Use DC power supply instead of AC - Page 1
Forum section: electronics / beginners

author: BinaryBits
author_rank: Contributor
timestamp: January 11, 2022, 12:39:50 pm
content: So I have this WiFi doorbell that uses three 18650 batteries, but it can also be powered from a power supply. The manual says that one should use AC power between 8-24V.So my question is, can I use a DC power adaptor instead? Since it can be powered with batteries which is DC one would think it should work with a DC adaptor? I imagine it normally converts the AC to DC inside the unit?And if it works with DC, would it also be between 8-24V, or are AC and DC voltage calculated differently?Thanks in advance.

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 11, 2022, 01:29:04 pm
content: I think it would work. Try and use a 9VDC power supply.

author: ledtester
author_rank: Super Contributor
timestamp: January 11, 2022, 01:30:59 pm
content: The safest approach would be to connect your DC adapter output to the battery terminals. The doorbell shouldn't be able to tell the difference between the two. Since there are three 18650 cells I would use a 12V DC power supply, although the 8-24V AC range for the AC source suggests you could use an even lower DC voltage. Check to see if the batteries are in series or in parallel.That said, it is very likely that that the AC power input is simply rectified and then sent through a regulator in which case you could hook up the DC adapter directly to the AC input terminals. I successfully powered a Wifi thermostat that way, but I first took it apart to verify the circuitry.I'm sure the manual references "AC power between 8-24V" because most houses have such an AC transformer installed to power older technology doorbells.

author: Gyro
author_rank: Super Contributor
timestamp: January 11, 2022, 01:43:12 pm
content: Yes, looking at installation videos, they just seem to put a bridge rectifier on the supply input so the installer doesn't have to worry about polarity at the terminals (or can use AC).P.S. The minimum of 8V AC RMS means a peak voltage of about 11.3V. As the rectifier will normally charge the reservoir capacitor to near peak, I would take 12V as the lowest permissible DC input.

author: CaptDon
author_rank: Super Contributor
timestamp: January 11, 2022, 02:55:05 pm
content: When LEDTESTER says hook your supply to the battery terminals PLEASE BE AWARE that means WITH THE BATTERIES REMOVED which wasn't implied in his text. NEVER hook any external supply directly to Li-ion batteries!!! A friend of mine just had a fire in her office. She bought a cheap chinese piece of shit Li-ion battery pack (Terra Earth brand) that has sat dormant on her office desk for nearly a year. It self destructed a few nights back and set the desk and a pile of report paperwork on fire!!! Lucky she was home!! She smelled the smoke and saw light in the room before the smoke detector triggered. I just took all my old Li-ion batteries that have been laying around to recycle. Series singular cells don't seem to flame out as often. It is a different story when they are in parallel. Her battery pack had three cells in parallel, a certain recipe for disaster if one cell shorts!!!

author: ledtester
author_rank: Super Contributor
timestamp: January 11, 2022, 04:09:31 pm
content: Quote from: CaptDon on January 11, 2022, 02:55:05 pmGood point!