems.com/troubleshooting/

Figured I'd post it to help future members. It doesn't specifically go into troubleshooting a problem with the 5A fuse blowing, but, armed with a couple dozen fuses, hopefully I can power through this troubleshooting guide to find the problem.

One question, where is the voltage regulator/connector located? I don't recall seeing it when I was replacing my points and such the other day. There is only so much access one has while the unit is hanging down from the back of the RV.

[87Itasca]

Well, I think I've managed to kill my control board. Put in a slo-blow fuse yesterday and it ran (with me holding the start button down) for a good 30-45 seconds before popping the fuse.

Put another fuse in, verified that it still would crank (it did) and went home.

Came out with a helper this morning to check to see if I was getting any voltage while it was running (now that it would run long enough to verify), and nothing. Pulled the fuse holder out, and sparks went everywhere for a split second. Fuse wasn't blown. Replaced it with another just to see, and nothing.  Crap.

Going to attempt to verify that it's actually bad this evening, per the troubleshooting guide I found:
"
If it does not crank, check the control fuse (5A Slo Blo, except models with electronic governor 10A). If the fuse is good, jumper the positive battery post to the coil terminal on the start solenoid. If the engine cranks, there is a poor connection, wiring damage or the control board is defective. If the engine
cranks when the BATTERY POSITIVE pin is jumpered to the START SOLENOID pin, the board is defective"

[tmsnyder]

It may just need the slip rings cleaned, the board will shut off the generator if it isn't making power.  Can't hurt to clean them, I used a piece of maple ripped to 1/4 x 1/8", wrapped in fine sandpaper to clean the slip rings on mine while it cranked.


If you do end up needing a control board, the ones from flight systems, link above, is good and much less money than the OEM replacement.  I ended up needing one in mine, it wouldn't even crank, lots of corrosion was on the board.  About $100, great company, made in USA.


After a new board, cleaned up carb, new fuel pump, cleaned slip rings, oil and filter change, governor adjustment ...  runs good. 

PS:  While troubleshooting, disconnect the remote wiring from the generator just in case the signal to shut down is coming from a problem at the remote switches in the dash .  It's the harness that is on the right side of the board as you look at it, just unplug it, there's probably 4 wires there.

[87Itasca]

Where do you access the slip rings? I've no idea where they are.

[87Itasca]

Okay all,


Found the slip rings after work. Measured 28.7 Ohms between the terminals. Pulled the brushes out, rings were pretty grungy.  Gave them a good cleaning with a scotch-brite, put it all back together, it measures 11.1 Ohms.  What the heck?  Did I clean them too much? Anything under 20 is a sign the rotor is shorted, correct? Could it be rewound if so?

Genset still will not start and run. It will start now, I had to repair a loose connection, but it will not continue to run unless I keep the start button depressed. It will also still blow a fuse, but it takes a while to do so.

[tmsnyder]

Flight Systems sells slender abrasive tipped sticks to poke in through the vent slots on the end of the generator and clean the rings while cranking or running the generator.  I made mine from a 12" long stick of maple and some sandpaper b/c I couldn't wait for shipping time.  If I'd known I would have bought them at the time I bought the control board.  I never removed the brushes, only 11 hours on the generator so figured they were probably fine .

How did you clean the rings, with generator rotating? The ohms might be low if you're reading them directly at the slip rings instead of at the board where the troubleshooting guide indicates b/c it wouldn't include the resistance at the brushes, connections, etc. You couldn't have over cleaned the rings, not possible. 

Also I don't know what kind of ohm meter you have but check the calibration of your meter, make sure it's 0 ohms when the leads are shorted together, and make sure the battery in the meter is good.  They read goofy when the battery gets low.


I would step back and read through the troubleshooting steps one by one here starting at the very beginning and going word by word:

https://www.flightsystems.com/pdf/onan-rv-troubleshooing-guide.pdf

[87Itasca]

The digital meter I used is a Fluke, with a recently replaced battery.  It measures 0.1 with the leads shorted.

I measured from the terminal of one brush to the terminal of another, per this article:
http://blog.goodsam.com/cleaning-generator-slip-rings-and-brushes-part-19

I fashioned various pieces of scotchbrite to a popsicle stick (after eating the popsicle, yum) with a rubber band, and replaced as needed. Didn't get them 100%, but it's clean enough I can see a reflection across the width of the rings, and it shouldn't present an issue. They didn't seem to want to get any cleaner than this. I was chasing daylight at this point, so I wrapped it up. I just held the start button down as I cleaned each ring. Never nicked a finger, but I almost lost the stick a couple times. 

Tested it with a helper this morning, holding down the START button, I am getting 25-26V in the coach. What might this be indicative of, if anything?

[tmsnyder]

Ok that's a good meter, great.  There's some things to look at using the flight systems troubleshooting guide https://www.flightsystems.com/pdf/onan-rv-troubleshooing-guide.pdf


The guide above says "The most common complaint is that the engine starts but will not keep running when the START switch is released. This happens because the control board will not allow the engine to continue running if the generator is not producing voltage or if the oil pressure signal is not present."  Did you check the oil pressure signal?


