Home » Public Forums » GMCnet » HELP WITH ALTERNATOR (GEMRECS)
| HELP WITH ALTERNATOR [message #122319] |
Tue, 19 April 2011 09:27  |
Michael Bozardt
Messages: 367
Registered: January 2007
Location: College Station, Texas
Karma: 1
|
Senior Member |
|
|
Let's assume my little tester is correct.
The new alternator-changed to correct pulley-shows 13 volt output and "Low" rating on the tester, where 14 volts is normal.
What would cause this? Voltage regulator? If so, where is it? (I know, I can look in the book, but time is critical here).
Possibly, the incorrect alternator from O'Reillys? Anyone have a cross reference number so I can check it?
Using my voltmeter, Where do I connect it-neg to a ground and positive to the small wire or to the twin outlets?
I appreciate the advice and encouragement....Thx, Michael at GEMRECS
|
|
|
|
|
|
| Re: HELP WITH ALTERNATOR [message #122326 is a reply to message #122319] |
Tue, 19 April 2011 10:40  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
|
Senior Member |
|
|
I think that the "sense" cable back to the alternator needs to be on the engine battery side of the isolator. If it is not and on the centre post the output to the batteries will be low due to the voltage drop you get across the diodes in the isolator. This is a fractional voltage but that is all it takes to make a charge or not charge situation when there are only 12Vs that is a large percentage.
John Lebetski
Woodstock, IL
77 Eleganza II
|
|
|
|
| Re: HELP WITH ALTERNATOR [message #122330 is a reply to message #122326] |
Tue, 19 April 2011 10:59 |
 |
WD0AFQ
Messages: 7111
Registered: November 2004
Location: Dexter, Mo.
Karma: 207
|
Senior Member |
|
|
Michael, once you get this thing going I suggest what Gene said. Take one of the bad ones to a local guy to have it rebuilt. I bought an alternator from Jim K. back in 07. It got me to Blaine Merrell's home, in Indiana. Then it gave up and was blasting 18 volts onto everything. Jim wanted to warranty it, I said no. Blaine took me to 2 autozones and both were no good. Diane picked one up in Indianapolis for me and I am still running it. That was, count them, 1,2,3. I paid the core charge to Autozone and kept the one I got from Jim. That one goes to a local builder, when I get around to it, for a rebuild to be my spare. Thanks for the reminder. This will go to the top of my list when we get home later this week.
Bottom line: you never know what you might get from a parts house.
Dan
3 In Stainless Exhaust Headers
One Ton All Discs/Reaction Arm
355 FD/Quad Bag/Alum Radiator Manny Tran/New eng.
Holley EFI/10 Tire Air Monitoring System
Solarized Coach/Upgraded Windows
Satelite TV/On Demand Hot Water/3Way Refer
|
|
|
|
| Re: [GMCnet] HELP WITH ALTERNATOR [message #122332 is a reply to message #122319] |
Tue, 19 April 2011 11:35 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
|
Senior Member |
|
|
Michael, place the black (-) wire from your tester onto the negative battery
terminal of your engine battery. Then place the red(+) lead from your tester
to the output stud on the alternator. Usually a large red wire attatched
with a ring terminal to a insulated post on the back of the alternator.
Often times will have an insulation sleeve or cap covering it. With the
engine running at about 2000 rpm, note the voltage. Should range from 13.8
Volts to 14.5 volts or slightly higher if your batteries are discharged. If
within range, then go to the post on the isolator where the wire from the
alternator terminates. Voltage should be very close to the same. Then check
voltage at each of the orther studs on the isolator. Max voltage drop
shouldn't be over .5 volts, and the same at each post. If any corrosion is
present on any of the cables that go to the batteries, remove the cables one
by one and clean them bright and shiny and repair any corroded bolts that
hold the cables. High resistance here will limit the charge rate. Loose
connections and bad grounds account for about 90 percent of all low voltage
electrical problems. Incidentally, when alternators have to go "full field"
to compensate for bad connections and wiring, they frequently do not last
very long. Also, do not neglect to verify that the alternator case is well
grounded to the engine block, and that the engine block is well grounded
back to the batteries. Hope this helps.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Tue, Apr 19, 2011 at 7:27 AM, Michael Bozardt <ilse@earth-comm.com>wrote:
>
>
> Let's assume my little tester is correct.
