Presence Sensor battery upgrade

It’s exciting to see more people do this. Week 2 and no loss of battery percentage.

My regularly configured presence sensor with the 2032 battery has dropped to 90%.

Any way to mod st presence sensor to usb car charger?

Combined with

Ya, that one looks better than what I used. I have a bunch of boxes in the basement along with battery holders, etc… But I didn’t have one that was perfect.

I just ordered these parts to try this mod.

I have a SmartThings Multisensor in my attic just for temp readings, but the Battery is a CR2450 button cell. Even with the cell lasting about 1.5 years, it drops off fast at the end from 54% to 1% in a few days. I know that isn’t really what is happening, but it is the way ST calculates battery.

  1. I did the same thing but ran the wire from the sensor to my guest room below.
  2. Then I connected the wires to a AC/DC battery eliminator, that I had from years ago. Now I never have to worry about a failing battery in the attic.
  3. The AC/DC eliminator is in a single gang box near the ceiling with a blank white cover with a 1/8" hole drilled in it so that I can see the LED.
  4. Of course I ran a romex from the outlet below to the box housing the power supply. The 14/2 romex is terminated in a single plug from a heavy duty extension chord. In order to meet code the female plug had to be spliced in the box.



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Looks good, I like the idea of insulating the connections with glue.

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Sure, get the same project box or maybe a smaller one… use any old cigaret lighter adapter, and drill a small hole into the project box for the lead.

Use a buck converter step-down and hot-glue it to the bottom of the project box, then connect the leads to the sensor and then hot glue that to the opposite side of the project box. Hot glue the hole to seal the lead coming into the box.

Not sure why you might want to do this since most of the time the cigarette lighter comes on with the key, but maybe you have a use-case for this.

EDIT: Wouldn’t be a bad idea to put a small fuse on whatever lighter plug you’re using. The one linked comes with a 2a fuse which is pretty good for this.

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If you use the cigarette adapter which you posted, you don’t need a fuse. The fuse is already built into the nose portion of the adapter and can be unscrewed.

I had one like this and it came with a fuse built in.

Yeah I mentioned that the one I linked comes with one. Hah

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Just finished the battery upgrade but the project box in this link is just a little too small to fit the battery holder in your link and the arrival sensor with its case on. :cry: Looks like it needs to be just a little bigger. But it does fit nice and snug if I take the arrival sensor out of the case like @lmosenko did above.

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No way! I’ve gotten the exact products and they fit perfectly. Maybe you
received a wrong item?

LOL. I just reopened my project box and it is different than the one you have a picture of. If you look at the box from @lmosenko and yours they are different. The number inside of mine is the 1591M and your listing shows 1591MBK. No big deal though. I was still able to use it. I did report it to Amazon though.

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Sounds like you got the same box then. Mine is also printed with 1591M. That’s the mold number, and BK is just ‘Black’ as in they used black plastic for that run.

I’m pretty sure the components should fit though! I’ve made 3 of these and I’m getting ready to make a 4th.

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Exactly. Mine will fit if I take the sensor out of the white case just like in your picture but wont with the white case.

ohhh yes yes. I didn’t even think of keeping the white case on. I figured fewer layers of plastic around the sensor the better for connectivity sake… and since the black case IS a case, no need for a case-inception.

If you’re worried about it getting damaged IN the case, I’d think that a line of hot glue to keep the battery case in place would do well.

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@ethayer How is it holding up?

I was debating using lithium primary cells in an AA package for my car. The lithium battery curve will utilize almost the full capacity of the cell whereas I’d expect the alkaline to leave quite a bit in the tank when it dies. The EM3585 zigbee MCU requires a minimum of 2.1V and maybe even higher with regards to the other circuit components. Most alkalines steadily decline in voltage whereas lithium primary will hold it’s level longer and utilize most of the available capacity. You might only get to use about 30% of an alkaline.The self discharge rate is quite good as well.

Alkaline AA’s are still a solid choice…especially at the price\availability.

Did anybody ever measure average current drain from the sensor?

Interesting. The device itself still reports 100%… I kind of don’t expect it to move until it’s final month-ish of usage. I’ll stick it on the multimeter to see what voltage it’s putting out when I get a chance.

Much appreciated.

I haven’t looked at the “battery percentage” circuit much but it looks like a large voltage divider with a FET controlled by software. There is no true fuel gauge so the developers more than likely picked points along the coin cell’s voltage curve to represent a rough percentage. If that’s the case, the percentage won’t translate very well for other batteries.

I suspect you are right, you might not see it move much until the last hurrah. That or you will see it jump from something whacky like 100% to 10%.

With the runtime and an updated battery voltage (and the cell make\model) it might be possible to calculate your actual expected runtime. A multimeter averaged current measurement from a controlled source over an hour or so would be more likely to provide a good estimate of runtime. I’ll try to measure one on a DC supply in the next few days.

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Reporting back. I measure an average 0.15mA DC at 3.0V utilized by the sensor. This allows for some reasonably accurate estimates of runtime.

The zigbee microcontroller in the sensor stops functioning at 2.1v (1.05v per cell).

If we take the Energizer Ultimate Lithium AA (Datasheet) we can see that the cell will provide roughly 3500mAh at 1mA. Since we are less than 1mA, it may provide more runtime, but there are no curves to support an estimate at less than 1mA so we will go with the worse case of 3500mAh. This calculates out to 972 days of runtime not including the small amount of self discharge and other likely losses. If you look at the datasheet, you can see that the lithium curve stays well above 1.05V until the very end. Pretty decent performance and energy use.

The way manufacturers publish alkaline curves makes it a bit more difficult to get realistic curves at sub 5mA levels. If you look at a typical Alkaline discharge curve at 1mA or under, you will find that the point at which the battery reaches 1.05V is much earlier than what is in the battery. Even with the unused capacity and higher self discharge, you might very well get a lengthy run-time and probably at a better value per day.

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