How to Build a Generator From a Lawnmower Engine

Building a generator from a lawn mower engine takes a lot of time and patience, because the two parts you need (lawn mower and car alternator) weren't exactly built to go together. But it can be done, and when you finish or if you finish the job, you could have a handy tool that can charge batteries or provide a little power in case of an outage. It might not be as reliable as a store-bought generator, but it might be an interesting project. The first thing you need to do is find a vertical shaft lawn mower engine, and am alternator that has a single wire connection and an internal regulator. It must have this to keep the voltage steady at 14 volts. An alternator without an internal regulator will keep increasing voltage as the belt spins and eventually melt your alternator.

Instructions

1

Mount your lawn mower so you can get at the blade. Put it on a secure hoist, on on 2 x 4s. Then remove the blade by taking off the mounting bolt (you will have to brace the blade to do this) and then remove the coupling from under the blade. You may have to rent a pulley puller to pull off this job.

2

Attach your cast iron pulley to the lawn mower blade. You will have to determine what size pulley you will use, taking into consideration the proper resistance needed to balance out the mower's throttle output and keeps the motor running consistently at a steady throttle. This pulley wheel will actually work like a fly wheel, and must be iron to give enough weight and resistance to work properly. You might have to test out a few sizes before you find one that works.

3

Trace and cut a pattern in a piece of plywood or steel to mount both the mower and alternator to the base. They need to be the right distance apart for the belt you plan to use, so get all the materials together, fit the belt on, and make a diagram to build this part. You can cut your holes longer to allow the alternator to be moved, in case you want to use a different size belt.

4

Cut additional holes for the bolts that will attach the lawn mover and alternator to the base. Each one has mounting bolts on them. The lawn mower has bolts that attach the engine to the mower shield and the alternator has bolts that attach it to the engine block.

5

Mount the lawn mower engine to your mounting bracket. Slide the bolts used to mount the engine to the mower shield into the holes on the plywood and bracket, so the shaft and pullet goes through the bracket. Use any type of rubber cushioning or shivs you need to keep the motor even and steady.

6

Mount the alternator engine to the bracket face down, so the pulley goes through the plywood, using the bolts that mount it to the engine block, or by modifying another attachment if these bolts don't cooperate. Again, use rubber cushioning or shivs if needed. Usually the lawn mower shaft is longer than the alternator, so adjustments need to be made to align them perfectly.

7

Build a base with 2 x 4 boards. Cut them to a length longer than the bracket and just as wide, then cut a cross brace and the two sides, and secure them together. It will be a simple box with a cross brace that looks like an "H" with a top and bottom.

8

Attach the belt to the engine pulley and alternator and set the bracket and generator on the base. Secure with bolts, screws or large nails.

9

Test the output of the alternator by connecting a simple voltage reader to the alternator. In addition, test the internal temperature of the alternator by inserting a thermometer into the casing. Be sure it doesn't get too hot, and the voltage is not to high. They may run around 150 degrees F, and output anywhere from 30 to 50 amps.