Home » Public Forums » GMCnet » Burnt Resistor on Onan Board
| Burnt Resistor on Onan Board [message #317260] |
Tue, 09 May 2017 13:00  |
Jon payne
Messages: 495
Registered: May 2008
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Guys,
Have a problem with with the Onan. It starts but immediately shuts down. First was thinking it was the LOP circuit but after thoroughly checking that circuit no faults were found. Also, if it was the LOP I would expect it to run 3 to 5 seconds. The scenario I'm facing it runs as long as the start switch is pressed, once released it stops. I inspected the control board and found one of the resistors burnt, pictured below. Trying to figure out which resistor this is I read up on the control board operation by Duane Simmons, and I'm thinking it is resistor R1 (pictured below) which is part of the circuit that controls the K2 relay which controls the K3 relay which keeps the Onan running.
So, I need to obviously replace the resistor but wondering how I determine the correct resistor. This board is not the original board but is the replacement from Dinosaur. On the PC board it appears to be marked "56 ohms" but if that is right I still think I need to know the specs, volts & watts?
I'm sure I can contact Dinosaur but wondering if one of the electronic gurus here could lead me to the right resistor I need.
Thanks,
Jon
http://www.gmcmhphotos.com/photos/data/5607/Onan_Board.jpg
http://www.gmcmhphotos.com/photos/data/5607/Onan_Board_Schem.JPG
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: Burnt Resistor on Onan Board [message #317263 is a reply to message #317260] |
Tue, 09 May 2017 14:00  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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My understanging is the Dinosaur is a reengineer/rededign so the Onan drawings are not of use. I'd contact them as I remember reading something about a recuring issue
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Burnt Resistor on Onan Board [message #317267 is a reply to message #317260] |
Tue, 09 May 2017 14:44 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Very Interesting.
George Zhookoff, Jim Miller, and I have been investigating that issue for a long time. George has gone through 3 of them and at least one Onan board for the same issue. We are not sure what the issue is that is causing the problem as the resistor only burns up every couple of years. At Bean Station last week we took a couple of voltage readings just to see where George's alternator was running on output voltage. His read 31.5VAC at 250 cycles. We think the voltage should be 26 to 32 VAC.
We also have looked at the value of that resistor and found that it varies based on when the board was made. Dinosaur sent him two different modified boards to try and both burned the resistor after a year or two of operation. So I do not have an answer as two what is causing the problem, and I do not know what the correct resistor value is. I can tell you one of the modified boards George had has a pair of 45 ohm resistors in parallel for a value of 22.5 ohms.
If you are going to be at the work rally next week, we can look at mine and see what it's value is. Mine has been in for many years without a problem. I do not have my coach at home so I can not look at it now to see what the resistor value is. I was going to take one more reading on George's now operational board but did not get to it before I left the rally.
You might want to contact Dinosaur engineering and tell them you are also having the same problem. They might send you a modified board. Contact George for the Engineer's name. I do not have it.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Burnt Resistor on Onan Board [message #317270 is a reply to message #317260] |
Tue, 09 May 2017 15:21 |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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Maybe the capacitor is shorted, causing the resistor to burn.
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: [GMCnet] Burnt Resistor on Onan Board [message #317272 is a reply to message #317267] |
Tue, 09 May 2017 16:43 |
k2gkk
Messages: 4452
Registered: November 2009
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I suspect that the resistor in question MAY be of inadequate wattage dissipation rating!
If any resistor can be accessed during operation, a measurement of the voltage drop across that resistor can be measured. At that point, Ohm's law can be used to determine the actual wattage being dropped across that resistor.
Power P (in Watts) = Current I (in Amps) times voltage E (in Volts).
Ohm's Law states that I (Amps) = E (Volts) divided by R (Ohms).
Putting that equivalency into the Power formula means that P in Watts = voltage
squared times the resistance. A resistor with double that wattage should be chosen for the task.
The following is Mac's Law to explain and use Ohm's Law:
Let E represent an Eagle. Let R represent a Rabbit. Let I represent an Indian.
If an Eagle looks at a Rabbit and an Indian, the Rabbit and the Indian will be on the same level so: E = R x I.
If an Indian looks at the Eagle and the Rabbit, the Eagle will be above the Rabbit so:
I = E/R or E over R (E divided by R).
If a Rabbit looks at the Eagle and the Indian, the Eagle will be above the Indian so:
R = E/I or E over I (E divided by I).
