Home » Public Forums » GMCnet » Alternator woes.
| Alternator woes. [message #287676] |
Mon, 21 September 2015 08:31  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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The deity obviously didn't want me to attend last weekend's show in Anniston in the GMC. Friday morning i fired it up. no charge. So, off to Advance, new alternator, put it on, fired her up, charge on both batteries. So I loaded the coach, hooked up the toad, fired her up, and the DigiPanel went into alarm. 18 volts, and both ammeters pinned on charge. Rats. At this point, I transferred stuff to the toad and off we went for a good weekend. Jeremy Knezek, wife, kids, and grandparents met me Saturday at the show. We had a fun day, everybody petted dogs, the kids were well behaved (!), and they learned a lot about the intricacies of dog shows. Jeremy's Dad and he and I repaired to the hotel after the show for Sevenses and a late afternoon of football and lies, and then had a delicious dinner at Top O The River in Anniston. Highly recommended, Dixielanders will remember the Top restaurant in Gadsden. There are about three more scattered around.
So, now the move is to figure why the alternator went to full excitation. I suspect the 100Ohm wire, which has been spliced. I'm minded to go get a 100Ohm wirewound resister and hook it in in place of the resistance wire. Someone mentioned a nichrome section in this wire, does anybody know if that's true? If it's just Sitz wire, a fixed resistor will work as well. If it's nichrome, the operation will be different, although depending what the wire is doing, it probably won't matter. (Nichrome acts as a ballast, the resistance will increase with temperature) About all it looks like would happen is the alternator will be a bit slower to come up to current with a fixed resistor... not a great problem.
Thoughts?
--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
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| Re: Alternator woes. [message #287678 is a reply to message #287676] |
Mon, 21 September 2015 08:49  |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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Johnny Bridges wrote on Mon, 21 September 2015 06:31The deity obviously didn't want me to attend last weekend's show in Anniston in the GMC. Friday morning i fired it up. no charge. So, off to Advance, new alternator, put it on, fired her up, charge on both batteries. So I loaded the coach, hooked up the toad, fired her up, and the DigiPanel went into alarm. 18 volts, and both ammeters pinned on charge. Rats. At this point, I transferred stuff to the toad and off we went for a good weekend. Jeremy Knezek, wife, kids, and grandparents met me Saturday at the show. We had a fun day, everybody petted dogs, the kids were well behaved (!), and they learned a lot about the intricacies of dog shows. Jeremy's Dad and he and I repaired to the hotel after the show for Sevenses and a late afternoon of football and lies, and then had a delicious dinner at Top O The River in Anniston. Highly recommended, Dixielanders will remember the Top restaurant in Gadsden. There are about three more scattered around.
So, now the move is to figure why the alternator went to full excitation. I suspect the 100Ohm wire, which has been spliced. I'm minded to go get a 100Ohm wirewound resister and hook it in in place of the resistance wire. Someone mentioned a nichrome section in this wire, does anybody know if that's true? If it's just Sitz wire, a fixed resistor will work as well. If it's nichrome, the operation will be different, although depending what the wire is doing, it probably won't matter. (Nichrome acts as a ballast, the resistance will increase with temperature) About all it looks like would happen is the alternator will be a bit slower to come up to current with a fixed resistor... not a great problem.
Thoughts? Jim bounds has an article a few years back that shows how to eleminate that troublesome nichrome wire by substituting a fused 100 ohm wire wound resistor circuit in its place. It is a good upgrade to protect the wire loom. It sounds like your replacement alternator has a bad voltage regulator? Did you get the old and replacement ones checked? I always carry a spare one on board easy side of the road repair.
