I plan to use a contact sensor (Ecolink) to monitor the mailbox. I might put the magnet on the bottom of the door so when the door is opened, the magnet swings around closer to the sensor located underneath the mailbox, closing the connection.
I'm not sure how the electronics work in these sensors so my question is, might there be a negative impact on battery life if the contact sensor is normally open. Such as if a small current is flowing in the open state but not the closed state. Is anyone using a contact sensor in a normally open configuration and had fine battery life?
I’m not 100% certain, but I don’t think Ecolink or other common contact sensors that use a magnetic reed switch inside are constantly sending voltage through the circuit when the switch is closed.
So whether your use case depends on the magnet being in proximity to the sensor as the baseline state, or not in proximity to it, the sensor is designed such that the battery use should be about the same (all other things being equal).
If I’m way off, an actual engineer will probably correct me soon .
I hope you are right, the information is pretty elusive, perhaps an expert in circuit design will have some input. I did a lot of searching and never found anyone complaining of short battery life attributing it to the contact being open most of the time, so I have to believe your intuition is most likely correct.
I had my Ecolink tilt sensor opened up to change the internal switch to a mercury switch. From the parts on the board it looked like this board could be a tilt sensor, contact sensor or and external contact sensor.
In theory I believe the battery on a sensor with an open switch would last longer. As the switch must have at least some current going through it all the time. However I believe the actual difference is "lost in the noise". Meaning other factors are likely to far out weigh the contact current effect. One could see the sensor was connected through a resistor to some voltage (likely Vbattery but I didn't measure it.)
For instance other variants could be:
Temperature
Battery brand or lot to lot battery variations.
My opinion:
If you are using a reed switch or hall sensor the NO/NC question does not matter.
If you are using a mechanical switch (micro switch etc) I would recommend NC because an open contact closing is more of a risk (of not making contact) than a closed contact opening.
That's great info, thanks! This one (Ecolink DWZWAVE2.5-ECO), I believe has a reed switch inside, I will go ahead and use it the way I planned and see how it does. It does also have screw terminals for an external contact sensor as an option. It claims to have a 3-year battery life. I don't expect 3 years due to outdoor use but If I get less than 6 months I'll report back here!
Yes that was exactly why I picked this one, so I have that flexibility, since I wasn't sure how I was going to mount it. For now I don't think I will need the external reed but time will tell. Great little Z-wave device. I initially tried a cheap Zigbee one but it wouldn't reach to the mailbox. This one easily reaches that far and beyond, I think my Z-wave mesh just happens to be more filled out than the Zigbee mesh.
I’m using an Ecolink contact sensor outside in a weatherproof box for my gate, and the battery reports 100% after almost two years. Of course, it depends in part how often the gate is opened. Our gate is not opened every day, but some days it is opened multiple times.
My experience is that the Ecolink contact and motion sensors have really good battery life.
My sensor is in the attached garage (i.e. not under a heated space).
I live in Connecticut.
My current unit was installed from new August 2020.
The device page shows the battery at 99%
Not that its the same but my monoprice PIR sensor battery just died. The battery report was a 1%.
When I removed the battery (Duracell) the voltage was just above 1/2 volt. It had been working the day before it died.
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