Motion Detector Issue

Discussion in 'General Electronics Chat' started by circuitbob, Aug 29, 2011.

  1. circuitbob

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    Aug 29, 2011
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    I have a standard outdoor Motion Detector made for controlling incandescent lamps. I need to operate a relay from the Motion Detector. My relay coil is 44k ohm, The 100 watt bulb I tested with is 18 ohms. The Motion Detector will work with the light but not the relay, it will run relay if it is connected in parallel with the 100 watt bulb, What do I need to do to replace the bulb so I can use the relay by itself?
     
  2. praondevou

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    Can you post the model of the relay and the motion detector?
     
  3. circuitbob

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    Heath/Zenith Motion Sensor Model #SL-5316-BZ-C
    Tyco Relay Model #KRPA-11AG-120
     
  4. praondevou

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    According to the datasheet, the relay coil is 2.25k. Unfortunately the motion detector datasheet doesn't say anything about a minimum current.

    They probably use a triac to switch the load (and not a relay). A triac has a parameter called holding current, which is the minimum current to maintain it conducting.

    There are a few options:

    1. you could open the motion detector and verify if it has indeed a triac, then find it's holding current parameter via model number/datasheet. Then you would know what load you have to put at the output the keep it ON. The load could be a resistor, a capacitor or a relay with a higher current consumption.

    2. You could do the same thing, but finding out what current is needed experimentally.

    3. you can open the motion detector, find out, what drives the triac and drive a relay directly or replace the triac with one that has a lower holding current.
     
  5. circuitbob

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    Any suggestions on wattage of resistor?
     
  6. praondevou

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    A fast search on digikey reveals a holding current ranging from 10mA to 60mA for 4A to 10A / 200V to 250V triacs. That means there shouldn't much more current needed.
    Wattage depends on the resistor value. Let's say you want an additional 50mA, that gives you 2.4k, that means it will dissipate 6W, so you choose more than this. e.g. 10W.

    Choose power dissipated (P = V*V / R) + a safety margin, let's say one third more than what you calculated.

    If you have two relays, you can also try to put the two in parallel, just to having an idea if that would be sufficient.
     
  7. circuitbob

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    Alraedy tried two relays in parallel and it still didn't work.
     
  8. praondevou

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    then I suggest you open the detector a get the model number of the triac... if there is one...
     
  9. circuitbob

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    Any thoughts on a Motion Detector that will work?
     
  10. praondevou

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    Yes, any motion detector with a relay output. Either you can use it's contacts directly or you can drive your power relay with it.
     
  11. circuitbob

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    Thanks but I can't seem to find any with a relay out, I have been googling for hours before I posted on this forum. I'm open to suggestions, I need to resolves this by Thursday. With that said.


    The resistance of the coil is 2.2k ohms and the resistance of my 100 watt lamp is about 18 ohms. When in parallel, according to my calculations, the resistance will still be about 18 ohms. Is this what I am shooting for? trying to get a total resistance of 18 ohms at the coil?
     
  12. circuitbob

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    Aug 29, 2011
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    Thanks but I can't seem to find any with a relay out, I have been googling for hours before I posted on this forum. I'm open to suggestions, I need to resolves this by Thursday. With that said.


    The resistance of the coil is 2.2k ohms and the resistance of my 100 watt lamp is about 18 ohms. When in parallel, according to my calculations, the resistance will still be about 18 ohms. Is this what I am shooting for? trying to get a total resistance of 18 ohms at the coil?
     
  13. Kermit2

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    You might get lucky at your local radio shack store. They offer a large 10 watt sand/cement type resistor of 8 ohms value sometimes used as dummy loads on amplifiers etc. Three of these in series should satisfy your requirements for wattage and current flow. I suggest three instead of two so there will be less electricity wasted as heat. The circuit should work the same as if you had a 60 watt bulb installed instead of a 100 watt bulb. Just put them in parallel to the relay coil and give them plenty of space to radiate the heat and not damage anything nearby.
     
  14. praondevou

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    No, you'd put a resistor in parallel with your coil to increase the current above the holding current of the triac, which is in the mA range.
     
  15. praondevou

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    120Vac on 3x8Ohm = 24 Ohms ? That's 200W for each resistor! :eek: Or am I missing something here?
    I understand that the OP is having a motion detector with a built-in triac as the switching element, when used with a relay instead of a light bulb the current is lower than the holding current of the triac, so he only needs to increase that current to above the holding current. Voltage at the coil and any paralleled resistor will be either zero or 120VAC.
     
    Last edited: Aug 29, 2011
  16. praondevou

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  17. circuitbob

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    Waiting for Kermit to reply, I found 8ohm 20 watt resisters but now you have me concerned.
     
  18. praondevou

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    I don't know why someone would try to dissipate hundreds of watts in resistors....
    If you take a screwdriver and open the detector and have a look at the triac we can surely find a better solution.

    8 Ohms or 16 or 24 is a too low resistance if you put them as a load on the 120Vac output of the motion detector. Just for comparison, a 100W light bulb would have a resistance of 144 Ohms (when ON). Imagine the amount of heat you generate with 24Ohm resitors on 120VAC.

    Question: Why do you want to put the relay in there? To drive a bigger load?

    Edit: just found out that your detector has a dual brite function, that means it has to have a triac, since it regulates it's output voltage (probably by cutting one halfwave). Have a look at it, we find out the triac model/holding current, and then you'll know what resistor you need.
     
    Last edited: Aug 29, 2011
  19. circuitbob

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    Aug 29, 2011
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    We use this to trigger scenes in a haunted house. We need to run controllers and solenoids, etc so we have to go through relay. anyway hers the info on the
    triac

    BTA10-600C
    GK1E4 VU
    CHN 046

    Hopefully this helps
     
  20. circuitbob

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    Aug 29, 2011
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    Also, the dual brite function can be turned off and I have it turned off
     
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