I’m sure this must have already been discussed but I couldn’t find it. My 10 y/o house has wired alarm sensors on all the windows. How feasible would it be to use those wires to feed DC power to Z-Wave blind motors and install wireless windows sensors for the alarm?
I would think that anything connected to the alarm switch circuits would cause that sensor to always be shorted. Wont work. Have a look at the alarm installation manual for your alarm.
Sorry! Missed the switching to wireless alarm sensors.
I suppose you could wire things appropriately but I’d be concerned about current and voltage drop. Alarm wire is pretty small gauge and over long runs, alarms are usually wired home-run, the voltage drop would be significant with any useful current draw. Easy enough to test, get yourself a length of the same gauge wire and try driving a comparable motor. An ammeter and voltmeter at the motor end would be ahelpful
As the OP is intending to replace the wired sensors with wireless sensors, the issue of shorted sensors is moot…
The alarm sensor wire can be reused to deliver power to devices… most commonly used alarm sensor wire is 22AWG 1-pair or 2-pair… so the power capacity is somewhat limited… Most commonly used security wire is rated for up to 70VDC and 1Amp. (although it is not entirely uncommon to have installations with 18AWG 1-pair or 2-pair)
Also of concern is the voltage drop experienced… With a 22AWG wire, connected to a 12VDC power supply (the same as a typical alarm panel provides - BUT NEVER uses the panel supplied power to run a motor!!), and a 1Amp load… with 100ft of wire, your device only receives ~8.7VDC (using a single pair)… This may not be enough voltage to run the motor reliably… If you have 2-pair wire and use both pairs, the voltage delivered to the device is ~10.4VDC, which has a much better change of powering the motor properly.
If you go with 24VDC motors, the higher voltage exhibits less voltage loss (using the previous example - ~20.8VDC and ~22.4VDC respectively) and is more likely to provide reliable operation. (you could also use a 24VDC power supply for a 12VDC motor, if the motor has an internal regulator or if you use an external regulator)
You should determine exactly what type/size of wire is run to the sensor(s), the length of wire between the sensor and the panel (longer wire = more voltage loss) and the specifications (minimum/maximum input voltage, current draw, etc) of the motor(s) you intend to use.
It would be my suggestion going forward, that anyone building a house should use 18AWG B cable as rough in wiring to the window alarm sensors. This would give you two pairs at each window: one pair for sensors and one pair for some other purpose. I see a future that will use that extra pair, either for the power for the window treatment or window film etc., OR perhaps some new invention not yet on the market. This would add only modestly to the rough in wiring cost and the 18AWG size of the wire would alleviate the voltage drop issue.
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As mentioned voltage drop is a concern and motors will not work properly.
Only way is to find a way to shorten the run is to connect individual power supplies locally (for each motor). It might be difficult depending how accessible your wires are (would be impossible in my house)
With DC motors make sure to use power supplies that are fused properly
We had a job where the customer misread the specifications for a 24VDC blind system and he ran 24AWG wire to all locations (essentially CAT5 size wires but only 2 wires). We recommend 16AWG wire to reduce any concerns about voltage drop. In the end he successfully ran the Somfy Sonesse30 24VDC RTS motors on that wire, in a home probably 1700-2000 sq ft with all of the wires homerun to a central power panel. The trick with the Somfy Sonesse30 RTS motors is that they are sensitive to voltage drop, so having a power supply that has an adjustment screw on it allows you to turn up the voltage slightly so that the motor likes the voltage it receives at the end of the run.
You’ll probably be OK with the alarm wire if it is larger than 24AWG which I believe it should be.