Power Module for non battery zigbee devices

I have some Sonoff SNZB-06P Human Presence Sensors I wish to install, I wish to ‘spur’ out from a mains wall socket, and provide power from a power supply module fixed inside a surface box (I not want the device to be unplugged by anyone)
This requires an Input Voltage of 5V 1A.

I note the input voltage for this is rated at 1A, this seems quite high for such a small device, is that because the Voltage is very low (5V).

I am considering something like this:

240v > 5v
Input voltage: AC 85 ~ 265v 50 / 60HZ or DC100v-370v
Output voltage: DC5V (± 0.2V)
Output Current: 350 mA
Power: 3.5W

Or

5V 2A
It but doesn’t quote a Wattage.

I calculate the power consumption as W=amp x volts, but cant work this simple equation out.
How can a 5V 1A Output supply, equate to 350W ?? (5W=1A x 5V) …confused.

I presume these little Power Supply modules are what you will get in say a plug in mobile phone charger, like this (bigclive.com is not a fan: https://www.youtube.com/watch?v=jiqHU7L7Dk0)
1 Port USB 3 Pin Mains Wall Charger USB Charger UK Plug Power Adapter 5V 1A Lot | eBay

I also want to power a TRVZB Radiator TRV with a Power Supply, rather than run it off the batteries:

It takes 3x 1.5V AA batteries, so Power Input is 4.5V, but it has a motor in it, so will assume the power required will be more than the Human Presence Sensor mentioned above (the SNZB-06P)

Any thoughts appreciated.

Might be easier (and much safer) to simply plug in a genuine mobile phone charger from a reputable brand. I bought one of those transformers you linked to - one look at it was enough to put me off considering having it powered 24/7.

If the phone charger bothers you due to aesthetic or space constraints, mains sockets with additional built in USB sockets are pretty common too. Even the older models provide at least 2A at 5v, so more than enough to cover requirements. Again - get something from a decent brand and not whatever is the cheapest.

Yes Fire Safety is a big consideration, as this will be continously plugged in.

I will make sure that any IOT PS’s plugged into a mains voltage are not cheap c**p.

I note the use of AFDD (Arc Fault Detection device) now a requirement for sockets here in the UK, a welcome requirement.

bigclive.com’s break down of cheap USB chargers uncover the possible dangers, he gives a thumbs up to BG USB Sockets.

I want to avoid the USB coming out of the charger - either being damaged by vacuums or feet, as the socket is near the floor, or unplugged by the occupant, if they want to start charging something of their own…

I have some thoughts:

I have employed the 220AC>5V power supplies for many projects and they have functioned well. You will find many vendors on AliExpress selling these. The challenge is finding the one that meets your needs.

The output voltage is usually known. Then measure the actual current your device draws. I usually double this when looking for a power supply. The input voltage depends on your location. 120AC? 240AC?, 220AC? These supplies are usually rated 86VAC-220VAC, so they won’t work for 240AC. Find one that is rated more than your AC voltage. I think the UK is 220VAC, so find one that is rateed to at least up to 240VAC. If you’re in the USA and powering from 240, get one that has an input spec of 277VAC

Because these supplies are usually switching power they work on pretty much any frequency, including DC.

I have found that fuses for these devices are more than double the price of the device itself! One might consider that the device itself is the fuse :dizzy_face: . I saw the pictures of cables that were burnt at the connector. In the USA, I find typical electricians lacking. If the connection is poorly made and the device is drawing excess current but not enough to blow the fuse, the wires will burn at the connection. Be sure the connections are good: do not use the quick connect, full 180° turn on the wire, torque down hard on the screws.

I have considered mounting the power supply in the (double gang?) outlet box and running the 5VDC power over tape wires One could make a 3D printed box using flame retardent PLA.

-OSD

Thanks for your thoughts.

I note your comment re the 240V - yes I am in the UK, and 240V +/- is the reading off our mains.

One could use one of these to ascertain the current requirement:

I cant get my head around ‘screw nuts’, we dont have them here in the UK, its connection blocks or boxes, with a screw clasp arrangement, I assume when you refer to ‘quick connect’ you mean ‘Wago’ type connectors …
If the cable is very thin (ie the split end of a USB cable, I will try solder where I can.

If your mains are around 240, then get the power supplies rated at 270+. I’ve found that anything Chinese meets the specs they publish, but not a bit more!

Wago are good, better than “wire nuts” When I wrote “quick connect” I really meant “push-in type”…the push-in type are trouble waiting to happen!, Typical connectors on outlet/receptical are a screw and a plate with the wire in between. Better ones are a wire betwee two plates which are clamped with a screw.

Yes, I have a couple of those for measuring USB current. One of the ones I have is a bet sketchy and pulls noticeable current for itself.

-OSD

Yes it seems some chinese made devices lie or mislead about their specification, and are not to standard.

I have bought one of these, yes I was aware some of these USB power meters have their own draw, I guess if you can measure what that is, you could deduct the value from your measurements.

Agree about ‘push fit’, I have used some of the Wago push fit, and regret it now, the ones with the lever are better, but as you say screw and plate better, above that is crimping, I did hear that some screw and plate arrangements can loosen themselves under heavy current, but I think it it very rare.

I’m using Chinese crap that I installed on my own. I didn’t have any problems with it for a three years or more.
But I did have problems with electricity done by certificated electricians.

I have now received the FNIRSI FNAC-28 USB meter.

I have plugged in one of the devices I wish to support, a Sonoff SNZB-06P Human Presence Sensor, the meter reads:

5.081V
0.065-0.75A
0.334W

So if I understand correctly, this device is pulling 65-75mA, the above PS rated at 350mA would be plenty ? the spec advises a 1.0A 5V PS, I cant see if this meter has a Hi and Lo reading.

Other numbers its reading are, which are incrementing:
00:19:23
0.02074Ah
0.10576 Wh