Portable gasifier for home made mini generator

Hello to all !

This is the first time i’write here but i’knew this forum for a long time to learn about gasifiers and the rather extensive science behind them, as well as videos and other tutorials =)

I’have a project to make a very small, portable gas generator where weight and size are rather important.
Basically the idea is to use it for my equipement (like recharge drones, or computers…) and also small powertools in remote locations like mountains for hiking or for handiwork at a remote shack i’have.
These are rather power hungry and my solar battery i’bring depletes very quickly as you can imagine and bringing a powerful enough solar panel is impossible as well as not inconsistent (the sunlight which can’t reach me for example …)
There is no such small generator (4stroke at least) in the retail and also i’d like to construct one by myself so i’d try it

I’have an old GX35 (35cc - 1.3 hp/7000 rpm) and want to turn it to a very small portable generator capable of delivering around 350 W for powering the portable solar battery/inverter which can deliver an output of 700 W and 1000 W peak for a 350 W input.
I’also have a 170 KV brushless motor from an electric skateboard which i’will connect directly to the gx35’s shaft and bolt it to it’s frame to avoid shaft misalignement a bit more (was a hassle to do ) and an electronic voltage regulator where i’can change parameters.

Now, the part i’am the most unfamilliar with : The fuel part =)

I’am very interested in using a gasifier as it’s fuel source because, well wood/charcoal is available everywhere and the weight is an issue so an “on the spot” fuel source is much more interesting than bringing gasoline which add weight (i’don’t plan to use the generator while walking, but when i’stop) and is rather dangerous and not efficient because the stock will be depleted in no time and the refueling would be impossible till i’go back to a city/gas station of course.

I’have seen similar endeavours on Youtube, but there is no technical details, for example this video, which was my first dive into the gasification world =)

-How to Make a Generator that Runs on Wood!!! (wood gas gasifier) Experiment - YouTube which worked, and seems coherent with the pot size he used. Even if the big reactor barrel is a nono because of the size

and this

-Running a Gasoline Engine on Firewood | Woodgas Biofuel - YouTube which didn’t worked but the engine was stuttering and the bee smoker seems perfect for myproject but will it work ? Which modifications it does need more than a filter and better blower ?

So i’am here to ask some, well a lot, of advices concerning this project and have questions also which seems important to me, for example :

-I’gathered that using charcoal is better for small engine, tar free (so a much simpler, smaller and lighter filter for the dust) than wood? What do you think ? Why is that ?

-The best temperatures of each "part’, especially for the pyrolysis to occur the best (900°C-1100°C to crack the tar for wood, but how hot is the best for charcoal?) I’plan to use battery powered small blower to control the temperature of the “firey core”, even if it means losing a few watts

And more to go hehe, i’really want to make this project happens (if it is physically possible of course) so the best thing to do is to ask the much more experienced and knowledgeable people I’think =)

Thanks for reading this long post and hope this project will be possible at least

Wishing all the best to all !


The billows idea can work to start up a charcoal gasifier, but a bee smoker itself integrated to the gasifier itself wouldn’t be a great idea I think.

Koen’s gasifiers from the “Some School in Thailand” thread would probably be the most ideal size range. He makes vertically tallish but small diameter bodied charcoal gasifiers for sidecar mopeds, you can find the thread using the Search function here on the forum. Very simple design and for a 35cc you’ll need something that doesn’t require a lot of vacuum draw. I couldn’t fathom anything other than an updraft charcoal unit.

In a charcoal gasifier that’s properly sized you will achieve the temps no problem, the issue is actually getting the temps DOWN using either exhaust gas return at the air intake of the nozzle, or water drip vaporizing into steam and cracking water into hydrogen gas and cooling the reaction.

Bear in mind you’ll be running conservatively at 50% power output of the engine, but output could be maybe 65-75% of gasolines output. I would personally consider going for a little Honda clone in a 50cc size range at the smallest. The size difference isn’t much between the two.
Oversize the engine by twice over to what you’d need for gasoline so at it’s worst it will achieve the energy you need, and at best it will be making power effortlessly.

Updraft charcoal gasifiers like height, and thoroughly converted charcoal. It isn’t difficult to make the fuel but you must be diligent in the fuel preparation. If you’re concerned about weight, charcoal weighs less in comparison to volume than similar sized wood chunks.

I have a few questions for you.

