Comment by walrus01 | Hacker News Reader

Comment by walrus01 | Hacker News Reader

If the author is reading this, I did a ctrl-f in your writeup for "battery" and "life" and didn't find anything specific about how long the batteries on these last. Can you elaborate a bit more on the battery types in use and lifespan? Charging? Since use lithium? 18650? CR2032 or CR2477 size coin cells? Any other details would be very interesting to read.

My biggest barrier to doing something like thins in my home automation setups is that I already have an extensive schedule of things that need periodic disposable battery changes (like CR2477 cells in zigbee humidity/temperature sensors), and I'm really hesitant to add even more into my house. In addition to things like battery-backed smoke detectors in every bedroom, etc, which need periodic 9V replacements on a schedule.

In fact I've started looking at going the opposite direction, where I can run a cat5e cable from my utility room, down and across the ceiling of my basement, and come up in a location where I can install an 802.3af to arbitrary DC voltage DC-DC converter (3.3, 5VDC, 12VDC out, or similar) as a PoE splitter, to make some of these things not dependent on batteries. Same idea as how you can find 9V or AA battery to direct DC wiring "dummy battery" battery eliminators now. Obviously such an approach wouldn't work for garbage bins but that's how much I am trying to eliminate having dozens of batteries to replace, as they're already all over the place with window and door sensors.

It’s in there, specifically noting that I am going to be watching that over the coming weeks.

The BLE tags I previously used lasted about 2 years of a CR2045. These are much larger CRs, and I have tuned it right down on the report timing when stationary, so I am anticipating more than 2 years.

> In addition to things like battery-backed smoke detectors in every bedroom, etc, which need periodic 9V replacements on a schedule.

Just as aside, lithium-battery powered smoke detectors are a godsend. The battery lifespan lasts the recommended life span of the detector, i.e. around 10 years. No battery replacements needed, although you still ought to test them once in a while.

In Scotland, building regulations now mandate sealed-in lithium batteries (and interlinking) on fire alarms. Which is annoying, given most smart systems still have replaceable batteries.

The local regulations around here require those smoke detectors. I can attest that they do indeed last the full 10 years. They seem to have a timer because exactly 10 years after activation it starts complaining several times per day.

However one downside is that they also can't be turned off (by design) and the hush function on the ones I've tried (two models, both from Kidde) has been defective. No matter if I repeatedly press it, hold it, it doesn't care. It says hush mode then immediately blast again.

I destroyed the first one because it was night time and I have neighbors. Now I put them in the freezer. Next time I'll get another brand!

> (two models, both from Kidde) has been defective [...] Next time I'll get another brand!

Probably a wise choice. In Wirecutter's review of basic smoke alarms they have this to say about Kidde:

>> With placement on the shelves of Home Depot, Kidde is the most prominent competitor to First Alert. Their most up to date line of smoke alarms is called Detect and they have models with features similar to the recommended First Alerts. The downside is that Kidde's overall track record is, in a word, disturbing. In 2021, the company recalled 226,000 smoke and combination smoke/CO alarms. In 2018, they recalled more than 450,000 dual-sensor smoke alarms. In 2016, another recall involved 3.6 million smoke/CO alarms. In 2014, another 1.2 million smoke and smoke/CO alarms were recalled. In addition, since 2005, Kidde has enacted four separate fire extinguisher recalls of 470,000 units (2005), 167,000 units (2009), 4.6 million units (2015), and 37.8 million units (2017). In early 2021, a federal judge ordered Kidde to pay a $12 million civil penalty “in connection with allegations that the company failed to timely inform the Consumer Product Safety Commission about problems with fire extinguishers manufactured by the company.” For these reasons, we can’t in good conscience recommend any Kidde products to our readers.

>> Although First Alert is not immune to recalls (it recalled nearly 150,000 smoke alarms and combination smoke/CO alarms in 2006 and roughly 600,000 fire extinguishers in 2000), none of them are recent or on the scale of what Kidde has had to do.

What hardware do you recommend for 802.3af to arbitrary DC power? Granular configuration and remote monitoring are considerations in my use cases.

These same ones from China are sold under like 40 different brand names:

https://www.amazon.com/Splitter-Compliant-Surveillance-5-5x2...?

You can also find variants of them that are microUSB or USB-C power out. Finding ones that are natively 3.3V or 5VDC out is more difficult and rare, it seems the most viable option if I do this is to buy a very tiny DC-DC converter that's 12VDC in and then 3.3 or 5VDC out, and glue/stick it to the poe splitter, perhaps in an enclosure of some sort. Then wires out to the battery dummy eliminator.

The thing above is a 'dumb' device so any monitoring of the power you would have to do from your 802.3af PoE switch, entirely depending on what model/capabilities your switch has for port status, wattage, etc.

edit: Google "USB AA battery eliminator" and you'll find products which have a USB-A male input, expect standard 5V USB input, and output either 1.5V, 3.0V or 4.5V or 6V (1S, 2S or 3S or 4S AA battery voltage). You could then plug one of those into the many 802.3af to USB-A female (5V2A) poe splitters which exist on the market. Example: https://www.amazon.com/Battery-Eliminator-Supply-Adapter-Rep...

Many thanks.

I forgot to mention that in some cases if replacing a single AA battery as a 'battery eliminator' you would need native 1.5VDC out. Tiny 12V to 1.5V DC-DC converter do exist. Same idea for 12V to 9V battery. It looks like a fair number of the small ones I'm seeing on mouser and digikey are meant to be soldered onto a board as part of a larger project, but I don't see why they wouldn't work if soldered directly to a couple of wires coming from the 12V out of a poe splitter such as that.

I do love me some PoE-powered network gadgets, but I mean: My house came pre-wired with electrical sockets. I just use existing wall sockets to power the little home automation widgets in my life like it's still 1975. :)

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