I have long wanted my own generator, but a $500 and up price tag kept me from purchasing one new. After some internet searching and sleepless nights I found a good tutorial online . What I liked best about the tutorial is that Brian at epicenter has already worked out the kinks and sells the materials. I have no connection with epicenter, and the only things I have bought from them were for this project, but what dealings I have had with them were fair and honest.
A co-worker gave me an older Craftsman brand lawnmower for this project. It did not run, but with a little bartering, I had it repaired. I ordered the plate, an alternator, wiring harness, pulley, and two belts from the Epicenter web site. (Together these cost approximately $160 with shipping).
While waiting on the parts, I laid the mower on its side in the bed of my truck (being careful to keep the gas tank side up) and wedged a 2×4 between the truck bed and the mower blade to keep it from spinning while I unscrewed the blade. I did use some kerosene to loosen the nut (liquid wrench is almost pure kerosene).
I then drove to the local auto parts store to use their loan a tool program so I could get a pulley puller. The blade mount pulled off the shaft very easily, so I returned the puller and went home. On the way home I stopped by the hardware store to purchase longer bolts and spacers to not only attach the engine to the generator, but also to align the pulley on the mower to the one on the alternator. It took me a while to find the right bolt/nut/washer combo, but I got 5 bolts, 10 washers, 1 lock nut, and 4 1 inch spacers for about $15.
Once the plate arrived, I measured it and built a frame from scrap 2×4 lumber. The plate measured 12×24 so I cut two 2-ft lengths of 2×4 and two 9-inch lengths. After screwing them together, it made a perfect frame. Just because I had some, I painted the box with the leftover green paint from making a chicken tractor a few months ago.
As soon as the paint dried I screwed the plate to the box and attached the alternator. It fits just like a traditional alternator in a car. One screw fits in a whole in the plate, while a bolt fits in an adjustment slot in the plate and through the alternator the locks with a nut. To tighten the belt you loosen the bolt and move the alternator in the adjustment slot.
Next I installed the pulley on the shaft. I set in a 3/16 keyway in the shaft and pushed the pulley onto the shaft. I used a dead blow hammer to knock it flush. Be careful and think about what your doing, one side of the pulley has set screws so its longer, and I put that end toward the engine, so once I installed the alternator and the belt, it did not line up, forcing me back to the part store to get the puller to remove the pulley and put it on the opposite direction.
Once the pulley was installed and tightened, and I installed the engine. The cut outs for mounting the engine were larger than my bolt heads, so I sandwiched the plate between two large fender washers, the spacers fit on the bolts on the top of the plate raising the entire engine over the frame. This is because the shaft it much longer than the alternator shaft.
Depending on the type of alternator you use and how it’s regulated, there are different ways of connecting everything. I used an external switch and my alternator had an internal voltage regulator, so I ran a wire from the voltage regulator to the + battery terminal on the alternator, then the + terminal of the battery. I ran another wire from the second terminal on the voltage regulator to a switch that draws power from the battery. Because of this you need to have a battery to use your alternator. You have to energize the regulator to get it to produce electricity. You need a switch because if you leave the field on when you try to start it, it will put a load on your engine and it won’t crank. If your smart and get a single wire alternator with an internal voltage regulator it just wires up directly to the batteries. I would stay away from external voltage regulators as the wiring gets more complicated.
To keep things easy I paid an extra couple bucks for the wiring adapter for the alternator. You don’t have to use epicenter’s alternator or their harness, but since I would have to either buy a new one or go to the junk yard and remove one on my own I kept it simple and bought theirs.
I used their adaptor, some 14 gauge red and white wire, a 50 amp switch, some connectors, and heat shrink tubing to rig up a wiring harness that snaps in to the alternator. 6 gauge battery cables go from the battery to the alternator.
Most lawnmowers come with a safety device that you must hold in order to keep the engine running. Mine was on the handle of the lawnmower. I looked at it and decided to keep it functional rather than safety wire it closed. What I did was wire a washer to the linkage which allows me to pull it tight and loop it over the linkage bracket. That way if need to stop the engine quickly, I can just pull the washer off the bracket.
In order to use the generator, you must have a battery; this is because the voltage regulator needs to be energized to function. This generator is really just a souped-up battery charger as the alternator’s voltage regulator puts out the exact right voltage for charging car batteries. (Imagine that.)
Some other things to consider are that because lawnmowers use light flywheels, since they depend on the mass of the mower blade to idle correctly. So when choosing a pulley make sure you get a cast iron pulley with a little mass to it. You do not have to use store bought parts if you have parts at hand. I could have gotten by with using a piece of plywood as a base. If I had drilled a hole for the shaft to sit, I could have used the engine as a template to mark where to drill my mounting holes. This is a project for using your mind instead of your money to come up with a solution to a problem. I used more money than needed so I could spend less time considering solutions to problems of mismatched parts. Lastly, don’t scrimp on the belt quality, and buy more than one. If you are relying on a generator you made from your dead car then it’s a really bad day, and you probably aren’t in a position to go to the auto parts store.
I really liked doing this project, its one of my favorites I have attempted this far. I will say that using a credit card to order parts and have them shipped to my door made this a lot more fun. I could have completed this project for little cash by using donor vehicles from the junk yard, but it would have been a lot dirtier and took more thinking about how to make things fit.
The moral of that being, reading about projects is nice, but taking the next step and actually completing them is better. Nothing beats having your plan in the books before you need to start using it.
Since I cannot leave well enough alone, I plan on taking it a couple steps farther. The first major upgrade is I plan on making a little switch board to mount the throttle assembly and switch a little neater. Next I plan on converting the carburetor to run on LPG  gas from bottles which will make the logistics of fuel storage safer while allowing me longer run times and faster refuels. Lawnmower engines have small tanks with limited run time, and you do not want to refuel them when they are hot. By converting to propane, I solve both problems. I also plan on making a second lawnmower alternator combo, which I want to modify into an electric welder. This is something that 4WD  enthusiasts have done for years. The only reason I haven’t done so is that then I would have to learn to weld, which would lead me to more project.