Alternator Woes

B

Bruce Hart

Active member
Oct 18, 2011
1,414
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38
I had thought that my alternator was fixed last fall but no it isn't working again.
What is going on?
Tested alternator at NAPA. Tested ok with DC output at 14.6 volts. That is a good thing!!
Batt voltage at 12.57
Wire to #1 post on alternator at 12.1 volts (Ignition on)
Wire to #2 post on alternator at 12.40 Ignition off 12.35 ignition on

Started engine and took reading at isolator center post and got 2.0 volts.
Disconnected lead to output post on alternator. Installed test lead on output stud of alternator, ran engine, and measured 40.0 volts. Revved up the
engine and overloaded meter setting of 60 volts.

Isolator diodes checked out good.

Anyone have any ideas?

The alternator output is there I just can't get it where it is needed.


--
Bruce Hart
1976 Palm Beach
Milliken, Co
 
Check the ground connection!

Sent from my iPhone

>
> I had thought that my alternator was fixed last fall but no it isn't working again.
> What is going on?
> Tested alternator at NAPA. Tested ok with DC output at 14.6 volts. That is a good thing!!
> Batt voltage at 12.57
> Wire to #1 post on alternator at 12.1 volts (Ignition on)
> Wire to #2 post on alternator at 12.40 Ignition off 12.35 ignition on
>
> Started engine and took reading at isolator center post and got 2.0 volts.
> Disconnected lead to output post on alternator. Installed test lead on output stud of alternator, ran engine, and measured 40.0 volts. Revved up the
> engine and overloaded meter setting of 60 volts.
>
> Isolator diodes checked out good.
>
> Anyone have any ideas?
>
> The alternator output is there I just can't get it where it is needed.
>
>
> --
> Bruce Hart
> 1976 Palm Beach
> Milliken, Co
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
I was using the alternator case and, alternator bracket, and engine block
as my ground for my readings.

I have another isolator that I can switch out just to be sure that the
isolator is not the issue.

On Sat, Mar 7, 2020 at 6:41 PM Rich Shoop via Gmclist <

> Check the ground connection!
>
> Sent from my iPhone
>
> > On Mar 7, 2020, at 2:37 PM, Bruce Hart via Gmclist <

> >
> > I had thought that my alternator was fixed last fall but no it isn't
> working again.
> > What is going on?
> > Tested alternator at NAPA. Tested ok with DC output at 14.6 volts. That
> is a good thing!!
> > Batt voltage at 12.57
> > Wire to #1 post on alternator at 12.1 volts (Ignition on)
> > Wire to #2 post on alternator at 12.40 Ignition off 12.35 ignition on
> >
> > Started engine and took reading at isolator center post and got 2.0
> volts.
> > Disconnected lead to output post on alternator. Installed test lead on
> output stud of alternator, ran engine, and measured 40.0 volts. Revved up
> the
> > engine and overloaded meter setting of 60 volts.
> >
> > Isolator diodes checked out good.
> >
> > Anyone have any ideas?
> >
> > The alternator output is there I just can't get it where it is needed.
> >
> >
> > --
> > Bruce Hart
> > 1976 Palm Beach
> > Milliken, Co
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
 
When you disconnected the output terminal you lost feed to isolator, thru engine side diode over to horn relay terminal to sense cable back to
alternator, so regulator tried to compensate That says alternator is working. How about bad connection at 2 cavity connector to regulator?
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
You really, really, do not want to allow your alternator go Open Circuit on
the output conductor to the isolator. Totally unregulated it can allow the
voltage to go very high. It will let the smoke out of some important
windings and solid state stuff. Just off the top of my head, I would
suspect your isolator. You should have nearly identical voltages present at
the two output terminals with the engine running. Probably somewhere in the
range of .7 volt less than the center tap.
Jim Hupy
Salem, Oregon

On Sat, Mar 7, 2020, 7:20 PM John R. Lebetski via Gmclist <

> When you disconnected the output terminal you lost feed to isolator, thru
> engine side diode over to horn relay terminal to sense cable back to
> alternator, so regulator tried to compensate That says alternator is
> working. How about bad connection at 2 cavity connector to regulator?
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Pin 1 of the alternator is the exciter current. At 12.1V that tells me you have very little current flowing in the field windings ( engine OFF, key
ON) Your GEN light should not even light in this condition (if it is, then you are not reading Pin 1 voltage correctly).

I would check your 2 wire connector on the alternator. Pin 1 should read something like 6 volts or so with the engine OFF and IGN switch ON.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
The reading that you got on the alternator output with the output wire disconnected is a bogus number. Ignore it. You need to take all readings with
the wiring and electrical devices in their operational conditions.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Removed the isolator and installed a combiner today.
I have voltage but it is at 18.0+ volts and climbs when rpm increase.
I now have a rough idle that I didn't have before.
Had to take GMC back to storage as my 72 hours were up.
Disconnected lead from alternator to combiner and my voltage gauge was
pegged on the 1.5 mile journey to storage.

On Sun, Mar 8, 2020 at 10:01 AM Ken Burton via Gmclist <

> The reading that you got on the alternator output with the output wire
> disconnected is a bogus number. Ignore it. You need to take all readings
> with
> the wiring and electrical devices in their operational conditions.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
 
Bruce,

One more voice of alarm: You're seriously risking the alternator (and
everything connected to it) by running it without battery load!!! The main
reason is that leaving the chassis battery disconnected from the voltage
feedback to pin 2 drives the alternator into an unsuccessful attempt to
fully charge the battery. Unfortunately, most regulators these days seem
to lack the supposed 18 VDC output limit. NOTHING in the GMC's 12VDC
systems was designed to withstand 40VDC!

