Denso Window Motors, Warning - Don't use with Jaguars !

[Mike Betts]

All,

As alluded to by several people, the window motors have a positive temperature coefficient (PTC) resistor in series with the motor windings.

The motor was designed for moving a window up and down and the PTC is designed to keep your son from decapitating his little sister. Since a window is not a variable speed device, the PTC is designed to sense a motor stall. The PTC increases its resistance as it gets hot which causes the current to diminish reducing the power of the motor...

While it is possible that the switching frequency of the Jaguar causes more heating than a Victor, it is far more likely that the problem is how it is being used.

When operated at "full on" and "stop", you are likely at a good efficiency point on the motor torque curve. This is why a properly designed system using a spike has no problems.

However, at variable speeds, the Jag (or Vic) accomplishes speed reduction via reducing the voltage. For the same torque at lower speeds, you end up off the optimum efficiency point of the curve and motor heating results.

So the motor heat adds to the heat that the PTC uses to detect a stall and it cuts back the current giving you exactly the symptoms you have described.

Therefore, the problem is not in the Jaguar but in the use of the motor.

Regards,

Mike