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A capacitor will only give a small phase-shift, enough to give a single phase cap-start motor a sense of direction.
You are suggesting running a three-phase motor on two phases, in industry there are protection circuits fitted to protect motors from running like this - or they end up burnt out :!:
The three-phase motor on 1phase with condenser give only 65...70% of original power (lower torque) , but if i remember right, need 70uF capacitor for each kW. (no elko, only MP or oil dielectric for AC use!)
It is possible to take a small 3 phase motor and wire it up as a rotary convertor. Diagrams can be found in older electrical engineering books. The convertor motor must be spinning in order to get things started - usually a small fractional HP pony motor does that - disconnected once the convertor is on line. While this might seem terribly clumsy many machine tools have very special motors (Bridgeport mills come to mind) making outright motor replacement very expensive. My brother used a home brew convertor for several years before he moved his shop to a location with 3 phase power. The rotary convertor apparently results in some imbalance and full motor hp isn't available so it's not perfect.
A friend of mine sells AC motor drives which can be configured for single phase input and 3 phase output. The price for one new for a 3 hp motor was less than $400. Note that this item is minus things like reactors (for RFI suppression, among other things) and bypass relays but may be sufficient. Given the common-ness of these things there might be used equipment out there.
I have already used a 3 phase moter as a phase conveter to run other 3 phase moters. Itis actually quite simple. You need some way of getting the moter into speed i.e. capacitor, other moter, etc. Then by running the moter on 2 wires it acts as a phase convertor by outputting on the third leg of the moter. If you need any help just give email me at Dcat127@yahoo.com
Hi, It looks like you have had plenty of replies. I have built several of these before, They are called static phase converters, very easy to make and run about 2/3rds of the original HP. The 6x550 is a potential relay, its available from www.grainger.com The other pic is of a rotary phase converter, if you have any other questions, just email me @ firstname.lastname@example.org