Onan Generators at high elevation

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DonTom

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The manual for my NEW RV says:

"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".

That means I should expect around 75% of the genny capacity at above 7K'. So my 3.5 KW (continuous) 4 KW genny becomes 2.62 KW genny at above 7K feet.

That is if my Y2K genny is expected to do as well as the genny in my new RV.

-Don- Auburn, CA
 

DonTom

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Electronic fuel injection – industry first for maximum performance.
Since mine is that model (in my Class A) I wonder why it has an elevation setting and choke. I never heard of an elevation setting and choke with TBI. A couple of my motorcycles are TBI and they take care of elevations changes by themselves--no adjustments of any type. No choke.

Or did they not change the model number when they went with TBI?

-Don- Auburn, CA
 
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Ex-Calif

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The manual for my NEW RV says:

"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".

That means I should expect around 75% of the genny capacity at above 7K'. So my 3.5 KW (continuous) 4 KW genny becomes 2.62 KW genny at above 7K feet.

That is if my Y2K genny is expected to do as well as the genny in my new RV.

-Don- Auburn, CA

All internal combustion piston engines that are not turbocharged or supercharged will do the same thing.

This is regardless of mixture or timing or carburetion type. There simply is not enough ambient air pressure at altitude.

If anything mixture and timing adjustments only assure that you can get that 75% power at 7000 feet.
 

Larry N.

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A couple of my motorcycles are TBI and they take care of elevations changes by themselves--no adjustments of any type.
And electronic fuel injection takes care of needed adjustments on most modern cars with ICE, but they still, as Dan says, lose that 25% power at 7K ft. with the adjustments just allowing you to get that 75%. It's just physics, and you lose even more power at higher altitudes.

Even at sea level, on a hot day you lose a little bit of power vs std temps (59º), and you potentially gain a little power in cold temps. It's air density...
 

DonTom

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If anything mixture and timing adjustments only assure that you can get that 75% power at 7000 feet.
Advanced timing should be much like more compression and get some of that lost performance back. Something that cannot be done at sea level without damage to the engine.

If they don't compensate as best they can, I doubt we can expect 50% of the sea level performance.

I remember the poor performance of the old muscle cars on Donner Summit (uphill on freeway to 7,240 feet elevation) very well. Gutless compared to the small EFI engines of today. Normally cannot even tell the difference between sea level and 7K feet with modern EFI engines.

-Don- Auburn, CA
 

Mark_K5LXP

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Problem with timing advance is how do you do it without a computer to monitor MAP and O2 to dynamically adjust timing and mixture? My last carbureted vehicle I ended up advancing timing an additional 10 degrees I recall to work here at 5K feet, but I'm not aware of any generators that do that (do the new EFI ones?). Seems it'd be a fairly static number with non inverter types as they operate at a fixed RPM but guessing it was a design decision to accept reduced output vs having to educate users on what to set. As evidenced with this thread, even just the carb adjustment can have it's own set of issues. Put a knob on it, and it's an opportunity for someone somewhere to get it wrong. Get the timing hosed and you can damage an engine.

Mark B.
Albuquerque, NM
 

Ex-Calif

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Advanced timing should be much like more compression and get some of that lost performance back. Something that cannot be done at sea level without damage to the engine.

If they don't compensate as best they can, I doubt we can expect 50% of the sea level performance.

I remember the poor performance of the old muscle cars on Donner Summit (uphill on freeway to 7,240 feet elevation) very well. Gutless compared to the small EFI engines of today. Normally cannot even tell the difference between sea level and 7K feet with modern EFI engines.

-Don- Auburn, CA

Trust but verify Don. You are repeatedly saying thing that are against the laws of physics.

Timing will not compensate in any way towards the atmospheric pressure phenomena. The only way timing can help an engine is if the timing is advanced the flame front starts sooner and can result in higher BMEP (Brake Mean Effective Pressure) in the combustion chamber.

The huge drawback is that advancing the timing can result in detonation - uncontrolled burning - which can dangerously raise pressure levels and result in failed head gaskets and even broken pistons. This can somewhat be reduced by running a higher octane fuel. Contrary to what you said this can happen at any altitude and is often noticed at higher altitude or hotter days when one is naturally pressing the gas pedal harder.

A motorcycle or car engine is also suffering the same power loss at altitude as a generator if it is not turbo or super charged. You don't notice it because rarely is one using "full throttle" to leave a stop sign and there truly is "excess horsepower" available in most vehicles. I can guarantee that my '59 VW microbus with a 25hp engine was sucking wind at 4,000 feet much less 7,000 feet - LOL.

If you ran the same vehicle on a 1/4 mile strip you would have much lower times at 7,000 feet vs. sea level.

Just so we are using somewhat precise definitions.

Detonation - The ignition and uncontrolled burning of the fuel air charge caused by excessive cylinder pressure.

Pre-Ignition - The early lighting of the fuel air charge prior to the ignition event caused by a carbon hot spot or other unnatural ignition source in the cylinder chamber.

Edit to add - As Mark indicates modern engines have knock sensors, O2 sensors and computers to adjust the timing on the fly to maintain the best efficiency. This does (for sure) maintain the maximum power possible to the highest altitudes possible.

In adjusting the twin carbs on my MG I road set the timing. Basically it's driving up a shallow hill in 3rd gear from low rpm to redline. Each time you advance the timing until you start to get a ping and hten you back off a bit.

This does two things. Get the BMEP up as high as possible for a given octane and because combustion starts earlier and has longer to complete results in better gas mileage and lower emissions - less unburned fuel exiting the exhaust.
 
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DonTom

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Problem with timing advance is how do you do it without a computer
In modern engines, it is done with a computer. In the case of my 1984 Yamha Venture motorcycle, it uses an air pressure sensor to control the TCI (Transistor-Controlled-Ignition) to advance the ignition timing whenever it safely can. Has carburetors and no computer, just the TCI. It runs very well at 7K feet compared to bikes that have no pressure sensor such as with my 1971 BMW.

At higher elevations, the timing advances more. Also, when there is not a large load on the engine--IOW, it advances when it safely can.

-Don- Auburn, CA
 

DonTom

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My main point here is that Onan can do many things to help get some of that performance back at higher elevations, just as they did with modern cars. Of course, you're not going to get back 100%, but will get back enough that most people will probably never notice the difference between 7K' compared to sea level.

Isn't anybody else here old enough to remember how poorly cars of the late 1960's and early 1970's performed at the high elevations? Perhaps 45 MPH max up a slight hill at above 7K feet? With today's cars with smaller engines, go around twice that speed up there.

The air pressure has not changed since then, only the car's electronics have changed. And it's more than just the fuel-air mixture.

-Don- Auburn, CA
 

Mark_K5LXP

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Once you add computer control the sky's the limit to what parameters you choose to monitor and control. EFI was the gas engine turning point in my opinion, then more recently variable valve timing. You can get the same horsepower today from a small-ish V6 that would've been impressive from a strong carbureted V8. Back to gensets though, it seems they've been behind the technology curve for decades, only just playing catch up with emission regulations. The fuel injected Onan seems to be the beginning of a transition, once that gets propagated across the product line one can hope for a paradigm shift for portable power consistency and reliability.

Mark B.
Albuquerque, NM
 

Mark_K5LXP

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In the case of my 1984 Yamha Venture motorcycle, it uses an air pressure sensor to control the TCI (Transistor-Controlled-Ignition) to advance the ignition timing whenever it safely can.
Going back that far, interesting. My honda from back then just had points. My carbureted harley in the 90's had a "VOES" which basically was a manifold vacuum sensor that flipped timing between two ignition module pre defined advance curves. If you romped on it in too low a gear you'd get dropped into the "less advanced" curve and the thing would bog, so it was common to disconnect it. Mostly there to meet emissions, certainly not performance.

Mark B.
Albuquerque, NM
 

DonTom

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You are repeatedly saying thing that are against the laws of physics.
Where? Perhaps in my message number 14 above where I said "I realize there is nothing that can be done with rarefied air to get back the lost power".

If that 25% loss at 7 K feet, includes modern-day tricks such as a computer controlled advanced ignition and valve timing (which I doubt it does), which is not as safe to do at sea level and then backs off, then Onans must have an efficiency of less than 50% at 7K feet elevation. At least get them to that 75% if that is all that is all that is possible. Get them up to at least mid-1980's technology in 2022! Is that asking too much?

-Don- Auburn, CA
 
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DonTom

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Mostly there to meet emissions, certainly not performance.
I find it interesting how at first, smog requirements (early 1980's) were the worse thing that ever happened to cars and motorcycles. Later changed to being the best things that happened when the specs got so tight that efficiency became important and all the engines were redesigned.

If it were not for today's smog requirements, most cars would probably still have carburetors and nothing to help with higher elevations.

IMAO, it's time for these new smog regulations to apply to Onan gennys. Sure, they will cost a bit more, but will be more than worth if. But also perhaps a lot less maintenance. At least Onan carb problems will be done with for good.

A chip to set the RPMs for 3600. EFI with automatically advancing ignition and valve timing as air pressure drops. A constant 14.7 to 1 air-fuel mixture after warm up. Info from air pressure sensors, etc. That will be at least Y2K technology!

BTW, I can get my full power out of my genny here at 1.4K' elevation. Or enough of it so I cannot tell the difference. Very unlike the 7K feet problems I had last week near Tom's Place.

But if the genny is only used to run the converter, there was no issues even at 7KW feet other than I had to lower the RPMs to 3,300 RPMs (55 hz) or else the genny would keep on dying. Perhaps not getting enough gas for the extra rich mixture to keep the RPMs up? Not sure why, but it would keep on dying at 3600 RPMs even with lower loads.

Here in Auburn, it works perfectly at 3600 RPMs (60 hz) with no trace of any issues.


-Don- Auburn, CA
 

Reinigm

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It's my understanding that this all becomes a moot point in California in 2025. I believe they won't be able to be sold then. (Anything gas powered?)
 

