Portable Generator Repair

[Friartuck]

Folks,

This is a question pertaining to a Generac 5500 portable brushed type generator. The particulars are:

1. It is a brushed rotor where regulated DC is provided to the rotor's slip rings via two brushes,
2. Both stator windings measure under 1 ohm of resistance and are the same for both windings which is consistent with the service manual values of 1.2 or so ohms (hence low resistance),
3. The excitation winding measures 3.2 ohms,
4. No shorts in windings to case,
5. Rotor had one wire break at one of the two slip ring contacts and was re-soldered. Rotor now measures 62 ohms (at the slip rings), seems consistent with many hundreds of feet of small gauge wire. Rotor also measure 30 ohms per side, which seems right given the total of 62 ohms.
6. 10 HP B&S Engine repaired and runs well (original problem was piston ate a valve). Unit had 30 hours on it before engine failure.
7. When running AC output measures about 2 volts, well under the 220 it should.
8. Excitation measurement is about 1.6 AC volts and about 1.6 DC volts from the regulator to the brushes.
Q1. This seems that the residual magnetism in the rotor has been lost. Can it be brought back by supplying DC from an external source like a 12 volt battery to the brushes? Is there another way to revive the magnetism in the rotor without taking the unit apart? The unit spent at least two years out of service.
Q2. Could I temporarily supply DC to the brushes and run the unit to verify that the alternator at least produces AC before I invest any more time and $$ into this project?

 

[rlitman]

You can flash the rotor with a corded drill plugged in and the engine running. Look on youtube.

 

[frankzlt1]

to reestablish the rotor semi permanent magnetic field you need to just flash the slip rings some how with a 12v dc battery by its self not in a car running. make sure you got the polarity right. just take the jumper wire and just put it on for only a split second it will spark a little but that will wake up the rotor.

 

[nick2010tundra]

Generac has a video on youtube using a corded drill to do this. Can be done without taking apart the generator

 

[Cruzingoose]

Follow the two wires from the brushes. They usually go to a rectifier. Replace the diode or bridge assembly. How it works....As the rotor spins, the tiny amount of magnetism generates a current that is fed to the slip rings. From there this AC current is rectified to DC. This feed back re-enforces and builds itself up untill the rotor is saturated. Then the genset will output power. This is a self regulating system and works fairly well, unless ther genset is severly overloaded. Excessive current usually burns and shorts the diodes and no more DC on the rotor.

 

[Friartuck]

Wanted to follow up on this generator problem (and for the archive). Using the drill method did not flash the magnetism back. Maybe its the difference between brushed and brushless versions. I used a small motorcycle battery and connected the positive and negative leads directly to the brushes while the unit was not running. Gave it two make-break connections and reconnected the regulator wires back onto the brushes. Generator works fine. 124 VAC output. Now I have to adjust the frequency which is directly proportional to speed. Thanks for the suggestions.