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ Since 30 November '53 ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ Member GMCMI and Classics ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ ~ TZE166V101966 ~ ~ ~ ~
~ ~ ~ '76 ex-Palm Beach ~ ~ ~
~~ k2gkk + hotmail dot com ~~
~ www.gmcmhphotos.com/okclb ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
______________
|[ ]~~~[][ ][]\
"--OO--[]---O-"
________________________________
From: Gmclist on behalf of Ken Burton
Sent: Tuesday, May 9, 2017 14:44
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Burnt Resistor on Onan Board
Very Interesting.
George Zhookoff, Jim Miller, and I have been investigating that issue for a long time. George has gone through 3 of them and at least one Onan board
for the same issue. We are not sure what the issue is that is causing the problem as the resistor only burns up every couple of years. At Bean
Station last week we took a couple of voltage readings just to see where George's alternator was running on output voltage. His read 31.5VAC at 250
cycles. We think the voltage should be 26 to 32 VAC.
We also have looked at the value of that resistor and found that it varies based on when the board was made. Dinosaur sent him two different modified
boards to try and both burned the resistor after a year or two of operation. So I do not have an answer as two what is causing the problem, and I do
not know what the correct resistor value is. I can tell you one of the modified boards George had has a pair of 45 ohm resistors in parallel for a
value of 22.5 ohms.
If you are going to be at the work rally next week, we can look at mine and see what it's value is. Mine has been in for many years without a
problem. I do not have my coach at home so I can not look at it now to see what the resistor value is. I was going to take one more reading on
George's now operational board but did not get to it before I left the rally.
You might want to contact Dinosaur engineering and tell them you are also having the same problem. They might send you a modified board. Contact
George for the Engineer's name. I do not have it.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Burnt Resistor on Onan Board [message #317274 is a reply to message #317260] |
Tue, 09 May 2017 17:24 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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> On May 9, 2017, at 2:00 PM, Jon Payne wrote:
> Have a problem with with the Onan. It starts but immediately shuts down. First was thinking it was the LOP circuit but after thoroughly checking that circuit no faults were found. Also, if it was the LOP I would expect it to run 3 to 5 seconds. The scenario I'm facing it runs as long as the start switch is pressed, once released it stops. I inspected the control board and found one of the resistors burnt
I’ve written this up on GMCnet a couple of times and have a page on it:
http://www.jcmco.com/gallery/album30
The circuit design is such that they half-wave rectify the output of the flywheel alternator, run it through a series current limiting resistor and then into the coil of a 12VDC relay. The voltage presented at the relay coil is way too high - which causes the coil’s insulation to melt and short out - which begins to reduce the coil resistance - thus increasing the heat in the coil even more - and eventually the melted coil’s resistance is so low that the power dissipated by the series resistor becomes high enough to roast it.
I suspect that on some machines the flywheel alternator voltage is not high enough to cause this particular failure mode - but on other machines it is.
My fix involves changing to a 24V relay and a larger series dropping resistor. Both are drop-in replacements for the Dino components.
—Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Burnt Resistor on Onan Board [message #317275 is a reply to message #317272] |
Tue, 09 May 2017 17:35 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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Sorry, but that's the most confusing thing I have read in a long time.
Much easier for me to just substitute E/R for Iin the power equation
Emery Stora
> On May 9, 2017, at 3:43 PM, D C _Mac_ Macdonald wrote:
>
> I suspect that the resistor in question MAY be of inadequate wattage dissipation rating!
>
> If any resistor can be accessed during operation, a measurement of the voltage drop across that resistor can be measured. At that point, Ohm's law can be used to determine the actual wattage being dropped across that resistor.
>
> Power P (in Watts) = Current I (in Amps) times voltage E (in Volts).
>
> Ohm's Law states that I (Amps) = E (Volts) divided by R (Ohms).
>
> Putting that equivalency into the Power formula means that P in Watts = voltage
>
> squared times the resistance. A resistor with double that wattage should be chosen for the task.
>
> The following is Mac's Law to explain and use Ohm's Law:
>
> Let E represent an Eagle. Let R represent a Rabbit. Let I represent an Indian.
>
> If an Eagle looks at a Rabbit and an Indian, the Rabbit and the Indian will be on the same level so: E = R x I.
>
> If an Indian looks at the Eagle and the Rabbit, the Eagle will be above the Rabbit so:
>
> I = E/R or E over R (E divided by R).
