Convert battery power to low voltage?

Is there an easy way to convert a security system sensor from battery (2 3V lithium batteries) to a wired low voltage line? I have pulled the cover off the sensor (image attached) and it doesn't look too complicated.

Other options would be to convert it to POE or USB. Don't know if that's doable or practical.

I'm building a house and have an opportunity to never have to replace those batteries, which are not on my "be nice to the environment" list. I have plenty of low-voltage in the house already. There is also built-in solar backup for 12-15 hours for power outages.

Thanks for the help.

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seandogue2 years ago

Yes, no big whoop. no need for a book.

Me, I'd slave a 3V regulator off a UPS to ensurepower in the event of griddown

I think the first step is to examine the existing batteries, and
battery holders, and sort of ponder what those batteries are doing.

For example, from looking at the picture you have attached, a I wondering about these CR123A cells

Are they wired in series? Are they wired in parallel?

are wired in series when the device wants more voltage than it can get
from just one cell. E.g. it wants 3 volts, and it gets this from 2 AA
alkaline cells (1.5 volts per cell, nominal) wired in series.

Batteries are wired in parallel when a device wants more current, or more battery run time.

it is kind of rare to find a battery powered device, with its batteries
wired in parallel. I have seen it only once or twice, in a device I own and
have taken apart.

But this thing you've got looks kind of
weird, like its designers might have wanted extra-long battery life.
And that is consistent with your description of it,since it is some
sensor gizmo. Also just looking at the picture, it kind of looks like
the circuit board might have a trace connecting the anodes (positive
terminals) from both CR123A cells to each other.

Also, by the way, if those two cells are wired in parallel, the device
should run with only one installed and the other holder empty. Amirite?

you should probe this thing with your multimeter, and discover the
truth of how its batteries are wired. Drawing pictures, erm, circuit
diagrams, may help you visualize this.

The next sort of obvious question is: How much current is this device using, at what voltage(s?)

Those are the two main questions you must ponder: How are the batteries wired? How much current must they supply?

you have discovered the answers to these questions, the notion of
replacing these batteries with some AC powered DC source, aka DC
adapter, this notion will seem more clear to you.

By the way,
people have written 'ibles on this general topic of replacing batteries
with DC adapters, but probably none that are totally specific to your
device. e.g.

When you are right your Right. A close look at the large 2688 x 1520 pic does show to me the positive of both batteries joined together.

A 3 Volt DC regulator inclded.

iceng2 years ago

YES, here is your circuit !

verence iceng2 years ago

Yep, should work. But he said it's for a security sensor. I'd not like my security sensors stop working because the burglar cut the mains line or there is a power outage... Some systems are run on batteries for a reason.

iceng verence2 years ago

Very astute, as should the alarm sensor receiver.

However OP said "There is also built-in solar backup for 12-15 hours for power outages." which I presume is some kind of battery.

Igpitman has no skills posted so an efficient solution may not be for his house.


that's exactly what you need !