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Here's an easy and inexpensive way to build your own personal power generator. It's a handy little back up system to protect your family from black outs, storms, Y2K, etc.
Or, maybe you simply want to get away from it all for a while. It's always nice to know that you can
produce your own power whenever and wherever you are.
We'll be the first ones to admit, these homemade units do have their limitations and they
aren't pretty, but they are practical. If you want pretty, go out and spend a pile of your hard
earned money on a generator. If you can find one.
We have come up with 4 different ways to build these homemade generators depending on your preference
of items, or the availability of parts in your area. We will use the complete lawn mower version for this tutorial.
First off let's discuss using the vertical shaft lawn mower engine, complete with the mower deck,
handle and the works. It's a great idea to build this generator on its own mower deck because
you then have an instant transportation system built in. We'll also show you a neat little device you can
use to help your generator operate under heavy loads a lot smoother. Mount this on the handle next
to your throttle and you will have full control of your generator right at your finger tips.
To drive our project we are going to use what is probably the most common lawn mower engine around,
the Briggs & Stratton vertical shaft four-stroke gas engine, in the 3 to 3.5 horsepower range.
You will have to remove the cutting blade and replace it with a drive pulley. It's important that
the motor shaft extend at least 1 ¼" out of the bottom of the motor, as you will want your
pulley to clear any obstacles like the motor mounting bolts.
Take a good look at the motor shaft, in most cases you have a 9/16" mounting bolt holding the
cutting blade to a hub that's attached to the end of the motor shaft. The hub has a 3/16" key
built in it to match the slot on the motor shaft, which is normally 7/8" in diameter.
Make sure the motor shaft is keyed so that your pulley can be fastened securely. This will be
the easiest set up you can find. If you run into a motor with a shaft that has only a threaded
end and no key way, then walk away from this type of set up as it's way to much work and
aggravation to attach a pulley to this type of shaft.
While shopping around for all the different makes of alternators, Ford, Chrysler
etc. We found the GM alternator the most favorable for our systems. There are two types of
GM alternators, one with a built in voltage regulator and the other with an external voltage
regulator. Use only a GM style alternator with a Built in Voltage Regulator, as they are easier to wire up and work
with. We had three main goals in mind when we built our generators. Build em' cheap, safe and
simple.
We built our projects using two different alternators with a 40 and 65 amp output. You may also run into different size casings of GM alternators, we stuck with the most common sized casing which measures slightly over 6 ½ " at the mounting hole openings. Your alternator should come with a two-wire molded connector/harness that plugs into the casing. You need this connector to hook up your alternator properly later on. Make sure you have it when you purchase or salvage your alternator. If not, you can pick one up at an automotive supply shop for a couple of dollars (more on this later).
The inverter is an electronic device that converts low voltage DC (direct current)
electricity from a power source into a standard 120 volt AC (alternating current) that
we use in our homes. The power generated from our alternator is a low voltage DC usually
around 14 volts. In order to maximize our power capabilities we are going to add an
inverter to the system. Inverters are sized by the amount of wattage they can output.
In the case of an emergency you will no doubt want to power some 120volt AC devices in
and around your home. You will need to decide what you think is absolutely necessary
to run during a power interruption and then calculate how much wattage (power) each
device consumes.
You can do this by finding the manufactures rating plate on the appliance you wish to operate. Take the amperage rating of
the device and multiply this by the household voltage. Example: An appliance drawing
5 amps of current multiplied by the household voltage. (5 amps x 120 volts = 600 watts).
Inverters start as small as 50 watts, and an average household would use an inverter
anywhere between 2500 to 4000 watts for "normal everyday operation". Their price tags
start at about $40 to approximately $1000 to $2000 for the average home. So the choice
is up to you as to which size inverter is right for you. Just remember, your planning for an
emergency. If you use good power management you can keep your power consumption to lower levels.
When we plan for emergencies, we normally store food, water and extra supplies......why
not power? With your home built systems you have the better of both worlds. You can use
the generator to charge a battery or bank of batteries then switch over to directly
powering a DC to AC inverter for 120 volt purposes. Then you can use your batteries
to power up a selection of 12 volt lights and gadgets. You did buy some 12 volt back
up lights didn't you? Or you can reverse the process and run your power inverter off
the batteries, the choice is yours.
In an emergency you have a readily available supply of batteries around the house to
store power. They can be found in your automobile, your motor boat, your spouse's car, your neighbor's,
even your mother in law's car. All can be charged quickly and cheaply with your generator.
Here are a few tips for selecting a desirable lawn mower that will keep your time and
labor to a minimum. The simpler the design of the lawn mower the better. You will need
to bolt a set of mounting brackets and an alternator to the back of the deck, so choose
one that is as flat as possible. We are also going to cut a slot in the backside of the
deck so make sure this part is as flat up and down as possible too. Now take a look
underneath. Some mowers have a shroud circling the cutting blade, try to avoid this on the rear side of the mower deck,
as we want to keep our cutting to a minimum. And make sure your deck is made of metal,
stay away from the plastic ones.
We have used two different styles of pulley's, aluminum and cast iron. A strange thing happens when
you remove the cutting blade and hub off your lawn mower engine........ It will not start! The
flywheel on your motor is most likely made of lightweight aluminum and it needs the extra weight
and momentum of the cutting blade assembly to rotate it through a complete revolution. A flywheels
main purpose is to store energy so it can carry the crankshaft through the 3 non-power strokes of
a 4-stroke engine. So, the flywheel must shoulder the burden of the rotation for 75 % of the time.
If you take away some of it's mass on the motor shaft, it will not run smoothly, heck, it won't even start.
So if you have a lightweight flywheel you're going to need a pulley with some weight on it.
So, how do you tell if you have a cast iron or a lighter aluminum flywheel? Take your blade and hub
assembly off your motor shaft and start pulling the cord. If after 4 hour's you haven't started the
engine, well.... it's a pretty good bet that your flywheel is aluminum and you will have to use a
heavier cast iron pulley. Or you can remove the top motor shroud that reveals the flywheel area,
put a magnet near the flywheel fins. If the magnet doesn't stick, it's aluminum, if it does
stick then you have a heavy cast iron flywheel and you can get away with using an aluminum
pulley.
Our motor shaft was 7/8 " in diameter. It seems that as soon as you look for a pulley with a bore
bigger than ¾ ", they are very difficult to find in the normal "Retail" stores. So we went to a
bearing and transmission shop to buy our pulleys. We found aluminum pulleys gave good service but
they didn't stand up to the long hours and wear and tear, as did the cast iron pulleys. So we opted
for a cast iron pulley from a company called TB Woods. It uses a system with two parts, an inner
bushing and a main pulley. The inner bushing has a split in it. When you tighten these two items
together with the mounting bolts supplied, the split bushing closes onto the shaft with a tremendous grip. The pulley
was also keyed, so once it's installed, it stays put. We used ½" wide pulleys on all our projects,
with diameters ranging between 3"and 6". We'll discuss the proper pulley diameters later on.
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