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Ir motion sensor switching a fan

Discussion in 'Sensors and Actuators' started by bevinp, Jul 24, 2011.

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  1. bevinp


    Jul 24, 2011
    I want to use an off-the-shelf IR motion detector to switch on a toilet exhaust fan. I want to use the IR sensor delay feature instead of building a PCB based circuit.

    My experiments so far:
    1. I tried to operate the fan as the load of the IR motion sensor, but found that after the IR sensor delay, the sensor would frequently immediately restart and was totally unsatisfactory. The power source for both the sensor and the fan is the same lighting circuit for the house, and I think this is the cause of the poor performance. But I don’t want to run a separate circuit from the house fuse board; I am not a licensed electrician and don’t want to touch anything on the fuse board and invalidate my house insurance. I am looking for a circuit that will enable the sensor to operate correctly as if the load was a simple incandescent lamp.

    2. I then used a halogen lighting solid state transformer as the load of the IR sensor, driving a relay that switched the fan on. Once again the fan and the IR sensor were on the same house lighting circuit. The sensor suffered occasional restarts, but not as frequent as my first attempt. So it seems that the sensor was still being affected by the inductive load of the fan on the same power circuit, and not by the solid state transformer. (But I could be wrong.)

    I was going to purchase a zero switching relay to be operated directly by the sensor, but Tyco, a manufacturer of solid state relays, has an article that says zero switching with inductive loads will cause drastic current overloads.

    A fan motor is an inductive load, so consequently, I need a “random switching” relay, but I have the feeling that the sensor is being falsely triggered by the switching occurring at non-zero voltage.

    So any advice on a circuit and its logic would be greatly appreciated.
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