--johnny
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Alternator woes. [message #287682 is a reply to message #287676] |
Mon, 21 September 2015 09:23 |
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wally
Messages: 643
Registered: August 2004
Location: Omaha Nebraska
Karma: 5
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Senior Member |
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Johnny Bridges wrote on Mon, 21 September 2015 08:31The deity obviously didn't want me to attend last weekend's show in Anniston in the GMC. Friday morning i fired it up. no charge. So, off to Advance, new alternator, put it on, fired her up, charge on both batteries. So I loaded the coach, hooked up the toad, fired her up, and the DigiPanel went into alarm. 18 volts, and both ammeters pinned on charge. Rats. At this point, I transferred stuff to the toad and off we went for a good weekend. Jeremy Knezek, wife, kids, and grandparents met me Saturday at the show. We had a fun day, everybody petted dogs, the kids were well behaved (!), and they learned a lot about the intricacies of dog shows. Jeremy's Dad and he and I repaired to the hotel after the show for Sevenses and a late afternoon of football and lies, and then had a delicious dinner at Top O The River in Anniston. Highly recommended, Dixielanders will remember the Top restaurant in Gadsden. There are about three more scattered around.
So, now the move is to figure why the alternator went to full excitation. I suspect the 100Ohm wire, which has been spliced. I'm minded to go get a 100Ohm wirewound resister and hook it in in place of the resistance wire. Someone mentioned a nichrome section in this wire, does anybody know if that's true? If it's just Sitz wire, a fixed resistor will work as well. If it's nichrome, the operation will be different, although depending what the wire is doing, it probably won't matter. (Nichrome acts as a ballast, the resistance will increase with temperature) About all it looks like would happen is the alternator will be a bit slower to come up to current with a fixed resistor... not a great problem.
Thoughts?
--johnny
Something you may want to consider
http://gmcmotorhome.info/APC.html
Wally Anderson
Omaha NE
75 Glenbrook
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| Re: [GMCnet] Alternator woes. [message #287685 is a reply to message #287681] |
Mon, 21 September 2015 09:44 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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Nichrom. Have an APC cable?
On Monday, September 21, 2015, Bruce Hislop wrote:
> Johnny,
> I believe if you look closer at the wiring diagram it shows 10.0 ohms, not
> 100. I've heard fellows using 100 ohms, but the alternator is slow to
> start-up.
>
> I think the nichrome wire was used for ease of assembly being part of the
> harness.
>
> I have a 10 ohm resistor and 3amp diode rolling around in the Murray for a
> rainy day project.
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
> Hubler 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
>
> _______________________________________________
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> Unsubscribe or Change List Options:
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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: Alternator woes. [message #287706 is a reply to message #287676] |
Mon, 21 September 2015 15:11 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Cable? No. Large sack of diodes? Yep. I'll add one.
--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
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| Re: Alternator woes. [message #287722 is a reply to message #287676] |
Mon, 21 September 2015 18:07 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Well, I just went out and fired the coach off and did some looking and listening and I think I have some poor connections, or corroded connectors, or both... and there >may< be a phantom connect across the house battery isolator diode. I't is getting dark, I will chase tomorrow. However... Stuck my charger on the chassis battery, it ran ten minutes at 6 amps and reported full charge. House battery showed full charge at hookup - it has a solar charger, so that's normal. Pulled the plug off the alternator, between the plug and the accessory bus, ~~ 50 Ohms. Incidentally, my diagram says 100 Ohms +- 10. Fire it up, DigiPanel says 13 at idle, 15 at engine speed. Chassis battery ammeter says heavy charge, speed the engine up charge tapers off to eventually discharge. WTF. Go out front at high idle. On the isolator .3 volt drop to chassis battery, and the wire is warm. 1 volt drop on the house side. 15.5 in the middle, 15.3 to chassis, 14.5 to house. WTF. So.. I could be looking at one shorted and one open diode. Or I could be looking at a lunched sense wire. Or I could be....
Tomorrow's drill is, disconnect the isolator completely and prove its integrity or failure and points of fa8lure. disconnect the sense wire and measure it alone. Polish the hell out of every connector on the thing. clip both ends of the sense wire and wire around it with a 100Ohm resistor. If these do not produce a problem and its solution, insure the coach heavily and burn it to the ground 
In the midst of this it occurred to me, I may of removed a working alternator and replaced it with an unknown one,. So off I went to Advance to take advantage of their tester. Which was busted. I left the alternator with them to test when the test set is fixed. Meantime I'm looking through my junk box, I thought I had some 100 Amp diodes kicking around. I can do a DIY isolator if need be.
