F: Genset – AC Generator…

Genset problems – Aug. 2011 to June 2012

Onan Marquis 6500 LP

The genset had been giving me grief off and on for months starting around Aug. 2011. It had been hard starting in moist weather for years but we won’t consider that right now. When I got down to Mazatlan in January of 2012 I was determined to have it at least serviced. So I had my favorite Mexican mechanic pull apart the LP carb and check it out for gumming. Nothing found. He did find that one of the spark plug wires wasn’t crimped tight enough…which accounted for the rough running I’d been experiencing. I wasn’t watching him the entire time but when he finished, it was all clean, like he’d washed the cabinet. Perhaps getting some water where it didn’t belong.

After servicing, each time we started it, it died immediately. Hmm. Didn’t use to do that. Around that time a RV mobile tech (Canadian who comes down every year and works on RVs in the various parks here) stopped by to pick up a thermostat I’d fixed for him, he thought it was the oil. Asked what type we’d put in and then showed me in the genset user manual that the type we’d filled it with would be too thin in the weather we were having in Mazatlan (80°F days) and suggested I put in the recommended type. I couldn’t find 30W so I settled on 40W.  No real change in the symptoms, but each time we’d try to start it, it would run a little longer. Since I didn’t really need it at the time, I put that project on the back burner. A couple months later, planning the trip back up to the US, I knew I’d need the damn thing to run the roof AC since the dash AC has never worked. When we (I’d offered to give my friend Stacy a ride back up to the US with all her stuff) got into the desert of northwest Mexico it was pretty hot and I tried to run it. Funny, it would run for an hour and then shut off the couple times I tried it. One day it ran for six hours before it shut off.

I did some on-line research and found a web site  that gave me some understandable instructions on what to test for and when I measured the resistance of the slip rings I found that instead of 22-28 ohms, it was running at 32 ohms. That can cream the voltage regulator (VR) and sure enough, when I checked the AC voltage it was running at 132Vac instead of 120V +/- 2V. Back to the web I found a replacement VR at ASAP LLC. They have two types, the one I ordered is a direct replacement except the mounting holes only line up with one hole in the frame. But since it’s $86 less then the exact replacement, I could deal with only having one mounting point.

I also ordered a slip ring burnishing tool, the Slip Stick for $22. Was kind of pissed when I got it because it’s just a piece of 12″ X 1/4″ square plastic with some fine sandpaper glued to the end. I could have made that using a round dowel and sandpaper for $1. Well, whatever, today I got ambitious and did the burnishing of the slip rings. There are specific instructions at the Slip Stick link and it only took a few minutes to get the slip rings all clean. Measuring the resistance afterwards showed 22.2 ohms. Great! Then I plugged in the old VR and tested…still showed 132 Vac. So, I remove the bad VR and the two extra mounting screws. The one on the top and the one in the middle of the mounting plate.  Although ASAP says you should mount the new VR with the top mounting screw, with my genset, this is impossible (the new VR mounting wing doesn’t fit there) so I used the lowest mounting screw. Had to remove what I think is the mounting plates middle mounting screw because it interferes with the case of the new VR.

After getting it mounted and the multi-wire connector in place, started it up and checked the output voltage. Back down to a nice 120Vac. Turned on the air conditioner and it’s been running for a couple hours. Nice and smooth.

Here’s some pictures:

The old VR ready for the trash. I’ll clip off the wiring bundle for other uses.

Here’s the tool set needed. Most of Onan’s screws are ‘Star’ security screws. This set cost me $20.

The Slip Stick for cleaning the slip rings, and the extra screws…not needed now.

The new VR there on the right of the case.

It was a pretty easy job…only took around 45 minutes. The big bundle of wires was  a chore to route but there is plenty of room under the cover. Would have cost another $100 or so to have a shop do it. Total cost was $201 for the parts and shipping. Edit: July ’17 – checked the link for the VR, and now they are $319 instead of the $86 I paid back in 2012. Yikes! No longer own that genset though.


Genset remote start failure – May 2011

Several months ago, I discovered that when I would try to start my genset from the dash remote ‘Start’ switch, that it wouldn’t turn over. It would start fine from the start switch on the genset. Being an electrical/electronic guy, first thing I did was remove the remote switch and check it out. Measured fine. Moving down to the Start Controller (SC) on the genset, and after checking that the wires in the connector down there were fine, I removed the cover and then the SC. Since I had it out, and had the time, I created a schematic of the board and measured all the components I could. Everything seemed to be in good shape! But, it still wouldn’t start from the remote switch. Well, it had to be something so I chased down and ordered replacement relays for the three on the board. Since the circuit board is conformal coated for moisture proofing, it was a bitch getting them off. After installing new relays, still had the problem. Hmmm. Guess I’ll have to look closer at the board.

