running 3 phase motors from single phase...

I KNEW I saved this for a reason... Everybody knows that 3 phase power is expensive to get, and most homes only have single phase (110 or 220) power. But 3 phase motors run smoother, because power is constant, so they would be nice to have. You can even get ahold of them used for free/next-to-nothing *because* Nobody Has 3 Phase Power! You can buy some very expensive electronic converters, but why bother? You can run a 3 phase motor from standard 220 single phase power. Really. It is an old technique, known mostly only to old tinkerers and the like. It works like this: First, you get the 3 phase motor turning it (manually, or better, with a small 110 v motor), and THEN turn on the 220 (connected to two legs) it will run. It will not run at rated power, or smoothly, but it will run (at speed). This is OK for some machines. Now for a magic trick. Take a second (free, same size or smaller) 3 phase motor, and connect it to the first (three leg switch, and zing!, the second motor turns on instantly, and both motors run smoothly! And with more HP than off of just 220. The first motor is acting like a "generator" to provide the third leg. This is not "full three phase power", but it works quite nicely. The 220 supplies power to both motors, with one more wire to connect them. You can can connect additional motors also. This works best if the first motor is a larger HP (2 vs 1), or higher speed rating (3400 vs 1750) than the slave. Older, "beefy" motors are preferable. A 3 HP, 3400 RPM motor works nicly. The reason for this is that if you try to start a bigger load than your master motor, you may reverse the rotation direction of the master (3 phase can be wired to run either way). A large/fast motor will have enough momentum to resist changing directions. The more motors you get running, the more stable the system becomes. The limit may be the amount of power drawn through the third leg of any given motor, or your switch, etc. A real world, functioning system: master motor: 3 HP, 3 Ph., 3400 RPM Starter "pony" motor- 110, 1/2 HP, 1 Ph washing machine motor Slave Motor- 3 Ph, 1750 RPM punch press or lathe. (Insert your machine here) The Washing machine motor and the master are mounted to a board/bench, and their shafts are connected with a flexible coupling. Power to them is switched with a Double Throw, Double Position, CENTER OFF switch. The 3 legs of the master also go to a 3 pole switch, To the slave machine. (DP/DT/C off Switch, shown (Three phase Switch, in 110 V motor on position) Shown off) SWITCH 1 SWITCH 2 / 220 leg1 o--------------------------------+-----------/ o----> \o | Three | / Phase 220 leg2 o---------------------------+----------------/ o----> Power \o--------| | | Machine | | | / Motor Neutral | | | |--------/ o----> | | |--------------| |------------| | 3 HP, 3 Ph. | |(110V Motor) |==[]====| Motor | |------------| | MASTER | |--------------| Operation: 1) Start with Switch 1 OFF. 2) Make sure that Switch 2 is OFF. 3) Turn on the 110 V "start up" motor with switch 1. (as drawn) This will drive the master motor. 4) Once running, flip Switch 1 so that power now goes to the Master Motor. It will now run at it's speed, and drive the 110 motor. (note that power is NEVER connected to both at once) 5) You may now turn on Switch 2, which will start the machine motor. 6) Turn off BOTH switches when done. Additional motors must have their own switch (of course), wired to the master, and should only be started one at a time. CAUTION: Always observe proper safety proceedures when working with electricity! If you don't know what you're doing, DON'T! copyright 1989 Roger Garnett ________________________________________________________________________ Roger Garnett (Roger-Garnett(a)cornell.edu) http://www.wayward.team.net/ "The South Lansing Centre For Wayward Sports Cars" "All donations of stray, orphaned, odd, neglected, etc. sports cars and bits in need of a good home accepted." "The drop off bin is right there- behind the barn..." On Tuesday, Mar 30, 2004, at 05:56 US/Pacific, Jules Richardson wrote: