Home » Public Forums » GMCnet » Onan will not stay running
| Onan will not stay running [message #132177] |
Mon, 27 June 2011 01:46  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Over the last several years I have worked on several of these start but not stay running problems. There is an alternator in the Onan that generates around 28 to 30 volts AC the Onan board then changes that voltage to around 18 volts DC. A dropping resistor (R1) drops that voltage to around 12 volts DC. That 12 volts is used to pick relay K2 which keeps the ignition and fuel pump running.
On two GMCs over the past few years I have found that the value of R1, which should be 200 ohms, has changed and accordingly the voltage on relay K2 is not enough to pick it.
Well guess what. I found a third one today. Mine was measuring 7.3 volts on the relay coil, not the 12.0 or so that I expected. The 200 ohm resistor measures 299 ohms for a 50% increase. I have never see resistors that weren't damaged or cracked do this before. But now finding a 3rd one I feel something is going on here. Age? Heat? I do not know. I see no evidence of damage or cracking. In the other two I fixed I just soldered another resistor in parallel across the points on the back of the board to bring this back to an effective 200 ohms. My quick calculation in my mind say I'll need a little over 600 ohms in parallel to bring this back into spec.
I just thought I would let every one know what I am stumbling across.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan will not stay running [message #132186 is a reply to message #132177] |
Mon, 27 June 2011 04:26  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Ken, when I took electronics classes, my instructor told me that "resistors
always fail open". Me being young and inexperienced with resistors at the
time believed my Instructor to be telling the truth, and perhaps he was,
according to what ever engineering book he had read that crap out of.
Several years into my working career I had the troubleshooting problem of
weak spark on a mopar product with a ceramic resistor in the
ignition primary to reduce voltage to the points to make them last longer.
When I cranked the engine it would start immediately and when I moved the
ignition switch from start to run, the engine would falter and run very
poorly. Turns out that ceramic resistor could and did have more resistance
than the book said. I checked it against a known value new resistor, and the
new one had what the book said it should have. My training to the contrary,
I refused to believe what the meter was telling me until it dawned on me
that perhaps my Instructor didn't know what the hell he was talking about in
the real world. Have run into that problem a few times on GM products with
the infamous resistance conductor in the ignition primary also, although the
GM products have the added issue of a failed ignition switch to contend with
that adds to the troubleshooting issues. Life teaches us the REAL solutions
to problems, not just the textbook ones. Sounds like the ONANs have led you
down that same path. Me too.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sun, Jun 26, 2011 at 11:46 PM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> Over the last several years I have worked on several of these start but
> not stay running problems. There is an alternator in the Onan that
> generates around 28 to 30 volts AC the Onan board then changes that voltage
> to around 18 volts DC. A dropping resistor (R1) drops that voltage to around
> 12 volts DC. That 12 volts is used to pick relay K2 which keeps the
> ignition and fuel pump running.
>
> On two GMCs over the past few years I have found that the value of R1,
> which should be 200 ohms, has changed and accordingly the voltage on relay
> K2 is not enough to pick it.
>
> Well guess what. I found a third one today. Mine was measuring 7.3 volts
> on the relay coil, not the 12.0 or so that I expected. The 200 ohm resistor
> measures 299 ohms for a 50% increase. I have never see resistors that
> weren't damaged or cracked do this before. But now finding a 3rd one I feel
> something is going on here. Age? Heat? I do not know. I see no evidence of
> damage or cracking. In the other two I fixed I just soldered another
> resistor in parallel across the points on the back of the board to bring
> this back to an effective 200 ohms. My quick calculation in my mind say
> I'll need a little over 600 ohms in parallel to bring this back into spec.
>
> I just thought I would let every one know what I am stumbling across.
>
>
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
> _______________________________________________
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| Re: [GMCnet] Onan will not stay running [message #132189 is a reply to message #132186] |
Mon, 27 June 2011 05:34 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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It just bothers me that this is the third one of these I have stumbled over in the last 5 or 6 years. I do not work on that many Onans. In all three Onans R1 was the resistor that failed. I probably need to calculate it's power consumption. It may be near it's 1/2 watt rating. I'm throwing another in parallel because I hate soldering to those foil patterns even though I use low temp solder I tend to lift them off of the board. Also this will reduce the power consumption on the existing resistor by about 1/2.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan will not stay running [message #132198 is a reply to message #132186] |
Mon, 27 June 2011 07:10 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Those of us who play with FM transmitters have seen this occur on a particular Harris design. Three carbon resistors dissipate some RF energy in one circuit, and they are known to lower in value over the years. My theory is, the RF fuses the carbon... but I never took one apart. On the Mopar dual ceramics (the early electronic ignition), I've once seen the 'run' resistor short, leading to premature coil failure - several coils before I even suspected it.
