killervette
Active Member
Ok, so in my rush to wire my house, I accidentally ran a 2 lead wire instead of 4 to a motion detector. So, I have the 2 wires for the signal, but no power. Any ideas how I could get this working or is it a lost cause?
Motion detector, only 2 wires at location :(
- Thread starter killervette
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pete_c
Guru
Did a quick google search and really wouldn't know but I guess there is such a way to utilize two wires. DSC has an addressable multiplex loop device which appears to allow the use of just two wires to carry the power and switch info. I guess other companies would have similar devices. Not sure what the price is or if its even cost effective.
killervette
Active Member
Can you power it from an outlet? Is there some sort of device to regulate the voltage?
If you powered a motion from an outlet and there was a power failure the motion would trip and cause a false alarm if there was no battery backup. One of the reasons a motion draws so much current compared to many other devices is that there is always a relay energized. Once the power is removed it would open the circuit causing the alarm.
I would put a wireless motion detector in if you already have an RF receiver.
I was going to suggest the same thing.... wireless.
icellama21
Active Member
There is a way to do this, buy will require some trial and error.
1) Determine the voltage range and current requirements for the motion detector power (aka 10-18V and 200ma). Don't exceed these.
2) Use your 2 wires to run power to the detector.
3) Pick a resistor to put in series with the - supply of the detector that will ensure the detector receives adequate voltage for operation. Possibly some trial and error here.
4) Pick another resistor to be switched between the + and - terminals of the detector based on the status(motion, no-motion, etc). Must be large enough to not drastically effect the voltage available for the detector.
5) Measure the voltage between the first resistor and the motion detector to determine if the detector is violated.
+ power ------------ Detector + ------- Common Contact Closure
- power ------ R1 ------- Detector - ------- R2 ------ NC/NO contact closure
1) Determine the voltage range and current requirements for the motion detector power (aka 10-18V and 200ma). Don't exceed these.
2) Use your 2 wires to run power to the detector.
3) Pick a resistor to put in series with the - supply of the detector that will ensure the detector receives adequate voltage for operation. Possibly some trial and error here.
4) Pick another resistor to be switched between the + and - terminals of the detector based on the status(motion, no-motion, etc). Must be large enough to not drastically effect the voltage available for the detector.
5) Measure the voltage between the first resistor and the motion detector to determine if the detector is violated.
+ power ------------ Detector + ------- Common Contact Closure
- power ------ R1 ------- Detector - ------- R2 ------ NC/NO contact closure
Lagerhead
Active Member
Clever idea. So the zone connection is located between R1 and the detector? This would (usually) mean that R1 will be located at or near the panel? And the voltage measurement is relative to "ground" (the - terminal)?
icellama21
Active Member
Better approach may be to model the detector as a 2-wire smoke detector. Many panels are already set up to handle this. Not sure if there is a motion detector that can be made compatible, but worth looking up the spec.
NOT ALL Motions change state when the power is off. "If you powered a motion from an outlet and there was a power failure the motion would trip and cause a false alarm if there was no battery backup. One of the reasons a motion draws so much current compared to many other devices is that there is always a relay energized. Once the power is removed it would open the circuit causing the alarm."
NOT TRUE. THE reason a motion draws power(25ma is SO much.)is to discriminate motion from no motion. IF the relay is active at that point or not is up to the particular model. Example-DSC bravo6 or the Crow-genius.
BTW- the addressable multiplex DSC motion is 4 wire not 2 wire.
Bring on the angry mobs.....
NOT TRUE. THE reason a motion draws power(25ma is SO much.)is to discriminate motion from no motion. IF the relay is active at that point or not is up to the particular model. Example-DSC bravo6 or the Crow-genius.
BTW- the addressable multiplex DSC motion is 4 wire not 2 wire.
Bring on the angry mobs.....
Actual motion detector circuits draw very little current (about 8 to 10 ma for most if it has a modern micro etc). Having a constantly energized relay is about another 15 ma or more.
If you have 4 wires (positive, negative, common and normally open) and power is lost the the detector (wire break, nail through a cable etc) how will the panel know since power is not supervised (just the zone is with a EOL resistor) and the relay is not energized from what you are saying? The detector will never trip if power to the detector is lost and no trouble will occur if only the power or ground are interupted. An addressable detector would be different as it would lose communication with the panel and the panel would know that.
There are ways to design motions etc without a relay for a conventional zone but I have not seen anyone do it yet.
Have you used the motions I used as an example- I agree with the power loss situation, but it happens.
http://www.tycomarine.com/docs/security/in..._2003-02-19.pdf
Please read page 2 carefully, especially the part where is refers to standby current draw vs. alarm current.
Your statement to read page 2 carefully regarding the current draw rating means what? You are reading a mfg advertising and determining its design based on its advertising? So the alarm current is slightly higher but not by much. That does not mean that it needs the current to sense the alarm at all.
I work for a mfg of alarm devices as an engineer. Granted I mainly handle the compliance of the devices but that does require me to know how the products are designed and the rationale for the design.
Maybe you are more experienced then me but I dont see how a mfg advertising can lead you to the conclusion that the device requires more current to sense the alarm (granted that can be the scenerio for 2 wire smoke detector designs in some cases).
PaulD
Active Member
Is the wire a fairly straight run? Could you use the 2 wire as a pull cable to pull a 4 wire thru the same route? In my house, this would be easy to do on the second floor via the attic but I could not do it on my first floor PIR's.
killervette
Active Member
no chance!
Yeah, of all places it has to be the first floor. I have pretty much given up on the idea.Similar threads
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