Discover How To Easily Build a Portable Low Budget Power Generator
The Basic Parts You Will Need
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.
Automotive alternators are little power producing jewels that will be the heart of our systems. When driven by a lawn mower engine, we can produce a steady supply of quick, cheap and reliable power whenever we want. You can purchase alternators from Auto wreckers rebuilt or as is with a warranty for about $ 25. 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 Power Inverter
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.
The Lawn Mower Deck
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.
We stuck with half-inch wide belts to simplify things. We also found out that not all belts are the same. Our alternator is designed to work best with an automotive type belt and our motor pulleys were designed to work best with utility/industrial belts. So, what's a fellow to do? An automotive belt has a sharper angle or "pitch" on the side of its surface, so it will ride deeper in the motor pulleys. And if you are using a cheap pulley, it will start wearing a groove in the side of the pulley. The better choice is the industrial belts, but we have differences here too. The half-inch industrial belt is covered by two different styles, the "L" series and the "A" series. The "L" series belt is designed for fractional horsepower applications....light duty. On the other hand the "A" series belt was designed for full horsepower applications, heavy duty. It has more polyester cords built into it for more strength and durability. We tried all 3 different types of belts and they all worked fine. For short-term use you can get away with using the "L" series fractional horsepower belts or the automotive belts. For heavy work loads and long term use we found the "A" series industrial belts gave us the best service. We purchased our industrial belts at the same place we got our heavy-duty pulleys, a commercial bearing and transmission shop. The general all-purpose belts can be found in the furnace sections of your hardware and building supply shops. And of course the automotive belts are available at your local garage or auto supply shop.
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