> If a Rabbit looks at the Eagle and the Indian, the Eagle will be above the Indian so:
> R = E/I or E over I (E divided by I).
>
> ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
> ~~ ~ D C "Mac" Macdonald ~ ~~
> ~ ~ Amateur Radio - K2GKK ~ ~
> ~ ~ Since 30 November '53 ~ ~
> ~ ~ USAF and FAA, Retired ~ ~
> ~ Member GMCMI and Classics ~
> ~ ~ ~ Oklahoma City, OK ~ ~ ~
> ~~ ~ ~ "The Money Pit" ~ ~ ~~
> ~ ~ ~ ~ TZE166V101966 ~ ~ ~ ~
> ~ ~ ~ '76 ex-Palm Beach ~ ~ ~
> ~~ k2gkk + hotmail dot com ~~
> ~ www.gmcmhphotos.com/okclb ~
> ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
> ______________
> |[ ]~~~[][ ][]\
> "--OO--[]---O-"
>
>
> ________________________________
> From: Gmclist on behalf of Ken Burton
> Sent: Tuesday, May 9, 2017 14:44
> To: gmclist@list.gmcnet.org
> Subject: Re: [GMCnet] Burnt Resistor on Onan Board
>
> Very Interesting.
>
> George Zhookoff, Jim Miller, and I have been investigating that issue for a long time. George has gone through 3 of them and at least one Onan board
> for the same issue. We are not sure what the issue is that is causing the problem as the resistor only burns up every couple of years. At Bean
> Station last week we took a couple of voltage readings just to see where George's alternator was running on output voltage. His read 31.5VAC at 250
> cycles. We think the voltage should be 26 to 32 VAC.
>
> We also have looked at the value of that resistor and found that it varies based on when the board was made. Dinosaur sent him two different modified
> boards to try and both burned the resistor after a year or two of operation. So I do not have an answer as two what is causing the problem, and I do
> not know what the correct resistor value is. I can tell you one of the modified boards George had has a pair of 45 ohm resistors in parallel for a
> value of 22.5 ohms.
>
> If you are going to be at the work rally next week, we can look at mine and see what it's value is. Mine has been in for many years without a
> problem. I do not have my coach at home so I can not look at it now to see what the resistor value is. I was going to take one more reading on
> George's now operational board but did not get to it before I left the rally.
>
> You might want to contact Dinosaur engineering and tell them you are also having the same problem. They might send you a modified board. Contact
> George for the Engineer's name. I do not have it.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: [GMCnet] Burnt Resistor on Onan Board [message #317277 is a reply to message #317272] |
Tue, 09 May 2017 18:02 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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On May 9, 2017, at 5:43 PM, D C _Mac_ Macdonald wrote:
> I suspect that the resistor in question MAY be of inadequate wattage dissipation rating!
The issue is not the resistor’s wattage rating - the problem is the design of the circuit in which it resides; even if you put in a higher wattage resistor the relay coil would still melt and cease to function.
In essence the problem is the resistor’s _value_ coupled with the resistance of the relay coil it is in series with.
In developing a fix I experimented with changing the resistor and keeping the 12V relay but the resistor had to be so large that the relay coil would not pull in reliably - hence the change to a 24V relay of the same pinout.
There are pictures of the melted relay coils on the photo album I linked to earlier.
—73, Jim N8ECI
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Burnt Resistor on Onan Board [message #317279 is a reply to message #317278] |
Tue, 09 May 2017 18:31 |
A Hamilto
Messages: 4508
Registered: April 2011
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A Hamilto wrote on Tue, 09 May 2017 18:28]Mr. Miller, Sir,
Can you tell us a manufacturer and part number for the 24V version of your K2 replacement? Enquiring minds want to know.
Thanks Never mind. I took a closer look at the photo here and found the part number. JW2SN-DC24V Sorry about being a pest.
[Updated on: Tue, 09 May 2017 18:32] Report message to a moderator |
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| Re: Burnt Resistor on Onan Board [message #317298 is a reply to message #317269] |
Tue, 09 May 2017 23:06 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Please keep in mind that we are discussing Dinosaur boards and NOT OEM Onan boards.
On the OEM Onan board usually the K2 coil fails, while on Dinosaur boards the series resistor (R1) seems to fail leaving the diode, relay coil, and filter capacitor intact.
