s0 Traingirl Era
@s0@cathode.church  ·  activity timestamp 2 weeks ago

Here’s a #teardown of one of these cheap, unbranded “65W”/33W GaN chargers from AliExpress!

The one I tested was purchased from this listing, for only AU$5 each! (At the time.)
https://www.aliexpress.com/item/1005006320421253.html

First up, the advertising is a bit misleading, as they only support 33W on either outlet, one at a time (or shared, at 5V only). But it does support QualComm QC 2 and 3 on the USB A port, providing up to 20V 2A there.
On the USB-C, it also supports USB PD 3.0 and PPS from 3.3-16V, 2-3A.

I tested one non-destructively for insulation resistance at 500V and as well as sustained USB output, and it passed just fine. But taking things a step further, here’s what’s inside.

One decent quality 2-layer FR4 PCB with solder mask and full silkscreen! It’s marked “BK-384B 33W / Rev 1.0 / 2024.01.18”

(Cont. 1/2)
#Electronics
s0 Traingirl Era
@s0@cathode.church replied  ·  activity timestamp 2 weeks ago

(Cont. 2/2)
✅ Pins are sheathed per AS/NZS 3112, and dimensioned correctly (not to the thinner Chinese standard). They are relatively sturdy and don’t come free with vigorous wiggling.

✅ Wires from pins to board are real copper with silicone insulation, with no more exposed copper than necessary.

✅ The PCB is held firmly in position between front and back of the case and in moulded slots. The case is 2.5mm thick and securely glued shut. There’s also foam protecting the top of the transformer and caps from colliding with the top of the case. Well built physically, albeit no heatsinking to the case.

✅ A fuse on the active side, in thick heat shrink to prevent damage.

✅ 2.4mm clearance between L and N traces on the mains side.

✅ 2.8mm clearance across isolation barrier between mains and ELV traces at narrowest part (under mask), and 4.9mm between exposed conductive parts. This is great.

✅ Mains side caps are bled down to <1V within a few minutes of losing power under no load. No voltage across mains pins when unplugged.

✅ YuChang (YJH) and ShiCaXon electrolytic caps, seem fine. The DC side cap might be Aly-Poly, even better.

✅ Appropriately sized transformer, looks of decent quality.

✅ PD 3.0 & PPS Support.

All told, I’d call this a really well made budget power supply, and absolutely endorse it for use by friends and family! Just make sure to only use one port at a time.

#Electronics
Joel Michael
@jpm@aus.social replied  ·  activity timestamp 2 weeks ago
@s0 ok yeah this looks pretty decently made. Can you do one test on a working one for me? Resistance and voltage from USB shield to mains earth, ideally should be a handful of ohms and approximately 0V. I do see a transistor of some kind bridging AC N and something, probably DC GND.

I discovered one of my USB charging banks was giving me a 200V tingle through about 8Mohm resistance between USB shield (exposed metal) and mains earth (which all sensible devices use for the USB shield)
s0 Traingirl Era
@s0@cathode.church replied  ·  activity timestamp 2 weeks ago
@jpm that’s sort of impossible to avoid in an isolated PSU with no earth pin, and it’s not really about the voltage but the current.

I measure 66-78 VAC from USB shield to Earth using my bench meter, which has an impedance of about 10MOhm in that range.

That gives single microamp range, about 7.8uA of leakage current, which is safe and acceptable though can be felt as unpleasant by people depending on their skin resistance and sensitivity.
Robin ╰(ಠ_ಠ✿)╯
@buzzyrobin@chaos.social replied  ·  activity timestamp 2 weeks ago
@jpm @s0 please forgive my ignorance, but:

- Is this requested test ‘put a probe into earth pin of wall socket + probe on usb shield of cable plugged into charger’?
- if so: to what end?

(I have an un-disassembled brick here, but that I’m asking this is indicative that I don’t know enough to actually do this test.)

The device only has two pins and no connection to earth, so I don’t understand what is being tested. …