Experiment with Inverter Generator on Charcoal

I recently was playing with my charcoal gasifier and Predator 8750 inverter generator and wanted to perform an experiment to see how much charcoal is consumed when running the generator in regular mode versus ESC mode (or ECO mode as I call it).

Basically when ESC mode is turned on, the engine will run at a lower RPM when there is no load on the generator. When a load is detected on the generator, the engine will increase RPM to accommodate the increase in load. Once the load is gone, the engine will return to the lower RPM. This is different than regular mode in which the generator runs at a consistently higher RPM all the time (more like a regular non-inverter generator). ESC mode is supposed to save gasoline.

In my tests with the charcoal gasifier, I have noticed that when the generator is running on ESC mode and no load, the gasifier runs much cooler than on regular non-ESC mode. So, I wanted to see if there was a significant or even noticeable difference between the two modes with how much charcoal is consumed with no load on the generator.

My test was to basically fill the gasifier hopper, flare the gasifier until good stable gas was achieved, run the generator on regular mode for 20 minutes, shut down the generator, open the hopper and measure the drop in charcoal with a tape measure. Then, I allowed the gasifier to cool down completely and repeated the process except I ran the generator on ESC mode for 20 minutes.

What I found was that, even though the RPM is definitely lower on ESC mode and the gasifier is running noticeable cooler, the amount of charcoal consumed appears to be almost identical between the two running modes.

Now, I have only done this test once and so my sample size is very small, but I thought it was an interesting result. Based on how cool the gasifier ran and the lower RPM, I thought I would see a more noticeable difference in charcoal consumption. Of course, measuring the drop in charcoal with a tape measure isn’t exactly accurate. I also don’t really know the difference in RPM between the two modes so I can’t calculate how much less air is actually being drawn though the gasifier.

A major caveat to my testing thus far is that I have been using my “Big Bag O’ Charcoal” as the source of charcoal for all of my running of the gasifier. The “Big Bag O’ Charcoal” is filled with the charcoal that I have recovered from my fire pit after we have campfires in the back yard. The wood used in the fire pit is mainly maple, but there could be a pine board here or there that gets thrown into the fire pit on occasion. So, regarding the test, I cannot confirm that the mixture of hardwood to softwood ratio is equal on both runs. There could be more hardwood or softwood on one of the runs that is throwing off the results. I plan on making a bunch more charcoal from maple and trying the experiment again to see if that consistency yields different results.

Does anybody have any thoughts on this? Am I incorrect to assume that the consumption of charcoal should be different based on the 420cc engine running at two different RPMs? Perhaps the difference just isn’t enough to measure with my crude measuring technique.



When I do these test I measure by simply refueling. So on the refill if it takes a whole 5 gallon bucket I know it consumed that much. Then the next run you refill it again to measure the different even though you may not run it again.

Check your filters is there a noticeable difference in moisture accumulation. Keep in mind not all will be collected in the filter and steam will carry into the engine. I bet your water shift is lower in ESC mode so the gasifier is consuming more charcoal to supply the demand.

I have not really paid attention I just know I get roughly 2 hours run time on my units. But I bet the more you drive the unit the more water you crack. The higher the water shift the less charcoal is consumed along with lower nitrogen in the mix.


Thanks Matt.

I actually ran both mode tests without water. I don’t remember if I checked to see if there was a difference in the amount of moisture that made it through.

On other runs I noticed that I do have to turn the water drip down when I switch to ESC mode otherwise a bunch of it just drips off the bottom of the air intake/nozzle.

Once I get a good amount of charcoal made, I am going to try it again and I will try it with and without water drip.


Hi Bryan,
Interesting test and result. I don’t have much knowledge on this but I remember reading somewhere the ICE engines use pretty much the same amount of fuel on full load and idling. Maybe this is why. May be that’s why all new cars come with stop-start feature.

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Hi Bryan White,
I do not know the RPM charateristics of the Habor Freight Predator 8750.

On my older designed Yamaha EF 2700 it high speeds at ~4000 RPM, Eco modes at ~2600 RPM.
The much newer designed Honda EU2000 high speeds at 4200-4400 RPM. Eco modes at 2800 RPM.

Both of these will hold a 1/4 output loading in Eco mode. 450 watts and 500 watts.
Variably load your 8750 Inverter unit to see how much you can load it without triggering it up in RPM.
Then do your fuel consumption running tests at that electrical loading at both RPM’s.
This is the only way to have any validity.

Go out to any throttle by cable vehicle. Ease up your standing RPM to 2500. Just be barly cracking open the throttle. Now increase and hold vehicle standing up to 4000 RPM. You will not be using even 20% of the throttle travel. You are only just pumping a bit more oil; water on a water cooled; a bit more air.
Driving loaded there will be a big difference.

The biggest reason for vehicle stop-start features is air-pollution reduction.
Think of all of those vehicles sitting standing at all of those city-urban four-way, six-way, eight-way controlled intersections. All running, idling, emitting.
Newly manufactured vehicles are tested in closed cells driving dynometer rollers. All emissions in that closed cell are counted for the certification’s ratings. Run-stop is how you can have IC engine vehicles rated as PZEV. Partially Zero Emissions Vehicle.

