Home » Public Forums » GMCnet » Electrical problem
| Electrical problem [message #146175] |
Tue, 11 October 2011 15:25  |
Bill W
Messages: 21
Registered: July 2005
Location: Sheboygan, WI
Karma: 0
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Junior Member |
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I need some guidance in figuring out what's going on with the voltage in my '77. Started it last week and everything was fine. While idling I pumped up the air bags. My digi-panel alerted me to the fact that voltage had dropped below 11 (went red), but the gen light on the dash didn't come on. Next day, everything was fine again, but after about 10 minutes of driving, same readout on the digi-panel. After that, only red on the digi-panel, still no gen light. Replaced alternator (6 year old Duralast from Autozone) and charged battery (it was a bit low). Now, voltage is steady but still low: 12.89 at battery when not running, 12.77 at battery when running. Battery tests OK. I cleaned grounds and tightened connections. What's next? Another alternator or ?? I do have the standard battery disconnect switch on the firewall and boost switch on dash. Thanks!
Bill Wetzel
77 Royale 26RB
Sheboygan, WI
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| Re: Electrical problem [message #146225 is a reply to message #146175] |
Tue, 11 October 2011 20:20  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Yes take a VOM with engine running and meter at the output terminal of the alt, which is same as centre terminal of the isolator. if in the upper 13s or low 14s you should be good. Then check each of the two other terminal of the isolator to ground. These should be just a touch lower but in the high 13s I believe. If lower on either side the isolator is bad. It can them be removed after diconnecting the negatives at both batteries and tested out of circuit with an ohm meeter to check the diodes.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Electrical problem [message #146241 is a reply to message #146225] |
Tue, 11 October 2011 23:00 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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After doing John's suggestions, if the voltages were OK, (14.7 on the center terminal of the isolator and 14.0 the other two (give or take a few 10's of a volt)), then read the voltage across the battery. IT should match what you read on the upper and lower terminals of the isolator. If it doesn't then you will need to back up and find out where you voltage drop is.
I'm also wonder if the digi-panel is lying to you. I wonder where the digi-panel is attached and sensing the voltage? Did you get your ground for the digi-panel off of the instrument panel?
Finally have you looked at the fusible link wire that everything runs through? I have seen a few of those go bad.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Electrical problem [message #146252 is a reply to message #146246] |
Wed, 12 October 2011 00:52 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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The fusible link is a black 16 gauge piece of wire about 6 inches long. It is located under the passenger side hood. One end is connected to the "Battery Pick Up Junction Block" which is that BIG single terminal, which I think is a 5/18 x 18 stud, and a medium size terminal on the horn relay/buzzer.
If you do replace it make sure you get fusible link wire. Auto Zone has it in 6" lengths in a bubble pack in the electrical section for about $3.00. Throw a volt meter across it and see how much drop you have. Also wiggle it around. I have seen a few of them badly deteriorated.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Electrical problem [message #146310 is a reply to message #146301] |
Wed, 12 October 2011 14:24 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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If your Voltage is that high, the internal regulator in the Alternator is
defunct. Have it rebuilt. Now. Do not run it like that. Your digi panel
won't like that much voltage nor will any other of your GMC components.
Remove the isolator connections and check to see if the diodes have failed
by first checking them with an ohm meter in one polarity and then in
opposite polarity. They should have almost no resistance in one direction,
and nearly infinite resistance in the other. If either post shows continuity
in both directions, replace the isolator with one rated as many amps or
higher than the one you have.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Wed, Oct 12, 2011 at 10:50 AM, Bill Wetzel <billandpatwetzel@gmail.com>wrote:
>
>
> OK, now I'm confused. Voltage at the isolator (middle alternator terminal)
> and at the back of the alternator is very high, between 45 and 50. What
> gives??
>
> Bill
> --
> Bill Wetzel
> 77 Royale 26RB
> Sheboygan, WI
> _______________________________________________
> GMCnet mailing list
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| Re: [GMCnet] Electrical problem [message #146312 is a reply to message #146310] |
Wed, 12 October 2011 14:26 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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Or, the voltage regulator might still be all right but the sensor lead to the alternator that tells it to keep stepping up the voltage might be bad or a loose connection.
Emery Stora
On Oct 12, 2011, at 1:24 PM, James Hupy wrote:
> If your Voltage is that high, the internal regulator in the Alternator is
> defunct. Have it rebuilt. Now. Do not run it like that. Your digi panel
> won't like that much voltage nor will any other of your GMC components.
> Remove the isolator connections and check to see if the diodes have failed
> by first checking them with an ohm meter in one polarity and then in
> opposite polarity. They should have almost no resistance in one direction,
> and nearly infinite resistance in the other. If either post shows continuity
> in both directions, replace the isolator with one rated as many amps or
> higher than the one you have.
