EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: mcinque on November 29, 2014, 04:36:03 pm
-
During a travel I've bought this (http://www.cellularline.com/catalog/en/product/dual_usb_micro_car_charger) "not-so-cheap" car usb charger and when at home I've put it in my car's lighter socket and connected it to my phone.
I discover it doesn't charge the battery. The phone, simply doesn't recognize any charger connected.
I can't return it to the shop because I'm too far from it, so I thought I could try to fix it, maybe it's just a cold joint on the output socket.
I've put a small load and a multimeter at his USB output and just after connecting it to a PSU at 13.8VDC I read 13.76VDC :wtf:
I hardly believe that value, so I check my connections. After 20 seconds, a loud POP come inside the small charger.
I disconnect all the cables and - gently - with a hammer, I open it.
I found that a capacitor (rated 10V) has vented (well... not exactly vented, but exploded, since it doesn't have a vent port on the top).
So that 13.7VDC value at the output was real.
Looking at the charger I discover it's built using an AF1210B step down converter, as the typical application circuit in his datasheet (www.alfa-mos.com/datasheet/IC/AF1210B.pdf (http://www.alfa-mos.com/datasheet/IC/AF1210B.pdf))
But looking at the components on the output, I found that the manufacturer has used wrong values for the resistors in voltage divider, so when the input is 13.8VDC the output is 13.76VDC (right the same as the input less some voltage drop of the cables)... :palm:
I've cut out the 2nd electrolytic and measured its output again. With a load, with 13.8VDC input, it provide 13.76VDC until 2.8A.
I'm lucky that my phone has some kind of protection at the charge input, otherwise I could have a nice paperweight. :phew: I bet not all the phones has this kind of solution.
Well done www.cellularline.com (http://www.cellularline.com) :clap:
-
It's more likely that the MOSFET inside the charger IC has failed short. Hence the output voltage ~= input voltage.
A 10 cent TVS and input or output fuse would have prevented this from being a problem.
Kudos to whoever makes your phone, surviving ~14V on the 5V USB input is excellent.
Just another importer. Importing cheap shit from China, packaged in pretty retail packaging and sold at a nice profit.
-
I doubt there are any discrete MOSFETs in the charger. The datasheet says it has an internal P-channel MOSFET and if it's failed short, the whole thing will fail.
If you can be bothered, correct the potential divider, replace the blown capacitors and test it with a suitable load resistor, before you risk ruining your phone.
-
Kudos to whoever makes your phone, surviving ~14V on the 5V USB input is excellent.
Yes. :phew:
Just another importer. Importing cheap shit from China, packaged in pretty retail packaging and sold at a nice profit.
A horrible, common practice. |O
If you can be bothered, correct the potential divider, replace the blown capacitors and test it with a suitable load resistor, before you risk ruining your phone.
No fix, that shit has been tossed in the bin.
-
or output fuse would have prevented this from being a problem.
There is effectively an SMD fuse (F1 in the 2nd picture), but since the shit-charger provides the same voltage as the input till 2.8A (then the voltage drops dramatically as expected), it's ineffective, 14.8VDC~2.8A it's enough to cook many phones IMO.
-
The current limit would appear to be due to your 3A power supply.
The widget has a 133mA quiescent (woot, there goes the car battery if you leave it plugged in...)
If the output current is an additional 2.8A this would be close to the 3A current limit of your power supply.
So it has essentially just become a short from input to output with very low resistance.
-
You could have relabeled it 12V output (and use permanent marker to color the USB ports) and sold it to someone who has an Asus tablet that actually expects 10-15V on the USB for a fast charge.
-
otherwise I could have a nice paperweight.
High cost of low prices.
-
So it has essentially just become a short from input to output with very low resistance.
You are right. I've checked it again taking it from the bin, and it's an input-output short.
As tom66 said, "A 10 cent TVS [...] would have prevented this from being a problem."
High cost of low prices.
