Original poster: Frank <fxrays@xxxxxxxxxx>A SCR is just that a rectifier. It is on or off. The only difference it you can control the amount of time it is conducting. Where I worked, we had SCR motor speed controllers for 600-100 Hp DC motors. The bays were fed with 600 VAC and the SCR's were in a full wave bridge configuration. This means pulsating DC was fed to the motors.
As indicated in other posts, the only way to shut the SCR off is to basically reverse its polarity. This is typically done with a commutation cap and some basic circuits.
The DC out was 1/2 cycles of the AC with varying widths. The amount of work done (speed) is an integral under the curve area. The narrow width = less energy = less speed.
They work best by using AC as an input and not DC and your output will be pulsating DC.
Frank At 09:33 PM 2/12/2007 -0700, you wrote:
Original poster: FIFTYGUY@xxxxxxxIn a message dated 2/12/07 5:52:28 P.M. Eastern Standard Time, tesla@xxxxxxxxxx writes:>Can someone please >tell me if a SCR has states other then on and off. Can you vary the >amount of power passed thru them. I was thinking (probably wrong >again), that they either pass electrons or they don't.I think insufficient gate current or through current can result in erratic on/off cycling within the desired conduction time. But otherwise one designs for "all or nothing".-Phil LaBudde