*Do you live in the city or countryside
*How are you planning to transport this gasifier
*Can you weld
*Do you have a weight limit that you’d like to meet


Hi Georgeoz , I hate to be doom and gloom merchant here but you say you want something light and portable , so here is my thoughts take it as you will , I am somewhat of a Messer i hate being told this or that wont work for what ever reason , when i started running engines on charcoal 1 thing i found out was the smaller the engine the more critical everything down stream needed to be , the slightest air leak or adjustment of air to fuel mix was day and night to engine running with enough power to be able to use it properly to do work , sure the engine will run but wait till you try and get the 300 watts out of that generator ,that’s the hard part . so this is what i suggest .
Honda does make a very small generator a ED250 I have a few of them in fact one of them i have run of charcoal and yes it worked its a dc generator a 12 volt one so if the engine speed is dragged down it still makes some power ,its light weight about 8Kg’s from memory .
Is the a reason to run this on charcoal ? the amount of fuel this would use would only weigh a little more than the weight of engine grade charcoal , that would be used , if this was me i would fill the tank with petrol that would last you a whole day and save the head aches of trying to make power OR go buy one of these , ( i have the smaller camp fire one and charges phones and laptops )
( just noticed the large fire pit does not have the thermo generator like my small one does )
Sorry if i sounded negative please if you are like me and love messing then go ahead and build a charcoal gasifier its a great way of putting your brain to work , but in the real world you will end up going into the wild with a lot of extra weight .
By the way where are you located ?


Welcome to the site Geo. This is an interesting project. Not real sure about the feasibility of a gen gas generator that could be hiked around but I would think about something like Goran built for his moped which would serve to transport the gasifier and could also be use to carry the generator and fuel it when the moped engine was idle. Anyway it is a very nice little gasifier and you can get a lot of ideas from it.


Yup I agree anything under 200cc is just not practical or worth the effort. I could not get the 90cc alternator generator to sustain. It was hard enough just getting it to run unloaded.


Hello everyone !

Woww thanks for your answers, it will help me i’am sure, i’ll answer to each of you too =)

-Cody Edison Tate : Yep, i’also thought of an updraft charcoal gasifier as the only potential viable option. Wood would be bulkier and much more complex with the whole tarring issue.

For getting the gas which goes out the gasifier temperature down to ambiant, i’ve thought about a sort of pipe which would have radiator like cavities like a pre-intercooler pipe you could find on some supercharged/turbocharged car engines. And yeah maybe add a small jar of water, which could also serve as dust filter. What do you think ?

I’ve not found a lot of infos on the nozzles. I’don’t really understand what they are, how they work and their purpose?

Oh so i’need to have a bigger engine to have my required power output ? Dosen’t reving the small one higher works ?

Allrighty, so a long gasifier is better for charcoal.
How do you prepare the charcoal the “right way” for best results ?

Btw,I’ really liked the thread from Koen you showed I’was surprised by the really small diameter of the gasifier. Dosen’t it count for the gas production ? Is it not the larger the burning surface the better ? (Still asking questions sorry :x)

for your questions i’d be happy to answer :

-I’live in the countryside in a remote town at the base of a mountain range in the Alps (yeah a bit alone in space :smile: )

-I’thought about a metal frame with the genset and battery bolted to it and the gasifier encased in refractory brick or mortar. In the idea i’can either strap it and use it like a backpack or just by hand

-Yep, i’know how to weld and have the equipement

  • I’am used to heavy equipement of around 12 kg for hiking and usually stop every 1/2H - 1 hour more or less for my activities and observing. I’can reduce this equipement by half (reducing the tent size for example, not bringing the camera …) and add the generator weight so it would be roughly the same overall weight i’am used to

Dave & Brian

No your right, especially for a tricky project like this i’think it is very complicated, especially i’am novice in the gasifying world, i’don’t know much.
Yeah if a small engine is more sensible to the parameters and leaks i’agree the challenge is even more accentuated, do you have advices ?
I’ll look at the ED250, it seems to do the job but i’don’t know if any are available here

I’know petrol is more convenient, but my small engine would be on often and swallow it quickly because of the power requirements (battery wouldn’t stand the day at all ) and i’would run out of fuel in a few hours at best and i’often stay up there more than that. At least it is my reasoning it may be false =)

I’ve seen biolite, it’s a very smart device i’agree with you for charging small electronics. But their output is around 3-5 w if i’am not mistaking ?

Hehe no i’like the constructive critics, and yeah a part of this project is really to build my first gasifier and understand how it works.

