Picture of Chainsaw flashlight (gas engine powered spotlight)
concept sketch.jpg
I've been wanting to try this for a while as crazy as it sounds; make a mini electric generator with a small engine and a treadmill motor, add this to some car headlights and you get one very loud flashlight/spotlight. 

An electric motor is basically a generator and an electric generator is basically an electric motor. The chainsaw provides the power to spin the motor and booyah....electricity. I'm sure all kinds of electrically proficient peeps will shake their heads at the methods here, but it's all just fun, nothing serious. 

(I want to add that I squeezed this project out to meet the flashlight contest deadline; it still needs a voltage regulator, a protective shield for the chain and sprockets, plus some adjustments and fancy paint work.)
Final adjustments to this machine, a voltage regulator is not needed if the saw throttle can be incrementally adjusted with a hose clamp. Hook up a multimeter and set the throttle before plugging in the light. Also the gearing in this instructable is way too high, the DC motor sprocket needs to be much larger to slow it down. I can hand turn this DC motor and get 2 to 3 volts, so the chainsaw should barely be running above idle to get the right voltage. This project is a little dramatic; maybe next time I'll use a lawnmower engine ;).

Here we go:

1 old chainsaw
1 treadmill motor (DC permanent magnet motor)
1 one-piece 12 volt car headlight bulb
odds and ends tubing, wires, switches (see detailed steps)
bicycle spockets
bicycle chain
motorcycle voltage regulator
scrap wood and screws

welder or someone who can weld a sprocket to a chainsaw clutch and treadmill motor flywheel.

(Extra: With a few alterations, this project can be made into a mini generator or a go kart.)
Warning, this can be dangerous. I'm not liable for any injuries or whatnot incurred using the shown techniques. At your own risk and stuff. 
1-40 of 135Next »
devicemodder5 months ago


robbtoberfest (author)  devicemodder1 month ago


randomray10 months ago

Uhmmm, I love the insanity of the project.

wheredgo5 years ago
Leave the bar and chain saw on it, then you could saw in the dark! ok, probably still a bad idea..
dudes wheredgo1 year ago

that would be AWSOME!!!!!!!

finton wheredgo5 years ago
"saw in the dark"! And the award for best pun goes to wheredgo!! :] In fact you could see/saw* in the dark... Ooops, best pun goes to me. Love the idea of the chainsaw light robbtoberfest: I'll have to try it ... "come here little chainsaw ... where are you boy? ... come into this nice workshop ..." *Or I saw where I could see to saw a seesaw in the dark. OMG!!!: robbtoberfest built a SeeSaw!! [tm]
jj.inc2 years ago
This is awesome!
jlyvers7432 years ago
This is the ultimate man-cave lamp!! So awesome!!
TechDante5 years ago
this would be perfect for a horror film just the effect of building it then moving around a dark house with the pulsing light and the posibility of the motor cutting out (for teh film of course) to plunge teh character in darkness only for a shocking reveal make this a perfect prop and effect well done
Yeah, or I was thinking haunted house, live action. :-)
bennelson2 years ago
+1 vs. Zombies, upgrade to HID for +2 vs. Vampires.
I just love over kill! Nice project although isnt it a bit noisy
shortw5 years ago
Rob If you use a higher watt bulb ( high beam) 55watts, the bulb is less likely to burn out. Or use 2 bulbs or more. In addition, if you add a 12 volt battery and hook it up parallel to the light with respect of positive and negative, the battery would keep the voltage under control. But you have to add a switch right at the generator/ motor so if the chainsaw light is not in use the DC motor can not drain the battery. Using a battery with your chainsaw generator / motor has an advantage that you could run the chainsaw generator only part time and still have light, if the light dims down just start the chainsaw generator until the battery is charged again. Drawback using a battery with this; the battery could overcharge or heat up after a while. But if you match the wattage of the bulbs this is not a big problem. How many watts does your DC motor have? If you have only volts and amps listed you can calculate the watts. Multiply volt times the amps, that would be motor watts. Then since you use the motor as a generator you have some losses of about 60%-70%= about 65% average Now take the motorwatts and multiply by 0.65 that is about what your chainsaw generator can produce. For example if your DC motor says .... volt= 24V amp or A = 5...... 24 x 5 = 120 motor watts.......... 120 x 0.65 = 75 generator watts........ Now match the light bulbs to the wattage. Or in this case about 60-65 watts. Note: A chainsaw can make up to 12,000 RPM, do not turn the generator / motor with that high RPM it could and will fly apart. Stay within the RPM of the DC motor , that is listed on the name tag.
robbtoberfest (author)  shortw5 years ago
Thanks for the tips. What if I used an old dead motorcycle battery, would that level the voltage?
It depends on the watts of your generator if you can use a motorcycle battery or if it would be better to use a car battery. If the alternator of the motorcycle puts out about the same as your generator I would say maybe yes.

