Onan Adjustment

[gmctoyman]

Is it possible to adjust the voltage output on an Onan 4K ? Mine runs ~109V no load, and sags to 105V at half load.

[DiskDoctr]

Lynnmor wrote:
For those that have no fancy meter to check frequency, there is a way to do it with clocks.

Plug a clock with a second hand into the generator.

Use another clock/watch with a second hand that is battery powered or plugged into utility power.

Compare the the second hands with each other and when are the same the frequency is correct.

^^ Brilliant ^^

[Lynnmor]

For those that have no fancy meter to check frequency, there is a way to do it with clocks.

Plug a clock with a second hand into the generator.

Use another clock/watch with a second hand that is battery powered or plugged into utility power.

Compare the the second hands with each other and when are the same the frequency is correct.

[bounder39zman]

Depending on the "spec" letter, your KY Onan will have a voltage regulator separate from control board (around 2000, spec H and older).
Or the regulator is built into the control board (spec J and up).
Neither comes from Onan with a voltage adjust capability. As OP stated, verify your meter readings, the sign wave output is pretty "dirty" on
these sets, and an analog meter usually reads inaccurately.
Need to measure voltage and freq (hz) with a RMS digital meter. And yes, if engine running slow, voltage is affected. Governor speed should be adjusted at governor spring (NOT THROTTLE STOP SCREW) for ~62 hz no load, and if working correctly, will droop to ~59 hz or so at full load.
Vlotage should be ~125-115.
If speed correct, then possible causes are dirty rotor field brush slip rings, partially shorted rotor windings, or bad voltage regulator.

[DrewE]

MEXICOWANDERER wrote:

Be certain you do not have a fault in the neutral circuit of the generator. Unplug. Stop generator. Turn off all breakers. Unplug everything that has a plug.

Measure ohm resistance between neutral and the rig's earth ground wire circuit. What do you see? Neutral is never switched folks, so the test is viable. A full-on bond, can drive some generator regulators to err.

I'm not quite sure what you're saying about neutral not being switched, but it's possibly misleading.

A built-in RV generator should have neutral bonded to ground at the generator (permanently). However, the neutral and the hot line(s) are switched to the rest of the RV's electric system via whatever sort of transfer switch arrangement there may be--usually either an automatic transfer switch or a socket the shore power cord gets plugged into.

If there's an automatic transfer switch, the neutral from the generator will not be connected to the rest of the RV electrical system unless the generator is running and the transfer switch has switched over to the generator. They are usually set up so that the generator has priority, which in turn usually means the shore power cord would have it's neutral connected by default when there's no power on either input.

If it's a socket arrangement, then of course the neutral will be connected with the generator not running provided the cord is plugged into that socket.

At any rate, the ground and neutral should be bonded together at the generator if you're measuring on that side of the circuit. On my Onan KY installation, this is done by physically connecting them both to a single mounting lug doohicky in the generator where the chassis ground (which is also the negative DC return for the starter) connect. This does differ from portable generators, where neutral and ground are usually not bonded by the generator.

[MEXICOWANDERER]

gmc toy man,

Yep. Brains it what it took and you use yours 🙂

Unless the regulator circuit board has two potentiometers on it...



You're stuck...

note: Regulator adjustments when made field adjustable are USUALLY done as a pair -- the first being voltage, the second being response time.

The sensing network of the voltage regulator is malfunctioning. A voltage divider network or voltage comparator. Neither is repairable.

Be certain you do not have a fault in the neutral circuit of the generator. Unplug. Stop generator. Turn off all breakers. Unplug everything that has a plug.

Measure ohm resistance between neutral and the rig's earth ground wire circuit. What do you see? Neutral is never switched folks, so the test is viable. A full-on bond, can drive some generator regulators to err.

[gmctoyman]

The generator is a KY (no jelly involved). My meters are cheap, as am I, but used 3 different ones, in 3 outlets, get very similar readings. Forgot about the KillOWatt thing reading freq. I used an analog clock, ran it for an hour measured on the iPhone, and it read an hour.

[MEXICOWANDERER]

Slump slower than the 55 Hz frequency cornering of a voltage regulator and voltage drops.
If the generator is under load, field forcing ensues. This can blow a regulator to high heaven.
My Kubota has an incredibly expensive Delco H9000 voltage regulator that can withstand field forcing. But I have a 2.5 amp fast blow fuse in circuit to prevent this.
Big gensets have regulators that power an alternator that does only one thing -- make rectified power for the field of the main generator. Two stage process. Wish this critter had an inverter generator system sometimes. But 1,200 RPM inverter generators are merely a pipe dream.

[Isaac-1]

What model is your Onan 4000, some have a voltage regulator, and some the voltage output is proportionate to the engine speed. It just depends on if it is a 4.0 CCK, 4.0BH / BHE, 4.0KY, etc. even there it may depend on the exact revision on a few models.

[2112]

Measure your Hz with a Kill-A-Watt Monitor. If it measures below 60Hz the genny is running too slow. Adjust the RPM to 60 Hz (3600RPM).

[ksg5000]

As I recall my Onan 4K output is directly proportional to the rpm's.

[MEXICOWANDERER]

Verified your measurement device?

Verified your generator speed? Frequency?