On Fri, 14 Jan 2011 15:35:21 -0600, Terry
wrote:

My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.

Thanks to everyone for their input. I have a bigass finned aluminum
heat sink, about 10" square, that will go on the rectifier. And will
bolt the heat sink to the enclosure for good measure.

And I also appreciate the education on calculating heat dissipation.
My knowledge of electronics is none too good. I understood the
five-tube radio I built in high school, but these confounded
solid-state thingies just mess up my head. ;-)
--
Best -- Terry