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Peter H.
 
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Default Potential Relay for phase converter



I am working on building a 7.5 hp rotary converter. I plan on using a start
circuit with start cap that drops out after a potential relay senses enough
voltage in the generated leg. Grainger has a listing of potential relays but I
really don't like dealing with them as I am not a business and their past stock
levels leave much to be desired. I preferr McMaster Carr for service and ease
of ordering.


Grainger is just as easy, if not easier, to do business with, as McM-C. YMMV,
of course.

Grainger stocks General Electric and Steveco potential relays.

The Steveco 90-66 is the one most folks have had the greatest success with.

G.E. potential relays are rated 3 HP.

Steveco potential relays are rated 5 HP.

You will have to use an auxiliary contactor to start your converter, because
your idler rating exceeds the potential relay rating. Select a contactor rated
at least 7.5 HP at 240 volts, assuming a 240 volt converter, of course.

Figure on about 900 microfarads for your start capacitor, also assuming a 240
volt converter.

Figure on about 90 microfarads for your A-B capacitor (across which would be
connected the 900 microfarad start capacitor, switched by the auxiliary
contactor).

Figure on about 60 microfarads for your C-B capacitor, thereby giving you the
nearly ideal 60/40 percent balance (actually, an intentional imbalance).

Figure on about 30 microfarads for your A-C power factor correcting capacitor.