In the electric motor field, everyone generally accepts that integral horsepower motors are 3 phase. This is done to increase the amount of power that can be output from the motor. By putting three electrical phases in, staggered 120 degrees apart, it is possible to put more electrical power through the motor and get more mechanical work out of approximately the same space. Of course this is limited by the motor’s efficiency since all systems have energy conversion loses which are manifested as heat.
Smaller motors, most often referred to as single phase devices, are generally split phase or, more literally 2 phase with the second phase being turned off when a speed threshold is met. The second phase is required in order to start the motor and to determine which direction the motor will turn.
Another attribute of the AC motor is the starting current required to bring the motor and load to operating speed. The typical starting characteristic can be as much as 6 times the running current. In fact, AC motors will pull in more and more current until either the motor starts or it burns up. This is the reason for the use of thermal overload devices.
But the difference between starting and running power creates significant problems when applying solid state technology. Solid state starters and variable frequency drives, which depend on power semiconductors to control motor speed, are limited to the inrush current profile of the power device. This limit is usually double the running current and in fact is better defined by the dI/dt or current rate over time in addition to the temperature rating of the device.
But when you have to pump water for irrigation in remote locations, the cost of bringing 3 phase wiring is very expensive. Most of the time remote powered pumping has been powered with diesel engines. It is estimated that over 200,000 IC engines are in use in rural applications. And with rising fuel costs and high maintenance expenses, these IC engine solutions are threatening to close down many small farmers.
But John Roesel had a better idea. And in the mid 1990’s Precise Power Corporation was started, building integral horspeower motors based on a new single phase design called the Written Pole motor. These motors that produce 125% of full load torque with only 150% current, with efficiencies from 92-95% and 85% power factor. These results have been verified by stringent testing at motor labs like Manitoba Hydro.
And it only take 2 wires. So the cost for the utility to pull power to a remote location is reduced proportionately. This makes a lot of new applications cost effective, quieter and cleaner by far. Some ranchers are saving in excess of $10,000 per month compared with IC engine operation.
For something completely different in electric motor technology check out www.precisepw.comr