Originally Posted by
Carnel
Tricky stuff. A choke keeps the current running at the moments the SCR or the bridge diodes are closed. But where does this current came from? If there is no suitable source, very high voltages surges will occur and your electronics will die. So in a well designed circuit a flywheel diode is a must. For 50 or 60 Hz supply voltage I would recommend to use the choke for a more smooth and silent running. Connect a diode between the choke input connection (at the SCR/bridge side) and the mains return, with the cathode to the positive pole and anode to the negative pole. So for the normal motor voltage the diode is not conducting. The result is that the current is kept alive through the diode when the bridge or SCR is closed. Of course the diode must be specified for the peak voltage of the grid and the maximum motor current. Take ample margins!