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Speed Control


#1

So many of the machines we use operate at speeds that are too fast.
Does anyone know where I can find a reasonably priced, new or used,
speed control in the 10-15 anp range?

Jon


#2

Single phase AC 110 0r 220 volt induction motors are not adaptable
for variable speed operation period. 3 phase AC motors can use a
technique called VFD or variable frequency drive and can be
operated with a single phase input. A good example of this is
sold by Rio Grande as part of a very versatile lapidary unit. Item
203-003 page 374 --2004 tool catalog… The cost here is for a
whole package and it is not inexpensive. A drive system with the
proper components is not unreasonable though.

Another approach is to use a 90-130 volt DC motor with a Pulse
Width Modulation DC control . These are also fairly inexpensive (
particularly with new surplus components) and give excellent speed
range adjustment and good low speed torque. Current brush type
motors on portable power tools are probably using this technique. I
have used this on a number of lapidary and shop machines using
industrial surplus components. They work very well.

It takes more than normal ( I think) technical skills to chose
the components and get them working-- but it is not really
difficult.

I usually buy from: http://surpluscenter.com/ get the catalog and
find local help if you need it. You can find a lot of information
on the web about both techniques. jesse


#3
 So many of the machines we use operate at speeds that are too
fast. Does anyone know where I can find a reasonably priced, new or
used, speed control in the 10-15 anp range? 

Universal motors like the kind on most flexshafts are easy to
control by just reducing the voltage to the motor this is what the
foot control does. It is a cheap control mechanism. It is extremely
rare to find a large universal motor that would need 10-15 amps,
that would be a 1-2 HP motor (about the only place you find larger
universal motors is in fans like ceiling fans and they are still in
the 1/4 HP and smaller range). Most motors that are 1/4 HP and
larger are induction motors and they cannot be safely speed
controlled by changing the voltage if you try you may burn up the
motor and start a fire. To control a induction motor you need to
change the frequency not the voltage and the motor should have
special windings to handle the higher heat when running at slow
speeds (most motors are cooled by an internal fan that is on the
rotor and if the rotor is spinning slower then there is not as much
air flow therefore more heat) In fact with induction motors the only
ones I know of that are speed controlled are three phase motors.
There are large DC motors that are voltage speed controlled but they
tend to be quite expensive because they need permanent magnets to
make them work and these are quite costly in the size and power that
is needed.

I know that this is very long winded but the short answer is you

can’t do it unless you change the motors on most of your shop
equipment.

Jim Binnion James Binnion Metal Arts Phone (360) 756-6550 Toll Free
(877) 408 7287 Fax (360) 756-2160 http://www.mokume-gane.com
@James_Binnion Member of the Better Business Bureau