Onan Ky Generator Brush and Slipring Familiarzation




Introduction: Onan Ky Generator Brush and Slipring Familiarzation

About: Making or fixing things is how I relax.

This little KY unit had a damaged engine. The rotor pin was sheared also where it mates to the tapered crankshaft. After repairing and assembling the unit I thought it might be interesting to show what sliprings and brushblocks look like and where they are in this unit. The little KY hides it brushes behind a flywheel on the end of the rotor so it is a little harder than most generators to service the brushes. Due to the unit's weight and varied tools needed most people will find its easier and less frustrating to have this work done at a service center. Besides that you have to remove the unit from its mounting location. That means unhooking AC wiring, DC wiring, Gasoline supply, Exhaust piping and mounting hardware. Not to mention it weighs over 100 pounds. But i will go through the slipring clean process and brush change. The first picture shows the generator with the cover off so you see, from left, engine, generator main body, plastic wind tunneling.

Step 1: The Rotor

This is what the rotor looks like in this unit. It is a hollow shaft with tapered end where the flywheel goes. Then the outer bearing then the brush slip rings. Then the nylon shell where the windings are found. The far right end is an internal taper that seats on the tapered crankshaft end. The pencil point is pointing to one of the two sliprings. These rings are hooked to the windings in the rotor and electricity travels through them from the brushes that ride on them. These rings are dirty and need to be cleaned. The cleaning is easy. Just use a piece of scotchbrite and clean them until they are very shiny. In a later image you will see them clean. To check the rotor just put an ohm meter lead across both rings and see if the reading you have is what the service manual calls for. Usually if a rotor is bad it is because the windings are burned or broken. Then the entire rotor, as a unit, is replaced.

Step 2: The Outter End Housing

This housing is what bolts over the generator main bell housing.
The large hole in the center is where the bearing on the rotor sits. The two bolts the pencil points to is where the Brush block is bolted. The brush block is just a plastic or ceramic housing that holds 2 carbon brushes with wires coming out of them. The brushes are rectangular and made of a carbon material. They constantly rub on the rotor sliprings because they have springs under them in the brush block that push them twords the sliprings. Each brush has a electrical wire coming out of the end of it. That wire has a connector built on it and it connects to a spade on the brush block. The field (+) and field (-) leads from the control module plug on to the same spade as the brush does. So there are 2 brushes. One supply and one return. The wires are all marked on the insulation with letters and numbers. Look where they go before you remove them.

Step 3: Put on the Flywheel.

Once the brush block is in place and everything is rechecked for tightness put on the flywheel. There is a tiny key that aligns the flywheel to the rotor shaft. There is a slit milled in the rotor shaft and machined in the flywheel. The key lines them up. Keys do not hold them in alignment while running. They are only meant to line them up initially. The long bolt that holds it all together is torqued to spec and that torque and the tapered surfaces are what keeps everything aligned while it is running. A magneto is bolted on the end housing and is spaced so it does not rub the flywheel but sits very close to it. The flywheel has magnets in it and they cause a voltage to build in the magneto and this makes the spark to run the engine. The control module can ground out the magneto to shut off the generator if something goes wrong. Now all the plastic is bolted on and we hook up battery and fuel and a meter to see if it all will work. We should see around 120 volts and 60 hertz. There are adjustments on the engine to change its RPM(speed) to correct Hertz if need be.

Step 4: All Done

You can see this is a bit of a project. I did not mention tooling or specs because Those things change as the spec letter changes.
If you decide to try to tackle this buy a service manual. Generators are expensive and must be assembled correctly the first time. You can't unburn windings if something goes wrong. In this unit I had to repair the wiring harness and replace some ends in the control plug that had no pin drag(bad connections). Repair the rotor alignment pin. Repair the engine. This was a 2 month project that I worked on when Time allowed. Everything was checked and ohmed out with a meter. The time and extra checking paid off in the end because it worked first start. I also learned a lot and that made it worth it all.



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    11 Discussions

    I have one of these units that I am pulling from an RV this weekend to diagnose a locked up motor. It rotates about 1/4 inch at the fan end, but then no more. Is there a way to disconnect the generator from the motor easily so I can see where the lockup is happening?

    1 reply

    Oh, forgot to say, nice writeup. I appreciate being able to see what I am getting into for my Mom's RV before I tackle the job.

    I have seen odd things happen to b & s 5000 watt generators the older type with just a small gas tank. I have seen them oddly lose there residual magnetism & therefor when started there is no power. I have had to recharge once by zapping it with a 12 volt battery charger with the proper polarity ,And it worked perfectly fine after. The odd thing is I have seen the same thing happen to a exact same make & model as well ! but the perticular owner though it was burnt out & needed to be rebuilt ,the really odd thing is I never hear of this problem happen to any other brand of generator is this a common thing ? BTW the generator has had other problems like needing new oil seals the front was changed & now the rear sprays oil which is real nice ! & has recently siezed on a really hot day my guess was b/c of difference in temp of various engine parts but it has been freed & still runs I guess you get what you pay for since our other honda can't power a skill saw & it is around 1500 watts go figure !

    how about bump up the voltage? Seems every time I work construction we have 400 feet of extention cord and only 90-100 volts making the journey.

    3 replies

    I wonder what the wire gauge is of your extension cords?.
    If your using multiple cords hooked in series?. Also I wonder what the total out and back combined resistance is?. That is from line prong at gen out to neutral prong back. I bet if you ohmed that out you would be surprised at the total resistance in that supply. Ohms law sees that we have no free lunch when it comes to power transmission.
    see here
    take a look at the maximum current carrying vs gauge of wire. At 400 feet if you using a ky unit 4000 watts you should have 8 gauge wire cords if your pulling 80% of full current at continuous duty cycle. Voltage is controlled by how the generator winding are wound. Engine rpm can be tweaked but the rpm controls the Hertz. U.S. equipment uses 60 hertz.
    Bottom line is the generator is designed to put out a specific voltage / current / hertz.

    Though Power tools usualy have motors with brushes and some can even be ran on 120V DC... Sometimes HZ dosn't matter... What's funny is we (this week) had 2 100 ft extention cords running to a spider box (series) and were running (at least, I didn't care too much wasn't my stuff) 2 air compressors, 2 chop saws, 1 skill saw and 2 screw guns. when most of them were going you could REALLY tell in the screw guns they barely made 1000 rpm. Plus, fire is cool. Lol.

    Your right motors don't care too much if they are hand tools that don't run a continuous duty cycle. A couple of decades ago I heard about a connection issue at a transformer on the street utility pole. There was a factory that ran big presses with 480volt 3 phase motors. They ran 3 shifts round the clock so the presses only went down for maintenance. Every motor on every press had been cooked by the time they figured out one leg was low on voltage and current. I know things seem to work ok but it is hard on them. But we sure don't live in a perfect world do we...

    Are you talking of efficiency in terms of fuel consumption per KW/hour. Or the generating unit itself?

    Since this is an air cooled single cylinder engine there is a limited number of things you can do. The carburator does have an altitude compensator on it. This basically leans or richens the mixture. You could lean it out and monitor exhaust temperature to make sure it's not too lean. If you have a bit more money to spend you could use an o2 meter to set the o2 levels to optimum. Changing to a lighter weight synthetic oil would also help. This controller doesn't support idlematic to my knowledge. Idlematic allows the engine to go to low speed idle. approx 800 rpm then when AC is called for by a device it takes the engine to the run rpm. This unit runs at 3600 rpm all day long. The good news is 5 gallons of gas lasts close to 7 hours at 50% load.