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Registered Member #1165
Joined: Sun Dec 09 2007, 04:41AM
Location: GA, USA
Posts: 35
I'm designing a circuit to control the power windows in my car, but can't find anything on how to sense when the windows have reached the top. There has to be some change in the power input to the motor that can be sensed when the motor jams. Anyone have an idea?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
The motor current increases in the stall. You could just measure the motor current, and switch off quickly when the current increases beyond the operating threshold.
Quite a nice way to both protect the motor against too much torque in the stall and to sense the end stop is to supply it from a constant current source, set at several times the operating current. When it stalls, the current limits, the motor voltage drops, and this drop can be sensed to turn things off.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
I think an easier solution would be to put a sens resistor (probably about 1ohm) in series with the - terminal of the motor, and take the output of that into some kind of comparator or microprocessor input.
Registered Member #1165
Joined: Sun Dec 09 2007, 04:41AM
Location: GA, USA
Posts: 35
I think I'm going to scrap this idea, a few seconds of stall on a window motor while the other windows reach the top isn't going to kill it, so I'll just set it up so I hold down the button on the remote until all the windows are up...
Another question though - whats the cooling requirements of a MOSFET if its used to turn a 30-40A load on/off only? I don't have any on me to test with, but since its only in the switching state once in a few minutes max, I shouldn't need a heatsink, right?
I'll have to use P-channel on the ignition wires since everything is positive, can a N-channel connected to the gate convert the positive outputs of the remote starter to negative?
I'm planning out the car alarm install on my new car and would like to do a better job than I did on the current one.
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Motor Stop Sensing Circuit
