This is an improvised DC generator I built from an old gas-powered lawn edger and a permanent magnet DC motor. The inspiration behind this generator was to have a cheap way to charge up my battery banks on days when the weather is cloudy and calm, and my solar panels and wind turbine aren't providing much energy. It was a really quick, easy and cheap project. I got the lawn edger for only $5 at a yard sale. The permanent magnet motor came from an auction for another $5. The total cost of the project was only a little over $20! So far I have the output of the generator up to 10 Amps at 12 Volts. Further tinkering may improve that. This instructable will explain how I built it.

My eventual goal is to convert the generator to running on wood gas from my home-made biomass gasifier project. Stay tuned for that.

You can learn more about this project and all my other projects on my web site.
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Step 1: Obtaining the Gas Engine

Below are two photos of the 3 Horsepower edger I bought at a yard sale for only $5! It's not much of a looker, but it starts easy and runs great. I would have preferred to have about a 5 Horsepower engine, but at only $5, I couldn't pass this thing up.

I wanted a gasoline engine I could experiment with converting over to running on wood gas from my wood gasifier. Aside from just getting the motor running on wood gas, I wanted it to do something useful, do I decided to build a generator. I'll keep my eyes open for a cheap 5 horse or bigger engine to play with in the future. 

The edger is rusty and dirty, but basically sound. I almost didn't buy it because I couldn't get it to start at the yard sale. It seemed to have good compression though, so I took a chance for only $5. It tuned out I had the choke lever in the wrong position. Once I figured out the choke, it starts every time on about the 2nd pull and runs strong. It does vibrate pretty badly though. Something is out of balance on it. I'll live with it, considering the price

Nerdz4 years ago
Hmm Interesting. How come you used a (what looks to be a treadmill motor) instead of a alternator from a Car?
mdavis19 (author)  Nerdz4 years ago
Because I got it for only $5 at a nice air conditioned auction. No schlepping my tools out to the junk yard, sweating, getting greasy and paying whatever they want for an alternator these days (certainly more than $5).
JoeF4 mdavis1920 days ago

I bought a 63 amp Delco Remy 10SI at a scrapyard today for $5.

JoeF420 days ago

Good job on re-purposing "junk" into something useful. If your local scrapyards will sell stuff to you, start visiting them on a weekly basis. I guarantee you will be amazed at what people throw out, and I'd guess you'll find a good 5hp motor on your first visit. That said, a 5hp is like using a nuke to kill an ant if you keep your current DC motor. I've bought running generators, chainsaws, weedeaters, etc. for scrap price. Example: Onan 6500 watt generator out of a motorhome for around $140. Fresh gas and a new battery were all it needed.

As far as fuel consumption/efficiency goes, these small engines on yard equipment are not all that efficient to start with. Fuel consumption does not follow a linear line based on rpm or load either. Horsepower ratings for them are also based on a 3600 rpm engine speed. The newer overhead valve designs are more efficient than the older L head type, but not a lot. Running an alternator instead of the DC motor would be much more efficient in terms of fuel, and not a lot more expensive. That engine should pull a 100 amp alternator without any problems.

For what it's worth, one mechanical horsepower is equal to approximately 746 watts. AC or DC makes no difference.

tcambrón2 months ago

How is the bulb system setup and wired? I seen many of those type of bulb setups as a kid at the carnival events. Now I see the photos, it looks like such a simple cheap build. I bet those carnival people made profits after the park contract, toy prizes, pay some sellout guy at minimum wage to run the device. I still want to try win those giant stuffed animals. And still a build from today isn't much costly with arduino and LEDs, probably can be charged from solar panel.

allen_idaho4 years ago
A car alternator would work just fine in this type of setup. It just wouldn't work with a wind turbine. The reason being that an alternator is an electromagnet and not a permanent magnet generator and needs an initial charge in order to start producing electricity. Too inefficient for a wind turbine. Plenty efficient for a lawnmower engine.

