My Improvised DC Generator Build





Introduction: My Improvised DC Generator Build

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.

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


Step 2: Obtaining the DC Motor

This is the permanent magnet DC motor I used as the generator. It is a 90 Volt DC, 3/4 Horsepower motor. I got it at an auction for only $5. It acts as a generator when the output shaft is turned. The output voltage depends on the speed the shaft is spun and the load on the generator. I use motors like this to build wind turbines. They work great in that application too. The only problem I had with this particular motor is that it is a metric unit. It has a 14mm shaft. I couldn't find a pulley to fit on that size shaft. So I bored out a 1/2 inch shaft pulley to fit the 14mm shaft.

I also see motors like this on Ebay all the time. It is a good place to buy them if you can't find one cheap locally.

Step 3: Disassembly

The first step in the build was to remove the edger blade and arm assembly. It was only held on with one bolt, and came off easy. I saved the rod that connected to the lever that raised and lowered the blade. I planned on re-using that for adjusting the belt tension on the generator. I haven't found a use for any of the other parts of the blade assembly, yet.

That's about all for disassembly on this particular edger model. If you have a different model, the process may be more involved.

Step 4: Mounting the Motor (Generator)

I needed a place to mount the motor. I bolted a heavy piece of plastic to the handle of the edger using U-bolts. The plastic is 1/2 inch thick and very tough. I probably should have used metal, but the plastic was free and a lot easier to cut and drill.

The motor (generator) is mounted on another piece of the super-tough yellow plastic with big U-bolts. now I just need to mount a hinge to hold the two pieces together.

The third photo shows the hinge that holds the two pieces of plastic together and allows them to move relative to each other. This will allow me to adjust the tension on the belt driving the generator. I used a large brass door hinge. The beauty of this is That I only have to pop out the hinge pin to separate the two pieces. Next time I would probably use two hinges to give it added support and strength.

You can see that the plastic the motor is mounted to has warped a little. It was caused by over-tightening the U-bolts. This is where metal would have worked better like I said above. However, I found a way to fix the problem. See below.

In the last photo I have bolted a piece of scrap steel angle channel to the piece of plastic holding the motor. The steel channel straightens out and reinforces the plastic where it had been warping before. I also cut away part of the end and bent back a tab to make an anchor point for the rod that will raise and lower the motor to adjust the belt tension.

I shortened the rod that originally raised and lowered the edger blade. I put a new 90 degree bend in the end of the rod and drilled it to take the Cotter Pin that originally attached the rod to the blade assembly. To bend it, I clamped the rod in my bench vise, and heated it red hot with a propane torch. That made it much easier to bend. I got a nice clean 90 degree bend in it.

Step 5: Finishing Touches

The first photo shows the completed generator, almost ready to be rolled outside and tested. You can see how the rod goes from the lever on the handle, down to the motor mount. The lever works great for adjusting the belt tension.

Time for testing. At the last minute I decided to replace the belt with a new one, as can be seen in the second photo. The old belt was cracked and glazed and didn't look like it was going to last much longer. So I went down to the auto parts store and got a new belt. At nearly $10, the new belt turned out to be the most expensive piece of the whole project.

The third photo is an operator's point of view looking down on the generator. To operate, I first move the lever forward a couple of notches to take the tension off of the belt. Then I start the engine. Once it is up and running good, I can pull the lever back and engage the generator. Simple!

Step 6: Testing

The first photo below shows the dummy load I used for testing the generator. It is basically a big light bar with 20 lamp sockets wired in parallel. It takes 12 Volt light bulbs. Each bulb draws 2 Amps at 12 Volts. So I can adjust the load on the generator simply by changing the number of bulbs installed. This dummy load will handle up to 40 Amps at 12 Volts. My little generator won't put out anywhere near that amount of current.

For the first test of the generator. I started out with only 4 bulbs installed in the dummy load. This put an 8 Amp load on the generator. The generator handled the load easily. The lights burned brightly.

A check of the voltage shows perfect voltage for battery charging.

Later I got the generator up and running with 5 bulbs installed for a load of 10 Amps on the generator. The bulbs are all burning nice and brightly. 10 Amps, or a little more, seems to be the limit of what this little generator can produce at the moment. Adding more bulbs starts bogging down the engine. I may be able to tweak the engine to get more power out of it though. I doubt the engine has ever had any maintenance. It is in rough shape. A nice tune-up might help, and maybe some synthetic oil to reduce internal friction. Some adjustments to the carburetor might also help. I may also tinker with changing the pulley sizes on the engine and generator. However, even at only 10 Amps of output, this generator still produces enough power to supplement my wind turbine and solar panels on cloudy, calm days when I really just need a little extra power.

Step 7: Tweaking the Generator

A problem I was having with the generator was getting the belt tension just right. The correct tension seemed to fall between two of the detents on the lever (isn't that always the way?). So I cut a section out of the rod and welded in a turnbuckle. Now I can adjust the length of the rod so that the tension is perfect. I also added a nut and lock washer to one end of the turnbuckle. That allowed me to lock the turnbuckle in place once I found the sweet spot. The turnbuckle added a few extra dollars onto the cost of the generator, but it was still a super-cheap build.

Step 8: Battery Charging

I should probably mention that when using a generator like this to charge batteries, a blocking diode, at the very least, is needed between the generator and the batteries. The diode will prevent the batteries from back-feeding the motor and spinning it. I get around this issue by feeding the power from the generator into the charge controller from my wind turbine, and then into the batteries. The charge controller has a built in blocking diode, and is specifically designed to safely charge batteries. So I also don't have to worry about over-charging and damaging the batteries. Details on how I built this charge controller can be found on my wind turbine web page.

I will probably eventually attempt to convert this generator over to running on gas from my biomass gasifier. So stay tuned for further developments.

You can learn more about this project and all my other projects on my web site.

Step 9: Update

I've rebuilt the generator. I was starting to have a lot of trouble with the plastic warping and throwing things out of alignment. So I replaced all the plastic with steel plate. I replaced the brass door hinge with a heavy steel hinge much wider and sturdier than the old one. I built the hinge out of 3/4 inch threaded rod with big rod coupling nuts as the actual hinge points. By turning the rod, I can move the motor mount side to side to perfectly align the pulleys. Speaking of the pulleys, I have replaced both the pulley on the engine and the one on the motor. I found that the belt was slipping under load. The generator was needing more torque than the engine could supply with the old pulleys. So I put a smaller pulley on the engine and a larger one on the generator to increase the torque delivered to the generator.

The generator is now bolted to a 1/4 inch thick steel plate. Two arms welded to the plate extend back to and are welded to the two large coupling nuts on the threaded rod. This forms a very strong and stiff hinge with no play. The position of the generator can be easily adjusted side to side by rotating the threaded rod. The belt tension adjustment mechanism is essentially unchanged from before. These modifications have enabled me to nearly double the current output of the generator. See photo below.

Now the generator can easily power eight lights at a load of 16 Amps. That's pretty respectable battery charging current. I may be able to even further improve on this with more tinkering, but on the whole, I am pretty happy with the generator as is. It does the job it was designed for.



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    Dude take it off the edger frame and mount it on somthing, your killing me!

    Hmm Interesting. How come you used a (what looks to be a treadmill motor) instead of a alternator from a Car?

    2 replies

    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).

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

    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.

    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.

    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.

    1 reply

    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!

    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.

    1 reply

    hmmmp i'll have to remember that

    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.

    1 reply

    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.

    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!

    two thumbs up......i've been searching for this kind of project

    Crank up the RPMs. That motor has to run faster.

    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.


    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!