If it's not making voltage, the flight systems troubleshooting guide above wants you to check the resistance including the resistance through the brushes and wiring, it reads:


Check the field circuit by unplugging the regulator and measuring the resistance between pins 9 and 10 of the regulator’s mating plug. This reading should be 22 to 28 ohms. If this reading is too high, check the brushes and/or clean the slip rings (use the Slick Stick, or a similar tool). If this reading is too low, there may be a short in the rotor. Also, check the resistance from pins 9 and 10 to ground. This reading should be very high or infinity. If not, there is likely a ground in the rotor. If these readings are all good, the regulator is likely defective.


So that's something to check, I would really just work your way through that troubleshooting guide, it's a good one.

[87Itasca]

Per my testing, it would appear the control board is defective. Per the flight systems troubleshooter, the system cranked when I jumped the battery post to the coil terminal, then it also cranked when I jumped the battery positive to the start solenoid pin. New flight systems board is ordered, so fingers crossed that wil fix the problem.

[87Itasca]

New board is in!


Starts right up....and blows the 5A fuse.   

Before, I could crank it with the old board and as long as I didn't have the start button held down for more than 20 seconds or so at a time, I could run it 5-10 times before it would blow.

Now, it blows after about 2 seconds. Nothing has changed except for the board.

The gentleman I spoke with at flight systems said the rectifier that comes with the kit is generally the fix for this. The issue is, my genset is the NHE version, not the NHEL, and therefore does not have the bridge rectifier. I can see in the parts diagram where one would be, but I do not have one. I'm officially out of ideas at this point.

The flight systems guide has a troubleshooter for the voltage regulator, but the spokesman said since mine is an early spec with a transformer in place of the regulator, the information does not apply.

[87Itasca]

IT LIVES!!! 


For anyone who may stumble across this in the future, the NHE units DO have a rectifier, it is under the cluster of wires in the back left of the control panel, under the ring where a series of wires leave the panel.


I replaced the rectifier, and it fired right up!  Puts out 121V with no load, and 110V with both the AC units, fridge, and an alarm clock running. Does this seem reasonable?  I tried to check the Hz, as my multimeter has that function, but it just says 0.00, which is obviously not correct.

[legomybago]

I thought they put out 220v? Hm?

[87Itasca]

Mine is designed for a 30A 120V service, with an extra 20A breaker for the rear AC.

Newer coaches with big gensets run the 220V 50A service, but mine's a little too old for that.

[MotorPro]

I thought they put out 220v? Hm?

No ,you can move a few wires in the generator to get 220 but never in a rv. Unless you want to fry your electric system.

[tmsnyder]

Yes that's normal, there's a service manual with the specs but basically with no load it will run at more than 60hz and more than 120V.  Under load it drops down to near or slightly under 60 hz and 110v or so.  It's the nature of the beast.   

I set up mine to give about 130V at no load, it runs at 110V which the A/C on.

Yours sounds perfect, leave it where it is.


Congrats!!


Without a frequency meter, you might install a musical instrument tuner on your smartphone and see what frequency the motor is running at by listening to the sound of the exhaust.  You can probably do it from 10 feet away, don't stick your phone in the tailpipe  They read out in hz generally. It's a 4 stroke, 2 cylinder, so it should fire on every revolution and should sound close to 60hz to the tuner, I think, never tried it but I think it would work.

Be forewarned though, if you try to adjust the frequency by making changes to the governor, it will change the voltage.

[87Itasca]

Interestingly enough, I'm noticing when on the genset, the A/C units runs fine. Here recently, they would run for a while, go into "low power" mode for a bit, then cut back on. Running this on an extension cord hooked to a 15A adapter on a 20A breaker isn't the best way to get the power they need to them either, which is likely partly responsible for the melted terminal I noticed on my extension cord. At the end of the week, I'm getting a proper 30A connector wired to the shop that I can leave it plugged into. That should help greatly.

All in all I'm quite happy. It runs well (ran it for four hours yesterday), and has no problem taking the load. I figured best run it for a couple hours for a couple days to clean up the slip rings a little and get everything back in the groove.

So glad I didn't need to replace the transformer or rotor.

On these, it's best to disconnect the load, then let it run for a couple minutes to "cool down" before it's shut off, correct?

[legomybago]

On these, it's best to disconnect the load, then let it run for a couple minutes to "cool down" before it's shut off, correct?

I always have. I also like to let them run for a few minutes before powering up. I also install a fuel shut off just before the pump. Before you know it, you'll find yourself saying, "I haven't ran the genny in 3 months"! The fuel has been setting in it crapping up things that whole time. I like to shut the fuel off, and let the Onan run itself out and shut down. I haven't had a carburetor/fuel related issue since practicing this...MO