Re: Onan DJE generator update (electrical panel)

Does this generator have slip rings and brushes, or is it brushless?

Jack ( 2 old Onan 3KW Diesels)

Just gave this beast a good load test, and have some numbers from the frequency readout. It has a 6kW/7kVa rating on the nameplate. Onan DJE, 70 cubic inches air cooled diesel. Made in 1978 (younger than me)

Load test:

At idle, the frequency is about 61.5 Hz. At 4.5kw load, it is about 59 Hz. At 7 kw load, it is about 58.5 Hz.

After it warms up, even at 7 kW, there is relatively little smoke in exhaust. When it is warming up, there is more smoke. After it becomes warm, the smoke goes away.

The oil pressure starts out at around 50, and after warming up, drops to about 40, and goes even lower to about 38 or so as load increases.

The genset could hold on to the 7kW output for a few minutes.

It was not very loud, and visibly a lot of noise was coming out from my improper muffler configuration -- a very long flexible exhaust hose leading to the muffler, which is wrong. Muff should be close to the exhaust.

I am interested in any conclusions from the frequency and oil pressure as to whether this genset is in a good condition.

I have no idea. I only have manuals for engines. Great question.

My assessment would be that those steady state frequency numbers indicate that the governor is working pretty well, but could possibly stand some tweaking.

You'll never get rid of short dips and peaks around the addition or removal of large loads, but afer a second or two of settling you should be able to get back to the target frequency. +/- a couple Hz is good for a small generator and certainly well within the tollerance of just about anything you'd have in a typical house. Larger generators have moch more sophisticated governors than the mechanical ones on small sets and can hold the freequency tighter. Those larger sets also have the benefit of larger flywheels and more headroom on the enging capacity.

About the only thing in a typical house that would be affected by minor frequency variations would be timers that used AC syncronus motors for their drive, like those in typical landscape lighting transformers, and the only affect is that they would gain or loose a little time while on the generator. Old electric clocks would have the same effects.

What you really need is to record the instantaneous lows and highs when large loads are added and removed. The amount of undershoot and duration will tell you how well the engine/governor takes on the load, and the overshoot on removal and it's duration will tell you how quickly the governor reacts.

If the engine was able to take and hold the full load without complaints then I'd say it's probably in good shape. The oil pressure sounds quite reasonable.

So where do I find one of these, and how much? I'd love to stick one on the front of my 24' auto / cargo trailer. The extended shaft version that Onan makes for bucket truck hydraulics would be nice, but I've only seen that in gas.

Pete C.

Ignoramus30505 wrote:

Most likely all is fine. You will get some RPM droop with a mechanical governor, so the 61-59 hertz droop is normal. As far as the oild pressure it is probably fine. Greg

alt.energy.homepower,rec.crafts.metalworking,rec.woodworking

-> ^^^

Ignoramus30505, I notice that you set the No-Archive flag. That's your right but I wanted to point this out. You're getting a lot of helpful advice from people. Because your articles aren't being archived in google, other folks in the future who might have similar problems won't be able to search through your postings. They will see the replies, which may not convey enough information without the context of your original inquiries.