I hate to do this to you, after you wrote all that, but then please expalin shaded pole, and repulsion-start-induction-run motors. (No caps- single phase)
Originally posted by bornriding
Mark is right here !!
a start-capacitor has higher capacitance than a run capacitor. Is there to produce a strong starting torque, but is not manufactured to dissipate heat and causes an increase in current draw, therefore it cannot stay in the circuit & therefore must be removed. ( at app.75% speed )
A run capacitor is of smaller capacitance & is oil filled to dissipate heat, which allows it to remain in the circuit, mainly for operating torgue.
The torque needed for a motor to move from a still position and run is much more than the torque needed to keep it running.
And just to see if ya'll are paying attention:
A motor is an inductive device. That means that because of the inductance, the voltage & current are out of phase with each other. This reduces the power that is capable
from the device. The capacitor brings the phase between the voltage & the current closer together which causes an increase in power for the device.( purely resistive circuit provides maximum power )
The run capacitor moves the Voltage & current phase slightly closer together, to get a little more power (which is torque)
The start capacitor moves the phases even closer, and therefore allows the device to generate more power ( torque ). But the motors are not designed to handle the power from a start cap. for a long time, due to the size of wiring in the windings.
Remember power equals voltage times current. To get more power, with voltage remaining the same, current would have to increase.
[Edited by bornriding on 02-26-2005 at 12:17 PM]