Mark_K5LXP

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California Governor Gavin Newsom has signed legislation that aims to ban the sale of gas-powered lawn equipment, generators, and other small engines designed for off-road use.
...
The text of the signed bill specifically calls for the banning of small off-road engines (SORE), calling out emergency response equipment and generators as well as both residential and commercial lawn equipment.
 

DonTom

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California Governor Gavin Newsom has signed legislation that aims to ban the sale of gas-powered lawn equipment, generators, and other small engines designed for off-road use.
...
The text of the signed bill specifically calls for the banning of small off-road engines (SORE), calling out emergency response equipment and generators as well as both residential and commercial lawn equipment.
"The new law affects portable gas-powered generators that run under 25 horsepower. These types of generators may be used to power a fridge or other mid-sized appliances."

See here.


So as long as it's not "portable" it doesn't apply to us RVers. Mounted to an RV should be fine.

BTW, there is some nonsense in there, I see:


"Even in a power outage you can go to a gas station and get more gas."

Obviously, "Stephanie Lin" (the author) wasn't here in Auburn during our several power outages.

-Don- Auburn, CA
 

Ex-Calif

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Where? Perhaps in my message number 14 above where I said "I realize there is nothing that can be done with rarefied air to get back the lost power".

If that 25% loss at 7 K feet, includes modern-day tricks such as a computer controlled advanced ignition and valve timing (which I doubt it does), which is not as safe to do at sea level and then backs off, then Onans must have an efficiency of less than 50% at 7K feet elevation. At least get them to that 75% if that is all that is all that is possible. Get them up to at least mid-1980's technology in 2022! Is that asking too much?

-Don- Auburn, CA
Maybe I am misinterpreting a lot of your posts where you have focused on timing as a main cure for this and it just isn't.

The performance charts are sometimes dyno and sometimes theoretical.

At sea level on a standard temperature day the atmospheric pressure is about 14.7 PSI. Contrary to some views the engine doesn't "suck" air in. 14.7psi pushes air into the void left by the descending piston.

At 7,000 feet on a standard temperature day the air pressure is about 11.3 PSI.

11.3 / 14.7 = 76.8% - Pretty close to the 75% quoted in most HP charts. I am guessing the charts assume a proper mixture and timing unless they state otherwise.

Mixture is certainly a factor and may still be a factor in you genny that you say has to be run at 3300 rpm. My guess would be that it is still too rich to burn cleanly and that's why it eventually stalls out. The mixture wants to be pretty close to 14:1 at all times and with a manual mixture the genny is probably never at the optimum mixture.
 

Ex-Calif

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Seeing as how there is a ton of discussion around mixture I dug up a "cartoonish" chart to show how mixture affects HP.

Note this chart is not altitude specific. It reverences stochiometric baseline of 14.7. Note that in all cases the peak HP and torque is actually richer than standard. There are a lot of reasons for this that I won't get into.

The downside of running rich of optimum is pollution and fuel economy. Basically not all the fuel is getting burned.

I recall you mentioned one of your generators where you screwed the idle screw all the way in (and broke it off?) and if that is the one not running to peak at altitude you could have inadvertently made it too lean to run correctly at altitude.

Going back to my MG tuning - because these are "high performance" constant velocity twin carbs with pretty specific tuning requirements.

After getting the timing right as I mentioned before. There is a little button on the bottom of each carb. When you press the button it opens the butterfly a specific amount. From idle the rpm should climb a couple hundred and then drop back down. This indicates that the carb is a little rich and a minor amount of additional airflow causes a momentary non sustainable RPM rise.

If the RPM immediately drops then the mixture is too lean and there is no excess fuel to cause the RPM to rise. If the RPM rises and stays risen then the mixture is too rich.

Of course, if the mixture is adjusted in this last step another timing acceleration check needs to be done to make sure you aren't in the detonation zone after the mixture adjustment.

Tuning the MG twin carbs is really rewarding when done right.

mixture1.JPG
mixture2.JPG
 

DonTom

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Maybe I am misinterpreting a lot of your posts where you have focused on timing as a main cure for this and it just isn't.
It's just part of the several reasons why cars / motorcycles run MUCH better at higher elevations than they used to. But perhaps the main reason--seems to do a lot more than mixture, based on several vehicles I have owned.

and if that is the one not running to peak at altitude you could have inadvertently made it too lean to run correctly at altitude.
I have removed the sparkplug many times to check. By looking at the sparkplug, it was always too rich no matter how I adjusted it at 7 K'.

It runs perfectly here (1.4K') with the screw broken all the way in and the sparkplug now looks like about perfect mixture. I expect it will be fine as is at any reasonable elevation even without being able to adjust, just that I have to lower the RPM at 7K' feet and I doubt it will run at all if much higher than that.

This 4K Onan has the cheap $40.00 Chinese carburetor in it. According to the label, all the way in should be for 10,000' elevation. The Onan says 5K' max on their carbs when adjusted all the way in. I don't know if in realty the Onan will be better at 7K' or not. I don't recall ever being at 7K' running the genny when I had the Onan carb in there. Probably wouldn't be any better.

-Don- Auburn, CA
 
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