I’am in the Alps, I’think most of people on the forum are from the USA?

Tom Holton
Thanks for your support =) Yeah transporting it safely is important i’could get some ideas. Does the drums exploded because of the residual fuel ? In anycase, i’ll build it the best i’can thanks to everyone’s advices and see the result

Matt Ryder
It’s a challenging project sure, but i’ll at least try to make it work, even if it will not be perfect. It would be most useful for me and also i’ll make a huge leap forward to learn this science (it’s an important motivating factor =)

The problem is that i’don’t really have any other options, the retail gens are either too big/heavy (the honda EX7 for example was an idea i’had at first but too bulky. And the honda EX350 would have been perfect but very hard to find where i’live and is 2 stroke so i’am really not sure if it is possible to run a gasifier with a 2 stroke.

Thanks for you all ! Hope to get this project on tracks :slight_smile:

I’wish the best for you all !


You can make charcoal just by simply burning wood in a metal barrel, and when it’s filled up with hot coals just snuff it out with the lid. Once it’s cooled you can break the pieces down to a 1/8" to 3/4" size range.
Hardwood will give you the best charcoal, and well converted charcoal sounds like glass or fine pottery when you drop some of it on itself, like a “tink” sound. Scoop up a handful and drop it on the rest of the charcoal and you can hear it.

The nozzle is what supplies the air to the gasifier and depending on where it’s located or the material it’s made from it could burn away in the reactor.

For an engine that tiny I’d make a guess that your nozzle’s bore would be maybe 8mm? Just a guess without doing any flow math or knowing full engine specs.

With a DIY generator you’ll have to control the RPM, probably running it at max rated RPM which I assume is 3600? Your generator will produce a drag on the engine and if your engine on Gengas isn’t strong enough, will stall from the drag. You could maybe mitigate this with a charge controller like solar panels use to only demand so many amps. Not sure, I am not an electrician.

I’ve personally never attempted to run an engine below 196cc so this is entirely new territory for me. I think Koen’s mopeds are in the 100-150cc range.

2 stroke is doable but you’d need one that either has a separate oil pump, or add a needle valve to meter oil in the air stream going to the engine.

With a very small size I think optimistically you’d get an hour run per refill if 12kgs is your max comfortable weight.

Maybe with a sort of cart or travois you could pack this in the mountains. I’d consider a 150-200mm diameter pipe for the gasifiers main body. Central nozzle at the very bottom like Koen, the heat will stay away from it.

The only place oxygen should be allowed to enter is at the nozzle and at the gas mixer before the engine. Make sure it is airtight or you won’t have potential gas.
Also be careful of carbon monoxide, all gasifiers produce it and it is a deadly gas and only detectable with machines. In the open air you’ll be fine, so if you test your gasifier please do it outside.


You will have no problem building a small updraft charcoal gasifier Geo. Cooling the gas is not major issue as much of it is done as the gas passes through the charcoal fuel. That is one reason why the length of the thing is more important than the diameter. This is well shown in Koen’s gasifiers. There are many discussions about nozzles here for you to study. I think that designing a way for that nozzle assembly to be easily screwed in and out of the tube is important since it allows you to easily change nozzles when you have burned one out, which you will. A easily made nozzle that should work for you is one in these video’s made by Brian White. I have built a simple fire using one and it works.

Nothing to do now but grab the bull by the horns. Make sure you let us see what you have come up with. Too many people come on the site and pick some brains and then disappear and our whole purpose is the sharing of information and seeing what worked and what didn’t.


If I was you, I would look into powering a thermoelectric generator with a small woodgas stove for camping power.


Welcome to the DOW, Geo.
I used for several years a very small Honda brand mini-tiller with a GX25. You engines smaller brother.
Woodgassed engines produce power best at ~2200 rpm up to ~3000 rpm. This is because of the much slower woodgas and chargas in-cylinder compressed combustion speeds versus gasoline.
Scroll down on the Honda engine specifications to the power RPM graphs.
So your engine on gasoline at 4000 rpm could then barely meet your power needs.
On woodgas, or charcoal gas additionally power derated it simply will not.
These is why the recommendation to a 4X, even 5X larger displacement engine just to have any hope.
Sorry, man.

When I was a young man with different passions I was gifted a heat energy into shaft power-maker: a Wilesco D5 steam engine model. It could power up a bicycle wheel generator against it’s flywheel:

These are very, very quiet. Any IC piston engine is not, in comparison.
The more powerful D20 could be boiler converted to be heated with wood sticks burnt in place down to charcoal. And pulley drive your skateboard motor generating.

