for 11$ plugged into a UPS and youll never change another battery.
Looks okay..thanks for the link. may get one of these. how safe are these compared to batteries? Have you tried em? Are their power supplies ul listed?seems to be..how many amps does it supply?
3v1a from a usb port. i thought it was 5, hmm
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Cheaper but less easy.
I recently set down my own path after determining that rechargeable CR2s were not great. I spent about $40 to convert at least 5 sensors to mains power using these items:
5 pack of 10 foot Lightning cables (I have white walls): https://www.amazon.com/gp/product/B07NYYLCS7/
10 pack of 5v to 3.3v step down modules: https://www.amazon.com/gp/product/B07PRGVTH3/
3 pack of low profile top connecting USB chargers: https://www.amazon.com/gp/product/B07KY8D3R7/
Steps:
- Snip the lightning end off the USB cable.
- Snip 1 inch of the green and white (data wires) and set aside.
- Expose wire ends on the red (power) and black (neutral) wires.
- Solder red to VIN on the step down module. Solder black to GND.
- Flip over step down module and solder green leftover to the other side of GND.
- Solder white leftover to OUT on the step down module.
- Get your iron nice and hot and drop a couple beads of solder onto the battery terminals.
- Solder OUT wire to positive and GND wire to negative side of sensor.
- Stuff the module and wiring into the case. Cut or dremel out a slot for the wire to run.
- Mount that sucker and plug it into USB power.
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I noticed this brand of battery eliminator seems to have showed up on Amazon recently. They have AA and AAA versions as well. It’s tempting for those of us that never learned to solder, since they’re pretty inexpensive and plug-and-play. But I’d like to know more about safety certifications they comply with before I consider plugging them in to my house wiring...
If you don’t want to solder you can always use a wooden dowel as your “battery”. Components above would still work as this post was just sharing the idea of making your own batteries out of wood:
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Just saw this for $2.69 on eBay which means it's probably .50 on Alibaba or somesuch.. (select 3 volt type)
To me, one of the joys of battery-powered devices is they don't need wires. Batteries in my Zwave motion and contact sensors have lasted at least 2 to three years and longer, even outdoors through below zero winters. With the batteries about $2 each, I don't see much economic benefit to replacing them with external power. For me, replacing a battery every 3 years isn't a huge chore.
If I were going to use wires, I would just use inexpensive sensors wired to a central Hubduino device. I will be doing this to replace all my outdoor Smartthings sensors. The small coin cell batteries only last a couple of weeks outdoors in the cold of winter. I can easily wire up a half dozen contact sensors to a single esp8266.
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This whole thing thread just reminds me....
"The roof, the roof, the roof is on fire... we don't need no water let the M*fer burn".....
So there is still time for me to get that last bucket list checkbox ticked; appearing in a rock video!!!! I thought that hope had passed by years and years ago.
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The "charger" on the wall side is definitely something that should be UL listed (or ETL or similar). It looks like this product has three pieces: that charger, the USB cable, and the battery/adapater (including the dangling cable that plugs into the other USB cable). The low-voltage side of things--this is probably either 3V all the way or 5V with 3V conversion done inside the fake CR2--is less stringent on these requirements, so you're likely to find certifications there. The listing, unsurprisingly, mentions nothing for any part--but at least you can control the part that actually plugs into mains. 
That being said, I've thought about these in the past but can't quite make myself use them. My batteries last years (at least on most of my Zigbee sensors; the Aeon Multi 6 was the worst offender, which natively supports USB power and which I've plugged in now, though I might just try to sell it since I'm not otherwise a fan). Most of these solutions are...not pretty.
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I use a Drok buck converter to down step 12v to 3v.
It's been running great for a while now. The multimeter shows 3v right from the power adapter. And it does not charge a regular phone that uses micro USB. Also it says it's compliant on the thing it's just a 3v USB power supply that uses USB as a form factor because it's available.
The battery connector wire is by the way made from a hard plasticish thing not rubber so the battery case doesn't mess it up if u close the wire in the door.
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