What is it now? Generator issue.

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ken harland

New member
Dec 30, 2005
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Well, I'm finally back on it and still facing the same issue - no power. I almost started a new thread but then all that courteously responded to
this one would start all over and I'd have to answer all the same questions again.

Here's the backstory - two years ago generator was running fine, both A/C's on and cooling and I stepped away for a bit and came back to find
generator had stopped. Turned off A/C's and restarted, now no power coming out. Since it died with a load, suspected bridge rectifier had failed.
Then life got in the way and this problem went unaddressed since then. I've started and run the engine and driven it periodically during that time
but that's all I had time to do. And fortunately it still starts and runs fine.

So back to the generator and the rectifier - as I went to pull it out, I saw a wire off the lower brush housing. Wasn't sure if I pulled it off
accidently but pushing it back on was way too easy so it either fell off on its own and which would be my good luck, or I bumped and it came off.
Tightened the quick disconnect and pushed it back on, started the generator but still no power. Oh well, one can hope!

So I finished pulling the rectifier, tested it and found all diodes open, or so I thought. Bought a new one and just out of curiosity, tested it as
well and got the same results!! WTH! Changed the DVM to the 20k scale and diodes measure 9k ohms in one direction and open in the other. Checked the
old rectifier - same results! Turns out cheap DVMs don't put out enough voltage on the lower scales to pass current through a diode!

So anyway, back to my problem. I decided to check the condition of the lower set of brushes and found one with the wire misrouted and keeping it from
fully extending. I corrected that and with fingers crossed, re-installed and restarted the generator. Nope - no joy!

I spent some time reading all other 'Onan with no power' threads and it appears the only thing I haven't tried is flashing the thing. What I'm unsure
about it how do I determine F1 and F2? In all the reading I've done today, I haven't spotted the answer. I do read 38 ohms across the windings so
I'm not dealing with a short or open.

Something to keep in mind, it was 2 years ago when I started this thread. The generator at that time had not been run in some time (months) as I was
chasing a control board problem. I replaced the control board with one of the new Dino models and was running it when it died and then lost power.
Now it's been sitting for two years but still starts and runs smoothly.

So should I flash it?

Another question though, does the control board play any role in this power generation. I would think it does and that's the one thing that was
changed before this occurred with a new dino board. Could I be looking at some issue related with changing the board?
--
1978 Eleganza II
 
The control board has nothing to do with the charging only with motor starting and running and low oil pressure shutoff.
If your bridge rectifier tests all right then you could try flashing the magnetic field.
Check all connectors on the generator. There are some in plastic tubes by the brushes. The spade connectors are brass and they loose their tension and provide poor connections. I replaced mine with steel ones years ago and covered them with electrolytic grease to prevent corrosion. That took care of my charging problems.

Emery

>
> Well, I'm finally back on it and still facing the same issue - no power. I almost started a new thread but then all that courteously responded to
> this one would start all over and I'd have to answer all the same questions again.
>
> Here's the backstory - two years ago generator was running fine, both A/C's on and cooling and I stepped away for a bit and came back to find
> generator had stopped. Turned off A/C's and restarted, now no power coming out. Since it died with a load, suspected bridge rectifier had failed.
> Then life got in the way and this problem went unaddressed since then. I've started and run the engine and driven it periodically during that time
> but that's all I had time to do. And fortunately it still starts and runs fine.
>
> So back to the generator and the rectifier - as I went to pull it out, I saw a wire off the lower brush housing. Wasn't sure if I pulled it off
> accidently but pushing it back on was way too easy so it either fell off on its own and which would be my good luck, or I bumped and it came off.
> Tightened the quick disconnect and pushed it back on, started the generator but still no power. Oh well, one can hope!
>
> So I finished pulling the rectifier, tested it and found all diodes open, or so I thought. Bought a new one and just out of curiosity, tested it as
> well and got the same results!! WTH! Changed the DVM to the 20k scale and diodes measure 9k ohms in one direction and open in the other. Checked the
> old rectifier - same results! Turns out cheap DVMs don't put out enough voltage on the lower scales to pass current through a diode!
>
> So anyway, back to my problem. I decided to check the condition of the lower set of brushes and found one with the wire misrouted and keeping it from
> fully extending. I corrected that and with fingers crossed, re-installed and restarted the generator. Nope - no joy!
>
> I spent some time reading all other 'Onan with no power' threads and it appears the only thing I haven't tried is flashing the thing. What I'm unsure
> about it how do I determine F1 and F2? In all the reading I've done today, I haven't spotted the answer. I do read 38 ohms across the windings so
> I'm not dealing with a short or open.
>
> Something to keep in mind, it was 2 years ago when I started this thread. The generator at that time had not been run in some time (months) as I was
> chasing a control board problem. I replaced the control board with one of the new Dino models and was running it when it died and then lost power.
> Now it's been sitting for two years but still starts and runs smoothly.
>
> So should I flash it?
>
> Another question though, does the control board play any role in this power generation. I would think it does and that's the one thing that was
> changed before this occurred with a new dino board. Could I be looking at some issue related with changing the board?
> --
> 1978 Eleganza II
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
> I spent some time reading all other 'Onan with no power' threads and it appears the only thing I haven't tried is flashing the thing. What I'm unsure
> about it how do I determine F1 and F2? In all the reading I've done today, I haven't spotted the answer. I do read 38 ohms across the windings so
> I'm not dealing with a short or open.


