The Siren Board

[The Yelp signal was accomplished by a] Louis Allis motor that had 9 leads. It used three contactors that switched the motor from 2 pole 3500 RPM to 600 RPM 12 pole. That made the yelp sound. During the yelp the motor became a generator and put power back on the line. When Louis Allis went out of business we bought special made motors from Doerr Electric in Cedarburg, Wi. I designed a copper core motor that could take the heat made during three phase reversal. We used a two contactor magnetic starter with a timer that reversed the motor for 2 seconds to make the yelp then waited 5 seconds before switching to forward again. - Jim Biersach 12/2022