Bad 60 Amp Generator

[Jayo]

I took possession of a 1986 M998 a couple of weeks ago and I Love it.

When it arrived the batteries were dead, and one was leaking so I decided to purchase two new batteries, which I installed fully charged.

When my truck is running the Volt Meter is sitting in the middle of the yellow and never reaches green.

So I reckoned that either the Volt Meter was faulty or that the 60 Amp Generator needed to be adjusted.

I put a multimeter on the generator outputs and cranked her up. Im reading 23.8V on the generator.

I have tried turning the adjustment screw, but its not making any difference to the output reading which sits at 23.8. I can turn the adjustment screw about a 3/4 turn between min/max.

I am reading the same voltage in the battery compartment between the negative terminal and the positive post

I am guessing that I should replace the generator, but I am wondering if there is anything else that I should check first?

I also noticed that the generator gets pretty hot (85 C/ 185 F) after a couple of minutes - is this normal?

Thanks,

Jason

 

[papakb]

HEAT is a bad thing. The 23.8v your seeing is the battery voltage, not the alternator output. A running alternator should output around 27.5 - 28.5 volts which will put the voltmeter gauge needle on the line in the green section of the gauge. I would pull the alternator and remove the rear cover and take a close look at the brushes, brush block, and diodes. Make sure all the wires are connected. If the alternator is getting hot right away it's probably an indication of an internal short. If there's a buildup of carbon from the brushes wearing in the rear of the alternator housing blow it out with compressed air. There's not much you can do with the regulator assembly other than change it out but the large 50 ohm, 50 watt resistor can be replaced individually.

 

[155mm]

https://www.steelsoldiers.com/showthread.php?145991-60-amp-rebuild-I-got-stupid

 

[Jayo]

Thanks PapaKB,

I figured that the reading may be from the batteries and I was surprised by the heat, so I reckon you are right about it being shorted out inside.

Ive purchased a replacement unit and I am going to follow 155mm guide to take it apart and see if I can fix it up as a spare.

HEAT is a bad thing. The 23.8v your seeing is the battery voltage, not the alternator output. A running alternator should output around 27.5 - 28.5 volts which will put the voltmeter gauge needle on the line in the green section of the gauge. I would pull the alternator and remove the rear cover and take a close look at the brushes, brush block, and diodes. Make sure all the wires are connected. If the alternator is getting hot right away it's probably an indication of an internal short. If there's a buildup of carbon from the brushes wearing in the rear of the alternator housing blow it out with compressed air. There's not mucj you can do with the regulator assembly other than change it out but the large 50 ohm, 50 watt resistor can be replaced individually.

 

[Jayo]

Thanks 155mm - Im going to have a crack at following your guide to see if I can repair it or at the very least learn something!

https://www.steelsoldiers.com/showthread.php?145991-60-amp-rebuild-I-got-stupid

 

[papakb]

There are test and repair manuals for the 60 amp alternators on the Southern Automotive site here: http://www.southernautomotive.com/catalog/index.php/

They are also a repair parts source for either the Prestolite or Leece-Neville alternators.

 

[155mm]

Thanks 155mm - Im going to have a crack at following your guide to see if I can repair it or at the very least learn something!

I have told many people that you cant break it any more than its already broken, so you might as well learn something and maybe fix it. Even if you dont fix it, its not any more unserviceable than when you started.