The Green Disease

I've been looking for a 5 to 6 kilowatt 120/240 generator for a while now. You know, as a backup to the backup to the main generator. I finally found one that was close by and priced less than $200. Mind you, I wasn't looking for just any ol' run of the mill 5kw, but an Onan, and preferably the cast iron engine 1800 RPM CCK variety. Yes, I have the well-known and often diagnosed Onan green disease. As I've mentioned in the past, I have a 1950s Onan AJ 2500 watt 3600 RPM generator that my dad bought at a phone company auction back in the early 70's. Then in 2011 I picked up an Onan LK 2500 watt 1800 RPM generator out of a motorhome for thirty five bucks. Then in August 2019 the Onan CCK 3500 watt 1800 RPM generator fell into my lap free from Craigslist. All three of those are 120 volts only though, thus the desire to get a 120/240 unit. You know, as a backup....

This new generator produces 5000 watts, which should be enough to power my house and 1/2 horse well pump in an outage. According to the serial number, the generator was made in February of 1973. It has the words Solid State on the control box cover, indicating it has the infamous "859" circuit board in it. It seems to be working fine though, so I'll just let it keep doing its job.

I've read online that so many of these 859 boards failed early on that Onan came out with a retrofit that reverted back to relay control rather than Integrated Circuit control found on the 859 board. One redeeming quality of the 859 board is a two-stage battery charging circuit, so changing back to relay control would lose that function.

Other than the surface rust on the screw heads, my board looks to be in fairly decent shape, both topside and underneath.

The generator ran great when I went to look at it. When I got it home though, it was difficult to start. I guess that's why the previous owner had already warmed it up when I'd arrived. I always like to see that an engine is cold when I go to look at whatever it is I'm looking at, so I can see how it starts cold. I didn't bother asking the guy to not start it prior to my arriving. Anyway, I found that the electric choke on the generator was just out of adjustment, so I got the mechanism cleaned and dialed in so it starts easily now.

One other thing I found while doing a quick once-over was that the 12 volt fuse powering the control box had, shall we say, an interesting modification going on. Yep, that's aluminum foil.

And yep, there was a blown 9 amp fuse under the aluminum foil.

I wonder how much current a wrap of aluminum foil around a fuse can carry? All was good though, as I happened to find a good identical stubby 9 amp fuse in my fuse stash. What are the odds...

As shown below, two schematics of the electronics were found under the control box and connection box lids.

The generator was wired for 120 volts only when I got it, but I quickly changed it to the 120/240 configuration. The 120 configuration is shown below.