Backup Generator

Backup generators are very useful in the event of power loss. Purchasing a generator is the best way for large amounts of power. A home built generator can generate smaller amounts of power, enough for the freezer and a few lights. This is definitely a project for someone with mechanical background and maybe a little electrical know how. You could go the route of purchasing all the same components that a regular generator uses, but then the cost would no longer be effective. Also the speed regulation can be very tricky and require alot of tuning. A popular alternative is to use parts much more common, thus cheaper. Many of the parts can be purchased used for VERY cheap. A push lawnmower is a good mounting platform that already has an engine on it. Building a homemade generator will require some fabrication skills. A car alternator is used as the source for converting power into electricity. The mower blade will need to be removed. Then you will need to find a good flat spot to mount the alternator.

 

A hole will need to be drilled through the deck for the alternator shaft to pass through. A couple of holes will also need to be drilled for the mounting of the alternator. Try to not mount the alternator too close to the engine so that the pullies are not too close. When selecting the pullies for the two components, make sure the engine pulley has a good amount of weight to it. The additional weight acts like a blade to smooth out the engine. With too little weight the engine may backfire or not run at all. It is very good to start with an engine that has a cast iron flywheel instead of an aluminum flywheel, you would need little to no extra weight then. You will also need to plan for tensioning of the belt. If you preselect a belt that will fit snug you will be way ahead of schedule. You will probably need to make slots like the alternator uses on a car to adjust the distance between the two. Another way to deal with it would be to add a tensioner, which will automatically keep tension on the belt. This is a much better approach but is more involved. Make sure the pulleys are in line with each other so that the belt doesn’t wear out prematurely. You will wan’t to know a few more things about you small gas engine also. How much horsepower does it make? This will determine how large of an alternator that you should use. 3 hp engines should use 60 amp alternators, 6 hp engines could use a 120 amp alternator. You should also find out what rpm your engine runs at. If the engine runs at 3600 rpms full speed, use a slightly smaller diameter pulley on the alternator to make it slightly faster than the engine speed. Ideally you should run the alternator above 4000 rpms for full charging efficiency. Now you should take the output leads from the alternator and run them to a mounted car battery. You could argue that you shouldn’t need a battery, but they do a good job of smoothing out the power input, no surges. A battery will also give you a extra amount of capacity that the unit itself would not have. Say the refrigerator kicks on, if the amount of power supplied is not enough, it will not be able to start. Whenever an appliance starts up it requires much more power than it takes to continue to run. The battery gives the appliances this reserve needed to start appliances up without overloading the generator. You will need to purchase a power inverter made for a car. The prices of these have come down considerably. Look at the charts supplied by the manufacturer as to how much power the inverter can supply. The rating will be in watts, luckily appliances are labeled with how many watts that they require to operate. If you use a 3 hp engine with a large battery the generator may keep up a while but eventually run out of power, while trying to keep up. 3 hp will usually only run a refrigerator if everything is set up correctly. This is where you will have to decide how many things you will keep power running to, or if you need a larger engine and alternator to keep up. I like a self propelled mower for the larger engine and a 100+ amp alternator to be used with it. The power wires will run from the alternator to the battery to the inverter. At the inverter you can plug an extension cord in, to power up appliances. The nicest way is to have an external receptacle or drop cord connected to your fuse panel, then switch off the main so that you won’t be trying to power the neighborhood. This will require an electrician to make that type of a connection correct. This way you would have no cords running into the house and less risk of exhaust making it into the house.