What is it now? Generator issue.

Sad news...it appears that the armature is shorted. I replaced the partially failed connector on that one brush and with some difficulty, reinstalled
the upper brush assembly and no joy!

I decided to start over and re-check everything. Rectifier - ok; windings - ok; armature - uh oh, appears to be shorted. I found that during this
retest it was difficult to get a good ground connection with the meter probe and probably wasn't as diligent the first time. Once I was confident of
the connection, all brushes show zero resistance to ground. Crap!

Next step is to pull the entire genny, any advice on finding a replacement armature?
--
1978 Eleganza II
 
Ken,
Where do you live, as we know few that can help.

On Tue, Jul 16, 2019 at 8:56 AM Ken Harland via Gmclist <

> Sad news...it appears that the armature is shorted. I replaced the
> partially failed connector on that one brush and with some difficulty,
> reinstalled
> the upper brush assembly and no joy!
>
> I decided to start over and re-check everything. Rectifier - ok; windings
> - ok; armature - uh oh, appears to be shorted. I found that during this
> retest it was difficult to get a good ground connection with the meter
> probe and probably wasn't as diligent the first time. Once I was confident
> of
> the connection, all brushes show zero resistance to ground. Crap!
>
> Next step is to pull the entire genny, any advice on finding a replacement
> armature?
> --
> 1978 Eleganza II
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
> Sad news...it appears that the armature is shorted. I replaced the partially failed connector on that one brush and with some difficulty,
> reinstalled the upper brush assembly and no joy!
>
> I decided to start over and re-check everything. Rectifier - ok; windings - ok; armature - uh oh, appears to be shorted. I found that during
> this retest it was difficult to get a good ground connection with the meter probe and probably wasn't as diligent the first time. Once I was
> confident of the connection, all brushes show zero resistance to ground. Crap!
>
> Next step is to pull the entire genny, any advice on finding a replacement armature?

Give Jim Bounds a call (GMC Co-op - Orlando). He replaces the Onans with Hondas so he my have spare Onan parts.
Jerry B

--
Patti & Jerry Burt Fresno, CA.
73 Gmc 26' Canyon Lands
77 Palm Beach - Parts Coach
Members: FMCA - GMCMI - GMCWS
A truly happy person is one who can enjoy the scenery on a detour.
 
Used Onan goes for $ 200-300
So if you can pick one up you have a deal

On Tue, Jul 16, 2019 at 2:38 PM Jerry Burt via Gmclist <

> > Sad news...it appears that the armature is shorted. I replaced the
> partially failed connector on that one brush and with some difficulty,
> > reinstalled the upper brush assembly and no joy!
> >
> > I decided to start over and re-check everything. Rectifier - ok;
> windings - ok; armature - uh oh, appears to be shorted. I found that during
> > this retest it was difficult to get a good ground connection with the
> meter probe and probably wasn't as diligent the first time. Once I was
> > confident of the connection, all brushes show zero resistance to
> ground. Crap!
> >
> > Next step is to pull the entire genny, any advice on finding a
> replacement armature?
>
> Give Jim Bounds a call (GMC Co-op - Orlando). He replaces the Onans with
> Hondas so he my have spare Onan parts.
> Jerry B
>
> --
> Patti & Jerry Burt Fresno, CA.
> 73 Gmc 26' Canyon Lands
> 77 Palm Beach - Parts Coach
> Members: FMCA - GMCMI - GMCWS
> A truly happy person is one who can enjoy the scenery on a detour.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
Jim,
His registration says Central Florida. Jim Bounds territory. I was told one time that Jim had a grave yard of old Onans.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
> Give Jim Bounds a call (GMC Co-op - Orlando). He replaces the Onans with Hondas so he my have spare Onan parts.
> Jerry B

Thanks, that's a great idea.
--
1978 Eleganza II
 
It seems my conclusion that the armature was shorted was in error. When I reinstalled the upper brush assembly with the new brush connector, I
managed to pinch one of the connectors that goes to the brush assembly underneath the assembly in such a way as to provide a ground path from the
brush connector to the mounting surface. I found this by removing both brush assemblies and testing with a lamp and power source as recommended in
the manual and emphasized to me by Jim Miller (thanks Jim).

With the brushes removed, there's no short in the armature. I installed the lower brush and retested...no short. Reinstalled upper brush and short
came back. As anyone who's worked on these with it still in the coach knows, working around that top brush is mostly a blind operation. I used my
camera's phone to get some images from an angle I couldn't see otherwise and spotted the culprit. Moved the wire and retested - no short! That's the
good news, the bad news is I still am not producing AC, or should I say not a steady 120 volts AC.

I pulled out a better digital VOM and it's fast enough to catch a wildly fluctuating voltage output. Any hints as to what that might be? That's with
either the original rectifier or the new one. Rechecked all the brush connections as well as the two sleeved connectors in the harness and all appear
clean and tight.

Could it be because the brushes were moved around and haven't properly seated in their new positions?
--
1978 Eleganza II
 
Latest update: Generator is generating! I had to take a break from it and come back fresh, starting from ground zero on debugging.

Following the procedures outlined in the GMC manual:

1. Tested armature for shorts and opens - none found
2. Tested windings for shorts and total resistance - no shorts and resistance within spec
3. Tested rectifier bridge - all diodes function within spec
4. All brushes and their connections confirmed good

Given all those results with a generator that doesn't produce any voltage, the only thing left and not covered in the manual was sufficient residual
magnetism to excite the system. I had read previously about 'flashing' to restore the residual magnetism and had performed that procedure but
apparently had interpreted 'flashing' as to indicate a brief surge of current from a 12 volt source. Another source (Jim Miller) said the current
should be applied for 5 - 10 seconds, longer that I had done previously. So I did it again for the recommended period, lo and behold, the generator
now produces a steady 120 volts! Thanks Jim!

To summarize, the generator shut down under load two years ago. When restarted, it was not producing voltage. Life got in the way of further
investigation but I presumed the rectifier had failed. Fast forward two years, pulled and tested rectifier and no problem found but replaced it
anyway with no change. When pulling brush assemblies to examine their condition, found partially failed quick disconnect on upper brush. Repaired
and reinstalled but still no voltage output. Performed all tests noted above, then reflashed windings for 10 seconds, problem solved!
--
1978 Eleganza II
 
  • Like
Reactions: pvfjr
You must log in or register to reply here.
Applied GMC
GMCMI Spring 2026 Rally

Share this page

Share this page
Top Bottom
Back