Lathe DC motor break

**glens5** · Dec 18, 2018, 02:52 PM

This is a schematic of a DC break I made for the motor on my South Bend 9" lathe
I used the parts I had on hand and it could be simplified with a 120 vac coil on relay 2 thus omitting transformer 1.
I've been using this for a few years now and it works very well. The amount of breaking can be controlled with the resistance value between the bridge and the run winding of the motor. The time the DC is applied to the winding is controlled by an adjustable timer.
I honestly think this is preferable to a mechanical break as it allows for manually positioning the chuck after the motor has stopped and the timer opens the contact supplying the DC to the motors run winding.

The resistor(s) were hand wound with nichrome wire salvaged from a heating element.

I had originally experimented with charging a capacitor at line voltage and discharging it through a resistor.
I found the 170 volts DC on the capacitor was too high and that the twenty volts or so through a full wave bridge and the .8 ohm resistor worked quite well. The timer only applies the DC for a couple of seconds.

I should have mentioned this is with a run of the mill 1/2 HP single phase 120 vac motor with a separate start winding. The motor is reversed with a DPDT switch on the start winding and the break works in both directions.