240 DC volt motor control

[supateach]

Hi
I have recently been given a small lathe which does not work, I am assuming the circuit board is faulty. I need a circuit diagram of a rectifier circuit and a PWM? circuit to control the speed of the 240DCvolt motor. I have some electronics Knowledge as I teach it to GCSE. Any advice and information gratefully recieved
Thanks
Tony

 

[Hero999]

Use a bridge rectifier to power the motor from the mains and a standard lamp dimmer on the AC side of the bridge.

If you want to reverse the motor, you can use a DPDT switch to reverse the polarity to the motor.

Obviously, the motor's metal frame needs to be connected to earth, along with any other exposed metal surfaces which cover live wires.

 

[supateach]

Hi
Never thought of that, (a little knowledge is a dangerous thing,) thanks a lot
Tony

 

[tcmtech]

The other option is to use a variac transformer instead of the dimmer before the rectifier. You will get better torque and a more consistent speed regulation.

 

[supateach]

Hi
Sorry but I dont know what a variac transformer is, do you buy them or can I make one?
thanks
Tony

 

[Hero999]

It's simply a variable transformer, the primary is 230V and the secondary is 0 to 230V, but often a bit more than 230V.
Autotransformer - Wikipedia, the free encyclopedia

The disadvantage is, it will be more bulky and expensive than a lamp dimmer.

You need to know the current/power rating of of the motor so you can select an appropriately rated, rectifier and dimer or variable transformer.