More Chinese Horror PSUs - Page 1
Forum section: electronics / general

author: dexters_lab
author_rank: Unknown
timestamp: June 13, 2013, 12:58:41 pm
content: This is a PSU that i admit i have been using knowing it was a bit, erm iffyIts about 3 years old, came with some counting scales that has a rechargeable battery in.As you can see from the pics, it's a UK shaped plug with a metal earth pin which is odd in itself for a plugtop psu, it'a also missing the plastic shrouding from the L & N pins that's been a requirement since the 1980s.It was iffy as in it kept tripping our RCD (GFI), opening it up clearly reveals the reason why, the unconnected earth pin was shorting out on the live inputIts rated to 8v 500ma

author: steve30
author_rank: Frequent Contributor
timestamp: June 13, 2013, 01:26:54 pm
content: Love the Chinglish!

author: GK
author_rank: Super Contributor
timestamp: June 13, 2013, 01:30:54 pm
content: Something like this should have mains earth connected directly to an electrostatic "safety" screen in the transformer, IMO. That transformer is so small I I'd be surprised if there is adequate pri winding-to-sec winding creepage distance. The windings probably go right up against the ends of the bobbin. Would be worthwhile to dismantle the transformer and have a look.

author: c4757p
author_rank: Super Contributor
timestamp: June 13, 2013, 01:32:39 pm
content: I'm pretty sure there's no need to take apart that transformer - just imagine the most awful abomination of a transformer you've ever seen, and that's what you'll find. It's probably got every fault you could think of.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 13, 2013, 02:13:56 pm
content: Hi,It would be very interesting to take the transformer apart.Apart from the line voltage connection and the shorting to the ground pin, there is a little evidence that some attempts were made to meet some safety requirements.The pcb looks to have adequate spacing between the primary and secondary circuits. Much better than some of the Fake Apple USB chargers.The Transformer bobbin is also extended on the primary side. This is done to increase the creepage distance to the core. This indicates that the transformer designer may know what he is doing.If the transformer secondary is wound with the special quad (or triple) insulated wire the transformer will probably meet some approvals. This wire looks like thin hook-up wire.Your opinions may vary.Jay_Diddy_B

author: dexters_lab
author_rank: Unknown
timestamp: June 13, 2013, 03:14:05 pm
content: Not going to use this again so will pull the transformer apart later tonight

author: sophia2013
author_rank: Newbie
timestamp: June 14, 2013, 05:37:30 am
content: emm,Chinese Horror PSUs??

author: LEECH666
author_rank: Frequent Contributor
timestamp: June 14, 2013, 10:41:42 am
content: BUTTERY!!!!!!!! AHAHAHHA HAAAAA!!!!!!!HAAAAAA!

author: amyk
author_rank: Super Contributor
timestamp: June 14, 2013, 11:32:24 am
content: That doesn't actually look too bad compared to some of the newer ones... plenty of creepage distance, what looks like a real safety-rated EMI suppression cap instead of just a regular ceramic, relatively thick AC input wires (with heatshrink!), and they used a controller IC instead of a transistor-based oscillator.

author: dexters_lab
author_rank: Unknown
timestamp: June 14, 2013, 12:07:19 pm
content: Yes its not as bad as i thought but that resistor shorting out to earth is unforgivable

author: c4757p
author_rank: Super Contributor
timestamp: June 14, 2013, 12:38:03 pm
content: I'm sure the only reason for the creepage distance is the ("standard") size of the unit. The PCB has to extend to the edges to fit in the case, might as well use that space for a bit of free safety...

author: saturation
author_rank: Super Contributor
timestamp: June 14, 2013, 06:10:52 pm
content: I'm surprised the whole design didn't fail in droves from the get-go. If I interpret one of those photos correctly, the earth pin is so close to an input resistor fed by one of the live inputs, that is was bound to short and burn up, as it appears so in this fragment I made of it; the yellow arrows suggest that when the case is assembled ground rests right on this burned resistor.

author: dexters_lab
author_rank: Unknown
timestamp: June 14, 2013, 06:44:43 pm
content: Indeed, the long leg was clearly squashed where it was making contact with the earth. I am surprised it didnt burn it out, its a wirewound resistor and has burned off all the outer materialThere must have been zero testing after manufacturing

author: GK
author_rank: Super Contributor
timestamp: June 15, 2013, 12:51:26 am
content: Quote from: c4757p on June 14, 2013, 12:38:03 pmI was talking about this type of creepage distance:

author: c4757p
author_rank: Super Contributor
timestamp: June 15, 2013, 12:56:10 am
content: Quote from: GK on June 15, 2013, 12:51:26 amYeah, the transformer does look a bit scary. I was responding to amyk, though, who said there was plenty of creepage distance. I assumed the intent was "on the PCB", where there is indeed a decent amount.

author: dexters_lab
author_rank: Unknown
timestamp: June 15, 2013, 09:31:53 am
content: it's dismantled, didn't look too bad to me, i did get a bit lost when counting the two primary windings which were separated within several layers,i was going to detail the windings. But i guess that dont matter.There was three layers of tape separating each layers, the secondary winding looks like teflon coated or similar. There was a screen which was 4 wires soldered together at one of the pins and separated the primary from the secondary but obviously wasn't connected to earth but to part of the circuit the ends were wrapped into one of the layers of tape. I dont know enough to understand what it all means!

author: amyk
author_rank: Super Contributor
timestamp: June 15, 2013, 09:39:41 am
content: Looks like triple-insulated wire to me. Not bad at all.I'd say the only flaw in this PSU was the earth short.

author: dexters_lab
author_rank: Unknown
timestamp: June 15, 2013, 09:43:54 am
content: Yea, the irony now is i need to find a replacement which could be worse than the original!

author: GK
author_rank: Super Contributor
timestamp: June 15, 2013, 12:57:51 pm
content: Well had you not trashed the transformer it probably would have been repairable

author: dexters_lab
author_rank: Unknown
timestamp: June 15, 2013, 01:37:21 pm
content: All in the interest of science!I'm sure i can find something in my box of spare power supplies