Home » Public Forums » GMCnet » Gen Light When plugged to Shore power
| Gen Light When plugged to Shore power [message #198037] |
Sun, 10 February 2013 14:17  |
Donovan-formerly Jase386
Messages: 139
Registered: January 2009
Location: Greenville SC
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Today I was tinkering with the GMC, and started it up While the power was plugged to the house.
The generator light was on, and just to see if it being plugged in was the problem, unplugged the power cord from the house.
Gen Light cured.
What is causing this? Today is the first time ive seen this happen.
Donovan, Greenville SC
1975 Eleganza II
81,500 miles
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| Re: Gen Light When plugged to Shore power [message #198091 is a reply to message #198037] |
Mon, 11 February 2013 07:18  |
John Sharpe
Messages: 489
Registered: February 2006
Location: Texas
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| Quote: |
... started it up While the power was plugged to the house.
The generator light was on, and just to see if it being plugged in was the problem, unplugged the power cord from the house.
Gen Light cured. ....
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The AC generator (Alternator) or the Onan?
John Sharpe
Humble,TX
'78 Eleganza TBI
'89 Spectrum 2000 MPI V-10
'40 Ford Panel Delivery TPI
johnasharpe@gmail.com
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| Re: Gen Light When plugged to Shore power [message #198110 is a reply to message #198037] |
Mon, 11 February 2013 09:36 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| Donovan-formerly Jase386 wrote on Sun, 10 February 2013 15:17 |
Today I was tinkering with the GMC, and started it up While the power was plugged to the house.
The generator light was on, and just to see if it being plugged in was the problem, unplugged the power cord from the house.
Gen Light cured.
What is causing this? Today is the first time ive seen this happen.
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Donovan,
John asked if this was the dash light or the Onan. If it is the Onan, you have serious control board issues. If it is the dash light, you still have some problems, not as big, but still an issue.
What the light indicates is that the alternator field current is not being supplied buy the alternator, but by the main engine's ignition circuit. As you don't have the alternator protection cable (or this scenario blows up) and you do have a combiner installed. What I believe is happening is that your isolator has shorted to the engine side and the converter brings up the combiner. Now the alternator output is high and it is trying to supply the field and that field current is backing through the alternator light. This can only happen with the failure of a diode in the alternator's main bridge.
I think you better get out there with a meter.
With more information, a more precise diagnosis might be possible.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Gen Light When plugged to Shore power [message #198119 is a reply to message #198037] |
Mon, 11 February 2013 12:20 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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If it's the dash light and he has no combiner ( not sure) then unless the isolator is bad/miswired and alt is bad as well as Matt suggested, I'm stumped.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Gen Light When plugged to Shore power [message #198152 is a reply to message #198037] |
Mon, 11 February 2013 18:41 |
Donovan-formerly Jase386
Messages: 139
Registered: January 2009
Location: Greenville SC
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I am referring to the alternator light on the dash. When the house is plugged into its self I have no warning light on the dash. the only way this happens is when the house is plugged into shore power And the engine is running.
I do have a combiner, and I have the little wire on the alternator to keep it from catching fire.
Donovan, Greenville SC
1975 Eleganza II
81,500 miles
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| Re: Gen Light When plugged to Shore power [message #198156 is a reply to message #198037] |
Mon, 11 February 2013 19:33 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Next I would get the DVM and meter how much voltage the converter is putting out with the engine off. The smart type of converters have different stages of charge rate depending on battery condition and temp, but I would think 14v would be safe number. I would also look for same or similar number with unplugged converter and engine running. You can conveniently and easily meter at the isolator terminals to the aluminum ground plate One outer terminal is house batt side and other is engine batt side but since you have a combiner they effectively become the same within a couple tenths of a volt. Also with the engine only running the center terminal (alt) should read about .5 volt higher than the outside terminals due to normal diode voltage drop in the isolator. Other tests would be to check isolator for high/ low ohm values center to outsides on ohms when reversing the meter leads, but you need to shut down and disconnect battery negative leads first on both systems and then take the outer terminals off as it will then be out of circuit. I'm guessing the combiner is also wired across the outer isolator terminals as well. This won't guarantee the isolator is good in real world loading, but preliminary check for shorted or open diodes. That was too much typing on the iPhone.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Gen Light When plugged to Shore power [message #198174 is a reply to message #198152] |
Mon, 11 February 2013 22:42 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Donovan,
Is the Gen light bright, dim, super-bright? If it's dim, I'm not sure the
condition you're seeing is as unusual as it appears -- most of us don't
spend a lot of time running the engine with shore power connected. The Gen
light merely indicates if the battery voltage is above the alternator's
output voltage. With the engine at idle, the converter, connected to the
chassis battery through the combiner, may very well be producing a voltage
enough higher than the alternator, causing the Gen light to glow, at least
dimly. Increasing engine RPM should cause the light to go out. If it
doesn't, then the alternator is probably weak -- check its output with a
meter & report back.