--johnny
--- On Mon, 6/27/11, James Hupy <jamesh1296@gmail.com> wrote:
From: James Hupy <jamesh1296@gmail.com>
Subject: Re: [GMCnet] Onan will not stay running
To: gmclist@temp.gmcnet.org
Date: Monday, June 27, 2011, 9:26 AM
Ken, when I took electronics classes, my instructor told me that "resistors
always fail open". Me being young and inexperienced with resistors at the
time believed my Instructor to be telling the truth, and perhaps he was,
according to what ever engineering book he had read that crap out of.
Several years into my working career I had the troubleshooting problem of
weak spark on a mopar product with a ceramic resistor in the
ignition primary to reduce voltage to the points to make them last longer.
When I cranked the engine it would start immediately and when I moved the
ignition switch from start to run, the engine would falter and run very
poorly. Turns out that ceramic resistor could and did have more resistance
than the book said. I checked it against a known value new resistor, and the
new one had what the book said it should have. My training to the contrary,
I refused to believe what the meter was telling me until it dawned on me
that perhaps my Instructor didn't know what the hell he was talking about in
the real world. Have run into that problem a few times on GM products with
the infamous resistance conductor in the ignition primary also, although the
GM products have the added issue of a failed ignition switch to contend with
that adds to the troubleshooting issues. Life teaches us the REAL solutions
to problems, not just the textbook ones. Sounds like the ONANs have led you
down that same path. Me too.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sun, Jun 26, 2011 at 11:46 PM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> Over the last several years I have worked on several of these start but
> not stay running problems. There is an alternator in the Onan that
> generates around 28 to 30 volts AC the Onan board then changes that voltage
> to around 18 volts DC. A dropping resistor (R1) drops that voltage to around
> 12 volts DC. That 12 volts is used to pick relay K2 which keeps the
> ignition and fuel pump running.
>
> On two GMCs over the past few years I have found that the value of R1,
> which should be 200 ohms, has changed and accordingly the voltage on relay
> K2 is not enough to pick it.
>
> Well guess what. I found a third one today. Mine was measuring 7.3 volts
> on the relay coil, not the 12.0 or so that I expected. The 200 ohm resistor
> measures 299 ohms for a 50% increase. I have never see resistors that
> weren't damaged or cracked do this before. But now finding a 3rd one I feel
> something is going on here. Age? Heat? I do not know. I see no evidence of
> damage or cracking. In the other two I fixed I just soldered another
> resistor in parallel across the points on the back of the board to bring
> this back to an effective 200 ohms. My quick calculation in my mind say
> I'll need a little over 600 ohms in parallel to bring this back into spec.
>
> I just thought I would let every one know what I am stumbling across.
>
>
> --
> 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
>
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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] Onan will not stay running [message #132228 is a reply to message #132177] |
Mon, 27 June 2011 10:07 |
Terry Taylor
Messages: 113
Registered: October 2004
Location: San Lorenzo, CA
Karma: 0
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Senior Member |
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No, Ken, I have seen this before, resistors (especially carbon ones)
have a finite number of electrons available in them. After many years
of use, they can suffer from electron depletion. Lucas used to make an
electron replenishment kit (Lucas electrics were more likely to suffer
this than others), but it was removed from their product line
somewhere around the same time the the Lucas Genuine Smoke replacement
kit was discontinued. Your only recourse is to replace the carbon
resistor with a new one that is full of electrons. Beware of NOS
carbon resistors, as they can suffer electron depletion just sitting
on the shelf.
(Now running for cover before all of the bricks start flying towards me).
On Sun, Jun 26, 2011 at 11:46 PM, Ken Burton <n9cv@comcast.net> wrote:
>
> Well guess what. I found a third one today. Mine was measuring 7.3 volts on the relay coil, not the 12.0 or so that I expected. The 200 ohm resistor measures 299 ohms for a 50% increase. I have never see resistors that weren't damaged or cracked do this before. But now finding a 3rd one I feel something is going on here. Age? Heat? I do not know. I see no evidence of damage or cracking. In the other two I fixed I just soldered another resistor in parallel across the points on the back of the board to bring this back to an effective 200 ohms. My quick calculation in my mind say I'll need a little over 600 ohms in parallel to bring this back into spec.
>
Terry Taylor
74 ex-Eleganza SE
San Lorenzo. CA
Merchanise Web Site: http://www.dldesignstore.com
Duct tape is like the force.....
It has a light side and a dark side and
It holds the galaxy together.
