Safe In-Wall AC to DC Transformers??

  • @nca78

    Thanks a lot for this complete answer. I understand that i should use HLK but put in on a PCB and add varistor and fuse like described in the edit of the first post. The problem is that I really don't know a lot about eletronic. For arduino things in 5v or 3,3v I have no problem to try to do myself, in order to learn, but for 220v i prefer to use a finished product... Is there exist somewhere a finished product with the HLK and all necessary pieces, ready to wire to the 220 v and to the arduino/nodemcu ?



  • Hardware Contributor

    @matz I have made a breakout board. But using this and the pre-defined components you are on the right track. It's all easy to solder components (temp fuse can be a little tricky) . I don't have much time to source and solder assembled projects but have a look and you might get some ideas.

  • @sundberg84

    Thanks a lot it is very useful and i'm sure i can do it myself with tour board already designed.

    Juste one question : what are the sizes of the bard in all 3 dimensions ? I need to be sure it will fit in the wall where i need to put it before ordering the components. I could not find these info on the page you sent me.

  • Hardware Contributor

    @matz hmm, traveling now so can't measure but 50 long I'm sure. It's probably 35-40mm wide.

  • @sundberg84
    Quite small, so.

    In a link above i've seen a review of the HLK from one guy who seems to know about electronics.

    He recommends using the VIGORTRONIX VTX-214-005-105 AC/DC PCB Mount Power Supply . He said "for only a few quid more you win a switch mode PSU that stands a chance of not requiring external components to pass Class B!"

    Anyone here has tested the Vigortronix ? Is it better than HLK ?

  • @matz Never tried the Vigortronix, but I tried some from a company called Recom that were pretty good. Quite a bit higher in price though too.

  • @dbemowsk
    Ok thanks. I will try to build the sundberg84 board but i will try also to find a case built with a 3D printer as i prefer not to let all this stuff unprotected in case someone else than me in the futur open the wall socket

  • @matz Now that I have had my 3D printer for a year, I don't know why I didn't get one sooner. FOr these very reasons. If I need a case for something, I cad it out and make it.

  • @dbemowsk
    I'm planning to buy one, i'm sure there are plenty usage of it (sorry for my bad english i'm french :))

    Concerning the PSU, one question : we could just disasemble an iphone charger, the small one is 5cm x 1,5cm x 3 cm, and reuse it in the wall. IMHO it is more safe than build ourselves a PSU. Has anybody tried this ?

  • @matz Why disassemble it other than to solder on some external power wires. Leave the original protection in place and you shouldn't have to worry about shorting anything out.

  • @dbemowsk
    I'm afraid it won't fit in the wall socket because of the metal stem, so it would be better to solder the power wires to it :

    alt text

  • Hardware Contributor

    @matz said in Safe In-Wall AC to DC Transformers??:

    (sorry for my bad english i'm french :))

    Ce n'est pas une excuse valable 😛

    @matz said in Safe In-Wall AC to DC Transformers??:

    I'm afraid it won't fit in the wall socket because of the metal stem, so it would be better to solder the power wires to it :

    It doesn't look like an official charger, or even a branded one ? Then you would meet the same safety problems than the cheap power supplies. In that case have a look at to check if you can find a charger that's on the "safer side" of things.

  • Hardware Contributor

    @matz the problem with phoneadapters are all the fake and truly unsafe ones. Just Google phone charger teardown. If you are sure you are buying a genuine one it's most likely quite expensive. Safety vs money is one of the key aspects in this thread and offcourse you can probably buy smaller and safer ones but you are going to pay for it.

  • Hi guys (and gals?) new member here, and probably an absolute novice compared to most of you; however, I have been following this thread for quite some time. I recently acquired the components listed out by @petewill (thank you for the inspiration to try the project), and I have constructed the circuit in tune to the schematic also generously provided by @petewill. The only difference in my set up is that I have gone with a WeMos D1 mini instead of the arduino/radio combo solely due to having one laying around. The WeMos to relay connection works (as in flicks on/off the LED on the relay) in tune with the automation software I am using when the WeMos is being powered by micro USB. However, when attempting to power the circuit via a 120V outlet, I seem to keep blowing the 250V 300mA Slow Blow Fuse. In short, the LED on the WeMos briefly emits light, and then shuts off. When troubleshooting the circuit with a multimeter, I find that no current is flowing through the Slow Blow Fuse (therefore blown). I was wondering if anyone might have some ideas as to why this is happening despite the fuse being rated with the proper current and voltage ratings. I assume that there is a short occurring somewhere in the circuit; however, due to my novice knowledge, I have no idea why. I would greatly appreciate any and all pointers/criticism! Thank you.

  • Hardware Contributor

    @arp5z5 - my first thought was just like you said - a short. I would 1) remove everything from the DC side and replace the fuse. Then with a multimeter in continuity-mode see that you dont have a short on the AC side between Hot and Neutral. Did you wire everything correctly? If so - might be a bad varistor? If you dont get a beep - (with a new fuse) power everything up (without DC parts and see what happens. Works ok? Continue to add DC parts untill something happens.

  • @sundberg84 Thank you for the advice! I will take a look at it tomorrow and see what I can find.

  • @omemanti I have used some other RECOM modules and they are pretty solid. I like the fact that the incoming power leads are spread out to the edges rather than close in the center on the HLK modules. That alone makes them a heap safer.

