| [GMCnet] Excessive voltage at 1500 rpm [message #347538] |
Mon, 09 September 2019 07:39  |
Jeff Von Haden
Messages: 3
Registered: June 2019
Karma: 0
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Junior Member |
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Thanks for all the advice on solving my issue with excessive voltage...
Backstory... replaced regulator and still had 16-16.5 volts when over 1500rpm. Alternator tested fine at auto parts store.
I then took the ideas sent and explored.
- Cleaned and tightened the connectors on the alternator, including the voltage sensor wire. No difference.- Disassembled and cleaned the connections at the battery switches, starter solenoid, battery isolator. No difference.- Disconnected the aux battery from the battery isolator. Seemed to solve the problem... I reattached the aux battery to isolator and excessive voltage came back. Disconnected and excessive voltage went away. At that moment I'm thinking the isolator or something in the house wiring is my issue.
With the house battery disconnected from the battery isolator I took it on a test drive at dusk. Was working fine until I turned on the headlights. With the lights on, at 1500 rpm the voltage would pulse from 14 to 16+. At 2000 rpm alternator light was on and if I remember correctly my meter was reading 18 volts (higher than the 16 volts I had seen with house battery attached). When I turned off the lights the voltage went back down to 14, even at 2500 rpm.
I'm not sure what an isolator will, or should do, when you only have the starter battery attached...
I used my meter to test the battery isolator diodes and if I tested correctly, there is no flow in either direction. Is that a possible failure mode?
So my inclination is to replace the isolator and see what happens, but was hoping for your thoughts before I became a parts changer...
And if you think replacing the isolator will help, what are your thoughts on going to a solid state isolator rather than the standard diode isolator?
Thanks for any advice you can give,
Jeff Von Haden76 Palm Beach
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| Re: [GMCnet] Excessive voltage at 1500 rpm [message #347544 is a reply to message #347538] |
Mon, 09 September 2019 08:12  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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First, the isolator IS a solid state device. Second how's to put your meter on the sense wire to the alternator, fire it up, and read the voltage. Then see if that voltage changes when you turn the headlights on. If it doesn't, but the battery voltage goes up, there's a problem in the regulator regardless what Advance had to say. (I am assuming you removed the contacts from the two wire plug on the alternator, shined them, and checked connection before replacing. If you didn't pull the contacts out of the plug, do so. You cannot clean them very well when they're in the plastic shell. Use a jeweler's screwdriver to release the tab holding the contact in and pull the contact out while holding the tab down. I say this because your description describes an intermittent sense wire. If the sense wire feed has been mistakenly moved to the house battery side of the isolator the system would act as you describe when the house battery is disconnected.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Excessive voltage at 1500 rpm [message #347589 is a reply to message #347538] |
Mon, 09 September 2019 17:37 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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If you think that you have a flakey diode in the isolator, simply switch the top and bottom leads on the isolator and you have switched the diodes between house and the engine systems.
If the symptoms do not change forget the isolator and go back to what Johnny suggested.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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