Safe In-Wall AC to DC Transformers??

[rvendrame]

@Moshe Livne, yes I think I saw that website. The list of equipment there is surely respectable, at least. I just wrote to the info@ there, asking if perhaps he would like to test one of this HLK PSU. I can send one or two of my lot, lets see if we get some reply.

The varistor is a device widely used for protection. It is connected in parallel with the AC mains. It will short the circuit in case the voltage exceeds its pre-determined value. The ideia is to use it burn an internal fuse, or trigger the house circuit breaker in case of over voltage. A 20K-250V varistor will short the circuit if voltage is above 250V, and it supports voltages up to 20KV without produce any flame.

Using a varistor in conjunction with a PTC fuse (a fuse that automatically resets after some time) creates a very good protection for over voltage, with small cost and footprint.

I do agree with @Bertb and @ServiceXp , this HLK PSU looks good and safe for what we intend to use. Surely it is better than a phone charger. But as in any DIY, each one of us must know where to step on, assuming the involved risks.

[ThinkPad]

@Bertb I live in the Netherlands just like you. If you're interested i can make some thermal images of the disassembled HLK unit if you send it to me. I expect my FLIR One (Android) to arrive probably next week.

[Bertb]

Just to be sure everybody understands the schematic, hereunder a schematic.
I am not a fan of blowing mains fuses ...

Draft schematic

[Bertb]

@ThinkPad I am not sure it is still safe to operate.

[ThinkPad]

@Bertb The idea was to put it on my desk (with a mains cord soldered to it) running a resistor load, and then shoot some thermal pics of it
. I wasn't planning to touch the unit with my bare hands while it is powered hahaha

[Bertb]

@ThinkPad Well its your desk, so its fine with me.
Is there a way to get your address without shouting it from the rooftops?

[Atomfire]

Don't suppose anyone could tell me what components (values) need to be purchased for 230v (UK)? I have bought 10 of these and wish to make them as safe as I can.

[ThinkPad]

@Bertb Have sent you a chat, see the chat balloon top right corner.

[Bertb]

@Atomfire I will come back to that tomorrow.

[petewill]

@Bertb Once again, thank you for all your work with this! I can't wait to start building with this! This will be so helpful to have a safer method instead of just dismantling old phone chargers and rolling the dice.

I couldn't open the schematic. What is the file extension? Also, would you mind posting the required parts for 110v if they are any different than what you will be providing @Atomfire?

Thanks!

Pete

[rvendrame]

Hey guys, I wrote to the owner of the site suggested by @Moshe-Livne. He replied saying that he can test the HLK.

He mentioned that usually he takes at least two units (so if one burn he can continue the testing). I will send one from my lot, perhaps we have a brave guy to gave up one more? (a sacrifice of few to save many ) ;-) Let me know and I will share the address via PM (Denmark).

[Moshe Livne]

@rvendrame Considering cost of postage and logistics involved it would probably be cheapest to just order two units from Ali to him? its 8$ including shipping if i remember correctly

[Bertb]

@petewill The schematic is just a simple draft. It can be seen with IE.

[Moshe Livne]

@Bertb I tried adding "html" suffix to it but it didn't work.

[aproxx]

One option is to click on the link and download the file. After the file is completely downloaded, just add the extention .jpg to it.

The result is as following:

[Bertb]

Something went wrong with uploading the file, I think.
Herewith a new schematic with a suggested bill of material.
It is highly experimental still, but I ordered the components yesterday.

I am specially interested in working with the PTC fuse.

I hope the proposed circuit works for you. Please keep the maximim continuous output power in mind. It is only 3 Watts (600 mA).
In some cases you might need to add C1's (rule of thump 1 per chip or chip VCC) and/or need to increase the value of C2. This depends on the fluctuations in the power demand.

With the proposed values for C1 and C2, the ripple remained below 50 mV at 500 mA.
Also keep in mind that a remaining oscillation frequency residue appears in the output of some 60kHz.. If capacitors are not able to filter that out, a small coil might be needed.

Well it is experimenting that makes this fun, isn't it?

[Bertb]

@rvendrame said:

Hey guys, I wrote to the owner of the site suggested by @Moshe-Livne. He replied saying that he can test the HLK.

He mentioned that usually he takes at least two units (so if one burn he can continue the testing). I will send one from my lot, perhaps we have a brave guy to gave up one more? (a sacrifice of few to save many ) ;-) Let me know and I will share the address via PM (Denmark).

I am in for this.

[Didi]

@rvendrame said:

Let me know and I will share the address via PM (Denmark).

I will send him a powersupply too. :stuck_out_tongue_winking_eye:

[Moshe Livne]

@Bertb can now see the scheme! thanks. But can't see the BOM

[Bertb]

... it must be friday ...

voeding.doc