Generator Malfunction

[omoore]

I confess that generators and electricity are not my area of expertise. So
here is my problem. The Onan had been working perfectly when I shut it
down. When I fired it up a week later it would only charge 6-8 volts. If
I pushed the throttle arm I could get a few more volts. I removed the
solid state regulator boardand sent it out to be tested. It tested fine.
A tech from the local Onan dealer came out and "flashed" it using a D
cell. He diagnosed the problem as a bad diode or a shorted winding. I
have a service manual for the genset and the Onan tests are far more
detailed. So I am wondering if the tech really did enough to pin the
problem on diodes or windings?
When I removed the regulator board there were two cylindrical things not
wired on the board but connecting. I don't know what they do, but could
one of them go bad and causes the charging problem? My genset is
self-exciting. If the winding have really shorted I can get an entire
generating end cheaply. It is for the same model but older and has brushes
instead of the self-exciting circuit. Does anyone know if that would fit?
Any and all suggestions will be most appreciated.
Oliver Moore
1973 26-footer
Restored by Cinnebar with a Patterson Stage 2 engine and Thorley Headers

 

[Matt Colie]

> I confess that generators and electricity are not my area of expertise. So here is my problem. The Onan had been working perfectly when I shut
> it down. When I fired it up a week later it would only charge 6-8 volts. If I pushed the throttle arm I could get a few more volts. I removed the
> solid state regulator board and sent it out to be tested. It tested fine.
> A tech from the local Onan dealer came out and "flashed" it using a D cell. He diagnosed the problem as a bad diode or a shorted winding. I
> have a service manual for the genset and the Onan tests are far more detailed. So I am wondering if the tech really did enough to pin the problem
> on diodes or windings?
> When I removed the regulator board there were two cylindrical things not wired on the board but connecting. I don't know what they do, but
> could one of them go bad and causes the charging problem? My genset is self-exciting. If the winding have really shorted I can get an entire
> generating end cheaply. It is for the same model but older and has brushes instead of the self-exciting circuit. Does anyone know if that would
> fit?
> Any and all suggestions will be most appreciated.
> Oliver Moore
> 1973 26-footer

Oliver,

I kind of hate to say how little information you have provided, but I will try to work with it anyway.
Is the unit one that was OE for a 73 build? As such, It could be either and NH or a BF. If it is not one of those, then it will be real tough to
help.

If by "Solid State Regulator" you mean an aluminum three terminal box on the unit, then that is the part that recharges the generator starting
battery. If that starting battery is what you mean by self excited, well, they all are.

Most owners of 26 coaches have moved the house bank back to the space behind the generator. Then they start the generator with the house bank and
have one fewer batteries to take care of....

How are we doing so far?

One the house bank is in the rear, many people remove that charging regulator and just forget about a generator battery.

Matt - though playing pirate games.
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

 

[john r. lebetski]

Sounds like a no AC output issue? The circuit board with the start:stop switch is for engine control only. Nothing to do with AC power output. If
there is no AC output and he narrowed it to diode bridge or field windings, he really didn't narrow it very much for you. A set of tests with a meter
could determine that with a couple more steps. If the diode bridge is bad it's a fairly cheap and easy fix. If the field is bad you need a rewind or
good used. Hope I have interpreted your issue and this helps.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[jim kanomata1]

