You thought those cheap no-name USB/Phone charger were safe?

[mouser]

Here's confirmation of your worst fears: Those no-name generic usb/phone chargers really are inferior -- and sometimes unsafe.

In a lengthy and detailed blog article, Ken Shirriff compares a dozen usb chargers and finds some real differences in terms of electrical quality and safety.  his bottom line: "don't buy a counterfeit charger; the price is great, but it's not worth risking your expensive device or your safety."

http://www.arcfn.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html

from http://updates.lifehacker.com/post/34723084079/tests-show-why-you-should-stay-away-from-knockoff-usb

[Stoic Joker]

Sounds more like they're not safe for (Princes and the Pea) iPhones. We've got 20+ cell phones at the office mostly Androids, 2 iPhones, and my Windows 7 phone. All of them charge daily on the $3 (wall and USB)chargers that I got from NewEgg at various points (depending on what was on sale), and none of them died from anything other than getting dropped one to many times.

Come to think of it I don't really know what the iPhones charge off of ... But the Androids and I are perfectly happy with the cheap stuff.

[SeraphimLabs]

It's not so much an issue of if they work or not.

It's that a lot of the cheaper chargers are made out of low grade hardware, and in the past there have even been isolated incidents of poorly designed clone units outright catching fire due to serious flaws resulting from cost cutting by the manufacturer.

[Tinman57]

It's not so much an issue of if they work or not.

It's that a lot of the cheaper chargers are made out of low grade hardware, and in the past there have even been isolated incidents of poorly designed clone units outright catching fire due to serious flaws resulting from cost cutting by the manufacturer.

  In other words, instead of using resistors and other electronic parts with a +- 1% variation, they use parts with +- 10% variations.  They're cheaper parts.

[40hz]

I've found it a good rule of thumb to err on the side of caution and not be too frugal when it comes to AC current or anything that has enough electrical potential to kill or maim.

If it plugs into a wall, I generally stick with what the manufacturer recommends using.

[Renegade]

One day my lights stopped working. I fiddled with the dimmer and power switch, and no luck. Opening it up... black. Completely charred. Power can be dangerous to say the least.

[x16wda]

Opening it up... black. Completely charred.

Spoiler (click to show/hide)

That's what happens when they send the self destruct signal to the stealth microphones.

Seriously though, those ubiquitous cheap little power things crap out constantly, although usually mine don't fry anything.  The ones that come with those little USB/SATA/IDE drive adapters are the worst, I usually get about 6 months out of one if I'm lucky.  I finally pulled out an old power supply and shorted the green and black wires together, and that has enough power to spin up drives that wouldn't work with the included cheapie adapter.

[4wd]

A cheap 5V adapter that just died on me, (less than an hour ago): switched it on, waited 10 seconds....BANG!



Just as I was attaching the DMM leads to check it 

[Tinman57]

  Looks like it got a little warm. 

  I found out the secret to electronics a long time ago, it's "Blue Smoke" that makes it all work.  If there's a break and all the blue smoke escapes, the electronic item will cease to work.... 

[f0dder]

I found out the secret to electronics a long time ago, it's "Blue Smoke" that makes it all work.  If there's a break and all the blue smoke escapes, the electronic item will cease to work.... 

Nice one

[Stoic Joker]

I'd be inclined to think the second yellow wire came loose and shorted to something (first yellow?) cooking that corner of the board. There doesn't really appear to be any thing else there it could have hit.

The 4 diodes amount to a bridge rectifier, and give you a DC square wave, then the transformer drops the voltage. The rest is just for the green lite and power conditioning (to avoid the garbage in, garbage out scenario). Not a really complicated widget..

Just thinking out loud.

[4wd]

 Looks like it got a little warm.  

What usually happens with these cheap things is they use cheap/marginal/under-rated electrolytic capacitors.  They dry out due to ripple in the waveform which generates heat, which causes them to go high-ESR, which generates more heat, they bulge and then go BANG!

Or they cause other things to go bang as the voltages, (either within the regulator or at output), are no longer within the design spec - this regulator, (came with a USB hub), caused a AU$130 DVB-T tuner to burn out, (not mine).

In the image above, you can see the capacitor on the right has just started to bulge, note the top of the can has started to split along the fracture lines compared to the larger one on the left.

I found out the secret to electronics a long time ago, it's "Blue Smoke" that makes it all work.  If there's a break and all the blue smoke escapes, the electronic item will cease to work....  

We call it "Magic Smoke"

I'd be inclined to think the second yellow wire came loose and shorted to something (first yellow?) cooking that corner of the board. There doesn't really appear to be any thing else there it could have hit.

All that damage, (including the cutting of the yellow wire), was caused by a component that explosively destroyed itself.  The circular shimmer on the left of the photo, (above the remaining yellow wire), is the end view of what's left of it.

Here's a better view of the bulging capacitor, (now on the left), and the ex-component on the right.



I might pull the electrolytics out later and test them with my ESR meter just to see what they read.

Results:
Small capacitor:
Ratings: 680uF 10V 105deg C
ESR:
Expected: ~0.2 ohms (worst case)
Reality:    47 ohms

Large capacitor:
Ratings: 10uF 400V 105deg C
ESR:
Expected: ~2.0 ohms (worst case)
Reality:    3.0 ohms

[SeraphimLabs]

That burned stub looks like a coil or a resistor that burned out.

Most likely the transistor in the thing is cooked, and the resistor turned into a fuse as a result of the regulator transistor shorting out.

[4wd]

That burned stub looks like a coil or a resistor that burned out.

Resistor.  It blew hard enough to shatter the case and break the encapsulation of one of the TO-92 transistors.

Most likely the transistor in the thing is cooked, and the resistor turned into a fuse as a result of the regulator transistor shorting out.

Yes, my idea also - the state of the output capacitor, (235 times it's supposed ESR), may have caused the feedback to be off possibly leading the transistor to over-regulate and fail.

I've got another cheap adapter here that's never been used - think I'll measure the capacitors and see what they're like beforehand.

Electronics is so much fun  

[superboyac]

I've found it a good rule of thumb to err on the side of caution and not be too frugal when it comes to AC current or anything that has enough electrical potential to kill or maim.

If it plugs into a wall, I generally stick with what the manufacturer recommends using.

Very wise.

[Edvard]

  I found out the secret to electronics a long time ago, it's "Blue Smoke" that makes it all work.  If there's a break and all the blue smoke escapes, the electronic item will cease to work....   

AKA Magic Smoke or Factory Smoke:
http://en.wikipedia.org/wiki/Magic_smoke.

Looks like you need might need a refill:
https://www.sparkfun.com/products/10622?