Ken H.
On Mon, Feb 11, 2013 at 7:41 PM, jase386 wrote:
>
>
> I am referring to the alternator light on the dash. When the house is
> plugged into its self I have no warning light on the dash. the only way
> this happens is when the house is plugged into shore power And the engine
> is running.
>
> I do have a combiner, and I have the little wire on the alternator to keep
> it from catching fire.
> --
> Donovan, Greenville SC
> 1975 Eleganza II (Ella)
> 72,500 miles
> _______________________________________________
> 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: Gen Light When plugged to Shore power [message #198196 is a reply to message #198152] |
Tue, 12 February 2013 07:54 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| Donovan-formerly Jase386 wrote on Mon, 11 February 2013 19:41 |
I am referring to the alternator light on the dash. When the house is plugged into its self I have no warning light on the dash. the only way this happens is when the house is plugged into shore power And the engine is running.
I do have a combiner, and I have the little wire on the alternator to keep it from catching fire.
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OK Donovan,
That is more information...
What I believe you are looking at is to be expected and may also occur if you have the APU on line with the main engine running, or are trying to charge the chassis battery with the main engine running.
As I said before, that light indicates that the alternator field is being supplied from the ignition circuit and not the alternator itself. This can also happen if the chassis battery terminal is higher than the alternator set-point. When it is, the regulator will decrease the field current to the point that there is almost no alternator output at all. But there is still both a field winding and the regulator that can pull some load on the light circuit.
Question: Does the same thing occur with the APU on line?
If Yes, that is what you are seeing.
If No, hell, Iduno
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Gen Light When plugged to Shore power [message #198209 is a reply to message #198037] |
Tue, 12 February 2013 09:53 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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What converter do you have? I know the IOTA brand can be set up differently via the RJ 11 phone jack on the side to be 'smart' multistage or just dumb and do fixed output . If it is over charging the batteries then Matt's theory all makes sense. Without some accurate voltage readings it's an armchair guessing game.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Gen Light When plugged to Shore power [message #198362 is a reply to message #198037] |
Wed, 13 February 2013 18:01 |
Donovan-formerly Jase386
Messages: 139
Registered: January 2009
Location: Greenville SC
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When I crank the engine, the light is dim. when I rev the rpms up, the light gets brighter.
more info just in..
with the engine running and the alt light on, I had no house ligts except a tiny little dim flicker then nothing. I unplugged the cord from shore power still no house lights.
bumped the battery boost button and the lights came on (I heard the solenoid click in the dash) turned the engine off, no house lights. plugged it into shore power, no house lights. started engine, alt light on, bumped boost button, no alt light and have house lights now.
sounds like I need to clean all the connections tomorrow before I head out on a trip.
I will have to get you the converter brand, and combiner information. Where will the combiner be? im not totally sure it has one. I know I can leave the headlights on all night when plugged in and it doesn't drain the battery.
Donovan, Greenville SC
1975 Eleganza II
81,500 miles
[Updated on: Wed, 13 February 2013 18:13] Report message to a moderator |
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| Re: [GMCnet] Gen Light When plugged to Shore power [message #198429 is a reply to message #198362] |
Thu, 14 February 2013 07:39 |
Mr ERFisher
Messages: 7117
Registered: August 2005
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this describes when the light should be on
http://www.gmcmotorhome.info/engine.html#alternator
1) check the 10 amp instrument light fuse (look here for desc.)
