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OT - power window question

Discussion in 'Off Topic Threads' started by halfmile, May 29, 2011.

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  1. halfmile

    halfmile Well-Known Member

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    Put a new motor/window regulator in my daughters Kia Sedona wagon, very easy job that went like clockwork.

    So I took the old one and hooked it to my battery charger and it works perfect in both directions. But not in the car. Replacement unit works fine, so the wiring etc is all good. WTF?

    But the real baffling part to me is I do not know how the damn thing knows to stop at the top or bottom of the window's travel. There is just a 2 wire lead to the motor and that's it.

    Someone tell me how it works so I can sleep nights.

    HM
     
  2. HSLDS

    HSLDS Well-Known Member

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    Power leads (positive & negative) go into the switch. Depending on 'up' or 'down' the switch reverses polarity to the motor.

    There is no 'stop' on many motors (at night with lights on hold the button for the window and you will see the lights dim).

    Others have some sort of limit switch or sensor - the sensor will cut off the power to the motor if there is too much resistance being sensed (i.e., when the window stops traveling at the top or bottom of the window slide).

    I suspect the 'old' motor has started to fail - bearings going bad, brushes wearing, etc. and this is increasing the resistance in the circuit - enough to fool the sensor into thinking the window is all the way up or all the way down, so it trips the sensor and stops the current flow.
     
  3. Shooting Jack

    Shooting Jack Active Member

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    I haven't worked on one of those but most have a limit switch. When it gets to a certain point it creates a open on the circuit. Jackie B.
     
  4. birdtracker

    birdtracker Active Member

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    HSLDS is exactly 150% correct. Birdtracker
     
  5. need to shoot more

    need to shoot more Active Member

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    Also a motor that is defective or failing may work with no load on it ( not doing any work)but put some load on it and puff.
    Jim
     
  6. mixer

    mixer Well-Known Member

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    The rear windows on my car haven't worked for years either from the local or master switch but if I bang on the inside rear door panels they'll start again for a while. It's no big deal as I live in S.Florida and it's a/c all the time.

    Eric
     
  7. halfmile

    halfmile Well-Known Member

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    Yes, it could only be physical resistance. So when someone has their head in the window there is no decapitation.......

    I'll consider the question answered.

    HM
     
  8. Quack Shot

    Quack Shot Active Member

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    Go to the website above, register, and go to the Service Information area. You can look up the particular vehicle and get a wiring diagram. Many vehicles these days have a "Body" module to control things like lights, wipers, windows, etc. What the general principle is that when there is an increase in current, the module turns off power to the window motor, usually by tripping a relay. The original unit may have exceeded the allowable current draw and will not operate, since the current parameters exceed the programming limits in the processor. Same goes for a kid getting their head stuck in the window by the efforts of an older sibling or irate parent. :) Current sensing can be done many different ways, but one common strategy is to sense voltage drop across a small resistance. Voltage drop will increase with current. When the voltage drop reaches the programmed limits, the window control circuits are appropriately manipulated, hopefully.
     
  9. halfmile

    halfmile Well-Known Member

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    Their electrical schematic shows a transistor like symbol (no polarity shown) in series with a resistor on one side of the power input.

    That probably opens when current is over their desired parameters.

    Cheaper than limit switches and such for sure.

    HM
     
  10. Quack Shot

    Quack Shot Active Member

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    Now the trick is to find out where the Transistor is located.:) If they show a Transistor for direct circuit control, they usually sense the Voltage drop across the Transistor/Driver. The transistor has a bit of resistance and that is what they use to determine the current flow. They use the same trick on many control circuits and many times for diagnostics and monitoring for function. One common application is for fuel injector control. If the voltage drop is zero, then they know they have a circuit fault. DTCs can then be set according to the application. Hope you sleep well tonight!

    Quack
     
  11. TjayE

    TjayE Member

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    Another question on power windows.

    My buick left front window works fine in the summer, but will not go back up (closed) in the winter. Does the cold climate cause more resistance? Tom
     
  12. Auctioneer

    Auctioneer Well-Known Member

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    You should also check the wiring between the door and car frame. Some times the wire will brake with the door opening and closing. I have at times had to replace a wire or two in the door jam.

    Work the window up and down while wiggling the wires. If the wire is the problem the window will stop working.
     
  13. halfmile

    halfmile Well-Known Member

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    Quack, my guess would be the BCM. And I don't know where it is, and I don't care.

    The good part is how easy the R & R was. Viva Kia.

    HM
     
  14. Quack Shot

    Quack Shot Active Member

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    HM,

    Just like the spaghetti sauce, it's in there.

    TjayE

    Last Buick I owned you had to crank it in the other direction to close it.
     
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