Flash the field using a 12V battery.

How to identify? F1 is attached to the bridge + terminal and F2 to bridge - terminal. See pp. 44 of the 6kW service manual for the schematic that shows this.

Disconnect F1 and F2 from the bridge before flashing.

Use only a battery for this procedure... do not use a DC power supply because the flyback voltage pulse from the field windings can cook your power supply.


Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
 
Did you actually replace the bridge rectifier? That’s my first suspect.

The loose wire I had assumed was for the early starter battery charging before the house batteries did the trick.

I am frequently besotted with overthinking issues and under acting on them!

Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont California

>
>> I spent some time reading all other 'Onan with no power' threads and it appears the only thing I haven't tried is flashing the thing. What I'm unsure
>> about it how do I determine F1 and F2? In all the reading I've done today, I haven't spotted the answer. I do read 38 ohms across the windings so
>> I'm not dealing with a short or open.
>
>
> Flash the field using a 12V battery.
>
> How to identify? F1 is attached to the bridge + terminal and F2 to bridge - terminal. See pp. 44 of the 6kW service manual for the schematic that shows this.
>
> Disconnect F1 and F2 from the bridge before flashing.
>
> Use only a battery for this procedure... do not use a DC power supply because the flyback voltage pulse from the field windings can cook your power supply.
>
>
> Jim Miller
> 1977 Eleganza
> 1977 Royale
> Hamilton, OH
>
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Thanks for the responses, all are appreciated.

First thing I did today was pull the old rectifier and flash the magnetic field with a 12 volt battery. I actually closed the connection to the
battery 3 - 4 times, leaving it connected for 2-3 seconds each time. Does it take more than that?

Installed old rectifier - no power

Modified new rectifier to fit connector housing and installed it- no power.

What I did notice but may have not been looking for before was as soon as the starter disengaged, there was 3 - 6 VAC briefly at the breaker. In
earlier tests I was not holding the test lead to the breaker until after the engine was running. Today I held it there as I started the motor so what
I saw may have always been the case, whatever that means.

I have not pulled the upper brushes but have looked closely at the connections and they appear to be well attached. I can see why changing out those
brushes would be a pain! Based on the amount of brush remaining on the lower ones, and assuming all are the same age, the uppers should be fine.
There is approximately the same length of the braided wire loop from the brush to its connector in the uppers as is in the lowers.

What next?
--
1978 Eleganza II
 
I disconnected the wires to the lower brushes and there is continuity between them, so they're not open.

And assuming the armature is grounded through its bearing and into the housing, there isn't a short within the armature.

At this point,the generator should be putting out AC power! The only component not tested or replaced is the compounding reactor but it doesn't seem
to be related to a 'no power' condition.
--
1978 Eleganza II
 
Low ac voltage and high fluctuating hertz is more than luckily a problem with the bridge rectifier.
I noticed that the original is marked for ac but not + and -.
Try rotating it 180 degeres.

--
1977 Kingsley 455 as stock as it gets except lots of Ragusa parts
 
Did you check for voltage at both sides of the circuit breaker at the top of the Onan?

I worked on a friend’s Onan once that had 120 volts at both sides so I knew that the Onan was generating power. I found that the wire leading to the plug in the electrical compartment had an open. There was a connection at the wall where the wire from the Onan led inside the wall. The wire was broken there.

Emery Stora

>
> Thanks for the responses, all are appreciated.
>
> First thing I did today was pull the old rectifier and flash the magnetic field with a 12 volt battery. I actually closed the connection to the
> battery 3 - 4 times, leaving it connected for 2-3 seconds each time. Does it take more than that?
>
> Installed old rectifier - no power
>
> Modified new rectifier to fit connector housing and installed it- no power.
>
> What I did notice but may have not been looking for before was as soon as the starter disengaged, there was 3 - 6 VAC briefly at the breaker. In
> earlier tests I was not holding the test lead to the breaker until after the engine was running. Today I held it there as I started the motor so what
> I saw may have always been the case, whatever that means.
>
> I have not pulled the upper brushes but have looked closely at the connections and they appear to be well attached. I can see why changing out those
> brushes would be a pain! Based on the amount of brush remaining on the lower ones, and assuming all are the same age, the uppers should be fine.
> There is approximately the same length of the braided wire loop from the brush to its connector in the uppers as is in the lowers.
>
> What next?
> --
> 1978 Eleganza II
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
With AC that shouldn’t make any difference but go ahead and try it if you want.

