Have a diesel engine that puts out average 3000 RPM and max's out at 3600 RPM I want to belt drive to a generator head that only needs 1800 RPM to operate at 60 hertz what size pulley should I use. Also for further info the shaft on diesel engine is 1 inch and the generator shaft is 42 millimeters
The simple way to calculate the sizes of pulleys in you example is to use the following equation: RPMa*DaRPMb*Db Where: RPMa is the rpm of one end of the pulley system Da is the pulley diameter of the same end as RPMa RPMb is the rpm of the other end of the pulley system (opposite of RPMa) Db is the pulley diameter of the same end as RPMb In you case we have: RPMa3000 Da12 (we will use a starting point) RPMb1800 so: 3000 * 12 1800 * Db Db(3000*12)/180010 A 10 pulley should fit nicely on a 42 mm shaft so that should work as the pulley is much larger than the shaft.
If the engine is likely to be running for a long time, fuel consumption is likely to be important. You want to find out at what RPM the engine produces maximum torque.(If it's a car engine that will likely be related to the cruising speed of the car in top gear) All IC engines are most fuel efficient at the rpm for peak torque. If the engine can make enough power for your requirements at the rpm for peak torque, that's the rpm you should aim to run the engine at. Will depend on the engine of course, but peak torque is usually around about 1/3 of the rev range, I estimate that to be aprox 1800rpm [ie (3600-800)*1/3 +800 ] If aiming for 1800rpm for the generator, with an engine speed of 1800rpm, you don't need to change the rpm at all. That means the pulley's can be the same size, unless the belts slip (flat/ribbed belts slip aprox 3%- probably not enough for you to worry about) So that's the ratio sorted out. Physical size of pulley. All belts have a minimum diameter pulley which they can go around, so long as the pulley is larger there's no problem. Minimum size pulley depends on the thickness, and construction of the belt- and that depends on the power you're transferring via the belt. If you give some indication of the power you're wanting to transfer I'm, sure you get some additional help you'll probably need a governor for the engine to generate at 60Hz give or take a bit. Many diesel engines just have a max/min governor relying on the user to governing the rpm under varying load . You'll need fairly good control for electrically generation, but it needs be nothing much than releasing the throttle a little if the generator is running fast, and if the generator is running slow pressing the throttle. Hope that helps