Really. It actually could within your weight requirements. Costs though for this collectors item!!!

I’d much more practically go with thermal electric generators instead. For the in-the-mountains peace and quiet.
Steve Unruh


Well i hope you will be tempted to at least build a small stationary system for where you live , that will get you dipping your toe into the world of Gasifiying ,only trouble will be the ache on your face from all the smiling you will be doing when you first see your engine running on charcoal gas and then generating electricity , just remember that how ever much power you are going to need , then you must at least have a generator capable of delivering say about twice that amount , that way your in with a chance .
Start collecting items , don’t over complicate to start with , follow Gary Gilmores "simple fire " thread and watch him on youtube see how easy it can be , any questions just give us all a shout .
Cheers Dave


Hello everyone !

-Cody Edison Tate : Ohhh nice tip, do i’need to check the temperature or juste a simple wood fire below the metal container would do the trick? For how long do i’have to heat the wood ?

Okay, so if i’understand, it’s a small pipe at the bottom of the gasifier (for an updraft) which goes into the “reactor core” where the heat is the strongest ? And there is a blower outside to supply the air ?

Do you want full specs of the GX35 ? I’have this here GX35 - Honda engines =)

The max rpm is around 7000, the idle is at 2500-3000, but i’think i’can go lower (with no load for now)
You are right, for the drag induced by the power demand, that’s partly why i’want to put between the brushless motor/generator and the main solar battery a variable power supply, which fix/smooth the electrical power and i’can change the max amp with a turning knob, so i’ll find the sweet spot

Yeah, Gasifiers seems to be meant for bigger engines :sweat_smile:

Ahh yes, like the first video i’posted the link to? Control the oil flow seems to be a nightmare

An hour per refill would be super great, because i’ll do not need to run that much long to get the battery full and usable for several hours ! But how much weight of charcoal would last one hour ?

20 cm is not long at all indeed, above the engine and packed in refractory material I’d thought it can all fit in a special, solid and fire retardant/proof backpack i’dunno. A sort of a cart is possible, the terrain isn’t really steep, mainly forest and vales nestled in the mountains.

Ok, yeah like @d100f replied, the mix is critical, should i’remove the carburetor and add the ball valve directly to the intake port of the cylinder ?
Of course sir, only for outside, i’planned to put a CO detector in this generator even if it’s outside. Dosen’t cost much and never too careful.

I’ planned also to put two thermometers, one near the intake of the engine, to monitor the gas is at ambiant temp, and another one which directly take the temp of the “foyer/heart” dunno how to say that, where the pyrolysis/reduction occur and the heat is the most important. So that i’can control the blower power if needed and adjust.
Btw, what temp is the best in your opinion ? I’really don’t know :x

  • Tom Holton :
    Thats kind to say, thanks you =) ahhh understood, yes it makes sense
    Yes, i’do know nothing about nozzles, like i’ve asked about, is that a tube which goes straight to the heart of the gasifier ? Because on the second video, it isn’t a tube but a… round thing with holes ? I’don’t really understand how this one works hehe

Yep definitely, it would be just disrespectful to just do that. I’ll share infos when it goes forward and begin the “fuel” part don’t worry !
Right now i’am finishing the shaft connection between the engine and brushless motor, (that’s a pain btw in any generator to make a good coupling !!) and next step would be the gasifier… That’s why i’am starting to gather knowledge =)

-Don Mannes
I’thought about it as a “bonus” watts i’could get by placing peltier modules on the gasifier and cooling tube.

-Steve Unruh :
Yeah, i’figured the low energy wood gas with a slow flame speed would be a big challenge to resolve on a small chambered engine

Would you believe me if i’told you i’got the exact same Steam model from my father when i’was a child ? I’still have it and makes me want to fire it up again heheh It still has some model tools like a small drill press. He got the wilesco D406 for himself

Indeed those are quiet. You think those would work and generate 300 W? It seems a lot to me for a steam engine that size to do it ?

Sure, it would spare me a lot of work on the muffler :laughing:

  • Dave & Brian :
    I’ll surely do it for my home generator after i’ll understand this. The idea of the “hiking gasifier generator” is also that i’learn a big deal from it

Okay, thanks for the tip, i’ll check this channel asap. And thanks for the help from all i’really appreciate.