On the bright side, the new radiator and fan clutch are perfectly happy. fan cycles off and on while the coach is sitting idling and high idling. Trans temp and water temp track.
--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
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| Re: [GMCnet] Alternator woes. [message #287728 is a reply to message #287722] |
Mon, 21 September 2015 18:50 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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When people made copies of the manual and posted the copied manuals to the Internet the decimal point in the 100 disapeared
In the original manual that I purchased from GM in 1981 it clearly shows 10.0 ohms
Emery Stora
77 Kingsley
Frederick, CO
> On Sep 21, 2015, at 5:07 PM, Johnny Bridges wrote:
>
> Well, I just went out and fired the coach off and did some looking and listening and I think I have some poor connections, or corroded connectors, or
> both... and there >may< be a phantom connect across the house battery isolator diode. I't is getting dark, I will chase tomorrow. However... Stuck
> my charger on the chassis battery, it ran ten minutes at 6 amps and reported full charge. House battery showed full charge at hookup - it has a solar
> charger, so that's normal. Pulled the plug off the alternator, between the plug and the accessory bus, ~~ 50 Ohms. Incidentally, my diagram says 100
> Ohms +- 10. Fire it up, DigiPanel says 13 at idle, 15 at engine speed. Chassis battery ammeter says heavy charge, speed the engine up charge tapers
> off to eventually discharge. WTF. Go out front at high idle. On the isolator .3 volt drop to chassis battery, and the wire is warm. 1 volt drop on
> the house side. 15.5 in the middle, 15.3 to chassis, 14.5 to house. WTF. So.. I could be looking at one shorted and one open diode. Or I could be
> looking at a lunched sense wire. Or I could be....
> Tomorrow's drill is, disconnect the isolator completely and prove its integrity or failure and points of fa8lure. disconnect the sense wire and
> measure it alone. Polish the hell out of every connector on the thing. clip both ends of the sense wire and wire around it with a 100Ohm resistor.
> If these do not produce a problem and its solution, insure the coach heavily and burn it to the ground :)
> In the midst of this it occurred to me, I may of removed a working alternator and replaced it with an unknown one,. So off I went to Advance to take
> advantage of their tester. Which was busted. I left the alternator with them to test when the test set is fixed. Meantime I'm looking through my
> junk box, I thought I had some 100 Amp diodes kicking around. I can do a DIY isolator if need be.
> On the bright side, the new radiator and fan clutch are perfectly happy. fan cycles off and on while the coach is sitting idling and high idling.
> Trans temp and water temp track.
>
> --johnny
> --
> '76 23' transmode Norris upfit
> Braselton, Ga.
>
> "Sometimes I wonder what tomorrow's gonna bring when I think about my dirty life and times" --Warren Zevon
>
> _______________________________________________
> GMCnet mailing list
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| Re: [GMCnet] Alternator woes. [message #287742 is a reply to message #287728] |
Tue, 22 September 2015 03:01 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Emery,
I did a bit of poking around and found:
Maintenance Manual X-7425 / Section 6Y - Engine Electrical / Page 6Y-18 / Figure 20 - Connections for Alternator Testing & Generator
Output Test / Step 1
The same information can be found in MM X-7535 / Section 6Y - Engine Electrical / Page 6Y- 27 / Figure 31 - Connections for
Generator Output Test / Step 1
Regards,
Rob M.
The Pedantic Mechanic
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Emery Stora
Sent: Tuesday, September 22, 2015 9:51 AM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Alternator woes.
When people made copies of the manual and posted the copied manuals to the Internet the decimal point in the 100 disapeared
In the original manual that I purchased from GM in 1981 it clearly shows 10.0 ohms
Emery Stora
77 Kingsley
Frederick, CO
> On Sep 21, 2015, at 5:07 PM, Johnny Bridges wrote:
>
> Well, I just went out and fired the coach off and did some looking and listening and I think I have some poor connections, or
corroded connectors, or
> both... and there >may< be a phantom connect across the house battery isolator diode. I't is getting dark, I will chase tomorrow.