Check your bridge rectifier and always thevcircut beaker

On Tue, Mar 26, 2019 at 10:53 PM Matt Colie via Gmclist <

> > I confess that generators and electricity are not my area of expertise.
> So here is my problem. The Onan had been working perfectly when I shut
> > it down. When I fired it up a week later it would only charge 6-8
> volts. If I pushed the throttle arm I could get a few more volts. I
> removed the
> > solid state regulator board and sent it out to be tested. It tested
> fine.
> > A tech from the local Onan dealer came out and "flashed" it using a D
> cell. He diagnosed the problem as a bad diode or a shorted winding. I
> > have a service manual for the genset and the Onan tests are far more
> detailed. So I am wondering if the tech really did enough to pin the
> problem
> > on diodes or windings?
> > When I removed the regulator board there were two cylindrical things
> not wired on the board but connecting. I don't know what they do, but
> > could one of them go bad and causes the charging problem? My genset is
> self-exciting. If the winding have really shorted I can get an entire
> > generating end cheaply. It is for the same model but older and has
> brushes instead of the self-exciting circuit. Does anyone know if that
> would
> > fit?
> > Any and all suggestions will be most appreciated.
> > Oliver Moore
> > 1973 26-footer
>
> Oliver,
>
> I kind of hate to say how little information you have provided, but I will
> try to work with it anyway.
> Is the unit one that was OE for a 73 build? As such, It could be either
> and NH or a BF. If it is not one of those, then it will be real tough to
> help.
>
> If by "Solid State Regulator" you mean an aluminum three terminal box on
> the unit, then that is the part that recharges the generator starting
> battery. If that starting battery is what you mean by self excited, well,
> they all are.
>
> Most owners of 26 coaches have moved the house bank back to the space
> behind the generator. Then they start the generator with the house bank and
> have one fewer batteries to take care of....
>
> How are we doing so far?
>
> One the house bank is in the rear, many people remove that charging
> regulator and just forget about a generator battery.
>
> Matt - though playing pirate games.
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> 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

 

[Ken B]

I am so confused by this posing request that I did not respond. 6 to 8 volts measured where? DC or AC? Is he trying to get the on board alternator
to charge a starting battery? I am assuming that it has a separate starting battery because it is a 1973. That is the only thing I can imagine
charging anything. Or is he trying to get 120 volts AC output which is an entirely different section of the unit?

As far as the alternator goes, I can assume that it is putting out 28 to 30 volts AC or the engine would not stay running.

I cannot hazard a guess here with out more precise information on what exactly is failing. He needs to define more precisely what his failure is
before we can begin guess at a solution.

This probably a simple diagnosis once we figure out what his problem is.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[john r. lebetski]

We need a diagnosis diaganosis. Then we can diagnose. I took the ACV route, but could be wrong.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[jim miller]

> I am so confused by this posing request that I did not respond.


Hi Ken,

Count me confused as well - all the way to the point of not even being sure that the unit in question is an Onan NH based on the description.

I do know one thing: if the unit made AC a week earlier then the “flash the field with a D cell” procedure was not indicated and would make no difference; that procedure is only needed for a unit that has sat idle for a year or more and has lost enough residual magnetism that it does not have enough field strength to start the excitation process.

I also know that it is quite unlikely that the armature has magically developed a damaged winding in a week’s time of sitting idle.

FWIW a unit with a dead excitation subsystem (open field winding, defective bridge, or failed compounding reactor) will still make a few volts AC due to the residual magnetism mentioned earlier - and this voltage will increase a slight bit with increased engine RPM.

73, Jim N8ECI

Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH

 

[Ken B]

I started to wonder about the brand and model too. I figured that I had asked enough questions and if it was a different model that would come out in
his answers to the questions.

I think that we would love to help the guy but we need more information.

Ken B.

>
> > I am so confused by this posing request that I did not respond.
>
>
> Hi Ken,
>
> Count me confused as well - all the way to the point of not even being sure that the unit in question is an Onan NH based on the description.
>
> I do know one thing: if the unit made AC a week earlier then the "flash the field with a D cell" procedure was not indicated and would make no
> difference; that procedure is only needed for a unit that has sat idle for a year or more and has lost enough residual magnetism that it does not
> have enough field strength to start the excitation process.
>
> I also know that it is quite unlikely that the armature has magically developed a damaged winding in a week's time of sitting idle.
>
> FWIW a unit with a dead excitation subsystem (open field winding, defective bridge, or failed compounding reactor) will still make a few volts AC
> due to the residual magnetism mentioned earlier - and this voltage will increase a slight bit with increased engine RPM.
>
> 73, Jim N8ECI
>
> Jim Miller
> 1977 Eleganza
> 1977 Royale
> Hamilton, OH

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana