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Motor Start Relay With Keeper Magnet

IP.com Disclosure Number: IPCOM000046494D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Berglund, WA: AUTHOR [+2]

Abstract

Motor start relays are used to connect a start winding 5 and capacitor 6 (Fig. 2) in such a manner that torque is generated, causing the motor to come up to speed in a desired direction. The relay contacts 7 are closed by a start relay upon the occurrence of the in-rush current to the stopped motor, and open when the current drops to a design value where the motor is capable of completing its acceleration to running speed under the design load.

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Motor Start Relay With Keeper Magnet

Motor start relays are used to connect a start winding 5 and capacitor 6 (Fig.
2) in such a manner that torque is generated, causing the motor to come up to speed in a desired direction. The relay contacts 7 are closed by a start relay upon the occurrence of the in-rush current to the stopped motor, and open when the current drops to a design value where the motor is capable of completing its acceleration to running speed under the design load.

In the case of disk files, a large starting torque is required to quickly bring the disks up to speed, and a rather small torque is required to maintain that speed. The resulting slope of the starting current through the start relay is relatively flat at relay drop-out time, with the result that a "clean break" of contacts is difficult to obtain. The resulting relay contact bounce may continue for more than 250 milliseconds and causes electrical noise which can interrupt computer circuits and cause errors to occur.

As shown in Fig. 1, a small magnet 9 is added to "catch" and hold the relay armature 10 as the current through the coil 11 decreases and the spring 13 pulls the armature away from the core 15, causing contacts 7 to open. Properly designed and placed, the magnet will prevent the armature from being picked up again by variations in the motor current. When first applying power to the motor, the large in-rush current is sufficient to pull the armature away from magnet 9. The tens...