home made alarm


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Old 04-07-07, 09:57 PM
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home made alarm

here's one for ya'...i put a patio motion sensor in my garage as an alarm, but removed the light fixture from the circuit, and replaced with a 24 vac transfrmr, that when energized, powers a bell and hammer style doorbell in the house. about every 6 months or so, the motion sensor emmiter/reciever stops functioning.
any assistance is appreciated
 
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Old 04-08-07, 01:25 AM
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Does it have a batter?. I have installed motion sensors for out door lights that had a 9v battery. Been a while since I saw one like that though.
 
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Old 04-08-07, 04:50 AM
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I know just enough about this type of install to be dangerous.

In addition, unless we had some failure analysis done on one of the broken parts, we could not even be sure that I am on the right track.

I am not qualified to completely answer your question, but I may be able to nudge you in the right direction.

Your motion flood is designed for resistive loads like standard light bulbs.

Coils, like found in motors, relays, and transformers are inductive loads. They draw an inrush of current on startup, and produce a backlash when the coil collapses. This can damage electroronic control components.

Typiclly when this is a problem at work, an engineer designes a solutioin. I am just the installer.

A couple things I have seen done are:
1. Place an MOV (sometimes called a varistor) across the input of the coil that is causing the problem. A varistor is wired in parallel. It will allow no voltage to pass till a certain limit is reached, then it will allow the voltage to pass. If sized properly it will be the objectionable voltage, and hence the objectionable current that is chopped off of the circuit and absorbed by the varistor.
2. Use a pilot relay for isolation purposes. Pilot relays have much smaller coils and therefore draw less inrush and have less backlash. In this case you would use the photo electric cell to drive the pilot relay, then let the pilot relay control the transformer.

I hope this helps you to better understand the problem. I suggest you post your question in a forum like this one: http://forum.doityourself.com//forumdisplay.php?f=87 The electronics types are more likely to have better answers.


ONE MORE THING: Another dumb butt posibility is just simply that the system is not properly grounded. Be sure that you have a good gound wire run with the other conductors to all the equipment in this circuit.
 
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Old 04-08-07, 09:07 AM
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relay...

thanx for response. i have tried using an "ice cube relay", i'm not sure if this is a pilot relay...
 
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Old 04-08-07, 09:47 AM
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ice cubes are often used as pilot relays.

If that did not help, then you may have a grounding issue, you may need an Mov, or you may need to look into a security motion detector instead of a lighting motion detector.
 
 

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