At the very least, if you MUST run, to protect everything (except,
maybe, the battery), connect a heavy jumper wire from the alternator output
to the chassis battery positive terminal.

Ken H.

On Sun, Mar 8, 2020 at 7:34 PM Bruce Hart via Gmclist <

> Removed the isolator and installed a combiner today.
> I have voltage but it is at 18.0+ volts and climbs when rpm increase.
> I now have a rough idle that I didn't have before.
> Had to take GMC back to storage as my 72 hours were up.
> Disconnected lead from alternator to combiner and my voltage gauge was
> pegged on the 1.5 mile journey to storage.
>
> On Sun, Mar 8, 2020 at 10:01 AM Ken Burton via Gmclist <

>
> > The reading that you got on the alternator output with the output wire
> > disconnected is a bogus number. Ignore it. You need to take all
> readings
> > with
> > the wiring and electrical devices in their operational conditions.
> > --
> > Ken Burton - N9KB
> > 76 Palm Beach
> > Hebron, Indiana
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
>
>
> --
> Bruce Hart
> 1976 Palm Beach
> Milliken, Co
> GMC=Got More Class
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Sounds to me like you need to take a SERIOUS LOOK at your batteries, and
everything connecting them to the isolator and all their grounds. Sumpin'
ain't right there. Do it sooner rather than round-to-it later. Do NOT RUN
THE ENGINE any more with the alternator output disconnected. You risk
burning your coach down to the lugnuts, with you in it. Listen to the
advice given here. We will not steer you wrong.
Jim Hupy
Salem, Oregon

On Sun, Mar 8, 2020, 5:14 PM Ken Henderson via Gmclist <

> Bruce,
>
> One more voice of alarm: You're seriously risking the alternator (and
> everything connected to it) by running it without battery load!!! The main
> reason is that leaving the chassis battery disconnected from the voltage
> feedback to pin 2 drives the alternator into an unsuccessful attempt to
> fully charge the battery. Unfortunately, most regulators these days seem
> to lack the supposed 18 VDC output limit. NOTHING in the GMC's 12VDC
> systems was designed to withstand 40VDC!
>
> At the very least, if you MUST run, to protect everything (except,
> maybe, the battery), connect a heavy jumper wire from the alternator output
> to the chassis battery positive terminal.
>
> Ken H.
>
> On Sun, Mar 8, 2020 at 7:34 PM Bruce Hart via Gmclist <

>
> > Removed the isolator and installed a combiner today.
> > I have voltage but it is at 18.0+ volts and climbs when rpm increase.
> > I now have a rough idle that I didn't have before.
> > Had to take GMC back to storage as my 72 hours were up.
> > Disconnected lead from alternator to combiner and my voltage gauge was
> > pegged on the 1.5 mile journey to storage.
> >
> > On Sun, Mar 8, 2020 at 10:01 AM Ken Burton via Gmclist <

> >
> > > The reading that you got on the alternator output with the output wire
> > > disconnected is a bogus number. Ignore it. You need to take all
> > readings
> > > with
> > > the wiring and electrical devices in their operational conditions.
> > > --
> > > Ken Burton - N9KB
> > > 76 Palm Beach
> > > Hebron, Indiana
> > >
> > > _______________________________________________
> > > GMCnet mailing list
> > > Unsubscribe or Change List Options:
> > > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> > >
> >
> >
> > --
> > Bruce Hart
> > 1976 Palm Beach
> > Milliken, Co
> > GMC=Got More Class
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
When you removed the isolator and added a combiner, did you hard wire the alternator lead to the engine battery and then add the combiner to the
house? . I would have just temporarily jumped the center isolator to engine batt terminal on the isolator as a test. I still don't understand how
you pegged the gauge with the alternator disconnected??? If so, Nikola Tesla would be very proud as you accomplished his wireless power
transmission dream.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
John, I did not check the volt meter when I shut down the coach, maybe when
it pegged out and just stuck there. I wired up the combiner according to
the layout that Jim bounds gave out in the last GMCMI magazine. Alternator
wire went to the same battery post as the starting battery and a second
wire to the + terminal post just under the previous location of the
isolator.

On Mon, Mar 9, 2020 at 7:57 AM John R. Lebetski via Gmclist <

> When you removed the isolator and added a combiner, did you hard wire the
> alternator lead to the engine battery and then add the combiner to the
> house? . I would have just temporarily jumped the center isolator to
> engine batt terminal on the isolator as a test. I still don't understand
> how
> you pegged the gauge with the alternator disconnected??? If so, Nikola
> Tesla would be very proud as you accomplished his wireless power
> transmission dream.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
 
Thanks everyone for your suggestions and mostly for your concerns.

> John, I did not check the volt meter when I shut down the coach, maybe
> when it pegged out and just stuck there. I wired up the combiner according
> to the layout that Jim bounds gave out in the last GMCMI magazine.
> Alternator wire went to the same battery post as the starting battery and a
> second wire to the + terminal post just under the previous location of the
> isolator.
>
>
> On Mon, Mar 9, 2020 at 7:57 AM John R. Lebetski via Gmclist <

>
>> When you removed the isolator and added a combiner, did you hard wire the
>> alternator lead to the engine battery and then add the combiner to the
>> house? . I would have just temporarily jumped the center isolator to
>> engine batt terminal on the isolator as a test. I still don't understand
>> how
>> you pegged the gauge with the alternator disconnected??? If so, Nikola
>> Tesla would be very proud as you accomplished his wireless power
>> transmission dream.
>> --
>> John Lebetski
>> Woodstock, IL
>> 77 Eleganza II
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
> --
> Bruce Hart
> 1976 Palm Beach
> Milliken, Co
> GMC=Got More Class
>
>

--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
 
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