Steve unruh.


If i can jump in here Bryan and tell you my findings from running inverter generators for the past 5 years .
Running on eco mode is a waste of time from my point as the power loss from charcoal makes it almost impossible for the generator to fully powerup again unless you have a auto mixer on your charcoal fuel line , sometimes after running for an hour or 2 and the batteries are starting to get charged over half way the amps drop on the charger and i can then put the eco switch and it will then run ok most times without altering the air fuel ratio but if i am doing some cutting on the bench saw at the same time i can hear the engine slow and then speed up as it cuts the feed to the inverter leaving no power until the engine is at the desired speed for power to come back on and then the sudden inrush or power needed will stall the engine .
That’s what i have found anyway and that may just be down to the way7 i built and run my system your might work in a totally different way .
And as far as the amount of charcoal used , before refilling the gasifier poke down to the nozzle with a bar and watch the level of charcoal drop down as the void deep down collapses once stirred .
My rough estimate on fuel or rather run times on a drum of charcoal is 4 hours when maxed out and putting a lot of amps into the battery , or if i am running light loads cutting on a saw or washing machine running or topping up near fully charged batterys i can get over 6 hours run time

All the best Dave


Thanks for that.
Here’s a slightly more esoteric question. Could we take advantage of the fact that with woodgas a wide range of air and fuel ratios will burn?
It would seem that instead of running the engine against a partly closed valve, the throttle, we could control power output by changing the air and fuel ratio: lean for less power, richer for more power. Lower ‘pumping losses’ due to turbulence after the throttle plate. I think this would give better partial load efficiencies. Perhaps connect the rod from the governor to the mixture control valve and leave the throttle wide open except in special circumstances. This seems so simple, someone has to have tried it before.

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Hi Rindert, i’ve read somewhere about just what you describes, i think it was some of the Finn’s tried it, cant remember where i read it, probably now gone forum: Gengasdrift, at Yahoo.
I belive it was called “quality regulation” instead of “quantity regulation”.
If i remember correctly this was on a stationary diesel, adapted for woodgas, with spark ignition.


Did it work good? That sounds close to ideal. Wish I could learn about it somehow.


I think if there were an advantage to the above it would have been done by gasoline motor manufactures using the EFI .

Also the auto trans depends on vacuum in the intake manifold for the shifting .


I believe it had it’s drawback’s, mostly a way of rpm-regulation, more than power regulation.
And as Wayne says, it had been tested in cars, and probably not much benefits from it, i believe hard to get clean exhaust was a problem.
It reminds me of when i had problem with the idle adjusting on my truck on woodgas, it seized on very high idle, i had to choke the secondary air to lower rpm, to be able to shift into drive/reverse without “jumping” or break something.


They’re not allowed to because of NOx emissions. A gasoline and air mixture burns much hotter than woodgas. The high temp actually ignites nitrogen from the air and produces pollution. Just recently OEM have started putting thermocouples just outside the exhaust valves. Data from those is used to lean out the mixture when it is cool enough not to produce NOx. Before that they ran only stoichiometric or slightly rich ratios. Back in 1989 I saw a guy burn holes in two out four pistons when he ran his Porshe 911 (carburated, high compression) out of fuel. Burning nitrogen is mean stuff.
And gasoline just doesn’t have the very wide range of flammable mixtures that woodgas does. Woodgas is a true gas, whereas gasoline is a mist, or droplets. The flame has shorter distances to jump, on a microscopic level, when it’s in a true gas, so it doesn’t have to be as hot.


Hmmmm, that sounds like an ‘under damped’ control system. Shouldn’t be hard to correct.with a dash pot once the rest is up and running. Just one more potential improvement I want to try. As I go along I get the impression more and more that there is huge untapped potential in woodgas.



I made sure to shake the gasifier so the charcoal would settle before I measured the drop each time. At this point, it’s just me being curious about the ESC mode and it’s effect on charcoal consumption. I’m not going to be that disappointed if the ESC mode doesn’t save me fuel. However, it would be cool if it did.

I’m still experimenting on a bunch of stuff and I have tested several hand tools while on ESC mode running on the gasifier and have not had any problem with the generator and gasfier handling the in-rush current. Now, I haven’t tried it with something like my welder yet, but hope to do that soon to see how it handles that.

If I can find something that puts just enough of a load on it to not quite increase the RPM, I plan on testing between the two modes with a load as @SteveUnruh suggested.


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Has any body tryed dripping in some waiste veg oil, too measure if it saved on charo, or got more run time on same emount of charco… That might add run time?

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Gary Gilmore tried that, doesn’t work too good on an updraft. Just makes a greasy smoky mess.

Edit: misread and thought you meant mixing with charcoal

I’ve dripped different oils and it kept making flames. I was worried the oil wasn’t vaporizing fast enough or cooling the nozzle enough.

Dripping water does add some run time

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