With a magnifier, I finally found that the connection between the socket in the connector was open circuit. Should have checked that first. Seems as though corrosion had eaten clear through the thin metal that went from the outside of the connector down to the board (on the left side of the brown connector shown below). Tried to fix it with a jumper wire and that worked for a few weeks. Then again it wouldn’t start using the remote switch. Pulled the board again and this time I just added a jumper from the open circuited pin #3 solder connection on the bottom of the board to the unused pin #4. Then I moved wire #3 in the mating connector to empty hole #4. Problem solved. So far.


Genset controller with partial schematic. Brown connector on the right side of the board had one of the terminals corroded though…causing an open circuit.

While I had the PCB circuit on the workbench, tested all the passive components, cleaned the contacts, drew a schematic of it, than found the relays online at Mouser Electronics and bought them. Only cost a few bucks. Since the board now has new relays, and a jumper to correct the open circuit, plus all the other maintenance I’ve done on it, I’m hoping I won’t have much more trouble with the Genset for a while.

Genset goes bad at the Lake – Aug. 2008

While up at the lake with the group, I ran my genset whenever I needed to get on the internet with my satellite setup. It a Cummins ‘Onan’ brand with a 6500 Watt output (that is 54 amps at 120Vac).

The third day of use (about an hour per day), it just stopped. No winding down or noises or anything weird before hand, just dead stop. It weighs around 400lbs or so and lives in a cubby hole that is just under the driver’s seat. I enlisted some help and we worked a bit on what we could reach. Found that the main generator bearing had seized up. It was encouraging that after we knocked out some chunks of broken metal, the shaft spun and the starter would spin the engine and generator. Over the next several days, I worked on finding resources and equipment that would allow me to work on the thing myself. Eventually, Gordon talked me out of doing that. I first called Cummins NW here in Portland and scheduled an appointment for two weeks later. Then I called several mobile RV repair services and asked them who they would have work on it. Two of them suggested I have EC Power Systems at 1835 NW 21st AVE in Portland, (503-224-3623) do the job. Around this time, Cummins techs went out on strike.

EC got me in two days later and in the 30 minutes I was waiting out in the parking lot and talking to the other RV’ers that had arrived I heard the technicians diagnose and quote 3 other RV generator problems. These guys really gave me a sense that they knew what they were doing.

Anyway, I talked to my assigned tech and explained the symptoms and history of the genset. He fudged a little on time but didn’t try to snow me or bloat the quote like Cummins had. I already knew that it would cost me around $600 to $1000 from Cummins and they made me think that if I took it there $1200 would likely be the end bill. I decided to leave it with EC.

Here’s their building:


My rig doesn’t have a genset roll out tray like newer rigs have so there has to be some grunt work with pry bars and a forklift to get the thing out of it’s cubby. One interesting thing the tech told me was that those trays, since they have to be open on the bottom, gather lots of road debris and seldom work as expected so he would rather see my type of arrangement that just calls for removal of four bolts and then pry out the genset. He doesn’t need to repair the sliding tray afterwards either.


Here’s the guys getting the thing out:


A little more grunting:


And the bad bearing end of the thing, you can just see the ball bearings (shouldn’t be able to):


Here it is a couple days later all fixed. The tech tells me it runs like glass. Good news.



And here’s my technician, Russ, great tech, did exactly what needed to be done or that I asked him to do and no more and did a great repair job to boot:


I definitely recommend this place for genset repairs and servicing. Their shop charge is $77 per hour, the local Cummins NW shop charges $97. They are a little hard to get to since they’re downtown but the effort is worth it. The genset is very quiet now and my propane/monoxide detector doesn’t go off every hour of use anymore, so I guess that the genset was out of adjustment too…outputting too much unburned fuel. And the cost was $632. In my range and much better then having to buy a new one for $4400.


2 Responses to F: Genset – AC Generator…

  1. coal says:

    That was a pretty cheap repair considering all the work to get the unit out and then reinstalled. I use a Honda 3000- watt inverter type generator on my fifth wheel. Been using it for a number of years, mostly during the winter months up here in Canada. Very fuel effecient and very quiet. Yours is rated for a higher output, but I suspect with your rig and being by yourself, your generator is overkill for your needs. But better to have more power than not enough.
    Good luck on your travels

    Mine is a 6500 Watt, which is more then enough to run 2 AC’s or 3 electric heaters on high. Really haven’t had to use all that energy but it’s nice to know it’s available.

  2. Hafcanadian says:

    EC (Electrical Construction Co.) worked on the old Onan engine that powered our filbert sweeper when I was running the family farm; I don’t recall the issue now, except the engine required a good deal of work. They were an efficient outfit then, 30 some years ago, well before Cummins took over Onan. Seems like they were over on the east bank industrial area back then, but maybe they were downtown. They are the first place to take any problem with an Onan product, though I’m not sure that district is the ideal place to try and take a large RV.

    That’s the shop in NW Portland isn’t it? I’ve had my genset worked on there before. They replaced a bad bearing for me 4-5 years ago.

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