However... Stuck
> my charger on the chassis battery, it ran ten minutes at 6 amps and reported full charge. House battery showed full charge at
hookup - it has a solar
> charger, so that's normal. Pulled the plug off the alternator, between the plug and the accessory bus, ~~ 50 Ohms. Incidentally,
my diagram says 100
> Ohms +- 10. Fire it up, DigiPanel says 13 at idle, 15 at engine speed. Chassis battery ammeter says heavy charge, speed the
engine up charge tapers
> off to eventually discharge. WTF. Go out front at high idle. On the isolator .3 volt drop to chassis battery, and the wire is
warm. 1 volt drop on
> the house side. 15.5 in the middle, 15.3 to chassis, 14.5 to house. WTF. So.. I could be looking at one shorted and one open
diode. Or I could be
> looking at a lunched sense wire. Or I could be....
> Tomorrow's drill is, disconnect the isolator completely and prove its integrity or failure and points of fa8lure. disconnect the
sense wire and
> measure it alone. Polish the hell out of every connector on the thing. clip both ends of the sense wire and wire around it with
a 100Ohm resistor.
> If these do not produce a problem and its solution, insure the coach heavily and burn it to the ground :)
> In the midst of this it occurred to me, I may of removed a working alternator and replaced it with an unknown one,. So off I went
to Advance to take
> advantage of their tester. Which was busted. I left the alternator with them to test when the test set is fixed. Meantime I'm
looking through my
> junk box, I thought I had some 100 Amp diodes kicking around. I can do a DIY isolator if need be.
> On the bright side, the new radiator and fan clutch are perfectly happy. fan cycles off and on while the coach is sitting idling
and high idling.
> Trans temp and water temp track.
>
> --johnny
> --
> '76 23' transmode Norris upfit
> Braselton, Ga.
>
> "Sometimes I wonder what tomorrow's gonna bring when I think about my dirty life and times" --Warren Zevon
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: Alternator woes. [message #287754 is a reply to message #287676] |
Tue, 22 September 2015 12:56 |
jknezek
Messages: 1057
Registered: December 2007
Karma: 5
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Senior Member |
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Johnny Bridges wrote on Mon, 21 September 2015 09:31Jeremy Knezek, wife, kids, and grandparents met me Saturday at the show. We had a fun day, everybody petted dogs, the kids were well behaved (!), and they learned a lot about the intricacies of dog shows. Jeremy's Dad and he and I repaired to the hotel after the show for Sevenses and a late afternoon of football and lies, and then had a delicious dinner at Top O The River in Anniston. Highly recommended, Dixielanders will remember the Top restaurant in Gadsden. There are about three more scattered around.
I'm not going to mess with your alternator but I will say we all had a fun time. Always good when GMCers meet up, even if there isn't a GMC in sight!
Thanks,
Jeremy Knezek
1976 Glenbrook
Birmingham, AL
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| Re: Alternator woes. [message #287757 is a reply to message #287676] |
Tue, 22 September 2015 14:34 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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I'm using the original X-7525 maintenance manual shipped with the coach. For the diagram, the page marked "1975-1976 GMC Motorhome (With high energy ignition system) November 1975". Between connector BZ and the #12 BRN fed from the BATT 2 ACC position on the ignition switch is "24 BRN SGL WHT STR (100 +-10 OHMS)". From the alternator side of this wire at connector BZ is #20 BRN which runs to connector pin G on the Inst cluuster, marked GEN TELL TALE.
My 1976 supplement for this manual begins at sequence number 880, consequently it doesn't cover my coach which is sequence 825. The supplement shows the same wire with the same notes, but has a diode at the instrument cluster side of the 100 Ohm wire with the anode toward the alternator plug, this being the mod GM mentioned.
Given that the books which were provided with the coach call for 100 plus or minus 10, I'll be flying with 100, plus or minus 10. I'll also be flying with a piece of #16 wire because that's what I have a spool of kicking around.
