PeachParts Mercedes-Benz Forum - View Single Post

jay_bob · #20 06-18-2012, 10:19 AM

Yep, if the motor has electricity applied and the motor is not spinning, the motor will quickly overhead.

Conservation of energy; you are putting energy (electricity) in to the windings, but not removing the energy in the form of mechanical work. The energy has to go somewhere, this is what makes the motor get hot.

In case someone is still confused on the switching, first thing to know is a dc motor can be reversed by flipping the polarity of the applied voltage.

The motor has 2 wires, neither of which are grounded when the switch is in the resting position. The switch in the console has both power and ground connections for the motor.

Inside the switch assembly are two sets of contacts. One set is made with the switch at rest or in the up mode. The other has continuity at rest or in down mode. With the switch at rest there is 12 V applied to both sets of contacts so the motor has 12 v on both ends of the winding. Therefore the motor does not run because it has 0 V across it.

When you push the switch to the up or down position what you are doing is taking one side of the switch away from 12 V and instead grounding it. Depending on which contact is made, the motor now sees 12 V across it. The polarity determined by the contacts decides whether the window goes up or down.

The Otter is a thermal overload device. If the motor current increases beyond limits, due to over travel, jammed linkage, etc. the metal heats up and bends, which breaks the circuit. When it cools off it bends back and reconnects the circuit. Apparently from what I have been reading these tend to corrode and fail. However please do not bypass this, it is there to prevent overheating and potential fire. Not sure whether the fuse will clear fast enough to protect the motor/wiring/switch in a stall situation.