> The new alternator-changed to correct pulley-shows 13 volt output and "Low"
> rating on the tester, where 14 volts is normal.
>
> What would cause this? Voltage regulator? If so, where is it? (I know, I
> can look in the book, but time is critical here).
>
> Possibly, the incorrect alternator from O'Reillys? Anyone have a cross
> reference number so I can check it?
>
> Using my voltmeter, Where do I connect it-neg to a ground and positive to
> the small wire or to the twin outlets?
>
> I appreciate the advice and encouragement....Thx, Michael at GEMRECS
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
|
|
|
|
| Re: HELP WITH ALTERNATOR [message #122416 is a reply to message #122319] |
Tue, 19 April 2011 20:00 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
|
Senior Member |
|
|
Michael.
The normal output for the alternator on a GMC is 14.5 to 14.9 volts. It can easily be measured at the center terminal of the isolator. The negative lead of your tester / meter can be attached to the aluminum plate that the isolator is mounted on.
If the voltages is low there then move negative negative lead to the negative battery terminal of better yet if you can reach it to anything on or mounted to the engine block. I hate to mention this but the radiator is mounted directly to the engine block via the trans cooler lines and could be used for the negative connection for a brief period of time for a measurement.
If the voltage is still low when measuring with the negative lead attached to the engine block, then move the positive led to the big terminal on the back of the alternator. That is the real output of the alternator.
If the voltage is still low there then you could have one of several problems.
1. Slipping fan belt on the alternator. Tighten the alternator belt or replace it if the belt is too thin. Take a 10 mm. open end wrench and place it across the width of the belt If it goes over the belt then the BELT is TOO THIN. Get a new belt and measure it with the same 10 mm. wrench before you leave the store.
2. Very low batteries taking more current than the alternator can supply at full voltage. Fully charge the batteries (both house and engine) Then try taking the readings again.
3. A bad voltage regulator INSIDE of the alternator. Take the alternator back and get another one.
Note: The voltages I mentioned above are unique to the GMC, and other motorhomes, that use an isolator. They are .7 volts higher than a normal car or truck due to the installation of the isolator.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
|
|
|
|
| Re: [GMCnet] HELP WITH ALTERNATOR [message #122423 is a reply to message #122416] |
Tue, 19 April 2011 20:24 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
|
Senior Member |
|
|
Michael, what Ken B says is pretty much spot on. I am very anal when it
comes to 12V DC systems and therefore I use a systemic approach to trouble
shooting them. I ALWAYS check battery voltage before I start up the engine.
If you have good, 12 volt, wet cell sulphuric acid batteries, fully charged,
they should test above 12.6 volts without the engine running. This simple
step rules out the fact that you have bad battery(ies). After the voltage is
known, start the coach and listen. If you hear screeching belt(s), they are
too loose. After you tighten them, start the coach again and check the
voltage between the output lug on the alternator and the battery ground.
Should be as Ken describes more or less depending on your specific meter.
Can't be more exact than that due to the variance in individual meters.
Shouldn't be more than .5 VDC drop between posts on the isolator. Shouldn't
be more than .75 volts from one end of the coach to the other. If it is, you
more than likely have poor connections or failed conductors. Be systematic,
rule out parts of the system one by one. Otherwise you wind up chasing your
tail.
Jim Hupy
Salem, Or
78 GMC Royale 403
On Tue, Apr 19, 2011 at 6:00 PM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> Michael.
>
> The normal output for the alternator on a GMC is 14.5 to 14.9 volts. It
> can easily be measured at the center terminal of the isolator. The negative
> lead of your tester / meter can be attached to the aluminum plate that the
> isolator is mounted on.
>
> If the voltages is low there then move negative negative lead to the
> negative battery terminal of better yet if you can reach it to anything on
> or mounted to the engine block. I hate to mention this but the radiator is
> mounted directly to the engine block via the trans cooler lines and could be
> used for the negative connection for a brief period of time for a
> measurement.