http://www.gmcmotorhome.info/engine.html#ALTLIGHT
the APC cable eliminates all other false indications
I don't know if you can read electrical schematics
but
this one shows the ckt, with the apc cable in
http://www.gmcmhphotos.com/photos/10-ohm-alternator-wire-77-78-models/p3731-apc-cable-circuit.html
2) this is where to read and find the voltages,and how to test your
alternator
http://www.gmcmhphotos.com/photos/data/6225/How_to_check-out1.pdf
get a 3.5 digit meter from Harbor Freight (for free or $3)
http://www.gmcmhphotos.com/photos/gmc-chemicals-and-tools/p46161-digital-volt-meter-cup.html
keep looking, this light should not come when the engine is running
get back to us
gene
On Wed, Feb 13, 2013 at 4:01 PM, jase386 <jase386@aol.com> wrote:
>
>
> When I crank the engine, the light is dim. when I rev the rpms up, the
> light gets brighter.
>
> I will have to get you the converter brand, and combiner information.
> Where will the combiner be? im not totally sure it has one. I know I can
> leave the headlights on all night when plugged in and it doesn't drain the
> battery.
> --
> Donovan, Greenville SC
> 1975 Eleganza II (Ella)
> 72,500 miles
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: Gen Light When plugged to Shore power [message #198433 is a reply to message #198037] |
Thu, 14 February 2013 08:53 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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If there is a combiner it would be typically on the passenger firewall across the outer 2 isolator terminals and a lead to ground. These should be 10 ga wires and may have extra wire bundled up. Leave the extra wire as that is part of the design. The combiner is a little module about the size of a 1/4 cigarette pack. Check the house battery ground to rear frame as these are prone to corrosion from acid and bimetallic reaction. Remember when working to disconnect neg first and reconnect last for safety.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Gen Light When plugged to Shore power [message #198813 is a reply to message #198037] |
Sun, 17 February 2013 23:02 |
Donovan-formerly Jase386
Messages: 139
Registered: January 2009
Location: Greenville SC
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Just in From Charleston SC. The drive down was great. no problems.
Drive home: after stopping for gas around Orangeburg as we got back on I-26 I noticed the radio kept going on and off. Then the alt light came on and the dash fan and radio went out. we were at the orangeburg rest area so I pulled in and shut everything down, got out to smell wires burning.
got out and found that the battery cutoff installed in the house ground, and the cable end were melted. I separated the, now, two halves, and disconnected the ground at the house battery.
Back inside still alternator light and no dash power. I bumped the battery boost button and everything came on as normal. On the rest of the trip, the alt light came on once and I bumped the boost button and it didn't come back on.
Donovan, Greenville SC
1975 Eleganza II
81,500 miles
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| Re: Gen Light When plugged to Shore power [message #198827 is a reply to message #198813] |
Mon, 18 February 2013 02:42 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Shoot your problems as two different systems. The house system and the engine system. The only cross connections between the two systems are the isolator and the boost relay when it is energized by the switch on the dash.
If you do have a combiner, disconnect it until you get the two separate systems working on their own correctly. There aren't many combiners out there on GMCs and I have already seen more of them fail than I have seen isolators fail. After you get everything running correctly feel free to reconnect the added combiner if desired.
From your symptoms, it sounds like you have multiple failures or wiring errors going on.
Did you check the fusible link?
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Gen Light When plugged to Shore power [message #198908 is a reply to message #198833] |
Mon, 18 February 2013 15:54 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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The fusible link is about a 6" piece of 16 gauge black wire. Open the passenger side hood and it is right in front of you. It is connected between a stud on the horn relay and a big stud that I think is labeled vehicle positive. The big stud also has a 4 gauge and a 10 gauge wire on it. The 10 gauge wire goes to the isolator.
There is a picture of it somewhere on the GMC photo site but I could not find it.
I have seen several of those go intermittent over the years. Move it around and tug on it slightly to see if it falls apart.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Gen Light When plugged to Shore power [message #199018 is a reply to message #198037] |
Tue, 19 February 2013 08:13 |
Donovan-formerly Jase386
Messages: 139
Registered: January 2009
Location: Greenville SC
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1. I pulled on and flexed the fusible link but never got it to stretch,like on more modern vehicles. What am I looking for: crackling, cracking, stiffness or flexibility?
2. I think i found the cause of the melted cut off switch. The nuts were just barely on the bolt causing a very weak connection. Im going to change that whole set up.
Donovan, Greenville SC
1975 Eleganza II
81,500 miles
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