Onan 4K Genny Load testing

[DonTom]

I did the load testing with my 4.0 KY-FA/26100 J today.

I am at 1.5 K' elevation and my new Chinese after-market carb is set for such. Temp was 55°F ( 13.8C) at the time of testing.

I used various heaters, toasters, MW oven, Hott Rodd Water heater to do the testing. All my numbers are rounded off but within ten watts. These are measured on a Kill-O-Watt meter.

Tall tower heater=1,500 watts
MW oven= 1,150 watts
small round heater=800 watts

Total of above:3,450 watts

My genny ran perfectly with this above load of 3,450 watts.

Then I plug in the Hott Rod water heater, 440 watts.

Now the total is 3,890 watts.

The genny would then run for as long as one minute and die, with this 3,890 watt load.

Converter was only using a few watts (less than ten) on the fully charged battery, so I did not unplug it. Refrigerator was off.

I figure the max load I can use is somewhere around 3,600 watts here under this elevation and temp.

Is this within reason?

-Don- Auburn, CA

 

[Mark_K5LXP]

Did it flash an error code? That could reveal a detail why it gave up. Sounds like you're right there factoring altitude.

Mark B.
Albuquerque, NM

 

[DonTom]

Did it flash an error code? That could reveal a detail why it gave up. Sounds like you're right there factoring altitude.

I didn't check, but I don't think I needed to check it. I could tell by listening. Frequency went too low under the heavy load.

But it was at 60 hz with no load. IIRC, I read somewhere that with no load, it should be set to 62 Hz. At 53 Hz, the control board will shut down the genny. So perhaps the extra two Hz would make a difference under the heavy load.

I should have set it to 62 hz before I did this test. But I never even took the cover off the genny during this load testing.

-Don- Auburn, CA

 

[Primerump]

sounds like you hit the max load for the genny..

 

[DonTom]

sounds like you hit the max load for the genny..

I found this info. below form my 5.5KW Onan Genny in my 2022 Class A (but the one I am working on is my 4KW genny in my Y2K RV):

"If you travel at high altitudes or in extreme temperatures, your generator can lose power In such lower-density air conditions, you can't operate as many electrical devices as you could under normal operating conditions Power decreases 3 5% for each 1,000 feet above an altitude of 500 feet"."

4KW spec minus 3.5%=3,860 watts for the 1,500' elevation here. It looks like my genny is close to spec. It can do 3,450 watts continuously and can do 3,890 for around 30 seconds to one minute before a low frequency/RPM shutdown. Perhaps longer or will run continuously if I adjust my genny to spec for frequency, 63 hz with no load, which is now right at 60 hz with no load. The no load spec in my Onan service manual says it should be at 62 to 63 Hz (page 8-7). That could mean I have an extra 3 hz to go before the shutdown at a full load before the low frequency shut down. That could mean it would not shut down at all. I am tempted to adjust it and then do the load testing again. And I probably will do such soon just to satisfy my curiosity.

Of course, I will post here the results if it makes any difference or not.

-Don- Auburn, CA

 

[Kirk]

Is this within reason?

YES

 

[DonTom]

I am now all done with my genny load testing. Here are the results of my testing after adjusting the no load frequency to 63 hz (123 VAC).

Tall tower heater=1,500 watts
MW oven= 1,150 watts
small round heater=800 watts

Ran perfectly as above. And at exactly 60 Hz. But still could NOT handle the extra 440 watts of the Hott Rod water heater. No alarm at genny after it dies (must be more than 30 seconds CONTINOUS to set the code 15 when below 54 Hz, and it was right on the border at times going in and out before dying).

I wanted to get closer to spec, so I added a can opener which label said "1.5 @ amps at 120 VAC" IOW, 180VA.

But it measured as 140 VA (no can was opened, just turned on and ran). It only used 55 watts of that 140 VA! As measured on a Kill-O-Watt meter.

So here is the is the results of my final load test:

Tall tower heater= 1,500 watts
MW oven= 1,150 watts
small round heater= 800 watts
Can opener= 140 V*A
****************************

Total= 3,590 V*A, which will be the same as watts if with a pure resistive load.

It will run all day at 3,590 watts, but it does sound loaded down and is at 111 VAC. It requires to be below 108 VAC for five continuous seconds for error code 13 (low voltage).

