Home » Public Forums » GMCnet » [GMCnet] Alternator Problem?
| [GMCnet] Alternator Problem? [message #85922] |
Mon, 24 May 2010 19:58  |
George Zhookoff
Messages: 398
Registered: December 2004
Location: Snellville, GA
Karma: 6
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Just checked the output of the alternator to the isolator center post,
13.8 volts. Output to the outer post 13.2 volts. When I turn
headlights and clearance lights on output drops to 13.2 & 12.7.
Do I need a new altenator?
George Zhookoff, PMP
78 EL II
Snellville, GA
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| Re: [GMCnet] Alternator Problem? [message #85926 is a reply to message #85922] |
Mon, 24 May 2010 20:03  |
Sandra Price
Messages: 709
Registered: May 2006
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Bob, who was in auto repair business for 35 years, says he wouldn't worry
about it. Because of the age of the wiring system in these old coaches, you
will have voltage drop when you turn on lights, etc. Be sure to check that
the alternator belt is tight.
Sandra Price
On Mon, May 24, 2010 at 7:58 PM, George Zhookoff <gzhookoff@e2m.com> wrote:
> Just checked the output of the alternator to the isolator center post,
> 13.8 volts. Output to the outer post 13.2 volts. When I turn
> headlights and clearance lights on output drops to 13.2 & 12.7.
>
> Do I need a new altenator?
>
> George Zhookoff, PMP
> 78 EL II
> Snellville, GA
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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--
IN GOD WE TRUST!
Sandra and Bob in the 51st Year of our State of Marriage
“Life’s a Trip” in “The Roadhouse”
’73 Painted Desert
Huntsville, TX
Finally, all of you, live in harmony with one another, be sympathetic, love
as brothers, be compassionate and humble. Do not repay evil with evil or
insult with insult, but with blessing, because to this you were called so
that you may inherit a blessing. --1 Peter 3:8-9
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| Re: [GMCnet] Alternator Problem? [message #85927 is a reply to message #85922] |
Mon, 24 May 2010 20:07 |
C Boyd
Messages: 2629
Registered: April 2006
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| George Zhookoff wrote on Mon, 24 May 2010 20:58 |
Just checked the output of the alternator to the isolator center post,
13.8 volts. Output to the outer post 13.2 volts. When I turn
headlights and clearance lights on output drops to 13.2 & 12.7.
Do I need a new altenator?
George Zhookoff, PMP
78 EL II
Snellville, GA
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Sir: sounds about normal. The isolater robs about .6 to .7 volts so the 13.8 in and 13.2 out is right. when adding the draw of the lights and accessories, the coach battery drops to 12.7 and the house system stays at 13.2 isolated from the coach. Sorry unless you have a noise or vibration issue you will have to spend your money elsewhere.
C. Boyd
76 Crestmont
East Tennessee
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| Re: [GMCnet] Alternator Problem? [message #85952 is a reply to message #85922] |
Mon, 24 May 2010 21:32 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| George Zhookoff wrote on Mon, 24 May 2010 19:58 |
Just checked the output of the alternator to the isolator center post,
13.8 volts. Output to the outer post 13.2 volts. When I turn
headlights and clearance lights on output drops to 13.2 & 12.7.
Do I need a new altenator?
George Zhookoff, PMP
78 EL II
Snellville, GA
|
Sorry, but here is a dissenting opinion. The normal charging voltage on a 12 volt automotive battery should be 13.8 to 14.2 volts. That means you should see 13.8 to 14.2 volts at the top and bottom terminals of the isolator. The voltage out of the alternator into the isolator center terminal should be .7 volts higher or 14.5 to 14.9 volts. There is a remote sensing lead going to the alternator that is connected to the wiring system after the fusible link so most of the voltage drops due to wiring, the fusible link, and the isolator are taken care of by raising the alternator output. That is how they get the alternator to put out the higher 14.7 volts or so.
The voltage readings you have are low and at those levels you will never fully charge up your batteries.
The reason for the low voltage could be a slipping / worn fan belt or pulley. It also could be a bad voltage regulator (located inside the alternator). I would also check the condition of the BIG wire (and it's connections) going from the alternator to the center terminal of the isolator.
You are probably going to need a rebuilt alternator. Get to 100 amp Cadillac version if you need a new one.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Alternator Problem? [message #85958 is a reply to message #85952] |
Mon, 24 May 2010 21:54 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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| Ken Burton wrote on Mon, 24 May 2010 22:32 |
| George Zhookoff wrote on Mon, 24 May 2010 19:58 |
Just checked the output of the alternator to the isolator center post,
13.8 volts. Output to the outer post 13.2 volts. When I turn
headlights and clearance lights on output drops to 13.2 & 12.7.
Do I need a new altenator?
George Zhookoff, PMP
78 EL II
Snellville, GA
|
Sorry, but here is a dissenting opinion. The normal charging voltage on a 12 volt automotive battery should be 13.8 to 14.2 volts. That means you should see 13.8 to 14.2 volts at the top and bottom terminals of the isolator. The voltage out of the alternator into the isolator center terminal should be .7 volts higher or 14.5 to 14.9 volts. There is a remote sensing lead going to the alternator that is connected to the wiring system after the fusible link so most of the voltage drops due to wiring, the fusible link, and the isolator are taken care of by raising the alternator output. That is how they get the alternator to put out the higher 14.7 volts or so.
The voltage readings you have are low and at those levels you will never fully charge up your batteries.