The real problem is it took almost 3 years for George's most recent resistor to burn up. Since the most of the voltage drop is across the relay coil and not the series resistor, most of the heat is generated and power consumed is in the coil. In George's case it is always the resistor and not the relay coil that burns. It should be the reverse in my opinion.
The following is mostly from memory and if you see an error please say so.
I looked up or measured the relay coil once. If I remember correctly it was 275 ohms and the current draw was around 45 ma. at 12 VDC. That calculates to slightly over 1/2 watt consumed in the relay coil at 12 VDC. If I remember correctly a 1/2 wave diode should put out approximately .45% filtered (smoothed out) DC when compared to the input. So if we feed 30 VAC (RMS) in to the circuit from the Onan alternator, we should see around 13.5 VDC after is is filtered or smoothed out by the filter cap. So the series resistor only needs to drop about 1.5 volts to keep the relay happly.
That calculates to be a resistance of 21.4 ohms and .07 watts for the series resistor. This is very close to 22.5 ohms at 1/2 watt that Dinosaur did on their modded board for George.
Now maybe you can see why I am confused as to why George, and some others, continue to burn resistors and not diodes or relay coils. It appears to me that the the actual resistor wattage consumed is less than 1/10 watt while the one on the Dino board is rated at either 1/4 or 1/2 watt.
I have considered changing the relay too something like 24 VAC with a small resistor in series with it. There is no reason that K2 needs to be a DC coil relay and this would eliminate one component (the diode) although it never seems to fail. I'm not sure that would help the problem.
I have also thought of a Zener and another load resistor to bleed off some of the excess voltage when this anomaly occurs.
I do not know where to go next. I'll keep looking. .
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Burnt Resistor on Onan Board [message #317313 is a reply to message #317260] |
Wed, 10 May 2017 07:59 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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I wonder if the 'fail event' happens at shutdown. The unit works and does not die 'mid run' , but then fails to work the next time and resistor is observed as burnt. Is this assumption true? Perhaps a scope on the circuit during shut down would show some anomalies as the sine waves become fewer over time and the voltage output collapses. I am running an OE Onan board.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Burnt Resistor on Onan Board [message #317315 is a reply to message #317260] |
Wed, 10 May 2017 08:56 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Thinking out loud -- since the VR has been abandoned as a bat charger by most, can we rewire to feed the board with regulated AC to temper the Wild West environment the board resides in? This may require some value changes to run at lower voltage. Or build a simple VR to supply the board so it never sees above 30V.?
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Burnt Resistor on Onan Board [message #317316 is a reply to message #317260] |
Wed, 10 May 2017 09:02 |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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Senior Member |
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I believe that Dinosaur should have designed the board with a 1 watt resistor
and not the 1/2 watt that burns up.
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: Burnt Resistor on Onan Board [message #317317 is a reply to message #317313] |
Wed, 10 May 2017 09:13 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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JohnL455 wrote on Wed, 10 May 2017 07:59I wonder if the 'fail event' happens at shutdown. The unit works and does not die 'mid run' , but then fails to work the next time and resistor is observed as burnt. Is this assumption true? Perhaps a scope on the circuit during shut down would show some anomalies as the sine waves become fewer over time and the voltage output collapses. I am running an OE Onan board.
I honestly have no idea, but I'll ask people if they have had it fail running or just at start up. I can not see how the reducing voltage (and frequency) on shutdown would cause the failure, but I'm open to anything that might fix the issue.
It is a very simple circuit. The 30 VAC comes off of the alternator coils behind the flywheel. It goes through 1 diode and then the resistor and relay coil. There is one filter cap across the relay coil to smooth out the DC. There should not be too much DC ripple as the frequency of the AC is 250 cycles.
The confusing thing to me is why the 1/2 watt resistor burns when calculated wattage is less that 1/10 of a watt. This tells me that we are going way over voltage on the, or the relay coil, capacitor, or diode is shorting.
The problem is that I can not see what would cause us to go over voltage, other than over speed, and after the failure we have no evidence of any component failure (shorting) other than the resistor(s).
I have had two ideas for a work around. One would be a 1/10 or even 1/4 amp fuse inline and the other would be Zener diode to shunt off excess voltage. Neither of these are a very elegant solution. As I stated before in the previous posting, we might also look at changing K2 to a 24 VAC relay. I'm not sure what that might accomplish other than the elimination of the diode and filter capacitor.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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