Re: How to determine three-phase power

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <teslalist-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
 >
 > Original poster: "Stephen Conner by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>
 >
 > At 13:23 27/04/03 -0600, you wrote:
 > >Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 > >   There are rotary converters and such that convert single to three phase
 > > (motor/generator).  They are very cheap used and not to bad
 > > new.  Something like this:
 > >
 > >http://cgi.ebay-dot-com/ws/eBayISAPI.dll?ViewItem&item=2526540836&category=1267
 > >
 > >This place seems to have a lot of these,  Maybe ask if they have a single
 > >phase to three phase unit...
 >
 > You can use a regular 3-phase induction motor and a big run capacitor to
 > convert single-phase power to 3-phase. You feed one phase of the motor
 > straight off the line and another phase via the capacitor. The motor
 > generates the third one. A lot of folk who buy surplus 3-phase machine
 > tools use this trick.
 >
 > Steve C.

	Yes but!  In order to start the motor from single phase you need to
have some sort of circuit to excite the third line at a suitable phase
from the others.  I use a couple of three-phase motors running on single
phase to operate my lathe and my mill, but I had to use a "phase
inverter" as it seems to be called in the trade.  I bought one rather
than built it; contains a relay to disconnect that leg after the motor
starts and uses an electrolytic "motor starting capacitor".  If you're
trying to convert a significant amount of power you'll probably have to
start the "idler motor" under no load and then connect to it.

Ed