Author Topic: Toughest challenge for an electronics engineer  (Read 4995 times)

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Offline Connoiseur

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Toughest challenge for an electronics engineer
« on: December 31, 2015, 08:19:24 am »
Hi,

I recently bought some Christmas lights off ebay which came with this incredibly shitty power supply. The label says that it can output 500mA @ 5V.....but guess what ,it provides 27V OC and 2.2V @ 100mA :-DD (voltage regulation anyone? huh, who cares).

So I thought I would pop it open and see what's inside. AAAAnd horror of horrors, it was the worst thing I've ever seen. :palm:
No input protection fuse, no common mode choke, 300V rated cap for 230V mains! blah blah blah. Someone seriously wants to kill a large number of people.

I would suggest you consider generic Chinese mains adaptor for use so much as you would consider a rotten corpse for food.

Now here's the challenge. Looking at the PCB try to say something good about the adaptor.  :box:
 

Offline bktemp

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Re: Toughest challenge for an electronics engineer
« Reply #1 on: December 31, 2015, 08:51:15 am »
Now here's the challenge. Looking at the PCB try to say something good about the adaptor.  :box:
At least they have added a fuse in the layout: The thin track near the mains input.
 

Offline Cubdriver

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Re: Toughest challenge for an electronics engineer
« Reply #2 on: December 31, 2015, 08:57:56 am »
The mirrored silkscreen on the solder side is a nice touch...   :-//

-Pat

ETA - and I notice that it's rev 3 of the board.  You'd think they might have corrected that on one of the two respins.
« Last Edit: December 31, 2015, 09:00:00 am by Cubdriver »
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline SeanB

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Re: Toughest challenge for an electronics engineer
« Reply #3 on: December 31, 2015, 09:03:06 am »
Good thing is primary secondary isolation gap is correct, along with the reflow soldering being good and sufficient for the most part. Trace fuse is there, and it is thin enough that it will fail before any major fireworks occur that might damage the case integrity. Case is a relatively decent mould, though the join area should have had either solvent welding fully around it or some screws to hold it together.

Are you sure it is not a constant current supply, sort of done by accident? Seems like that would be the right thing to drive those cheap light sets which rely on the source impedance to provide current limiting. Universal input as well, you have the right set of pads to handle a US socket spacing as well, and the silkscreen with the reversed numbers and mirrored s as a 2 are nice touches, along with a double sided silkscreen. They actually have 2 earlier revisions of this board? rev 4 will remove 3 diodes and lengthen the wiggly fuse to cover the gap, along with making the traces thinner. Copper is expensive, recover as much as possible from the etchant.
 

Offline NANDBlog

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Re: Toughest challenge for an electronics engineer
« Reply #4 on: December 31, 2015, 10:01:49 am »
Ever seen power supply with capacitive dropper? This one tries to have isolation at least.
 

Offline Connoiseur

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Re: Toughest challenge for an electronics engineer
« Reply #5 on: December 31, 2015, 10:36:53 am »

At least they have added a fuse in the layout: The thin track near the mains input.

Wow what an ingenuity! I wonder is there any way one can be sure about the current rating. I mean heat will be dissipated by the paper phenolic thingy increasing the current required to melt the trace.


Are you sure it is not a constant current supply, sort of done by accident? Seems like that would be the right thing to drive those cheap light sets which rely on the source impedance to provide current limiting.

No! It doesn't seem to be constant current as
>It blew one of the lights (yes I was stupid enough to plug it in!)
 >The label says so
>I measured DC current in series with a range of resistors. However didn't dare to short it.

Ever seen power supply with capacitive dropper? This one tries to have isolation at least.

Yes I have. They come with those mosquito swats and cheap rechargeable torches. However there is no way one can come in contact with mains when it is in use. :-//
 

Offline Gyro

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Re: Toughest challenge for an electronics engineer
« Reply #6 on: December 31, 2015, 10:45:16 am »
Well I think the 0.1" LN header footprint for alternative mains input is a nice touch!  ;D

P.S. Its implementation is thankfully flawed!
« Last Edit: December 31, 2015, 10:51:04 am by Gyro »
Chris

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Online VK5RC

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Re: Toughest challenge for an electronics engineer
« Reply #7 on: December 31, 2015, 10:56:36 am »
That's really nice strain relief on the cable (or so it appears)
Whoah! Watch where that landed we might need it later.
 

Offline VK3DRB

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Re: Toughest challenge for an electronics engineer
« Reply #8 on: December 31, 2015, 11:24:14 am »
Mirror image silkscreen on some components :-DD

But there is something good about this PCB: It comes fully compliant with all the safety regulations set by Chairman Mao.
« Last Edit: December 31, 2015, 12:22:40 pm by VK3DRB »
 

Offline Stonent

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Re: Toughest challenge for an electronics engineer
« Reply #9 on: December 31, 2015, 04:48:07 pm »
Watch some of bigclivedotcom.  He takes apart lots of cheap led lights and many of them just use a dropper cap. Also many are 120/240 but have a 300 volt cap which is more than suitable for 120 volt operation but not 240.
The larger the government, the smaller the citizen.
 

Offline ConKbot

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Re: Toughest challenge for an electronics engineer
« Reply #10 on: December 31, 2015, 05:15:26 pm »
+1 to watching some bigclivedotcom videos, that adapter aint shit  :-DD   Does it run the Christmas lights? I'm presuming they are LED, so the poor voltage regulation isnt much of a problem, if its meant to be a constant-ish current output.  The 300v cap on 240v is obviously a problem, but I'd ignore the numbers on the casing. They obviously took an existing board from the cheapest usb charger they had(with no apparent form of feedback  :-DD, unless they are using extra wingdings on the flyback transformer to sense, and its just not used on this particular adapter), took off a few components stuffed it in existing cases (why pay to change even the printing?) and the only thing custom for this run was the cable strain relief which fits in a USB sized slot in the case. 

Cheap, safe, meets specifications on the case
pick 2
 

Offline SeanB

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Re: Toughest challenge for an electronics engineer
« Reply #11 on: January 01, 2016, 12:13:21 pm »
Cheap, safe, meets specifications on the case
pick 2

I would say 0/3 for that one. Not the cheapest, you can buy cheaper if you do not really care if they work on your test line, as you test using another power supply on the line and simply put the prepacked bag in the box.
 

Offline dannyf

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Re: Toughest challenge for an electronics engineer
« Reply #12 on: January 01, 2016, 12:40:14 pm »
Quote
bought some Christmas lights off ebay which came with this incredibly shitty power supply.

You bought cheap and you got cheap. What else should you expect? Quality is expensive.

Shitty engineering and shitty products exist to satisfy shitty consumers' demand for shitty products. If you don't want shitty power supplies, buy from a reputable source. I'm sure guys like Hermes or Bloomingdale would be happy to sell you one that's more than properly engineered. And if that's still no good for you, you can always commission someone to engineer it until your are fully satisfied. You just need to be ready to sacrifice a leg or an arm of yours.

So quality product or your arm? You cannot have your cake and eat it too.
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