Emery Stora

>
> Low ac voltage and high fluctuating hertz is more than luckily a problem with the bridge rectifier.
> I noticed that the original is marked for ac but not + and -.
> Try rotating it 180 degeres.
>
>
> --
> 1977 Kingsley 455 as stock as it gets except lots of Ragusa parts
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
> Low ac voltage and high fluctuating hertz is more than luckily a problem with the bridge rectifier.
> I noticed that the original is marked for ac but not + and -.
> Try rotating the new one 180 degrees.'
The original is marked 'AC' and '-' and the new one is marked 'AC' and '+' and they correspond with each other with the plus and minuses being
diagonally opposite each other. I guess if there's no harm I can rotate it but I've been careful to remove and install either correctly. Of course
working upside down often leads to disorientation which is why I took pictures with my phone then marked the housing accordingly.

> Did you check for voltage at both sides of the circuit breaker at the top of the Onan?
>
> Emery Stora

Yes but it's easy to see which side is which.
--
1978 Eleganza II
 
Did you have voltage at both sides of the circuit breaker? You said “yes, but it’s easy to see which side is which”.
That confused me.
If you indeed have viltage at both sides then you Onan is working.

Emery Stora

>

>> Low ac voltage and high fluctuating hertz is more than luckily a problem with the bridge rectifier.
>> I noticed that the original is marked for ac but not + and -.
>> Try rotating the new one 180 degrees.'
> The original is marked 'AC' and '-' and the new one is marked 'AC' and '+' and they correspond with each other with the plus and minuses being
> diagonally opposite each other. I guess if there's no harm I can rotate it but I've been careful to remove and install either correctly. Of course
> working upside down often leads to disorientation which is why I took pictures with my phone then marked the housing accordingly.
>

>> Did you check for voltage at both sides of the circuit breaker at the top of the Onan?
>>
>> Emery Stora
>
> Yes but it's easy to see which side is which.
> --
> 1978 Eleganza II
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
The original on mine was just marked with AC no + or -.
The AC doesn't matter but I was told the +and- does.
Was low voltage 5 to10 with 80 to 100 hertz before I rotated it.
When I changed mine I had to rotate it 180 deg ahd then it worked.
So it looks like +and - matter.

> > Low ac voltage and high fluctuating hertz is more than luckily a problem with the bridge rectifier.
> > I noticed that the original is marked for ac but not + and -.
> > Try rotating the new one 180 degrees.'
> The original is marked 'AC' and '-' and the new one is marked 'AC' and '+' and they correspond with each other with the plus and minuses being
> diagonally opposite each other. I guess if there's no harm I can rotate it but I've been careful to remove and install either correctly. Of course
> working upside down often leads to disorientation which is why I took pictures with my phone then marked the housing accordingly.
>

> > Did you check for voltage at both sides of the circuit breaker at the top of the Onan?
> >
> > Emery Stora
>
> Yes but it's easy to see which side is which.

--
1977 Kingsley 455 as stock as it gets except lots of Ragusa parts
 
Stand by, may have found my problem. I decided I had to pull the upper brush assembly just to covers all bases and one of the brush connectors was
partially failed. Can't continue right now and won't be back for a couple of days. I'll provide an update then.
--
1978 Eleganza II
 
> Did you have voltage at both sides of the circuit breaker? You said "yes, but it's easy to see which side is which".
> That confused me.
> If you indeed have voltage at both sides then you Onan is working.
>
> Emery Stora

All I meant was I know which side comes from the generator and which side goes to the coach, nothing more than that. It's still zero volts no matter
which side I test.
--
1978 Eleganza II
 
OK
Then I still suspect that you have a loose connection somewhere. Check all your wires going to and from the generator section. Especially those of the brushes. As I said before those spade connectors made of brass will loosen up and loose their tension. If you try to squeeze them they may break so you may have to crimp some new ones in place.

Emery Stora

>

>> Did you have voltage at both sides of the circuit breaker? You said "yes, but it's easy to see which side is which".
>> That confused me.
>> If you indeed have voltage at both sides then you Onan is working.
>>
>> Emery Stora
>
> All I meant was I know which side comes from the generator and which side goes to the coach, nothing more than that. It's still zero volts no matter
> which side I test.
> --
> 1978 Eleganza II
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
> OK
> Then I still suspect that you have a loose connection somewhere. Check all your wires going to and from the generator section. Especially those of
> the brushes. As I said before those spade connectors made of brass will loosen up and loose their tension. If you try to squeeze them they may break
> so you may have to crimp some new ones in place.
>
> Emery Stora

See my earlier post.
--
1978 Eleganza II
 
> All I meant was I know which side comes from the generator and which side goes to the coach, nothing more than that. It's still zero volts no matter which side I test.


