Buck power supply suitability

I have a couple of these to power my Wemos D1 mini's in an enclosure:

5V 700mA 3.5W AC-DC Precision Buck Converter AC 220v to 5v DC

|500x500

Does anyone have any experience of them, are they suitable?

It will be fed from a 6A MCCB, so I was thinking about installing a quick blow fuse before it (230V), not sure if carriers are available yet..

Or I am open to alternatives (230V AC mains to 5V DC).

I don't now anything about that board but if it works "as advertised" you should be fine.

But when you but the cheapest thing you can find on the Internet, "You're on your own". And, I don't see any regulatory approvals (UL, CSA, EC, etc.). In general, I like to by from reputable distributors & manufacturers.

I was thinking about installing a quick blow fuse before it (230V),

A fuse is always a good idea but a fuse is generally to protect you from a fire or "further damage" AFTER something has shorted out. It likely won't protect the power supply or your load.

I would not connect any random thing from Aliexpress or EBay to mains. My general rule is: If it has contact to mains, get it from a reputable supplier.

The safest cheap mains supply that I currently know is the HLK-PMxx series. I add a slow blow fuse on the mains side, a varistor between lines and a 73°C thermal fuse that is glued to both the HLK and the varistor.

Take care that you have sufficient trace clearances, especially between mains and 5V. If possible, I try to have slot milled into the PCB, regardless of the distance.

Here is a bathroom fan controller (230V sensing on one line + relay switching of another line) with a Wemos D1 Mini that I designed with it recently. It has roundabout credit card format:
Screenshot_20190219_190653.png

DVDdoug: I don't now anything about that board but if it works "as advertised" you should be fine.

But when you but the cheapest thing you can find on the Internet, "You're on your own". And, I don't see any regulatory approvals (UL, CSA, EC, etc.). In general, I like to by from reputable distributors & manufacturers. A fuse is always a good idea but a fuse is generally to protect you from a fire or "further damage" AFTER something has shorted out. It likely won't protect the power supply or your load.

Couldn't agree more, it's so tiny and "janky" looking I don't feel overly comfortable putting it in a box...

ElCaron: I would not connect any random thing from Aliexpress or EBay to mains. My general rule is: If it has contact to mains, get it from a reputable supplier.

The safest cheap mains supply that I currently know is the HLK-PMxx series. I add a slow blow fuse on the mains side, a varistor between lines and a 73°C thermal fuse that is glued to both the HLK and the varistor.

Take care that you have sufficient trace clearances, especially between mains and 5V. If possible, I try to have slot milled into the PCB, regardless of the distance.

Here is a bathroom fan controller (230V sensing on one line + relay switching of another line) with a Wemos D1 Mini that I designed with it recently. It has roundabout credit card format:

Nice PCB design!

Sure, if you have the space for the first or the third, go for it.

Don't worry about the inrush current. It is just the current that is drawn in the short period when caps charge and inductors build up their magnetic field.

Yes there is space, thanks :)

I've used those supplies without problems for an ATTiny85 project. They work fine - if you crack open cheap mains powered electronics, phone chargers, etc - you'll find modules like that.

Just be sure that you have a fuse in series with mains power to it, and that the box it's in is either non-conductive, or conductive and connected to ground (earth-ground, the third pin of a 3-pin outlet).

That is NOT a buck converter, though. A buck converter is a switching DC-DC converter that has an output voltage lower than the input voltage and a specific topology. That's a switch-mode power supply. EBay/Amazon/AliExpress vendors often throw related keywords into the description to get more views.

Thanks DrAzzy,

Yes I was thinking of a 1a cartridge fuse either way.

It’s going in a plastic enclosure, I’m a sparky by trade also.

Not being a buck psu makes sense as i had trouble finding alternatives.

While those modules are dirt cheap, USB "Phone Chargers" are not so much dearer and save you the trouble of mounting in a box and finding a power lead. I really don't think there is any value in assembling it yourself given that if they are sold retail, there is at least some implicit degree of certification that they are fit for purpose (and contain a fuse).

I think they are about $7 at Aldi. Mind you, I tend to buy them second hand for $1 each at garage sales. :roll_eyes:

Paul__B:
I think they are about $7 at Aldi. Mind you, I tend to buy them second hand for $1 each at garage sales. :roll_eyes:

Honestly, I have seen too many completely fucked-up noname chargers to prefer them over a module that was tested by people on the internet with published results, has a datasheet and has been equipped by myself with current and thermal fuse and varistor.

I would agree compared to noname Aliexpress modules, because “I bought it in [my country] with CE” at least makes a case for the insurance after the house burned down.

Paul__B: While those modules are dirt cheap, USB "Phone Chargers" are not so much dearer and save you the trouble of mounting in a box and finding a power lead. I really don't think there is any value in assembling it yourself given that if they are sold retail, there is at least some implicit degree of certification that they are fit for purpose (and contain a fuse).

I think they are about $7 at Aldi. Mind you, I tend to buy them second hand for $1 each at garage sales. :roll_eyes:

Yes a good idea, how do you connect the mains though?

For example, the arduino is controlling a light. So the feed to the arduino would be best to come from the same lighting circuit.

So, either fit a socket to the lighting circuit specifically for the arduino "phone usb charger", or connect mains directly to the mains pins of the phone charger pins (solder and heatshrink possibly?).

Would be interested to see how you do it.

ElCaron: Honestly, I have seen too many completely fucked-up noname chargers to prefer them over a module that was tested by people on the internet with published results, has a datasheet and has been equipped by myself with current and thermal fuse and varistor.

I would agree compared to noname Aliexpress modules, because "I bought it in [my country] with CE" at least makes a case for the insurance after the house burned down.

Same thoughts here, I do have some small Apple brand chargers laying around, surely they would be of a good quality.

But, probably can't beat a PSU with all the relevant tests/datasheets from a reputable dealer.

Powering arduinos is actually the hardest part for me to deal with! :)

877:
I do have some small Apple brand chargers

If they are Apple, they are probably fine, as long as you are not holding them wrong.
If they are “Apple”, though, there are certainly dangerous models around.

ElCaron: If they are Apple, they are probably fine, as long as you are not holding them wrong. If they are "Apple", though, there are certainly dangerous models around.

Yes will be genuine Apple ones, seems a waste though!