FAQ - Keppe Motor

1.10. There is a number of low power motors with efficiency exceeding 50%. Why is the Keppe Motor better?

Answer: Conventional low power AC monophasic motors have a very poor “power / volume” relationship, which makes them impractical for most domestic applications. This is simply a limitation of the conventional technology. These small motors with efficiencies exceeding 50% use iron cores, and this makes them very big, heavy and awkward for domestic use.

Furthermore, as mentioned before, even if a conventional motor is very efficient, this is true only for rated design load, i.e., the motor is delivering the mechanical work within the narrow range for which it was designed. Outside that range, it will be drawing energy from the power grid even if it is running idle, that is, without load applied to the shaft. In this case its efficiency will no longer be so good.

Consider a practical example of a low power monophasic AC motor used to drive a bench drill. While idling at 127V, it consumes 6.6 Amps. At an efficiency of 65%, this motor consumes around 470W just to keep rotating. This minimum consumption, when computed for a long period of work, reduces the motors efficiency greatly.

Another practical example is with a 24V-DC motor of 167W used for fan blade calibration in our laboratory. At 24V and idling, it consumes 24W to reach 2,380 rpm, or 1A. This means an enormous consumption without performing any mechanical work, only free rotation. This never occurs with a Keppe Motor, which under these conditions would consume about 2W maximum for the same speed.