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How to circuit a motion sensor to drive 30 amp relay

Discussion in 'Sensors and Actuators' started by ju1234, Sep 15, 2018.

  1. ju1234


    Feb 24, 2018
    Hello, I need some guidance please. I can hook up wires together properly. That is all my electic/ eletrocnic ability is. But I want to do the following:

    I want o make motion sensor device to automatically turn off the stove top (220 volt electric) if there is no motion in kitchen.

    I can use a regular motion sensor device of 110v or 220v or perhaps a 12-24v dc to drive the primary output (something like

    I need to take the output from this to actuate a 220v 30-40 amp relay switch that will turn the stove top (total maximum watts load of 4K to 5K) circuit on/off. I did not find any simple/cheap device already available to accomplish this.

    How do I need to hook up the circuit and what type of components will I need? I am thinking using a simple outdoor light motion sensor and a 30 amp relay that is normally used for Air conditioners.

    Thanks for the help.
  2. kellys_eye


    Jun 25, 2010
    You can get motion sensing switches to control room lighting quite readily and using one to switch a solid state relay to handle the stove current is straight forward.
  3. Bluejets


    Oct 5, 2014
    Being that it operates a stove, I would tend to give some thought to having it turn off BUT not turn back on again except by intervention.
    These things have a habit of false triggering from line surges or from insects or the cat for that matter, triggering it when no one is in attendance.
    ChosunOne and kellys_eye like this.
  4. ChosunOne


    Jun 20, 2010
    What Bluejets said, plus...common light-switching motion sensors use PIR (Passive InfraRed) sensors to detect motion. However, hot spots like heat registers, radiators, direct sunlight, metal surfaces in direct sunlight, and stove tops can simulate the conditions that PIRs interpret as motion.

    If you use a PIR motion sensor, position it so that it can't see the stove top or anything sitting on the stove top.

    Also, so that it's not looking at anything else I mentioned. Anything susceptible to sudden heating or cooling (e.g., an aluminum window frame in direct sunlight) can make the PIR sensor think someone is in attendance. Do not ever place a PIR where direct sunlight falls on it at any time of day during the year--keep in mind that where sunlight falls changes during the year.

    The places where light-switching is commonly needed (restrooms, supply closets, etc) generally don't have these considerations because they tend to be dark spaces during the day.
  5. Bluejets


    Oct 5, 2014
    Think you will find it's not so much "heat" on it's own that the sensor detects but rather the heat movement across the inbuilt zones.
    Usually there are 3 vertical and perhaps a dozen or more, horizontally.
  6. ChosunOne


    Jun 20, 2010
    I know. I've worked with the PIRs used in the alarm industry since they were introduced, sometime in the late '70's I believe. The PIRs used to switch lighting are less expensive and, I infer, less discriminating in what they'll interpret as "motion." Contemporary PIRs used in the alarm industry now have very sophisticated signal processing and can be configured to disregard the "hot spots" I mentioned, but any technician worth his salt still avoids aiming at them if at all possible.

    A PIR sensor, once it has "stabilized" after powering up--i.e., calibrated the heat signature in all of its zones, typically is "looking" at a mosaic pattern and "watching" for changes. A "hot spot" tends to waver in one of more of its zones and can fool a low-end sensor. You and I, watching in the visible spectrum, wouldn't see anything; but there's simulated "motion" in the IR. Really hot spots (like a steam heat radiator or stove top) will heat the air by conduction (air doesn't absorb nor emit IR radiation; it absorbs and transmits heat by contact and conduction) and can pass the heat on to surfaces above when the air rises, so sudden changes in IR radiation in a PIR's field of view are not necessarily limited to the one or two zones in the hot spot.

    I'm passing on my experience of decades of troubleshooting problems with PIR "motion" sensors: Don't aim one at a potential hot spot. PIR "motion" sensing is more complex that it appears at first glance.

    OT: PIR sensors replaced other motion-sensing technologies (microwave and ultrasonic) in the 80's because PIRs were less prone to false alarms.
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