The F1 and F2 leads are most certainly polarity sensitive for the reason described below. Are you sure that you have them back onto the original + and - positions on the rectifier to match their electrical arrangement when the old one was removed?

It is imperative that they go back onto the same terminals they originally came off of. In other words whichever lead was attached to rectifier + must be reattached to the new rectifier's +.

The voltage regulation system depends on the residual magnetic field in the iron of the field assembly in order for the excitation to begin. This residual field allows the armature to produce a couple volts of AC on its own when the unit starts to turn; this small amount of AC then goes through the rectifier and the resultant DC intensifies the residual magnetic field - which then produces more AC that is again rectified to DC and adds yet more magnetic field and yet more AC output. This process repeats in a continuous way until the output voltage reaches the point where it is clamped to somewhere near 130V by the thyrector device attached to the compounding reactor.

If the F1 and F2 leads are reversed from their original configuration then the voltage produced by the residual field reverses the magnetic field crossing the armature and the output voltage immediately declines to near zero. If the unit is run long enough in this configuration then the residual field in the assembly will start to reverse itself.

As delivered from the factory F1 is attached to rectifier + and F2 to rectifier negative... but you cannot bet on this being the case if some previous owner did a reversed field flash and then swapped the + and - leads on the rectifier. The only way to know for sure is to take good notes and pictures before disconnecting the old rectifier. This points out the problem with the facebook types who want a cookbook “tell me how to fix it” solution - one simply cannot assume anything with a 40 year old machine that has had an unknown number of random hands fiddling around with it in the past.

All bridge rectifiers are labeled in one way or another to indicate which terminal is +; it may be a printed or silkscreened indicator or there may be a notch on the side of the rectifier’s body that denotes the positive terminal. In some cases the pin orientation specifies the positive terminal but that situation is rare.

—Jim


Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
 
> This points out the problem with the facebook types who want a cookbook “tell me how to fix it” solution - one simply cannot assume anything with a 40 year old machine that has had an unknown number of random hands fiddling around with it in the past.


To clarify my comment about “facebook types” - I am by no means referring to the person who originally posted the excitation question.

Rather, I am making a generalization about what I see as a disturbing trend of people buying a TZE and assuming that there are quick and easy solutions to any given technical problem they may encounter - and that a correct answer to their question will be forthcoming after merely posting a picture or a video of whatever ails them. I try as hard as I can to stay with the FB group and help new owners with Onan problems but doing so has been quite challenging especially with the amount of patently incorrect and in some cases dangerous advice that respondents provide in response to questions.

And of course there is no effective way to search the FB group for previously answered questions and thus we are doomed to answer the same questions over and over in perpetuity. Maybe I should stick with GMCnet and sign off the FB group for good!


Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
 
>
> > All I meant was I know which side comes from the generator and which side goes to the coach, nothing more than that. It's still zero volts
> > no matter which side I test.
>
> The F1 and F2 leads are most certainly polarity sensitive for the reason described below. Are you sure that you have them back onto the original +
> and - positions on the rectifier to match their electrical arrangement when the old one was removed?

I think there's some confusion here, Emory was talking about the leads to and from the circuit breaker, not the field windings and that's what I
responded to. Quote:
> It is imperative that they go back onto the same terminals they originally came off of. In other words whichever lead was attached to rectifier +
> must be reattached to the new rectifier's +.

I did not remove the wires from the rectifier housing, I simply made up a pair of cables with male quick disconnects and plugged them into the
appropriate connections in the housing. And before I removed the rectifier the first time, I marked the housing with the AC & negative positions
noted on the rectifier. And then I confirmed those with the markings on the top of the housing.

Quote:
> --Jim
>
>
> Jim Miller
> 1977 Eleganza
> 1977 Royale
> Hamilton, OH
>
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org


--
1978 Eleganza II
 
OH. OK. I just read your post. Hope that solves your problem. I found that those spade connectors made of brass would crack when you try to tighten them so I replaced them with steel ones.
But you have to put some dielectric grease on them to prevent corrosion.

Emery Stora

>

>> OK
>> Then I still suspect that you have a loose connection somewhere. Check all your wires going to and from the generator section. Especially those of
>> the brushes. As I said before those spade connectors made of brass will loosen up and loose their tension. If you try to squeeze them they may break
>> so you may have to crimp some new ones in place.
>>
>> Emery Stora
>
> See my earlier post.
> --
> 1978 Eleganza II
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
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