On 1/14/2011 1:35 PM, 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.
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Best -- Terry

it's amazing how much just plain wrong information you are getting.

Vfd on a silicon diode is .7v. Fullwave rectifiers have two in the
forward path conducting on each half wave. 1.4V drop. If you pull 12
amps, power is therefore 16 watts. But, it is AC, so you won't pull the
12 amps continually.

But, as others pointed out, you would be much better served with a
SCR/Triac controller with feedback - the ones I like are made by
Minarik. They are frequently available on ebay but peruse the minarik
catalog first

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www.wbnoble.com