Geo you can just burn the wood in a barrel, start a fire in the barrel and once it gets to good hot coals feed it with limbs or old boards/planks. Once it’s full of coals or you run out of wood, put the lid on it to snuff it out.

Don’t have any holes in the barrel/drum, you don’t want air leaking in and burning up all the charcoal
The reason why the charcoal isn’t consumed is because of the flames from the burning wood consuming oxygen before it can get to the coals. Referred to as the Flame Cap Method.

For the gasifier, you will need the blower just for starting it. The engine will pull a draft on the reactor. That’s why the engine’s small size can be such an issue.


Hey ,i’am posting right away because @ForbiddenTuna replied while i’was writting the loong post hahaha

-Cody : Ok so it’s not rocket science to make good charcoal that’s nice.
Allright, I’ll check this aswell !

Ahhh understood. So the piping and filtering would also have a negative impact to the syngas on the reactor?
Yeah, because of the small size, the pulling would be less strong. Is letting the blower on, even at a small speed would help “pushing” the gas and helping the pyrolysis ?

I’ll disconnect and reply tomorrow guys, it’s nearly midnight there =)
Thanks again for all the advices !


I’ll go ahead and respond, but yes the filter will have a slight drag on the suction on the system. Not by an alarming amount depending on the filter, but something like a water bubbler would definitely put a lot of drag.

Positive pressure can be given to the system but it can throw off the air fuel ratio, as it could displace the fresh air at the carburetor/throttle body of the engine. It will also make the syngas leak from some spots that don’t leak under vacuum.


Hi Geo. I have several updraft charcoal gasifiers mainly to test different nozzles. One uses the hexaloy tube, one uses a bottom fed grate and then the one with the Brian White nozzle. That one can either be fed air from below the gasifier or from the side. I use one from the side with a elbow that the pipe cap with the holes sits on. That way you can have water injection. Now sure how you would do that with a vertical nozzle as Brian used in the video, but it would still just sit on a coupling on the end of the feed pipe. All very simple.


Charcoal isn’t rocket science, you heat wood with little to no oxygen. Then the gases like methanol evaporate, and tars evaporate, and some carbon chains thermally decomposes. So basically anything that you can keep most of the oxygen from the wood (or whatever) works. There are two types of ‘retorts’ open and closed. closed would be a paint can with a couple of small holes in it to allow gases to escape, and you throw it into a fire. An open retort is like starting a fire in a bathtub or a pit or barrel, and the sides of the bathtub, plus all the gases coming off consume the oxygen before it gets to the ‘coals’ which ends then when you are done, you cover it up to prevent oxygen from getting in. There are a 1000 variations of each system, but that is basically it.

As far as the engine itself, woodgas doesn’t have as much energy density as gasoline. it is around 20-40% that of gas, then you get some derating from the lower rpm. I would plan on about 20% of the rated power at the shaft.

You best bet will probably be a charcoal. I probably wouldn’t use dc for the generator, I would probably use ac then rectify it to dc because ac has a smaller footprint and higher efficiency, and you can smooth it for variances in the output before feeding it to the inverter to get the steady output.

IF you are in the US (which I suspect you aren’t), I would look at an old lawnmowing tractor, which without decks can be really cheap. and you can drive it around for your portability, and attach to the deck output to power the generator, It doesn’t fit the size requirement, but being able to move may change the size requirement.


Sean he’s proposing to take this rig hiking in the mountains, he lives in Switzerland.

I do agree on mounting it to some sort of vehicle, like a four-wheel ATV or a bicycle. An engine powered bicycle is not that difficult and you could make it belt driven to power an alternator. At least it could help propel you instead of being a drag like a cart.


I am enjoying thinking about back packing a gasifier and generator. I think you would have to be gama ray altered. (That’s how the hulk got to be the hulk) but one also has to consider stopping along the way to make enough charcoal to keep operating. Even a small charcoal gasifier is a hungry little mutt and cooking, cooling and sizing charcoal fuel would require extended stops along the way. It is a process that requires time. Not trying to inject negativity here but eyes wide open. If trails permit, then mechanical assistance would certainly solve a lot of problems.


When I am out camping I always have a camp fire going. Dana and I like to cook over a camp fire and sit around it in the evening it doen’t matter if it is warmer weather. In one evening you can make charcoal easy from dry brush, limbs, woods. I have pulled into some campsites and have found lots of charcoal left from the last campers too in the fire ring.