The reason for the low voltage could be a slipping / worn fan belt or pulley. It also could be a bad voltage regulator (located inside the alternator). I would also check the condition of the BIG wire (and it's connections) going from the alternator to the center terminal of the isolator.
You are probably going to need a rebuilt alternator. Get to 100 amp Cadillac version if you need a new one.
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Ken: when checking should the coach be idleing normal or fast??
Would it change the numbers??
C. Boyd
76 Crestmont
East Tennessee
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| Re: [GMCnet] Alternator Problem? [message #85969 is a reply to message #85958] |
Mon, 24 May 2010 22:51 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| C Boyd wrote on Mon, 24 May 2010 21:54 |
Ken: when checking should the coach be idleing normal or fast??
Would it change the numbers??
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The answer is it depends.
The voltage regulator is a limiter. Meaning it sets top limit that the voltage may go. If the 12 volt load (meaning lights, batteries, and other things) are accepting less current that the alternator can supply at an idle, then the voltage will be at it's upper limit meaning 13.8 to 14.2 or 14.5 to 14.9 into the isolator.
On the other hand, if the load is higher than the alternator can produce at an idle then the voltage will be lower than the limit and bringing up the engine speed will increase the voltages at the isolator and batteries.
Clear as mud. Right?
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Alternator Problem? [message #85970 is a reply to message #85922] |
Mon, 24 May 2010 23:02 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Unless it's really hot out and the regulator is dropping the voltage as it is supposed to to emulate the battery temps, I'd say you are at the low end of the acceptable range. Could be tired brushes or regulator or dirty conections. Disconnect the negative terminals and clean the plug at the alt and the all the connections first. And don't forget to check the belt slack as a gimmie as stated. I always thought that 1500 was the RPM to use as ref. You could lift the fast idle cam a click or 2 once warm that would probably keep it at 1500 for testing.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Alternator Problem? [message #85983 is a reply to message #85981] |
Tue, 25 May 2010 05:02 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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almost always a bad ground
I suggest a new ground wire from the dash to the engine (mother of all
grounds)
read here
http://gmcmotorhome.info/chassis.html#GROUND
and
http://gmc49ers.blogspot.com/2010/05/starting-issues-slides.html
gene
On Tue, May 25, 2010 at 2:48 AM, Barb & Tony Partridge <
tbpartridge@comcast.net> wrote:
> When my headlights are on my turn signals blink very slowly. Alternator
> output is normal. Any thoughts as to why?
>
> Tony Partridge
> Logansport, IN
> 78 PB powered by 454 TBI DynoSource
> ----- Original Message -----
> From: "Charles Boyd" <covered-wagon@comcast.net>
> To: <gmclist@temp.gmcnet.org>
> Sent: Monday, May 24, 2010 9:07 PM
> Subject: Re: [GMCnet] Alternator Problem?
>
>
> >
> >
> > George Zhookoff wrote on Mon, 24 May 2010 20:58
> >> Just checked the output of the alternator to the isolator center post,
> >> 13.8 volts. Output to the outer post 13.2 volts. When I turn
> >> headlights and clearance lights on output drops to 13.2 & 12.7.
> >>
> >> Do I need a new altenator?
> >>
> >> George Zhookoff, PMP
> >> 78 EL II
> >> Snellville, GA
> >> _______________________________________________
> >> GMCnet mailing list
> >> List Information and Subscription Options:
> >> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
> >
> >
> >
> >
> > Sir: sounds about normal. The isolater robs about .6 to .7 volts so the
> > 13.8 in and 13.2 out is right. when adding the draw of the lights and
> > accessories, the coach battery drops to 12.7 and the house system stays
> at
> > 13.2 isolated from the coach. Sorry unless you have a noise or vibration
> > issue you will have to spend your money elsewhere.
> > --
> > C. Boyd
> > 76 Crestmont by Midas
> > East Tennessee
> > _______________________________________________
> > GMCnet mailing list
> > List Information and Subscription Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
>
>
> _______________________________________________
> GMCnet mailing list
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--
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: [GMCnet] Alternator Problem? [message #147168 is a reply to message #85922] |
Thu, 20 October 2011 04:57 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Sorry
somehow this May 24 email popped up out of order and I didn't see the date when I replied..
Hope this didn't cause confusion.
Emer
On Oct 20, 2011, at 3:54 AM, Emery Stora wrote:
>
> On May 24, 2010, at 6:58 PM, George Zhookoff wrote:
>
>> Just checked the output of the alternator to the isolator center post,
>> 13.8 volts. Output to the outer post 13.2 volts. When I turn
>> headlights and clearance lights on output drops to 13.2 & 12.7.
>>
>> Do I need a new altenator?
>>
>> George Zhookoff, PMP
>> 78 EL II
>> Snellville, GA
>
> George
>
> That sounds about typical. You should be OK with that.
>
> Emery Stora
> 77 Kingsley
> Santa Fe, NM
>
>
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| Re: [GMCnet] Alternator Problem? [message #147173 is a reply to message #147168] |
Thu, 20 October 2011 08:10 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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You could always convert your headlight's operating voltage from the OEM wiring to a relay operated method. Putting a larger wire (smaller number) to the headlights would increase the ability of the wiring to carry more electrical power to the headlights. An easy to implement up-grade.
Tom Phipps, MS II
using a relay to increase the current to the Dana.
2012 Phoenix Cruiser model 2552
KA4CSG
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