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| Re: [GMCnet] Onan will not stay running [message #132235 is a reply to message #132228] |
Mon, 27 June 2011 10:38 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
|
Senior Member |
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|
| Terry Taylor wrote on Mon, 27 June 2011 10:07 |
No, Ken, I have seen this before, resistors (especially carbon ones)
have a finite number of electrons available in them. After many years
of use, they can suffer from electron depletion. Lucas used to make an
electron replenishment kit (Lucas electrics were more likely to suffer
this than others), but it was removed from their product line
somewhere around the same time the the Lucas Genuine Smoke replacement
kit was discontinued. Your only recourse is to replace the carbon
resistor with a new one that is full of electrons. Beware of NOS
carbon resistors, as they can suffer electron depletion just sitting
on the shelf.
(Now running for cover before all of the bricks start flying towards me).
On Sun, Jun 26, 2011 at 11:46 PM, Ken Burton <n9cv@comcast.net> wrote:
>
> Well guess what. I found a third one today. Mine was measuring 7.3 volts on the relay coil, not the 12.0 or so that I expected. The 200 ohm resistor measures 299 ohms for a 50% increase. I have never see resistors that weren't damaged or cracked do this before. But now finding a 3rd one I feel something is going on here. Age? Heat? I do not know. I see no evidence of damage or cracking. In the other two I fixed I just soldered another resistor in parallel across the points on the back of the board to bring this back to an effective 200 ohms. My quick calculation in my mind say I'll need a little over 600 ohms in parallel to bring this back into spec.
>
Terry Taylor
74 ex-Eleganza SE
San Lorenzo. CA
Merchanise Web Site: http://www.dldesignstore.com
Duct tape is like the force.....
It has a light side and a dark side and
It holds the galaxy together.
|
Where do the electrons go?
When we were in Dodge City this spring, Heather asked where Miss Kitty was. A guy there told us she went to Florida for the winter and would be back in May. Maybe that is where the missing electrons are.
I learned something today.
Do not let Terry Taylor around anything electronic.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan will not stay running [message #132259 is a reply to message #132228] |
Mon, 27 June 2011 11:58 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Well, acturally that depletion only made a difference in amplifiers feeding digital headphones and digital speakers.
--johnny
--- On Mon, 6/27/11, Terry Taylor <terry.n6mon@gmail.com> wrote:
From: Terry Taylor <terry.n6mon@gmail.com>
Subject: Re: [GMCnet] Onan will not stay running
To: gmclist@temp.gmcnet.org
Date: Monday, June 27, 2011, 3:07 PM
No, Ken, I have seen this before, resistors (especially carbon ones)
have a finite number of electrons available in them. After many years
of use, they can suffer from electron depletion. Lucas used to make an
electron replenishment kit (Lucas electrics were more likely to suffer
this than others), but it was removed from their product line
somewhere around the same time the the Lucas Genuine Smoke replacement
kit was discontinued. Your only recourse is to replace the carbon
resistor with a new one that is full of electrons. Beware of NOS
carbon resistors, as they can suffer electron depletion just sitting
on the shelf.
(Now running for cover before all of the bricks start flying towards me).
On Sun, Jun 26, 2011 at 11:46 PM, Ken Burton <n9cv@comcast.net> wrote:
>
> Well guess what. I found a third one today. Mine was measuring 7.3 volts on the relay coil, not the 12.0 or so that I expected. The 200 ohm resistor measures 299 ohms for a 50% increase. I have never see resistors that weren't damaged or cracked do this before. But now finding a 3rd one I feel something is going on here. Age? Heat? I do not know. I see no evidence of damage or cracking. In the other two I fixed I just soldered another resistor in parallel across the points on the back of the board to bring this back to an effective 200 ohms. My quick calculation in my mind say I'll need a little over 600 ohms in parallel to bring this back into spec.
>
Terry Taylor
74 ex-Eleganza SE
San Lorenzo. CA
Merchanise Web Site: http://www.dldesignstore.com
Duct tape is like the force.....
It has a light side and a dark side and
It holds the galaxy together.
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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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] Onan will not stay running [message #132437 is a reply to message #132177] |
Tue, 28 June 2011 09:29 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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On Jun 27, 2011, at 2:46 AM, Ken Burton wrote:
> Over the last several years I have worked on several of these start
> but not stay running problems.
That's funny, Ken, I have one that wants to start on its own! Well,
it doesn't actually start, but it gets ready to!
When sitting, shutdown, it turns on the fuel pump on its own. The
Hobbs meter runs during this event as well. Pushing the STOP switch
will stop it but only for a few seconds or minutes; it'll then start
doing it again moments later. Thank goodness it doesn't go ahead and
engage the starter! It accumulated 8 hours on the Hobbs before I
finally got ticked off and pulled the harness connector apart.
