| Onan will not stay running [message #132177] |
Mon, 27 June 2011 01:46  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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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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