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Hummer Knowledge Base

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Testing the 24v Alternator:

My humvee alternator wasn't working when I got it so I got real keen and pulled it apart. They seem to have a reputation for poor reliability but this may be because of a design problem.

I found that the regulator bit (at the back where the connections are and behind the fan) was the problem and was a relatively easy fix. Remove all the allen headed setscrews at the back of the alternator and pry the end cover off (there is an O ring in behind the cover to seal it which sticks). There are also 3 wires which have to be unplugged (they are labeled, both the wires and the terminals on the PCB.) What I found inside mine was a lot of grey powder and a resistor thingy floating around loose. The PCB is encased in clear epoxy and two wires come out of the epoxy which are connected to the ends of a coil which 'should' be inside a gold coloured heatsink. The grey powder came from the insulating material inside the heatsink which had shaken out due to heat and vibration. The wires to this coil had broken due to the stress and vibration as well which probably saved the voltage regulator. To remount the coil inside the heatsink I made two cuts in the heatsink at right angles to the hollow centre with a hacksaw, placed bits of cardboard with slots in them in the hacksaw cuts with the coil suspended inside the heatsink, then I filled the ends with epoxy and allowed it to set. Then I checked that the coil wasn't touching the sides of the heatsink with a multimeter and then connected it to the PCB with new wires. Reassembled the alternator and installed it back in the Humvee, started it up and it worked!

Peter J.
Sydney, Australia
M1026 Humvee

One sure way to test an alternator in the field that I learned from my uncle "Luckey", A retired GM mechanic, is to put any peice of metal on the back of it while the engine is running and if the altornator is charging the metal will stick to the magnitic charge generated by the field if it doesn't stick to the magnetic field it isn't charging.

'96' silver wagon

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