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Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ.

Steinmetz connection

Whilst I have no experience with the Ashland motor it sounds like you need a Steinmetz connection*.

For this connection the AC supply goes across two of the three motor windings. The capacitor connects between one of these terminals and the third (free) winding, so the three mconnections are:

Phase 1, AC supply and one end of capacitor.

Phase 2 and AC supply only (other phase, natch)

Phase 3 and other end of capacitor only.

The order of the windings will determine the rotational direction of the motor. If you wire it up and the motor runs the opposite way to that required, simply swap terminals 2. and 3. above.

AC rated capacitors do not have polarity, so it doesn't matter which cap terminal is used for which connection.

Before you start wiring, check the resistance between each of the three possible pairings of motor wires (green to blue/red, black to blue/red and green to black.) They should all be within a few percent of each other. If this is not the case get back to me.

It should be noted that the Steinmetz connection has several drawbacks. The third phase created by the capacitor is only approximately correct, and even then only at one value of load. It is usual to have this occur at the highest continuous load and for that to be no more than 80% of the design rating for the motor. At all other loads the phase is further off, one effect of which is that the start torque for the motor is greatly reduced, often less than 20% of design rating.

The practical upshot of this is that you may find that the 3 uF value doesn't give you the best phase balance for your load. You may need to try different values to get closer to balance.

*One caveat, generally the capacitor size for a Steinmetz connection on an induction motor is 70uF per kW motor power. Your recommended cap is about twice that but the extremely poor efficiency of the hysteresis motor would probably be enough to create that difference.





Mark Kelly


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