While spec is 3860 watts at the 1.5K' elevation I am at, that is for 70° F. Temp was at 50°F at the time of testing. 20°F warmer will give even a little more power.

My conclusion is:

It meets spec, but will not go above spec.

My experience shows most electric items will work just a little better than their specs, but this Onan probably cannot exceed its own spec by a microwatt. But that is nothing to complain about with a 25-year-old genny.

IAC, I would be nitpicking to do any more load testing. I am satisfied it is working as it should at 1.5K' elevation. I now only need to test at 7K' elevation and I will update this thread when I do but it could be many months away, but will be before April as by then I must drive it over the summit in the RV for the NV smog test. And there is a rest stop right at 7,240' elevation.

-Don- Auburn, CA

 

[Mark_K5LXP]

20°F warmer will give even a little more power.

Colder air is denser. So if anything, you should have more power at 50F than 70F. But I don't think that density change is as marked as what you see over altitude change. You're dancing around single digit percentage of expected vs actual, so you'd have to go with more than assumptions for operating parameters to nail down root cause.

Mark B.
Albuquerque, NM

 

[DonTom]

Colder air is denser. So if anything, you should have more power at 50F than 70F.

Yes, but there is more to consider than air density. Such as oil being thicker at cooler temperatures and then having more friction. Engines are usually more efficient at higher temperatures (within some limit).

I assume Onan does its testing at 70°F because that is where they get their very best efficiency. But I agree within normal temps, say between 50-80°F it will probably be a negligible amount.

Now, I am wondering if I should do my load test again when it is 70°F in a few months.

You will probably find this discussion here interesting:

"I conclude that an ordinary internal combustion engine would be less efficient at lower temperatures. And where I live, I certainly get significantly less mileage from my car in winter (but there are many other factors contributing - not just thermodynamics)."

But reading the entire thing, I would say it is inconclusive, and cars do not compare well to gennys for the reasons mentioned. So I need to do my load test at 70°F. TBH, I will be surprised if there is any noticeable difference, but the only way to know is to test the theory when it is warmer. It now only takes me a few minutes, the genny warmup is the longest part. I know what stuff to use to load test and I already have the genny set to spec., so it will not take long at all to test again.

-Don- Auburn, CA

 

[DonTom]

I did my Onan 4K high elevation genny testing a few days ago, at Donner Summit, 7,240':

At 2,840 V*A the Onan works perfectly, will run forever,

At 3,270 V*A dies in ~10 seconds

4k Genny spec:

(running watts spec)

expect loss of 3.5% per 1000' elevation

7 times 3.5%=24.5% or

24.5% less than 4K=980=3,020 expected watts at 7K'

To nitpick=.875% for the extra 240' elevation=35 watts more loss.


So then 2985 W expected output by spec.

~2840 actual output (could be a little more, but I have no way to add small loads from here)

So its within 145 watts of spec. at 7,240'.

And if I had an extra 145 watt load, I think it would still run, but be right at the edge of where it could die.

So my conclusion:

My Onan 4K Genny now meets spec at any elevation.

I assume the problem was the valve that had no clearance and probably didn't fully close, so it had low compression.

Looks like it is now all working normally. And from now on, the valve clearance is checked during every oil change.

2840 watts will work to charge my electric motorcycle at 1,400 watts which I had trouble doing at Flagstaff last November. And now I have another 1,440 watts left for other stuff.

-Don- Auburn, CA

 

[Mark_K5LXP]

I assume the problem was the valve that had no clearance and probably didn't fully close, so it had low compression.

Not likely. Combustion gases would burn the valve and seat in very short order. You've inspired me to check mine though, when I dewinterize in the coming weeks. Maybe I'll haul some electric heaters/loads out there and put the hurt to it to see what it does.

Mark B.
Albuquerque, NM

 

[DonTom]

Not likely. Combustion gases would burn the valve and seat in very short order. You've inspired me to check mine though, when I dewinterize in the coming weeks. Maybe I'll haul some electric heaters/loads out there and put the hurt to it to see what it does.

Mark B.
Albuquerque, NM

I doubt if it was run enough times or long enough to do any lasting valve or seat damage. But there were also other possibilities, such as not knowing when or where my choke tube fell out.

But the only important thing is it appears to now be working well at above 7K' elevation.

-Don- Auburn, CA