Discussion in 'Homework Help' started by scratch, Aug 14, 2010.
can i controll the speed of a lage DC seriese wound brush motor with a SCR.
A single SCR would only allow you to switch the motor on and unless you have a gate-turn-off SCR you can't then switch off the DC current. SCR's have been used in a forced commutation chopper (PWM) mode but the circuit requirements become more complex to achieve this. A single SCR won't do it - particularly if you have speed control in mind.
This must be realted to your electric vehicle thread.
A SCR is not made to control DC current. It will simply latch on and stay on until power is removed. Your DC motor needs either a resistive controller (wasteful) or some kind of PWM.
If you go back to the EV thread, you will find it is still active - just on a different page - http://forum.allaboutcircuits.com/showthread.php?t=41551&page=4
If you can give more information, help is waiting.
Universal motors (i.e., AC/DC motors) are series wound. I am not sure whether your motor will run on AC. If it does, then you could use an SCR to control it as such controls are quite commonly used for universal motors. Be aware that such controllers do not provide the same high-torque at low speed as PWM DC does for series wound motors.
Now, where are you going to the the AC?
thanks very much for help
There is a method, called commutation, in which the DC current through an SCR is shunted around it, dropping it to a value below the minimum holding current. Usually accomplished by triggering a second SCR that is in series with a capacitor. General Electric used this method in its industrial variable speed inverters.