> Jim Hupy
> Salem, OR
> 78 GMC Royale 403
>
> On Wed, Oct 12, 2011 at 10:50 AM, Bill Wetzel <billandpatwetzel@gmail.com>wrote:
>
>>
>>
>> OK, now I'm confused. Voltage at the isolator (middle alternator terminal)
>> and at the back of the alternator is very high, between 45 and 50. What
>> gives??
>>
>> Bill
>> --
>> Bill Wetzel
>> 77 Royale 26RB
>> Sheboygan, WI
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
> _______________________________________________
> GMCnet mailing list
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Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: [GMCnet] Electrical problem [message #146313 is a reply to message #146310] |
Wed, 12 October 2011 14:31 |
Dennis S
Messages: 3046
Registered: November 2005
Karma: 2
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Senior Member |
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In his first post I understoon Bill to say he had replaced the alternator... of course it could be a faulty replacement as well..
Dennis
| James Hupy wrote on Wed, 12 October 2011 14:24 |
If your Voltage is that high, the internal regulator in the Alternator is
defunct. Have it rebuilt. Now. Do not run it like that. Your digi panel
won't like that much voltage nor will any other of your GMC components.
Remove the isolator connections and check to see if the diodes have failed
by first checking them with an ohm meter in one polarity and then in
opposite polarity. They should have almost no resistance in one direction,
and nearly infinite resistance in the other. If either post shows continuity
in both directions, replace the isolator with one rated as many amps or
higher than the one you have.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Wed, Oct 12, 2011 at 10:50 AM, Bill Wetzel <billandpatwetzel@gmail.com>wrote:
>
>
> OK, now I'm confused. Voltage at the isolator (middle alternator terminal)
> and at the back of the alternator is very high, between 45 and 50. What
> gives??
>
> Bill
> --
> Bill Wetzel
> 77 Royale 26RB
> Sheboygan, WI
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Dennis S
73 Painted Desert 230
Memphis TN Metro
[Updated on: Wed, 12 October 2011 14:31] Report message to a moderator |
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| Re: [GMCnet] Electrical problem [message #146316 is a reply to message #146314] |
Wed, 12 October 2011 15:02 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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The output from the alternator is regulated by limiting the field strength
in the rotor. The circuit is best described as "load excited" or "demand
excited". The stator windings are a "wye". Three output wires insulated from
each other phased 120 degrees apart from each other. Both ends of each wire
terminate at a diode. There are 6 diodes in the rectifier bridge. 3 + diodes
and 3 - diodes. Their purpose is to take the AC output from the stator and
convert it to DC by only allowing current to pass in one direction. After
the bridge rectifier, their output goes to the large binding post that your
big red wire attatches to. The regulator receives voltage from the batteries
and excites the electomagnets in the rotor. The stronger the field strength,
the more current output on the stator. The regulator operates by turing the
field on and off thereby limiting field strength and output. It goes without
saying that any loose connections affect output. Push on connectors are
known for losing their grip and causing high resistance. That can limit or
fool the regulator into going "full field" which is what your alternator is
doing. Check those wires and connectors, make sure that everything is clean,
bright, and tight. It is all 30 plus years old.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Wed, Oct 12, 2011 at 12:34 PM, Wally Anderson <wallyand@aim.com> wrote:
>
>
> James Hupy wrote on Wed, 12 October 2011 14:24
> > If your Voltage is that high, the internal regulator in the Alternator is
> > defunct. Have it rebuilt. Now. Do not run it like that. Your digi panel
> > won't like that much voltage nor will any other of your GMC components.
> > Remove the isolator connections and check to see if the diodes have
> failed
> > by first checking them with an ohm meter in one polarity and then in
> > opposite polarity. They should have almost no resistance in one
> direction,
> > and nearly infinite resistance in the other. If either post shows
> continuity
> > in both directions, replace the isolator with one rated as many amps or
> > higher than the one you have.
> > Jim Hupy
> > Salem, OR
> > 78 GMC Royale 403
> >
> > ]
>
> Jim, I'm thinking if the isolator is open the alternator output voltage
> would be high. The regulator voltage sense input is on the chassis side of
> the isolator.
> --
> Wally Anderson
> 1975 Glenbrook
> Megasquirt 455 port injection science project-On the road 8162 miles
> Omaha Nebraska
> Greater Midwest Classics
> GMCES
> http://wallyandsue.blogspot.com/
> _______________________________________________
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| Re: [GMCnet] Electrical problem [message #146317 is a reply to message #146314] |
Wed, 12 October 2011 15:09 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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If the voltage is that high, the regulator has failed catastrophically.
Even with the isolator open on the chassis battery side, disconnecting the
voltage sense lead, the regulator should limit the output voltage to about
18 VDC -- MAX.
It may be that the voltage is actually a 1/2 sine wave rather than DC. Most
meters cannot read that voltage waveform accurately. As shown by Dave
Mumert's simulations some years ago, failed diodes can cause that condition
-- and a Nichrome wire catastrophe.
