Using an embedded miniature AC/DC power supply vs. USB wall wort

Thread Starter

ischonfeld

Joined Jun 22, 2019
15
I'm have a lot of experience with using Arduino/Arduino-like boards (MKR series, ESP8266/32, etc). for various designs. These are typically "one off" rather than for production. To date, power has been obtained through USB (wall wort) or an external PS. None require more than 1-2 Amps DC.

Some designs would be better (cleaner) if they could just be plugged in directly, or in some cases wired directly to 120VAC within an electrical wall box or enclosure.

I'm considering using an embedded miniature AC/DC power supply (they look like encapsulated relays). Obviously I would need to insure anything on the AC side is well insulated and protected from curious fingers if someone should open the enclosure.

Do you see any other safety issues that I'd need to be concerned about or best practices?

Thank you.
 

Delta Prime

Joined Nov 15, 2019
1,187
Hello there :)
Transformerless power supplies are dangerous and are taboo to speak of in this forum. I use them all the time and my family members have become very proficient with defibrillators
 
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nsaspook

Joined Aug 27, 2009
8,898
But aren't wall worts also transformerless PS's?
Most are high frequency switching supplies today with small transformers so there is isolation.
A embedded miniature AC/DC power supply like this should be fine.
https://www.alliedelec.com/m/d/4f054c50be7001f97eab7a840ccd7134.pdf 1W
https://www.mouser.com/datasheet/2/260/r1936_3-1109422.pdf 5W

I usually don't design using onboard AC/DC supplies on industrial systems that are expected to have decades of service. I like the physical isolation, test-ability and easy replacement of an off board high reliability chassis mount PS with small DC/DC converters on the PCB for each needed supply voltage.
 
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Thread Starter

ischonfeld

Joined Jun 22, 2019
15

nsaspook

Joined Aug 27, 2009
8,898
That's exactly the kind of unit I was looking at (although a different manufacturer). I was looking at Class II Isolation like the ones you referenced. Thank you.
I've had good short term experiences with that manufacturer for small embedded power supplies.
 

BobaMosfet

Joined Jul 1, 2009
1,896
I'm have a lot of experience with using Arduino/Arduino-like boards (MKR series, ESP8266/32, etc). for various designs. These are typically "one off" rather than for production. To date, power has been obtained through USB (wall wort) or an external PS. None require more than 1-2 Amps DC.

Some designs would be better (cleaner) if they could just be plugged in directly, or in some cases wired directly to 120VAC within an electrical wall box or enclosure.

I'm considering using an embedded miniature AC/DC power supply (they look like encapsulated relays). Obviously I would need to insure anything on the AC side is well insulated and protected from curious fingers if someone should open the enclosure.

Do you see any other safety issues that I'd need to be concerned about or best practices?

Thank you.
Wallwarts are usually Buck-regulated AC : DC supplies for electronics. For your purposes, it is far better continue using wallwarts- or actual psus than trying to build one yourself- for liability reasons. If you provide something to someone, and they get hurt because of the wallwart- liability is to that wallwart maker- not you. You don't get sued and lose everything.

Having said that, I'm sure there is a vendor out there somewhere that has made a PSU that would suit your needs- and again, they carry the liability & insurance to handle that liability.

One known vendor:

https://www.jameco.com/shop/keyword=Miniature-Power-Supply

And another:

https://www.mini-box.com/site/index.html
 
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KeithWalker

Joined Jul 10, 2017
2,034
I use these in many of my projects. They are well isolated and take up very little space. The safest way to use them is with a 3 Wire power cord with the project circuit common and all exposed metal parts connected to ground. Insulate all the high voltage connections with heat shrink sleeving. The hot side of the supply should be switched and fused. Use a good strain relief grommet where the power cord enters the cabinet. A power indicator lamp on the front panel is a must.
https://www.aliexpress.com/item/400...detail=20210611152115382079153523470003757375
 
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SamR

Joined Mar 19, 2019
3,606
But aren't wall worts also transformerless PS's?
Depends, some are, some are not. Typically, the XFMR wall wart PSUs are bulky and heavier (due to the weight of the XFMR) compared to those that are transformerless SMPSs. Hard to be sure just by looking. USB wall warts ARE typically Switch Mode Power Supplies and don't weigh much at all and are smaller. Don't think I've ever seen a XFMR wall wart with a USB connector. Working with Arduino, I am already connected to it via my computer USB to communicate via the IDE and use the serial monitor so it is already powered. The Arduino uses very little power and can only provide 200mA total from its pins. If I am powering a motor or other heavier demand circuit (>~100mA total or the 40mA pin limit), I am using my bench power supply and switching it with a FET transistor controlled from the Arduino. That is in addition to the USB used to supply power to the Arduino itself and the circuit to switch the transistor.
 
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