Tools
2003-03-14 by Mike Denman
While this is not exactly about British cars, it is
about some of the tools you might like to use. Many, if not most, industrial
tools use three phase motors. Some of these tools are real handy to own but how
do you run them off of single phase power. (if by this point you are not
interested in this discussion please delete this message and accept my
apologies.) Recently I re-visited this problem because I decided to move some of
my 3 phase tools back to my home which doesn't have 3 phase power. First I
investigated to see if it was possible to "re-wind" a 3 phase motor to make it a
single phase motor. The answer came back as NO. In some cases you can buy a
single phase motor to replace the three phase motor. This is what I did with my
metal cutting bandsaw. Expensive but it certainly takes care of the problem. But
how about those machines, like a Bridgeport vertical milling machine, that would
be difficult to adapt to a standard single phase motor. There you have a couple
of options. The first option is a "buzz box" that uses relays and capacitors (I
think) to get the motor started and then it runs on single phase 220 volts
with a loss of torque. "Buzz boxes" are relatively cheap with several brands in
the $90 range. I have never used a "buzz box" but apparently as crude as they
are, they work. The next option was a "rotophase" which is a motor that is run
off of single phase and "chops up" the incoming power so that it looks like
three phase. I have and still own a rotophase. The rotophase motor is noisy and
the "three phase" power it produces makes the three phase motor it is supplying
runs noisily. The rotophase units are not particularly cheap with the price
depending on the size of the unit. When I bought my rotophase some years ago, it
cost about $300 for a unit suitable for motors up to 1 horse power. A new option
is to use an inverter. The inverter takes in 220 volts single phase and using
solid state circuits, makes 3 phase power (D.C. but the 3 phase A,C. motors
don't seem to care). Again, the price of the inverters depends on the size of
the motor you want to operate. A unit suitable for a 1 horse power motor can be
bough for less than $200. While $200 is a lot of money, it is a lot less than
the inverters cost just a couple of years ago. It is also in the same price
range as buying a 1 horsepower motor. So I have bought and fitted one of these
inverters to my Bridgeport milling machine. It is really nice. Absolutely no
noise. The 3 phase motor it is supplying with power runs as quietly as it does
on "real 3 phase" power. The inverter gives you a variable speed so that is nice
if you don't have this feature. I am really please with the inverter. I have my
inverter hooked up "permanently" to my Bridgeport but it could be set up with a
plug/receptacle so several machines could "take turns" using the unit. Hopefully
this information is useful to someone and will save them some time trying to
"solve" this problem.
Mike Denman