Cleaning Onan Slip-Rings and Brushes

[peteco]

While working on my non-functioning Onan generator I came across an interesting find. First of all, the check of the slip-ring resistance showed it to be way above the max spec (22 ohms I think). This is measuring at the plug. I cleaned the slip-rings with Scotchbrite and that brought the resistance down to 21-22 ohms. The value would vary some as I rotated the rotor. I decided to pull the brush block. The brushes had some residue on them. I'm assuming some was from running over the tarnished slip rings and perhaps some from the Scothbrite cleaning process. So I cleaned the brush face with Deoxit (alcohol should work fine too) and reinstalled. The resistance dropped to 18 ohms, and is much more consistent when rotating. So I would say that cleaning the brushes is a key part of the slip-ring cleaning service.

BTW, this service was done as I prepped the unit to sell. The guy buying it had a newer carb so we put it on as my carb had been on for a few years with gas still in it, so I assumed it was gunked up. My major concern was that the voltage regulator had been damaged. Fortunately the unit fired right up and ran well under load.

Just wanted to pass this advice on to those with these generators. If I were going to reinstall this generator I would FAITHFULLY run the unit every month under load. It is just too much hassle and risk to not do this maintenance step.

 

[booster]

All very good advice and certainly true. Old school brush/armature type stuff have always had such issues to varying degrees. If peteco has the stuff needed to do an actual output test it would be interesting and probably show above rated output. I did that when ours was for sale, which was lucky because the buyer was very tech savvy. He saw it running for over 30 minutes at over rated by about 5% measured amps and paid full asking without issue. All it takes is a 12v battery, jumper cables, a length of romex split somewhere to separate the wires for a clamp on ammeter, and outlet box. I had a portable heater at 1500 watts, and an 1800 watt hair dryer running and used a Klein clamp on ammeter. I used the same setup to check inverter output later on but with more batteries.

Time without use or cleaning is certainly and issue, but I think environment also enters into it and I was just getting ready to add such comments to another generator discussion going on.

If the van is outside and near the salt water shore everything will corrode quickly, including the slip rings.

If you live in humid and always damp climate like the south or northwest and store outside they will corrode faster.

Parking outside in the winter in the north can also be and issue because of the cold retention of the metal parts that will get condensation on them as the day warms up and more moist air makes it under the van.

All the more reasons to appreciate the inverter style generators or no generator at all scenarios, IMO.

We sold our Onan, that still ran very well, about 10 years ago and have never missed it for even a minute.

 

[peteco]

Another thought: remove the brush block before cleaning with Scotchbrite. That way no sanding debris gets on or in the brushes. Still clean the brushes as well.

I'm slowly moving towards a lithium system install. Lot's of great info on this forum. I'll be asking questions I'm sure.