| [GMCnet] Excessive voltage at 1500 rpm [message #347395] |
Thu, 05 September 2019 15:05  |
Jeff Von Haden
Messages: 3
Registered: June 2019
Karma: 0
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Junior Member |
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In June took possession of a well maintained 1976 Palm Beach with the 80 amp alternator/455 Olds.
First two 100+ mile trips alternator worked as it should. On the third trip volts would jump to over 16 and dummy light lit when I went over 55 (2000 rpm. So my short term solution was to drive at 50. Unfortunately after another 100 miles, it would exceed 16 volts when I got engine to 1500 rpm. I attached my voltmeter and it showed a sudden jump from normal to 16.3 volts at 1500 rpm, then drop to about 16 volts at 3000 rpm. At 1400 rpm voltage would suddenly drop down to the normal 14-14.5.
I replaced internal regulator. Exact same failure. Then took alternator into Autozone and alternator tests fine.
Thoughts?
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| Re: [GMCnet] Excessive voltage at 1500 rpm [message #347397 is a reply to message #347395] |
Thu, 05 September 2019 15:47  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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You've probably got a bad/intermittent connection somewhere in the voltage
sense lead to the alternator. When that lead, which carries chassis
battery voltage to the alternator is open, the alternator's regulator
increases the output in an attempt to sense that the battery is receiving
the desired charge voltage. It will continue that process until the output
reaches the internally limited voltage. That should be 18 VDC, but might
be lower, and can even be higher -- I've seen 24 VDC output several times.
Ken H.
On Thu, Sep 5, 2019 at 4:06 PM Jeff Von Haden via Gmclist <
gmclist@list.gmcnet.org> wrote:
> In June took possession of a well maintained 1976 Palm Beach with the 80
> amp alternator/455 Olds.
> First two 100+ mile trips alternator worked as it should. On the third
> trip volts would jump to over 16 and dummy light lit when I went over 55
> (2000 rpm. So my short term solution was to drive at 50. Unfortunately
> after another 100 miles, it would exceed 16 volts when I got engine to 1500
> rpm. I attached my voltmeter and it showed a sudden jump from normal to
> 16.3 volts at 1500 rpm, then drop to about 16 volts at 3000 rpm. At 1400
> rpm voltage would suddenly drop down to the normal 14-14.5.
> I replaced internal regulator. Exact same failure. Then took alternator
> into Autozone and alternator tests fine.
> Thoughts?
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Excessive voltage at 1500 rpm [message #347427 is a reply to message #347397] |
Fri, 06 September 2019 00:51 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I endorse Colonel Ken's posting 100%. I stated this here before. On the way to a rally in Georgia or Alabama I had your exact same symptoms. When I got there I pulled and replaced the alternator under free exchange and had the same symptoms. Problem turned out to be the plugin connector to the alternator. The voltage sense line was not making a good connection. A little squeeze with a pair of pliers on the female terminal fixed the problem permanently.
If you need to prove it to yourself, slide a very thin piece of wire into the connection between the wire terminal and alternator terminal. Run it up into the cab and monitor the voltage from there under failure conditions. For the ground side I would use the ground side on a different wire connected to something on the engine (Not something inside on the dash).
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Excessive voltage at 1500 rpm [message #347430 is a reply to message #347395] |
Fri, 06 September 2019 08:36 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Only problem is, a wire in the connector is likely to make it connect.
--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 #347438 is a reply to message #347430] |
Fri, 06 September 2019 15:38 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Johnny Bridges wrote on Fri, 06 September 2019 08:36Only problem is, a wire in the connector is likely to make it connect.
--johnny
That is part of what I was hoping for. If the voltage problem went away we could assume that the added wire did just what you suggest and that and the connection was bad. I was hoping that he would use two meters. One where he is metering now and a second to the added wire.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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