--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
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| Re: Alternator woes. [message #287759 is a reply to message #287676] |
Tue, 22 September 2015 14:57 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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I believe there is confusion developed by the test sequence given in the maintenance manuals. When testing the alternator disconnected from the coach wiring and running into a test load, the procedure calls for the #1 pin to be connected to battery through a 10 (ten) Ohm resistor. This low values ensures that the alternator is forced into full output, but the current on the line is limited to 1.2 Amps to preclude overheating the divider inside the alternator. I've no interest in such a test, I'd rather see how it behaves in situ - it already passed that test at the rebuilders'. For those who wish to eliminate the resistance wire, I strongly suggest you use the same value as the wire, which is 100 plus or minus 10 ohms. Should there come a short internally in the unit, you have limited current to about 150 milliamos (Well, 126 on a fully charged battery) instead of an amp and a quarter. This difference in current at a failure may well make a difference in the amount of smoke produced. Had you rather dissipate 15 Watts or .15 (under two tenths) of a Watt?
--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
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| Re: [GMCnet] Alternator woes. [message #287760 is a reply to message #287742] |
Tue, 22 September 2015 15:46 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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Rob
We are not talking about testing the alternator.
What I was referring to is the values of the wire that is printed on the wiring diagram in the X7525 maintenance manual for the 1975-76 GMC Motorhome (with high energy ignition system) November 1975.
The decimal point is hard to see but in my manual it clearly shows the 24 BRN SGL WHT STR (10.0+/- 1.0 OHMS.
Many people have mistaken this for 100 +/- ohms.
I have the blown up wiring diagram obtained from Ken Henderson and it also show it as 10.0 +/- 1.0 ohms.
Gene Fisher commented on this many years ago and on his Internet site he discusses the problem with using 100 ohms rather than the 10 ohms called for by GMC.
Gene, if he reads this, might want to comment again on it.
Emery Stora
> On Sep 22, 2015, at 2:01 AM, Robert Mueller wrote:
>
> Emery,
>
> I did a bit of poking around and found:
>
> Maintenance Manual X-7425 / Section 6Y - Engine Electrical / Page 6Y-18 / Figure 20 - Connections for Alternator Testing & Generator
> Output Test / Step 1
>
> The same information can be found in MM X-7535 / Section 6Y - Engine Electrical / Page 6Y- 27 / Figure 31 - Connections for
> Generator Output Test / Step 1
>
> Regards,
> Rob M.
> The Pedantic Mechanic
>
>
> -----Original Message-----
> From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Emery Stora
> Sent: Tuesday, September 22, 2015 9:51 AM
> To: gmclist@list.gmcnet.org
> Subject: Re: [GMCnet] Alternator woes.
>
> When people made copies of the manual and posted the copied manuals to the Internet the decimal point in the 100 disapeared
>
> In the original manual that I purchased from GM in 1981 it clearly shows 10.0 ohms
>
> Emery Stora
> 77 Kingsley
> Frederick, CO
>
>> On Sep 21, 2015, at 5:07 PM, Johnny Bridges wrote:
>>
>> Well, I just went out and fired the coach off and did some looking and listening and I think I have some poor connections, or
> corroded connectors, or
>> both... and there >may< be a phantom connect across the house battery isolator diode. I't is getting dark, I will chase tomorrow.
> However... Stuck
>> my charger on the chassis battery, it ran ten minutes at 6 amps and reported full charge. House battery showed full charge at
> hookup - it has a solar
>> charger, so that's normal. Pulled the plug off the alternator, between the plug and the accessory bus, ~~ 50 Ohms. Incidentally,
> my diagram says 100
>> Ohms +- 10. Fire it up, DigiPanel says 13 at idle, 15 at engine speed. Chassis battery ammeter says heavy charge, speed the
> engine up charge tapers
>> off to eventually discharge. WTF. Go out front at high idle. On the isolator .3 volt drop to chassis battery, and the wire is
> warm. 1 volt drop on
>> the house side. 15.5 in the middle, 15.3 to chassis, 14.5 to house. WTF. So.. I could be looking at one shorted and one open
> diode. Or I could be
>> looking at a lunched sense wire. Or I could be....
