Generator Question

[Mike & Molly]

Yesterday I was "exercising" the Onan generator on my 3010DS.
Once started , I turned on the AC unit, & the refrigerator to put a good draw on the generator, which I let run appox. 1 hour.
At the end of the hour, I shut down the AC & the Refrigerator, & had nothing else running in the RV, but left the generator running.
I noticed the RPMs did not go down to a lower idle, once there was little if any load on the system.
Is this normal (running at full RPM all the time)?
Or should the RPM adjust according to the draw/load?
It's still under warranty.
Any help/info is appreciated.

[trwmodela]

Mike,
I believe there should be a noticeable difference in the generator RPM's when the A/C unit is running and cooling. Maybe shut everything down again and just use the A/C as the load and see what happens. Have someone stand outside by the generator when you turn on the A/C to listen. The generator should vary its RPMs based on the load otherwise it is burning more fuel then necessary.

[wyo700]

The only time you will notice a change in rpm is when it's loaded and then the Rpms will drop just slightly. Other wise the Rpms you hear at idle are kinda high but normal.

[Geri]

Its generating a/c so freq = f(rpm). A change in sound when unloaded, but not speed

[BigJohnD]

Like they said. Constant 3600 rpm to maintain frequency / voltage etc. just change in sound by load demand. I prefer these over the ones that idle down when no load. My Hondas do that, and it gets aggravating hearing them change. Oy thing when exercising onan, let it run a little bit once loads are removed before killing it.

[trwmodela]

My Class "A" diesel generator was 8KW and it had a more noticeable change in sound with a load. But it was running two A/C units, a residential refrigerator and other goodies. I also have a large portable Honda generator for the house here in South, Florida. There is a throttle switch that allows it to run auto or full rpm's.

[budblack]

Most generators of the size and type ours are operate at 3600 rpm with or without load.

[MotocrossCamper]

Just to add to what most have said, the Onan will not change rpm, just sounds like its working harder under a load.

[trwmodela]

My Class "A" diesel Onan was 8kw. The fuel burn chart for it showed a use of about 1/2 gallon at 1/2 load and just over 1 gallon at full load. Not sure how is uses less fuel if the RPM's remain constant. What do our generator experts believe?

[Herk7769]

Well, this is a motorhome thread and I don't have one.

The way I understand AC power generators (NOT A EXPERT!), there are two ways of governing (controlling the speed) in order for the output to remain at 60 cycles per second and it depends on the type of inverter you have.

A solid state inverter can take varying cyclic input (rpm of the alternator) and still output 60 hertz. These generators are easily identified by the "ECON" setting which allows the ROM to ramp up and down depending on load. They are very fuel efficient in ECON, but are slow to react to rapid demands on current (like an Air Conditioner starting up). If you are going to run an AC off these generators, the manual recommends "NORMAL."

A "contractor" type conventional generator that uses a rotating (mechanical) inverter and they MUST run at a constant 3600 RPMs regardless of load in order to produce 60 cycle AC. As load increases, the RPMs start to slow down, (like a lawn mower getting into tall grass) and the mechanical governor increases fuel to keep the RPMs constant.

This must be the type of generator you have.

Source:
Conventional vs. Inverter Portable Generators - Cabin Life Magazine

[MotocrossCamper]

Originally Posted by trwmodela

My Class "A" diesel Onan was 8kw. The fuel burn chart for it showed a use of about 1/2 gallon at 1/2 load and just over 1 gallon at full load. Not sure how is uses less fuel if the RPM's remain constant. What do our generator experts believe?

The rpm stays the same but putting a load on it is making the generator work harder to maintain that rpm, therefore it's going to burn more fuel under a load.

[Taylorgso]

Originally Posted by BigJohnD

Oy thing when exercising onan, let it run a little bit once loads are removed before killing it.

Good advice! I had never heard this before; checked the owners manual (mine's LP model), and you're spot on. I have no idea why, but I'm sure there's a good reason. Now to REMEMBER this in the future!

[4Gcampers]

A limited off subject, but... We are on vacation heading home to FL from the Grand Canyon, sitting in a cummins Onan repair shop. We lost our second fuel pump on our unit. The first at 2hrs. The second at 21.0 hours. They are getting us fixed up with the wife and kids in the waiting room. Am I the only one having issues?

[MotocrossCamper]

Originally Posted by 4Gcampers

A limited off subject, but... We are on vacation heading home to FL from the Grand Canyon, sitting in a cummins Onan repair shop. We lost our second fuel pump on our unit. The first at 2hrs. The second at 21.0 hours. They are getting us fixed up with the wife and kids in the waiting room. Am I the only one having issues?

I did have issues with my last one, I went through 2 and then replaced it with a low output electric fuel pump and inline filter from napa auto parts and didn't have a problem in 500 hours. So far on my new one I had to replace it once but now it's been going ok...... Knock on wood.

[4Gcampers]

We got it replaced at Onan today in Amarillo Texas. Hopefully that will get us home to Orlando. Said they have been replacing tons of them. Some new coaches have been through 4 of them.

[MotocrossCamper]

It's not a hard job to replace them if you have some mechanical skills. I started carrying a spare. Took about 20 minutes to swap out.