Home » Public Forums » GMCnet » Low and high voltage issue
| Low and high voltage issue [message #296444] |
Mon, 29 February 2016 19:18  |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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When I started the coach today, I noted the voltage down around 10.5v. then suddenly went to 14.3 and stayed there for 45 minutes. It then went to 22.5v for about 1 minute and returned to 14.3v. for the remainder 45 minutes of the trip. I think I've seen this thing happen in two scenario's, one is when at battery is going bad and the other is a alternator is dying.
What do ya all think?
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
[Updated on: Mon, 29 February 2016 19:19] Report message to a moderator |
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| Re: Low and high voltage issue [message #296452 is a reply to message #296444] |
Mon, 29 February 2016 19:48  |
dr.diesel
Messages: 85
Registered: April 2015
Location: The Haute, Indiana
Karma: 0
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I once had a mid 80s Bronco off road machine. We were wheeling one night after dark when all of the sudden all the lights went out, all within a few seconds of each other. The headlights, dash lights, tail lights, marker lights, all of them!
Same thing happened, voltage regular fried, blew all the bulbs.
77 Kingsley
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| Re: [GMCnet] Low and high voltage issue [message #296453 is a reply to message #296448] |
Mon, 29 February 2016 19:43 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Or the isolator. If the chassis battery diode has a bad internal
connection, as is the most common failure mode, alternator output voltage
does not reach that battery, so the alternator's remote sense line tells
the alternator to increase its output. That SHOULD be (but is not always)
limited to 18 VDC. Since the output voltage reaches higher, it may indeed
by the regulator, but the easiest check is to put a jumper between the
isolator's center terminal and its chassis battery terminal. If the
voltage stays under control, the isolator's at fault; if not, the
alternator is most likely the problem.
Ken H.
On Mon, Feb 29, 2016 at 8:24 PM, Emery Stora wrote:
> Sounds like the alternator.
>
> Emery Stora
>
>> On Feb 29, 2016, at 6:18 PM, Larry wrote:
>>
>> When I started the coach today, I noted the voltage down around 10.5v.
> then suddenly went to 14.3 and stayed there for 45 minutes. It then went to
>> 22.5v for about 1 minute and returned to 14.3v. for the remainder 45
> minutes of the trip. I think scenario's seen this thing happen in two
>> scenario's, one is when at battery is going bad and the other is a
> alternator is dying.
>>
>> What do ya all think?
>> --
>> Larry
>> 78 Royale w/500 Caddy
>> Menomonie, WI.
>>
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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: Low and high voltage issue [message #296456 is a reply to message #296444] |
Mon, 29 February 2016 20:15 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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I played this game late last summer. New aloternator stabilized it at little or no charge, isolator was fine. The cure was to clean >every< connection in the system, including the firewall pass - through plug. On shining all the ring connectors on the chassis 12V feed point I found a couple with scurvy connectors which I replaced. I got a new regulator and brush assembly from the local auto electric shop, and cleaned the slip rings in the alternator up with some crocus cloth. Put it all back together and it works just fine. Poor connections and dying brushes were I believe the culprits. I replaced the regulator for two reasons.. 1) it's been stressed by wierd voltages and arcing connections; and two the same reason you put a throwout bearing in when you renew a clutch... the 12 bux or so for the module is way less than the PIA factor to take the thing off and apart again if the old one fails. Let me point out yet again, with two ammeters you can diagnose a lot of this stuff.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
[Updated on: Mon, 29 February 2016 20:16] Report message to a moderator |
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| Re: [GMCnet] Low and high voltage issue [message #296466 is a reply to message #296461] |
Mon, 29 February 2016 21:57 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Could try this
http://gmc49ers.blogspot.com/2014/03/check-your-battery-system-through-your.html
Or the flow chart at the end
On Monday, February 29, 2016, Ken Henderson wrote:
> Solves that problem!
>
> Ken H.
>
>
> On Mon, Feb 29, 2016 at 9:36 PM, Larry
> wrote:
>
>> Thanks Ken, but the isolator is long gone. Now got a combiner.
>> --
>> Larry
>> 78 Royale w/500 Caddy
>> Menomonie, WI.
>>
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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] Low and high voltage issue [message #296495 is a reply to message #296459] |
Tue, 01 March 2016 09:56 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Larry wrote on Mon, 29 February 2016 21:36Thanks Ken, but the isolator is long gone. Now got a combiner.
Larry,
Just because you have a combiner does not mean it is good.
When I was still doing a lot of boat work (before the depression), During any season I replaced quite a few both isolators and Combiners.
What I think you have is a multi-point problem. But, more accurate diagnosis would require knowing where your actual measuring point was then.
Simple:
10.3 says you have a battery/cable issue.
14.3 says that the alternator is wide open and charging something.
22.5 says that the alternator's regulator is not clipping the full output and that there is nothing holding the output down.
If the connections to the engine battery were lost (temporarily) and the only connection to the house bank in the rear remained, this could be possible at the alternator, but it still is more than a good regulator should allow. The alternator was probably running uncontrolled to the rear battery and the excessive voltage was allowed because the wired to the back is less than it really should be for that run. GM used #10SAE and I don't know what Coachman ran.
Matt
The return to 14.3 says that the alternator is salvageable. I would break it down and clean all the internal connections.
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: [GMCnet] Low and high voltage issue [message #296499 is a reply to message #296444] |
Tue, 01 March 2016 10:05 |
Olly Schmidt
Messages: 1265
Registered: February 2014
Location: Germany and Scottsville, ...
Karma: 8
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When I read about your voltage issues, a German saying came to mind:
Wer misst, misst Mist.
Do you know that your voltage meter is correct?
--
Best regards
Peer Oliver Schmidt
PGP Key ID: 0x83E1C2EA
'76a Eleganza II, VA
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Best regards
Olly Schmidt
PGP Key ID: 0x18a9 3a1f 4196 bf22
'76a Eleganza II, VA
'73 Sequoia, SH, Germany
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| Re: [GMCnet] Low and high voltage issue [message #296512 is a reply to message #296502] |
Tue, 01 March 2016 11:14 |
Olly Schmidt
Messages: 1265
Registered: February 2014
Location: Germany and Scottsville, ...
Karma: 8
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Nope. The one that measures measures junk.
----- Ursprüngliche Nachricht -----
Von: "D C _Mac_ Macdonald"
Gesendet: 01.03.2016 17:30
An: "GMC Mail List"
Betreff: Re: [GMCnet] Low and high voltage issue
Is that basically the same as saying that "scheiss ist scheiss," Peer?
Mac in OKC
> To: gmclist@list.gmcnet.org
> From: posde@theinternet.de
> Date: Tue, 1 Mar 2016 17:05:14 +0100
> Subject: Re: [GMCnet] Low and high voltage issue
>
> When I read about your voltage issues, a German saying came to mind:
>
> Wer misst, misst Mist.
>
> Do you know that your voltage meter is correct?
>
> --
> Best regards
>
> Peer Oliver Schmidt
> PGP Key ID: 0x83E1C2EA
>
> '76a Eleganza II, VA
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Best regards
Olly Schmidt
PGP Key ID: 0x18a9 3a1f 4196 bf22
'76a Eleganza II, VA
'73 Sequoia, SH, Germany
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