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
/// british-cars@autox.team.net mailing list
/// or try http://www.team.net/cgi-bin/majorcool
/// Archives at http://www.team.net/archive
|