Home » Public Forums » GMCnet » Alternator Woes
| Alternator Woes [message #352629] |
Sat, 07 March 2020 18:36  |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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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
1977 28' Kingsley
La Grange, Wyoming
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| Re: [GMCnet] Alternator Woes [message #352631 is a reply to message #352630] |
Sat, 07 March 2020 20:17  |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> Check the ground connection!
>
> Sent from my iPhone
>
>> On Mar 7, 2020, at 2:37 PM, Bruce Hart via Gmclist gmclist@list.gmcnet.org> wrote:
>>
>> 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
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> _______________________________________________
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--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
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Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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| Re: Alternator Woes [message #352632 is a reply to message #352629] |
Sat, 07 March 2020 21:19 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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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
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| Re: [GMCnet] Alternator Woes [message #352633 is a reply to message #352632] |
Sat, 07 March 2020 21:42 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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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 <
gmclist@list.gmcnet.org> wrote:
> 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:
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| Re: [GMCnet] Alternator Woes [message #352639 is a reply to message #352630] |
Sun, 08 March 2020 11:00 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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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
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| Re: [GMCnet] Alternator Woes [message #352648 is a reply to message #352639] |
Sun, 08 March 2020 18:33 |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> 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
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Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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| Re: [GMCnet] Alternator Woes [message #352651 is a reply to message #352648] |
Sun, 08 March 2020 19:13 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> 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 gmclist@list.gmcnet.org> wrote:
>
>> 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:
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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] Alternator Woes [message #352653 is a reply to message #352651] |
Sun, 08 March 2020 21:21 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> 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 gmclist@list.gmcnet.org> wrote:
>
>> 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 > gmclist@list.gmcnet.org> wrote:
>>
>>> 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
>
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| Re: Alternator Woes [message #352658 is a reply to message #352629] |
Mon, 09 March 2020 08:57 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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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
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| Re: [GMCnet] Alternator Woes [message #352677 is a reply to message #352658] |
Mon, 09 March 2020 20:06 |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> 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
_______________________________________________
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Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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| Re: [GMCnet] Alternator Woes [message #352678 is a reply to message #352677] |
Mon, 09 March 2020 20:08 |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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Thanks everyone for your suggestions and mostly for your concerns.
On Mon, Mar 9, 2020 at 7:06 PM Bruce Hart wrote:
> 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 gmclist@list.gmcnet.org> wrote:
>
>> 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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Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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