>> Tomorrow's drill is, disconnect the isolator completely and prove its integrity or failure and points of fa8lure. disconnect the
> sense wire and
>> measure it alone. Polish the hell out of every connector on the thing. clip both ends of the sense wire and wire around it with
> a 100Ohm resistor.
>> If these do not produce a problem and its solution, insure the coach heavily and burn it to the ground :)
>> In the midst of this it occurred to me, I may of removed a working alternator and replaced it with an unknown one,. So off I went
> to Advance to take
>> advantage of their tester. Which was busted. I left the alternator with them to test when the test set is fixed. Meantime I'm
> looking through my
>> junk box, I thought I had some 100 Amp diodes kicking around. I can do a DIY isolator if need be.
>> On the bright side, the new radiator and fan clutch are perfectly happy. fan cycles off and on while the coach is sitting idling
> and high idling.
>> Trans temp and water temp track.
>>
>> --johnny
>> --
>> '76 23' transmode Norris upfit
>> Braselton, Ga.
>>
>> "Sometimes I wonder what tomorrow's gonna bring when I think about my dirty life and times" --Warren Zevon
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
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>
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| Re: [GMCnet] Alternator woes. [message #287762 is a reply to message #287759] |
Tue, 22 September 2015 15:51 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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Johnny
There is no confusion between test methods and the resistance value called for in the GMC wiring diagrams.
You are reading it as 100 +/- 10 ohms but, believe me, there is a decimal point there. The diagram shows 10.0 +/- 1.0 ohms.
As I said in my reply to Rob’s email, the blown up diagrams that can be obtained from Ken Henderson clearly shows the decimal point.
It is small print in the maintenance manual but much more clear in the blown up ones.
This is not a new topic. This had been discussed several years back on the GMC net and at that time people agreed that there was a decimal point in the numbers.
If you are still in doubt, contact Ken Henderson or Gene Fisher for their input.
Emery Stora
77 Kingsley
Frederick, CO
> On Sep 22, 2015, at 1:57 PM, Johnny Bridges wrote:
>
> I believe there is confusion developed by the test sequence given in the maintenance manuals. When testing the alternator disconnected from the coach
> wiring and running into a test load, the procedure calls for the #1 pin to be connected to battery through a 10 (ten) Ohm resistor. This low values
> ensures that the alternator is forced into full output, but the current on the line is limited to 1.2 Amps to preclude overheating the divider inside
> the alternator. I've no interest in such a test, I'd rather see how it behaves in situ - it already passed that test at the rebuilders'. For those
> who wish to eliminate the resistance wire, I strongly suggest you use the same value as the wire, which is 100 plus or minus 10 ohms. Should there
> come a short internally in the unit, you have limited current to about 150 milliamos (Well, 126 on a fully charged battery) instead of an amp and a
> quarter. This difference in current at a failure may well make a difference in the amount of smoke produced. Had you rather dissipate 15 Watts or
> .15 (under two tenths) of a Watt?
>
> --johnny
> --
> '76 23' transmode Norris upfit
> Braselton, Ga.
>
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| Re: [GMCnet] Alternator woes. [message #287763 is a reply to message #287685] |
Tue, 22 September 2015 15:58 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
|
Senior Member |
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Johnny - I forgot to include in my last email message that if you use 100 ohms instead of 10 ohms you might find that you get a delay in the excitation of your alternator and a delay in its starting to put a charge into your system. With the 10 ohm there is no delay.
Emery Stora
77 Kingsley
Frederick, CO
> On Sep 22, 2015, at 2:51 PM, Emery Stora wrote:
>
> Johnny
>
> There is no confusion between test methods and the resistance value called for in the GMC wiring diagrams.
> You are reading it as 100 +/- 10 ohms but, believe me, there is a decimal point there. The diagram shows 10.0 +/- 1.0 ohms.
>
> As I said in my reply to Rob’s email, the blown up diagrams that can be obtained from Ken Henderson clearly shows the decimal point.
>
> It is small print in the maintenance manual but much more clear in the blown up ones.