DON'T run the engine with that alternator installed!
Ken H.
On Wed, Oct 12, 2011 at 3:34 PM, Wally Anderson <wallyand@aim.com> wrote:
>
>
> James Hupy wrote on Wed, 12 October 2011 14:24
> > If your Voltage is that high, the internal regulator in the Alternator is
> > defunct. Have it rebuilt. Now. Do not run it like that. Your digi panel
> > won't like that much voltage nor will any other of your GMC components.
> > Remove the isolator connections and check to see if the diodes have
> failed
> > by first checking them with an ohm meter in one polarity and then in
> > opposite polarity. They should have almost no resistance in one
> direction,
> > and nearly infinite resistance in the other. If either post shows
> continuity
> > in both directions, replace the isolator with one rated as many amps or
> > higher than the one you have.
> > Jim Hupy
> > Salem, OR
> > 78 GMC Royale 403
> >
> > ]
>
> Jim, I'm thinking if the isolator is open the alternator output voltage
> would be high. The regulator voltage sense input is on the chassis side of
> the isolator.
> --
>
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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] Electrical problem [message #146323 is a reply to message #146313] |
Wed, 12 October 2011 16:34 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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Hope you had an apc cable
Gene
FREE WIFI @ Mickey D
On Oct 12, 2011, at 12:31 PM, Dennis Sexton <dennisfsexton@aol.com> wrote:
>
>
> In his first post I understoon Bill to say he had replaced the alternator... or course it could be a faulty replacement as well..
>
> Dennis
>
> James Hupy wrote on Wed, 12 October 2011 14:24
>> If your Voltage is that high, the internal regulator in the Alternator is
>> defunct. Have it rebuilt. Now. Do not run it like that. Your digi panel
>> won't like that much voltage nor will any other of your GMC components.
>> Remove the isolator connections and check to see if the diodes have failed
>> by first checking them with an ohm meter in one polarity and then in
>> opposite polarity. They should have almost no resistance in one direction,
>> and nearly infinite resistance in the other. If either post shows continuity
>> in both directions, replace the isolator with one rated as many amps or
>> higher than the one you have.
>> Jim Hupy
>> Salem, OR
>> 78 GMC Royale 403
>>
>> On Wed, Oct 12, 2011 at 10:50 AM, Bill Wetzel <billandpatwetzel@gmail.com>wrote:
>>
>>>
>>>
>>> OK, now I'm confused. Voltage at the isolator (middle alternator terminal)
>>> and at the back of the alternator is very high, between 45 and 50. What
>>> gives??
>>>
>>> Bill
>>> --
>>> Bill Wetzel
>>> 77 Royale 26RB
>>> Sheboygan, WI
>
>
> --
> Dennis S
> 73 Painted Desert 230
> Germantown, TN
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Electrical problem [message #146331 is a reply to message #146317] |
Wed, 12 October 2011 18:04 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Dang Ken, We finally agreed on something! <Grin> Maybe there is hope for us
after all.
Just kidding
Jim Hupy
Salem, OR
78 GMC Royale 403
On Wed, Oct 12, 2011 at 1:09 PM, Ken Henderson <hend4800@bellsouth.net>wrote:
> If the voltage is that high, the regulator has failed catastrophically.
> Even with the isolator open on the chassis battery side, disconnecting the
> voltage sense lead, the regulator should limit the output voltage to about
> 18 VDC -- MAX.
>
> It may be that the voltage is actually a 1/2 sine wave rather than DC.
> Most
> meters cannot read that voltage waveform accurately. As shown by Dave
> Mumert's simulations some years ago, failed diodes can cause that condition
> -- and a Nichrome wire catastrophe.
>
> DON'T run the engine with that alternator installed!
>
> Ken H.
>
>
> On Wed, Oct 12, 2011 at 3:34 PM, Wally Anderson <wallyand@aim.com> wrote:
>
> >
> >
> > James Hupy wrote on Wed, 12 October 2011 14:24
> > > If your Voltage is that high, the internal regulator in the Alternator
> is
> > > defunct. Have it rebuilt. Now. Do not run it like that. Your digi panel
> > > won't like that much voltage nor will any other of your GMC components.
> > > Remove the isolator connections and check to see if the diodes have
> > failed
> > > by first checking them with an ohm meter in one polarity and then in
> > > opposite polarity. They should have almost no resistance in one
> > direction,
> > > and nearly infinite resistance in the other. If either post shows
> > continuity
> > > in both directions, replace the isolator with one rated as many amps or
> > > higher than the one you have.
> > > Jim Hupy
> > > Salem, OR
> > > 78 GMC Royale 403
> > >
> > > ]
> >
> > Jim, I'm thinking if the isolator is open the alternator output voltage
> > would be high. The regulator voltage sense input is on the chassis side
> of
> > the isolator.
> > --
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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