This sounds rather "standard" - you want Full-wave Rectification - a
Triac not an SCR -
This is within the relm of many hobby electronic types - with safety in
mind (not normally
the case with many).
Baring having a Ham friend or other, Try the local Motor repair shop or
I suspect Square D or such - has a standard unit that would simply bolt
on, wire in, and
away you go. - I'd take you motor spec's with you.
Also - And I suspect this might be plauguing people - Some of these
have 'anti-spilke' or "snubing circuits" within the control.
DC motors are DC generators also. Move a winding across a magnetic field
- and the
winding has voltage on it. -
What zaps controllers is they get 'back-e.m.f.' - or voltage generated
higher than what the controller can handle.
Many a ball pitch machine has/d this problem - I fixed a number years
A snubber is simply a 600V .1 uf cap in series with a 200 ohm resistor.
Wattage = (E**2)/R (worst case) or 120 * 120 / 200 = 72 watt. i.e. 100
watt 200 ohm.
(a 25 watt will do nicely for either resistor since the power isn't
The resistor doesn't draw current unless a spike (from a fast start/stop
The spike is composed of high frequency voltage/power/current - and it
will pass through
the capacitor like it wasn't there - and dump into the resistor.
The circuit should be across the motor leads. +/- doesn't matter for
The parts are available from Radio Shack - the resistors are square
ceramic blocks (power).
The caps are available there also. Higher voltage is ok. 250V is
marginal, but ok .
Put them in a box ! - observe safety. - Use electric tape as needed.
Isolate from the
box - and not a cheap plastic one - you want safety in the shop -
breakage might be
ignored until to late.
Wow - didn't mean to go on like that - but there are some ideas.
> I have a Delta DL40 Electronic Lathe. It has a computer control, which
> has caused me nothing but problems over the years. Now that this is a
> discontinued product, the cost of replacement is astronomical just for
> ther controller part. I decided that it is time to hard wire it to a
> switch. What I am looking for is some advice. It has a G.E. DC motor
> 1.25 Horsepower, 12.2 AMPs and 90 Volts with a permananet wound magnet. I
> would like to go variable speed, with forward and reverse.
> Any ideas would be greatly appreciated.