We have to define ' a dead battery ' first.
A Battery That Will Take A Charge But Will Not Hold A Charge After A Period Of Time. This could be maybe used, but first when you start your chainsaw light the battery will not control or balance the voltage, but after the battery starts to create bubbles then it would be ok.' but you could start charging your battery first without the light, then later on switch the light on.
A Battery That Will NOT Accept A Charge( no or little bubbles) At All Can Not Be Used At All.
     It is best to use a battery that is good.
Or the better option would be to get a load control used for windmills.
    The best option would be to use a battery and a car alternator with internal voltage regulator this way you would not have to worry about volts and amps, but a alternator consumes about 40 watts to operate and to function and you need a battery for it to function properly ,  higher or lower RPM would not mater if you stay between 1200RPM ( start of full power) to 4000 RPM of the alternator.......
I like what you done here. Some folks my laugh at you, but I think it is very very very useful and a cheap generator. It could be coupled with a battery and a inverter ( 12V DC to 120V AC ) and it could be used as a emergency generator to have a 120V light and / or a 120 V TV powered..............
Remember 1 HP  = 736 Watts in electrical terms.
Car alternators have between 60 amps to 100 amps, so the max  with a 100 amp alternator would be 12V X 100A = 1200 watts minus the 40 Watts = 1160 watts output. But you would need a chainsaw with about 2 HP or better output.
weldor shortw3 years ago
if you want to build a gen set based upon a car alternator your best (and least expensive) is a single wire Chevrolet. The older ones run about 63 amps. They can be rebuilt to produce higher amps but you may run into problems with over heating. This can be avoided by using an alternator from a mid to late 1980s 80 amp alt and have it rebuilt to a higher (about 120 I think) rating. Because it is physically larger it does not have the issues with the cooling. I learned this from the owner of the local automotive starter/generator/alternator rebuild shop. good luck!!
robbtoberfest (author)  shortw5 years ago
130 VDC and 6700 RPM, the other one I have is 90 VDC but no RPM listed. Next time building a system like this I'd probably use a direct drive instead of clutch and put a hose clamp throttle adjustment on the handle. I'm thinking of making a light duty welder with this, but I don't know what to do quite yet.
Use the 130 volt DC ( better choice ), or the 90 V DC and use a 110 volt light bulb about 40- 60-75-100 watts for it ( try and see). Use about 3/4 throttle for the 130 volt Motor, the 90 VDC motor should be about a 1750 rpm motor. With this high a voltage a battery will not regulate the voltage down to 12 volts.
shortw shortw5 years ago
Or the 130 Volt motor could make a good Wind mill or hydro project for 12v application ( low RPM ) . Yeah try it with a 110 volt light bulb, but you may to play with the watts. You got me exited now. Let me know.
zilcho3 years ago
See the problem with this is that most of the time when I use a flashlight its at night and my neighbors would get pretty mad if I fired up an old chainsaw engine every time I needed to see.
super tubes4 years ago
vrom vrom, im goin to blind you!
lukeyj154 years ago
May I suggest that you replace the permeant magnet motor with a internally regulated car alternator. That way, you will be putting out 13v no matter what. The only problem is a small amount of power is required to energize the fields.
My 2c
Also also, at a constant 13Vdc hi intensity chip LEDs become an option (an expensive one though). that would be A LOT of lumens!!
SirStokes4 years ago
Only in America does one need gasoline to see in the dark. Awesome instructable!
Terivia5 years ago
That is one BA flashlight, i want to bring on a boyscout campout. "WOULD YOU TURN THAT OFF?!?!?" "No, we need it to play magic"
I was thinking:

"NO!!!! I got to a good part in this book!"
quadracer4 years ago
You can adjust the carb so it idles high enuff to engage the clutch.
2 stroke 4 years ago
yo man is that an princess auto welder by the looks of the gun and ground clamp looks like the flux wire welder they have if so i have their 70 amp stick welder
nedfunnell4 years ago
Awesome build!
bart2455 years ago
That little flashlight project you built there is awesome! Great job!
wizworm5 years ago
You need to take that to Burning Man, that would be a hoot
Who cares about practicality, gimme internal combustion! Very cool survivalist/dieselpunk rig.....
treehouse245 years ago
to the Creator this is old news, i mean as a bush man i was hunting one fall day when i left my lights on when i walked away from my truck returning 6 hours later it would not start as the batteries were dead , sitting there i thought it is a 30 mile walk or better yet charge the battery, i used my small chainsaw to charge the battery, taking off the belt from the alternator and the chain and bar from the saw i put the belt over the clutch , making sure the direction of travel was the same , i started the saw hand pulled the belt tight and for a few minutes turned the alternator to charge up, replaced everything and started the truck , when home with no blisters , here is your next how to instruct able, take care thanks, gord, as for the light not practical , yet make it for loggers in the dark led to run off the handlebar heater ,to light you work area, or even cooler two leaser lights triangulated to set at 49.6 feet to make one dot ( saving running a tape to measure the log and cut
Many things on here are 'old news' but people still enjoy documenting their creations or instructing on their own particular way of doing things. Be nice, not jealous!
It was not my intention to make a negative comment on someone else's project , it was my intention to give him an idea to up his project to use of an application that probably has never before been demonstrated,such as the leaser lights triangulated to set a distance, but to others that may be old news as well as it was used on ww2 bombers using two lights to to set distance as well,so i am sorry if i offended anyone,
I apologise for being so tetchy!
It actually doesn't matter what direction the alternator is turning, either way you will have a positive or + on your positive lead or post and minus or - on ground / casing.
The alternator makes 3 phase AC power inside the alternator, that's why it would not matter what direction the alternator is turning . Then before leaving the alternator the power is going through 6 diodes or rectifiers that turns the Ac power into DC.
The reason i said '' actually '' is...
it don't matter , but you have a cooling fan on it and it matters what direction it has to run to cool the alternator under the hood under constant load and heat.
But for short run or with less load it would not matter either.
I never would had thought to use a chainsaw like that, that is very ingenious and easy to use when stranded.
Thanks for letting us know.
robbtoberfest (author)  treehouse245 years ago
Good ideas. I really like the laser light idea added to this to measure distance.
thats kool maybe me and my twin juan can do that one day
1-40 of 135Next »