Peter H. wrote:



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.
You might try USAMfg
href="http://ww2.usamfg.net/cgi-bin/onramp.exe?custnum=&password=&pgm=itemnum.bbx&item no=88617&button=Submit"
Shipping/handling will be more than the relay, but you will have a relay.
Real nice people and prompt service.
--
Keith Bowers - Thomasville, NC