Eddie Current Motor vs Simple AC Motor

Hi Signode:

They're both basically the same type of motor, except that the first, as you said is magnetically coupled by means of a magnetic clutch (eddy current clutch).

In your original system, the motors run always at full speed, but consume only no-load current, until an increase on output shaft speed is required or has a load that draws current above no-load levels.

An eddy current clutch control is basically an early variable speed drive for AC motors, very effective at its time but little understood by the new age technicians.

The modern Ac variable Freq. drives DO control the speed of the motor itself by varying the frequency of the output phases to the motor; but contrary to some manufacturers claims, the motor draws more current at low speed, high loads; than it does at higher speeds with the same load.

In a good portion of the speed span, both systems perform alike, add to this the effect of a BIG fly-wheel and you may not notice any significant difference in energy consumption.

The advantages you will attain with the use of inverters, are simpler wiring to the control, simpler trouble-shooting and constant monitoring of any parameters at your will. This is what we achieved after switching 9 of 10 presses from eddy current to AC inverters.

Regards

My understanding is different. Eddy current drives have a motor operating at normal speed and the drive is coupled through eddy current clutch ( For large motors it is two concentric drums with water circulating within to remove heat). The speed variation is done by varying the dc current in the field coil. As per Wikipedia:

"Eddy current drives are a type of slip controlled drive. Slip controlled drives are generally less efficient than other types of drives. The motor develops the torque required by the load and operates at full speed. The output shaft transmits the same torque to the load, but turns at a slower speed. Since power is proportional to torque multiplied by speed, the input power is proportional to motor speed times operating torque while the output power is output speed times operating torque. The difference between the motor speed and the output speed is called the slip speed. Power proportional to the slip speed times operating torque is dissipated as heat in the clutch."

Where as in VFD drives the losses are the heat dissipated in the electronics. Overall significant energy savings can result with VFD if the motor speed to load speed differential is substantial.

You went into a lot more detail, but the basic principle is the same, we only differ about energy consumption, the major savings we are having is the costly repair and spare parts for the old eddy current drives, along with reduced down-time.

But I liked your technical answer, my un-educated appreciation came from hands-on experience.

Regards