Help: Mains Powered DC Motor

[bobledoux]

I’m looking for some help with 120 volt DC motor control.

I want to power a micro lathe with this American Bosch 120 volt DC, 5.5 amp permanent magnet motor:

https://www.surpluscenter.com/item.asp?UID=2007093009084043&item=10-1023&catname=electric

I’ve been told I could use a bridge rectifier through my autotransformer to provide variable speed.

Would the small controllers intended for 90/180 volt DC motors also work for this application?

Would a dimmer switch through a rectifier also work?

Do I have to ramp up the voltage when starting the motor?

Are there other variable speed control options?

 

[Sceadwian]

There are many options for driving DC motors with variable speed control, more than you'll likley every want to know about. I like the autotransformer and bridge rectifier sollution though, it's very simple and would be very reliable if you properly over rate the diodes. The inductance/intertia of the motor will do some smoothing itself but you still may get 120hz pulsations without capacitors to filter the output. A dimmer switch will work if you can find one rated for the current, but it's output is pretty rough so the filtering requirements are going to be higher.

 

[bobledoux]

I'm considering a PIC controlled PWM motor control. In the past I've used transistor switches for low voltage applications. What is the mechanism for switching high current DC at over 100 volts?

 

[stevez]

I have several Baldor 90 dvc motors with controllers - maybe 1/2 hp or so each. The controllers appear to be very basic but I am told they are effective in maintaining reasonable control of RPM with varying loads. I've looked thru catalogs (McMaster Carr or Grainger I think) and see that these controllers are not all that expensive. I've also seen just the control boards from places like Jameco - maybe even kits.

Keep in mind that varying the voltage to a DC motor will adjust the speed. Without some kind of feedback there really is no control - and the speed will vary considerably in some instances as the load changes.

The plan for my motor - power my Craftsman/Atlas bench top lathe.

 

[Hero999]

You should be able to power a 120VDC PM motor from 120VAC using a bridge rectifier without any problems.

If you want to add variable speed controll then just use a lamp dimmer before the rectifier.