So I started to work on why my alternator is charging so high. The engine is from a 77 city bus so I assume it is native to 24v but my bus is a 68 and is all 12v. The starter seems to work fine so I assume it's a 12v version. When I start the bus it stays around the 12v area. After awhile the volt meter kicks way up and goes over 16v. This time frame is quite puzzling to me as the day I picked up the bus the volts remained just fine all day long for hours until I turned the lights on. That seems to be a tilt factor to when it starts over charging even if I shut them off it stays up way high. If I rev up the engine then the volts go even higher and peg the volt meter. I turned the voltage regulator all the way down and I can only get it down to 15v. I'm concerned I have either a 24v alternator or something quite flakey in my system. I have the original gm service manual but it mostly just talks about a non charging alternator. I'm not very familiar with these older units. Is there a way to confirm or deny if I have a 12v or 24v unit? Once I confirm the model then I can trouble shoot better.
Thank you,
Eric
Sent from my Droid phone
I think you have a ground problem between the alternator and voltage regulator I fought that on a 4905 for hours it was a 24V system and would go over 30 volts
good luck
Could be a bad 12v feed to the alternator, also. When I replaced my alternator and regulator, I had to run a new wire directly from the batteries to the regulator because
the original system caused a fluctuation in the field voltage and cause it to act weird. Adding the new wire from the batteries cleared it up and it's been working great
for 10 years now. The new regulator was a solid state model.
You can check out both of these possible scenarios by making up a proper gauge temporary jumper wire.
Ok, thank you all
I might get a chance today to try these out
Eric
Sent from my Droid phone
Don't go by the panel voltmeter, voltage at the batts is all that counts. Put your hand VOM there and check it.
Panel VMs can be off for many reasons since they are a long distance from the batts and panel gages are infamous for poor grounds.
I got it figured out! :-) the p.o. Hooked it up wrong. He hooked up the positive from the regulator to the relay post on the alternator instead of the positive on the alternator. I hooked it up right and now I have proper voltage! Yeah! 8)
I didn't hook up the generator relay. Anybody know what that's for? According to the manual it's hooked up to the blower relay. That's no longer in my unit so do I need this? Is this a terminal that only activates the relay when the alternator is running?
Thanks
Eric
Sent from my Droid phone
The R terminal indeed activates a relay only when the alternator is running. It can also be used to run a signal to a tachometer. The relay is usually running stuff that you don't want on if the alternator is not working, like the fan blowers for the AC and heater. On MCI's it also is hooked to the low air switch.
Brian
Oh ok. Thank you. So I don't have a tach yet. The relay terminal sends out a pulse to hook up to the tach?