  • Hardware Contributor

    I give up on soldering Temperature Fuses, for every one that I'm able to solder I blow up 5 of temperature rising from the solder. It would be a good safety improvement, but I'm going crazy with fazes burning ☹ 😐 😤 any recommendation? Who are you guys soldering without blowing them up?

  • @soloam I too had great trouble with this. The best trick that I found was to have the side of the board with the fuse on it resting on a frozen gel pack while soldering. As long as you keep the fuse cold it should not blow. It is called a thermal fuse for a reason. I have talked to others that have had some success with aluminum heat sink clips like these that you would clamp on the lead that you are soldering to pull the heat away before it reaches the fuse.

    I still prefer the gel pack solution though. If you set yourself up right with the gel pack, you can have the cold pack pressing the thermal fuse against the power supply module as you solder which is where you want it anyway.

  • Hardware Contributor

    @dbemowsk are you talking about this:

    alt text

    I'll try it out.

    where can I find that clamps? To try out also?

    Thank You

  • @soloam Those are the type I am talking about. Put them in the freezer for a bit. They should still be pliable when they come out.

  • Hardware Contributor

    You don't really have to buy anything - lots of things will work to keep the temperature down. A wet paper towel wrapped around the fuse or submerge it in a small cup of water (easy for through hole components when the board is upside down) or wrap with 2 wet sponges and some rubber bands, etc etc.

  • @sundberg84 I am building an efficient AC/DC power supply to avoid using the HLK-PM01. I design the power supply with flyback topology with high safety as it is fully isolated.
    in the current design i selected the component BF1550. It is a high performance AC/DC power supply control
    device which is operating in primary side sensing and regulation. It includes an internal power BJT and is designed for off-line power supplies within 6W output power.
    Based on that, i designed the transformer. I need to find a factory to produce it.
    My goal is to introduce in any nodes this AC/DC power supply for safety reason and efficiency DC regulation.

  • I know it's an old topic, but I need to ask...

    I read all this things mentioned on this topic, but at the end I did not find any answer to the fuses and for the varistor.

    So, I wonder what values was used:

    1. for fuses on mains 230v and for the 5V DC side?
    2. I don't see any varistor values like 10D271K, 10D471K or 10D561K?

    And also one suggestion about that thermal fuse, it would be better to use KSD-01 (normaly closed type) at 65C degree.

  • For anyone interested, and to correct my mistakes, I just put up an NRF52 node that is powered by an off the shelf ac/dc converter to be used as a repeater node.. feel free to comment

    This topic did most of the research for me, so thank you 🙂

  • Received some hilink transformers today from QIMEI Electronics Network Technology Co., Ltd in China; Compared to the posts above, the 3.3v ones look genuine, but not sure about the 5v ones.

    The side the pins come out of does not have the central hole and feels 'squigy' so I lifted it off one of them and the space inside is not completely filled with the encapsulation stuff, but it does feel slightly rubbery like the real ones...

    Maybe a new variant of the real thing? Or fake?

    These are destined for being outside in waterproof boxes, so I'll let you know if any catch fire....


    (1_1543265808836_IMG_20181126_202757159_2.jpg 0_1543265808835_IMG_20181126_202828525_2.jpg

  • anything new @rmh ?
    I just received five of them looking the same like yours.
    bought from user 7856632 from ebay

  • I recently ordered 10 HLK-PM01s from WAVGAT Store on The photo on their advertisement is the same, and looks like you expect, for a genuine Hi-Link product. The products I received recently were the same as @rmh received. The last time I ordered these in July 2018 from WAVGAT Store, I received the same product as their photo. I think I am going to open a dispute and see what happens.

  • @dbemowsk I tried a similar clip, but it didn't work (the fuse still blew when I soldered it). A small piece of wet sponge and a small clip to hold it around the wire lead work the best for me.

  • I emailed Hi-Link about the HLK-PW01 power supplies that @rmh, @yannik-mündler and myself purchased. These are the power supplies with a removable bottom.

    I sent the following email to Sunny at Hi-Link (contact info:

    Are the two HLK-PM01s in the attached images genuine Hi-Link parts? A major difference is the part on the right has a bottom cover that is easily removable.

    I bought the part on the left from an Aliexpress seller in July 2018. The part on the right was bought from the same Aliexpress seller in May 2019.

    Thank you very much for your help.

    Here is Sunny's reply:
    Now all of our module are use new version .

    The one you bought on 2019 is the new version, the old version is not used yet.

    By the way,May I know you are the final user or the reseller?

    If you are worried about it,you can buy from our website or our Aliexpress store directly.

    I went to the Aliexpress page in their email and found the HLK-PM01 page. On that page they say:
    Recently,there are many fake module in the market,in order to Standardize the market environment,keep benifit for the customers,We,Hi-Link,changed our module to the new but more quality version,the back of new version is show as the following picture,currently,the old version and new version were sent random,please pay attention to that!thank you very much!

    They also show images of the previous version (which we are all familiar with) and the new version (with the removable bottom).

    So, it appears the HLK-PW01 power supplies with the removable bottom, from a reliable vendor, or directly from Hi-Link, are genuine Hi-Link power supplies.

    Below is my two images of the bottom of the two genuine power supplies (old on the left, new on the right).