>
> This is not a new topic. This had been discussed several years back on the GMC net and at that time people agreed that there was a decimal point in the numbers.
> If you are still in doubt, contact Ken Henderson or Gene Fisher for their input.
>
> Emery Stora
> 77 Kingsley
> Frederick, CO
>
>> On Sep 22, 2015, at 1:57 PM, Johnny Bridges wrote:
>>
>> I believe there is confusion developed by the test sequence given in the maintenance manuals. When testing the alternator disconnected from the coach
>> wiring and running into a test load, the procedure calls for the #1 pin to be connected to battery through a 10 (ten) Ohm resistor. This low values
>> ensures that the alternator is forced into full output, but the current on the line is limited to 1.2 Amps to preclude overheating the divider inside
>> the alternator. I've no interest in such a test, I'd rather see how it behaves in situ - it already passed that test at the rebuilders'. For those
>> who wish to eliminate the resistance wire, I strongly suggest you use the same value as the wire, which is 100 plus or minus 10 ohms. Should there
>> come a short internally in the unit, you have limited current to about 150 milliamos (Well, 126 on a fully charged battery) instead of an amp and a
>> quarter. This difference in current at a failure may well make a difference in the amount of smoke produced. Had you rather dissipate 15 Watts or
>> .15 (under two tenths) of a Watt?
>>
>> --johnny
>> --
>> '76 23' transmode Norris upfit
>> Braselton, Ga.
>>
>
>
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| Re: [GMCnet] Alternator woes. [message #287765 is a reply to message #287759] |
Tue, 22 September 2015 17:43 |
Dave Mumert
Messages: 272
Registered: February 2004
Location: Olds, AB, Canada
Karma: 0
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Senior Member |
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HI
Is it possible to measure the resistance wire in the harness? Why not measure it and let us know?
Dave Mumert
> -----Original Message-----
> From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Johnny Bridges
> Sent: Tuesday, September 22, 2015 1:57 PM
> To: gmclist@list.gmcnet.org
> Subject: Re: [GMCnet] Alternator woes.
>
> I believe there is confusion developed by the test sequence given in the maintenance manuals. When testing the alternator
> disconnected from the coach wiring and running into a test load, the procedure calls for the #1 pin to be connected to battery
through
> a 10 (ten) Ohm resistor. This low values ensures that the alternator is forced into full output, but the current on the line is
limited to
> 1.2 Amps to preclude overheating the divider inside the alternator. I've no interest in such a test, I'd rather see how it
behaves in situ
> - it already passed that test at the rebuilders'. For those who wish to eliminate the resistance wire, I strongly suggest you use
the
> same value as the wire, which is 100 plus or minus 10 ohms. Should there come a short internally in the unit, you have limited
current
> to about 150 milliamos (Well, 126 on a fully charged battery) instead of an amp and a quarter. This difference in current at a
failure
> may well make a difference in the amount of smoke produced. Had you rather dissipate 15 Watts or
> .15 (under two tenths) of a Watt?
>
> --johnny
> --
> '76 23' transmode Norris upfit
> Braselton, Ga.
>
> "Sometimes I wonder what tomorrow's gonna bring when I think about my dirty life and times" --Warren Zevon
>
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> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: Alternator woes. [message #287766 is a reply to message #287676] |
Tue, 22 September 2015 17:50 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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OK, I went back and backlit the diagram and looked. I'm not the best sighted person going. I >still< don't see a decimal.... but I see the spacing is greater between the zeros and between the +- 1 and zeros greater than the distance between the 1 and first zero of the value. Yall get a ten. I'll put a ten.
This (10) is more in keeping with the value of a piece of nichrome cold than 100 - you'd need a fair length or either it would be a very fine and fragile gauge. Now the wonder is how I measured ~~ 50 ohms on two different meters... from the #1 pin of the alternator plug to the BATT2 lead on the switch. I suspect I have found it, I opened the plug through the firewall and discovered a certain amount of grot on some of the connections. I suspect some of my troubles lie therein, tomorrow's project is going to be cleaning them. Sigh.
--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
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