3v Step Down Converters for Sensors

Has anyone used these:

I want to wire some of my sensors to nearby 5v and 12v DC adapters so save on some batteries. The primary motivator right now is my Lowes Iris Keypad that’s eating batteries. I have a HEM very nearby that I could wire to this, stick it in the battery compartment and wire to the terminals inside it.

I know I’ve heard a few folks on here doing similar things with micro switches, but haven’t seen anything about actual step down converters.

Yup, I purchased a stock pile of these a year ago, and use them for a variety of projects.


That’s all the recommendation I need! Thank you sir!

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as an FYI, if you’re an aeon micro switch/dimmer user, they have a nice 3v dc supply built right in…
I have one I’m powering an ST temp sensor from…

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That was my reference to the micro switch. I know I’d heard you and some others mention that. I don’t have a single one of those though. So cheap Chinese items are the way to go!

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It’s much easier to get a 3v adapter so you don’t have all these extra parts to deal with. I have this.

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Yea, unless your trying to save space, and or you are looking to go DC to DC, which is what the OP is doing.


I can’t find the exact model of the one I have, but I use something almost identical to this in my car:


I have it soldered between an arrival sensor and a permanent live fuse behind the glovebox.

I use one of these to tap into the cars 12v circuit, avoiding the need to cut into the car wires:


In this case I want to use existing v or 12v supplies that are nearby. I don’t want to plug a wall wart in for every sensor, that’d be a royal PIA and parasitic loss would be high.

Some small wire strategically routed into drywall, around door frames, through the ceiling to easily get between rooms, will provide a good replacement for batteries.

Being able to have a higher input voltage, 12v for example, allows for a longer run without as much drop. If you tried to go more than a dozen feet with small wire and 3v, you wouldn’t have the 3v you need to run the gear anymore! :slight_smile:

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I wouldn’t go too over the top… I did the arrival sensor in my car because the battery needed to be changed 4 times in one year!! It was either suffering in the cold or it was just a faulty unit… Who knows!!

My wife’s arrival sensor is still at 38% after a year on the original battery.

All my other sensors are lasting ages too… I have a few that are older than a year but still have over 50% battery remaining.

Panasonic button batteries are cheap… When purchased in bulk they can cost as little as £0.30 ($0.37) each, so for the same cost as a dirt cheap step down converter, you can enjoy 10+ years using batteries.

You mention you don’t want the extra wall warts but are happy to run small wires around doorframes etc… Interesting…

Converting to mains has its use cases but I don’t think it’s efficient enough to warrant doing every sensor you have.

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Oh gosh no, not all. I just have a selection of them that would be convenient. These cost $0.58 each so not much more than the cr2450’s I just ordered.

Take a sharp knife, whittle out a bit of a channel for the wire, spackle shut, paint. Can’t tell you have itty bitty wires in the walls!


For me it’s a matter of convenience.
I have three sensors that have been converted to battery less:
–The 2 monoprice contacts that are rigged up to the Kiddie interface module as smoke and CO devices, and all buried behind a smoke detector.
–The temp sensor installed between the dishwasher and counter that notifies when the dishes are done.
–A contact sensor in the attic which provides a fixed point static pressure input to Keenect…


I’m just too lazy for that :sleeping:

And I think my wife would actually kill me if I started chasing out the walls.

Changing a battery every 1.5 to 2 years sounds like a safer option in my family


Now those are some use cases where it makes complete sense!!

I just wouldn’t bother for a motion sensor in a corner or the like

Agreed. My primary use as originally stated is a Lowe’s Keypad that has old firmware and eats batteries. I don’t have a Lowe’s within 5 hours of me so alternate plan (and less gas) is this! I’ll also do this with the Go Control contact sensor I made into a leak sensor that goes under my house with my water shut off valve. It has 12v, so this is perfect, no need to go under the house anymore.

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Just got my first one of these installed. Stupid holidays always getting in the way of the fun stuff!

Wired it into the USB adapter for a HEMv1, stuck it in the battery compartment of the Iris keypad, and it works great so far!

Setting the potentiometer is a pain, very very sensitive but got it to 3.1xx volts, as close as I could come to the nominal 3.26v I get from my batteries. Haven’t soldered it all together yet, but it’s running fine and not heating up at all. Input voltage from the USB adapter is actually higher than I thought, a bit over 6.2v vs the roughly 5v I expected.

Not sure if I mentioned this above, but anyone that wants to do this, remember to put the voltage regulator as close to the device it’s going to power as possible. Since you are dropping voltage, you want the strongest signal you can get from the power source, and losses at lower voltages like this can happen quick, so the 1.2v or 3.2v most battery operated devices use, will loose FAR quicker if you voltage drop at the power supply vs the device.

I used a single pair from a solid core CAT6 for the wires, couldn’t find my stash of garage door opener wire…but it worked great!

Hi…just curious to see if you ended up hardwiring your iris keypads for power? And if so what your solution was… I’m running into the same.problem with having to replace batteries regularly… thanks!