>
> If the voltage is still low when measuring with the negative lead attached
> to the engine block, then move the positive led to the big terminal on the
> back of the alternator. That is the real output of the alternator.
>
> If the voltage is still low there then you could have one of several
> problems.
>
> 1. Slipping fan belt on the alternator. Tighten the alternator belt or
> replace it if the belt is too thin. Take a 10 mm. open end wrench and place
> it across the width of the belt If it goes over the belt then the BELT is
> TOO THIN. Get a new belt and measure it with the same 10 mm. wrench before
> you leave the store.
>
> 2. Very low batteries taking more current than the alternator can supply
> at full voltage. Fully charge the batteries (both house and engine) Then
> try taking the readings again.
> 3. A bad voltage regulator INSIDE of the alternator. Take the alternator
> back and get another one.
>
> Note: The voltages I mentioned above are unique to the GMC, and other
> motorhomes, that use an isolator. They are .7 volts higher than a normal
> car or truck due to the installation of the isolator.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
|
|
|
|
|
|
|
|
|
|
| Re: [GMCnet] HELP WITH ALTERNATOR [message #122484 is a reply to message #122456] |
Wed, 20 April 2011 11:41 |
|
|
The actual forward voltage drop across a diode (as in the isolator) is spec'd at .7 volts. I reality, it runs between .6 and .7, but should not be .5 or 0.
On Apr 20, 2011, at 6:00 AM, Phil Swanson <woodyman1@sbcglobal.net> wrote:
>
>
> Shouldn't be more than .5 VDC drop between posts on the isolator. Jim Hupy
> Salem, Or
> 78 GMC Royale 403
>
>> 76 Palm Beach
>> Hebron, Indiana
>> _______________________________________________
> (Quote)
>
> This is one of the reasons I run a combiner. No voltage drop on a good combiner. Also, those Autozone alternators are pure garbage. Rebuilt in China. The computators are often totally worn out and just sanded smooth. Pure garbage. Rebuild your own. Not that difficult and common hand tools and a multimeter is all you need. You can find quality parts at http//www.alternatorparts.com
>
> Phil Swanson
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Terry Taylor
'74 ex-Eleganza SE
San Lorenzo, CA
http://www.n6mon.org
http://dldesignstore.com
|
|
|
|
| Re: [GMCnet] HELP WITH ALTERNATOR [message #122503 is a reply to message #122484] |
Wed, 20 April 2011 15:14 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
|
Senior Member |
|
|
I did not want to get into that precise of measurements as to voltage drops,
etc. There is waaaay too many variations in meters and users here to be lab
precise. Just to know the process was what I was trying to communicate to
Michael. Please, let's not get into splitting hairs. He is stranded on the
road, I was just trying to help him get home.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Wed, Apr 20, 2011 at 9:41 AM, Terry Taylor <n6mon@pacbell.net> wrote:
> The actual forward voltage drop across a diode (as in the isolator) is
> spec'd at .7 volts. I reality, it runs between .6 and .7, but should not be
> .5 or 0.
>
>
>
> On Apr 20, 2011, at 6:00 AM, Phil Swanson <woodyman1@sbcglobal.net> wrote:
>
> >
> >
> > Shouldn't be more than .5 VDC drop between posts on the isolator. Jim
> Hupy
> > Salem, Or
> > 78 GMC Royale 403
> >
> >> 76 Palm Beach
> >> Hebron, Indiana
> >> _______________________________________________
> > (Quote)
> >
> > This is one of the reasons I run a combiner. No voltage drop on a good
> combiner. Also, those Autozone alternators are pure garbage. Rebuilt in
> China. The computators are often totally worn out and just sanded smooth.
> Pure garbage. Rebuild your own. Not that difficult and common hand tools
> and a multimeter is all you need. You can find quality parts at http//
> www.alternatorparts.com
> >
> > Phil Swanson
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
|
|
|
|
Goto Forum:
Current Time: Sat Nov 16 16:50:19 CST 2024
Total time taken to generate the page: 0.01353 seconds
|
GMCforum
Search
Help
Register
Login
Home
