Relay & Sensor Battery powered

[Meister_Petz]

Hi,

has anyone an idea if it is possible to do a longterm (half a year) battery powered (2xAA) Relay & Sensor? The relay would have to stay on 5-6 hours a day. Or would it be necessary to have a power supply?

Many Thanks

Meister Petz

[boozz]

@Meister_Petz

No, not possible. Battery powered sensors only make sense if you could put the complete arrangement asleep, but even if the Arduino is asleep the relay would draw significant current....
To get some idea about how long this would work: You could calculate how much time it takes to drain the batteries when the relay is on. Simply measure the coil resistance R (in Ohm) using a multimeter. Calculate the current via Ohms law (I=U/R). You can then calculate the number of hrs. your arrangement will work with a fresh set of batteries.

BR
Boozz

[Meister_Petz]

I feared that answer... but it was what I expected. The best solution then, might be dissasembling very small USB chargers and use them? Or are there any special small ac-dc changers which could be recommended?

Thanks a lot

Petz

[mountainman]

You could use a bi-stable latching relay which would not draw power after it finished actuating.

[m26872]

@Meister_Petz Even if you find a bi-stable relay it's not easy with only 2 AAs. And then of course it will depend on the number of switches during the 6 months. Some talk about supplies here.

[daulagari]

For the size and cost I think you better chose an AC powered device.

Additional to the link posted by @m26872, @petewill just posted full instructions on how to build this on $8 Lamp (Outlet) "Smart Plug" Module