This failure mode seems to have no correlation with ambient
temperature or how recently the unit ran. It is also not an issue
with the remote start wiring, it exhibits this behavior with the
remote harness disconnected. I haven't looked at the schematic yet as
I'm going to put in a new board and then have a look at the old one on
the bench in my spare time.
73, Jim N8ECI
1977 Eleganza II
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Onan will not stay running [message #132450 is a reply to message #132437] |
Tue, 28 June 2011 11:07 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Jim Miller wrote on Tue, 28 June 2011 09:29 |
On Jun 27, 2011, at 2:46 AM, Ken Burton wrote:
> Over the last several years I have worked on several of these start
> but not stay running problems.
That's funny, Ken, I have one that wants to start on its own! Well,
it doesn't actually start, but it gets ready to!
When sitting, shutdown, it turns on the fuel pump on its own. The
Hobbs meter runs during this event as well. Pushing the STOP switch
will stop it but only for a few seconds or minutes; it'll then start
doing it again moments later. Thank goodness it doesn't go ahead and
engage the starter! It accumulated 8 hours on the Hobbs before I
finally got ticked off and pulled the harness connector apart.
This failure mode seems to have no correlation with ambient
temperature or how recently the unit ran. It is also not an issue
with the remote start wiring, it exhibits this behavior with the
remote harness disconnected. I haven't looked at the schematic yet as
I'm going to put in a new board and then have a look at the old one on
the bench in my spare time.
73, Jim N8ECI
1977 Eleganza II
1977 Royale
Hamilton, OH
|
Tacked or cruddy relay point on K2? I guess you need to see if K2 is energized when it fails.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan will not stay running [message #132465 is a reply to message #132450] |
Tue, 28 June 2011 12:58 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Strangely, I agree with Ken B: The NO contacts of K2 are stuck
closed, or partially so. But, there's a problem with that: If those
contacts are closed, the NC contacts must be open, so there's no way
to engage K!, the Starter solenoid relay, via either the on-board or
the remote switch. But then, you only mentioned using Stop, not
Start.
Let us know what you find.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Tue, Jun 28, 2011 at 12:07 PM, Ken Burton wrote:
> Jim Miller wrote on Tue, 28 June 2011 09:29
>>...
>> When sitting, shutdown, it turns on the fuel pump on its own. The
>> Hobbs meter runs during this event as well. Pushing the STOP switch
>> will stop it but only for a few seconds or minutes; it'll then start
>> doing it again moments later. Thank goodness it doesn't go ahead and
>> engage the starter! It accumulated 8 hours on the Hobbs before I
>> finally got ticked off and pulled the harness connector apart...
> Tacked or cruddy relay point on K2? I guess you need to see if K2 is energized when it fails.
> --
> Ken Burton - N9KB
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Onan will not stay running [message #132535 is a reply to message #132465] |
Tue, 28 June 2011 21:17 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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On Jun 28, 2011, at 1:58 PM, Ken Henderson wrote:
> Strangely, I agree with Ken B: The NO contacts of K2 are stuck
> closed, or partially so. But, there's a problem with that: If those
> contacts are closed, the NC contacts must be open, so there's no way
> to engage K!, the Starter solenoid relay, via either the on-board or
> the remote switch. But then, you only mentioned using Stop, not
> Start.
The unit will start and stop OK when commanded to do so at either the
local or remote switch.
The only problem is the fuel pump starting and stopping on its own
while the unit is not running.
--Jim
1977 Eleganza II
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Onan will not stay running [message #132542 is a reply to message #132535] |
Tue, 28 June 2011 21:32 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Did you say this only started after you installed a prime switch?
Ken H.
On Tue, Jun 28, 2011 at 10:17 PM, Jim Miller wrote:
...
> The unit will start and stop OK when commanded to do so at either the
> local or remote switch.
>
> The only problem is the fuel pump starting and stopping on its own
> while the unit is not running.
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Onan will not stay running [message #132546 is a reply to message #132542] |
Tue, 28 June 2011 22:20 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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On Jun 28, 2011, at 10:32 PM, Ken Henderson wrote:
> Did you say this only started after you installed a prime switch?
No, I never mentioned the prime switch. However: I did install a
prime switch well over a year ago but it only started doing this start-
the-fuel-pump-at-random thing recently - and it still runs the fuel
pump randomly even with the remote start/stop/prime switch wiring
harness completely disconnected.
I'm really not worried about it, I installed a new JimK board for the
time being. I posted the original description only so that others
could "enjoy" hearing about yet another Onan failure mode.
--Jim
73, Jim N8ECI
1977 Eleganza II
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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