So if you find yourself in a survival situation and maybe have an old car and lawn mower lying around, you should have just about everything you need to make a functioning generator. Aside from a power inverter, that is.
An automotive alternator WILL work, and quite well. Years ago when I used to drag race (sanctioned, on a race track only!) we cobbled together a battery-charging apparatus out of an old lawnmower engine and a GM internally-regulated alternator. The setup would kick out about 60 amps or so - perfect for charging batteries between runs (since the race car engines didn't have alternators). And the voltage was regulated perfectly for automotive batteries. Our setup was mounted on a pneumatic-wheeled dolly and could be wheeled easily to any location it was needed. That thing was worked year-round; in the winter it was frequently called up on to help jump-start cars. We later improved the device by adding a 26-series (smaller Ford-type) battery and even added a cheap fog light to serve as a work light.

Then someone stole it.
I need a garage and a place to work where my wife doesn't poke around, this build and lots of others on this site are inspirational!
soundmotor4 years ago
I have been thinking of doing a project like this as I just got a horizontal engine. To anyone looking to do the same, treadmills are good sources for large-HP DC motors. They can be found cheap on craigslist or at larger Goodwill / Salvation Army stores. Sometimes they are even free for the taking. Many good parts such as pulleys and belts are on them and the tread itself is a great bench-top surface.

hmmmp i'll have to remember that
mmv50044 years ago
FYI: You have plenty of room for improvement. If the gas motor is really putting out 3 hp (probably a good bit less than that since it's old) that means its putting out about 2,237 watts.

If your measuring 10 amps X 12 volts means your generator is putting out 120 watts.

That puts your efficiency at 100*(120watts / 2237watts) = 5.4%. Maybe up to 10% if the motor is half as powerful as it was once rated for.

You might try scaling your pulleys to match the optimal speed of your engine to the operating speed on the motors nameplate.

The claim of 5.4% efficiency is misleading, as you are more than likely not consuming 2237 watts worth of gasoline.

To put that in other words, your 3 hp engine has the capability of producing 2237 watts at some point on its power/speed curve. Just because you are not running at that speed doesn't mean that you are running more efficiently. If you are looking for maximum efficiency and don't need high amperage (i.e. you have a long time to charge your banks) you should find a point where your amps per gallon are the lowest.
uppfinnare4 years ago
Suggestion: for charging 12V batteries,how about using a used car alternator
with an adjustable V-regulator ?

This is perfect. If you put a bigger weel on the gas engine the electric motor-generator will go faster generating more power. "I thing the cluch is great!
wilmadan4 years ago
two thumbs up......i've been searching for this kind of project
redpillftw4 years ago
Crank up the RPMs. That motor has to run faster.
rjwarpath4 years ago
It looks like you have enough room to add a larger fuel reservoir. Could move the front wheel out a bit, add a platform and a simple 2.5gal gas can.
joen4 years ago
Let me second Phil B's thanks for a very good instructable. I am seriously looking into making one of these. This instructable gives me some very good ideas. Have you looked into adding a GEET fuel processor to your genetator?

I have nothing to do with them nor have I tried it Just wondering if you or anyone else has tried using one.

Again, well done!
Joen did you read the instructions "it only works if the exhaust is facing magnetic north" People here build things that work on the planet earth. That idiot running that site/scam is selling snake oil. run away
CaptSyn4 years ago
Excellent work. I haven't read the comments so maybe this has been suggested, but for a future upgrade, you could replace the dc motor with an automotive alternator and a decent dc to ac inverter to run power tools and such.

I suppose you could keep what you have and still add the alternator and inverter, and do some creative belt routing to run both at the same time. Just look at a car's engine for inspiration.

At any rate, excellent work. I hope to build something similar one of these days.
I dont know wat his motor is like but alternators arent the best to use for generating.
Maybe not, but since he's just charging what are most likely deep cycle marine batteries, then an alternator would be the better choice as it's designed to charge those type batteries.
CaptSyn CaptSyn4 years ago
I forgot to add that an alternator would also be easier and cheaper to repair than a dc motor, as you can go to any auto parts store and buy a cheap and commonly available rebuild kit.
Phil B4 years ago
Thank you for an interesting and useful Instructable. Some folks have used a World War II era aircraft generator and a slightly larger engine to make a DC welder. They also added an inductance coil to stabilize the arc. Output was around 75 amps, which is not bad for home repair and fabrication projects. I remember an article about this in an old issue of either Popular Mechanics or Popular Science from the 1960's or 1970's. A local college library near my home has bound copies of these two magazines back to day one.