Thermal Protection

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Posted by Dan.

Other on team - from Carnegie Mellon sponsored by -.

Posted on 7/25/2000 6:14 PM MST



What exactly does the 'Thermal Protection' on the window, seat, and sliding door motors do? Does it just cut off the current at a certain temperature, or does it limit the current to decrease the heating?
Thanks, Dan

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Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 7/25/2000 8:41 PM MST


In Reply to: Thermal Protection posted by Dan on 7/25/2000 6:14 PM MST:



Window & seat motor have a PTC (positive thermal coefficient?) in series with the motor. The PTC normally has a low resistance (much less than the winding of the motor). When the windings of the motor together with self heating of the internal resistance of the PTC raises the temperature of the PTC above a critical level, the resistance of the PTC climbs sharply (to something much more than the resistance of the motor windings), This has the affect of limiting the current passing through the motor, limiting the amount of heat that the motor will see in the case of a stuck switch or relay.

The power sliding door motor has a bi-metal breaker inside. Bi-metal has the property that it bends when heated. This bending action is used to open a set of contacts in the motor.

The basic difference between the two is that the PTC motors will sort of gradually loose there power while the bi-metal protected motors work just fine up to the second that the contacts open and then nothing.

Another difference is that the bi-metal motors will 'cycle' on and off if the motor is stalled and the power is held on the motor while a PTC motor will go off and stay off until the stall or the power is removed.

The spec that many automotive OEM's have is that a motor must be able to survive 24 hours of a stalled condition with full battery power at the motor terminals without a) starting a fire and b) degrading the motor performance by XX percent (XX varies by application and OEM).

Hope this helps.

Joe J.