On Apr 17, 2015, at 1:31 AM, W R WARN wrote:
>
> The 6KOnan is proving 127 volts at the outlets with no load. But under load with the hot water heater, andor the air conditioner on, the voltage rises to about 139 volts. What do I need to adjust? I didn't see that condition in the manual.

That condition is indeed not in the manual and there are no adjustments.

With the assumption that your engine is at the proper speed (1800 RPM) while under load then you most likely have a failure of the thyrector device in the generator's excitation circuit. The thyrector acts as a voltage clamp on the output of the compounding reactor between leads H1/H2 and X1. If this clamp fails then the excitation voltage to the field coils can rise beyond limits and produce exactly the situation that you've described.

The thyrector is a small molded device that is spliced into the wiring harness in the bell housing near the compounding reactor and it is typically unsupported by anything other than its leads...and in the high-vibration environment of the generator housing it is a candidate for mechanical (not electrical) failure. There's no test procedure for it in the book nor are there any specs on the device that I've been able to find. It might be possible to replace it with a couple back-to-back zener diodes but I've not experimented with doing so.

--Jim "saving the lives of Onans...one unit at a time" Miller
1977 Eleganza II
1977 Royale
Hamilton, OH

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On Apr 17, 2015, at 3:29 PM, Bob de Kruyff wrote:
>
> I thought the Onan voltage was directly proportional to the RPM's and both the speed and sensitivity to load were adjustable via the governor rod and
> spring.

The Onan's output frequency is directly proportional to rotational speed and the voltage is too - albeit to a lesser extent. And yes, engine speed and governor responsiveness are set by the screw and spring.

The output voltage regulation circuit consists of a simplistic (and therefore very reliable) closed-loop system comprised of the compounding reactor and thyrector driving a bridge rectifier and field coils that have specified electrical characteristics. The reactor/thyrector combination vary the amount of current through the field coils which consequently changes the intensity of the magnetic field through which the armature rotates. Decreased mag field intensity = less output voltage. Increased mag field intensity = more output voltage. No adjustments are necessary in order for the system to function within its design parameters.

Varying any of these components can cause the system to not work as intended. For instance, removing the thyrector or replacing it with a device of different characteristics will affect the output voltage across the range of electrical loads that are placed on the unit. Replacing the field coils with ones having a different number of turns or ones made of wire with different resistance characteristics will also change the behavior.

--Jim "saving the lives of Onans...one unit at a time" Miller
1977 Eleganza II
1977 Royale
Hamilton, OH

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OK Boys...my problem is somewhat different.
The good news is that I have the eng. running like a clock...the bad news is that the "unit"
does not put out any electricity !
I bought and installed a new dyno board and bridge rectifier...still nothing.
Since the new rectifier from Jimmy K. is not the same as the old one (the wiring receiver is not the same) I removed each wire singularly at a time and plug each one into what I believe was the right spot,
but I may have screwed up !! Didn't think so but it wont be the first time.

Since I am very electrically challenged...what do I do now ??

OK Boys...my problem is somewhat different.
The good news is that I have the eng. running like a clock...the bad news is that the "unit"
does not put out any electricity !
I bought and installed a new dyno board and bridge rectifier...still nothing.
Since the new rectifier from Jimmy K. is not the same as the old one (the wiring receiver is not the same) I removed each wire singularly at a time and plug each one into what I believe was the right spot,
but I may have screwed up !! Didn't think so but it wont be the first time.

Since I am very electrically challenged...what do I do now ??