€ 19,00 it's not a low price.
-
Warned by your post I just measured a simular one. The output looks fine and after taking it apart the build quality seems ok apart from the fact that they used a black wire for + and a red one for - :palm:
-
High cost of low prices.
This is a case of a retailer labelling cheap junk as expensive. You spend 20 euros on a charger, and you can usually expect it to be well made. (Case in point, Apple iPhone charger is £25/30euro and is well made.)
I have also seen cheap junk with brand names (that used to be trusted by me) such as Hitachi, Sharp, Toshiba on it. (Namely cheap LCD TVs, 32" or so.) They are sold at a premium compared to "supermarket" brands, but they are built exactly the same and frequently die after a few years.
-
This reminds me of my first generation TomTom GO (classic) sat nav. It cost me GBP412 and I was running it off of its internal batteries only (5 hour run time). I started hearing about units being destroyed by their official car adapter. It turned out to be failure of the sense wire connection and the cars full p.d being delivered to the 5V TomTom. It let the magic smoke out ! I have bever liked car chargers as to my eyes they tended to look cheap and built down to a price. I did some research and found an official Toshiba PDA car charger that looked far superior to most. It has a standard 12V cigar lighter plug feeding a decent sized box that sits in the middle of the generous length of cable . The output is spot on 5V. I delved inside the plastic box and found the regulator chip. I forget its ID but when looked at the data sheet it was a quality device from a known manufacturer. It has all manner of safety features built into it including output voltage monitoring with auto over-voltage shut-off. There was also filtering of the input to stop transient damage. Unlike many car chargers it appeared a quality build and worthy of my trust. It is the only 5V car charger that I use these days and is serving me very well indeed. I will not trust my expensive equipment to a poorly designed down converter.
When you consider that the Cigar lighter fuse is normally 30A it is quite scary to see some of the cr*p that is produced to use it. Imagine whilst driving having a loud bang or worse still a small fire coming from your cigar lighter socket :(
Aurora
-
Just another pitfall of buying cheap crap on auction sites (amongst countless others)
http://www.dorsetecho.co.uk/news/11633639.Warning_after_mobile_phone_charger_explodes_at_Weymouth_house/?ref=mr (http://www.dorsetecho.co.uk/news/11633639.Warning_after_mobile_phone_charger_explodes_at_Weymouth_house/?ref=mr)
-
This is a case of a retailer labelling cheap junk as expensive. You spend 20 euros on a charger, and you can usually expect it to be well made. (Case in point, Apple iPhone charger is £25/30euro and is well made.)
Yes, and I've always purchased Apple wall chargers. Unfortunately Apple does not provide any car charger, so I was forced to choose an alternative.
I would never purchase a "no-brand-chinese" charger for € 5,00... so I choose to buy a product from a (I thought it was... ::)) respectable brand name here in Italy (Cellularline).
Indeed I knew they were only importers of chinese products (also the "Incase (https://www.goincase.com/shop/chargers/incase-high-speed-dual-car-charger-with-lightning-to-usb-cable/)" sold by Apple store it's a chinese product) but I thought Cellularline were importing well tested/engineered products.
Of course chinese companies CAN effectively produce quality products (the original Apple charger, the iPhone itself and so on) but it's difficult to recognize them without opening/testing them: usually it's the price that can make you smell something about the product's quality, and mostly because of this some companies raise its products prices in a way you would think they're well made products.
I never expected to have to deal with this kind of problems with a car charger USB: I always thought they were designed providing protection if the output exceeds 5.25VDC, the maximum allowed by the USB specification. I was wrong! Luckily, SOME phone manufacturers have already anticipated this eventuality.
apart from the fact that they used a black wire for + and a red one for - :palm:
Just details, uh? :--
Imagine whilst driving having a loud bang or worse still a small fire coming from your cigar lighter socket :(
Exactly!
Just another pitfall of buying cheap crap on auction sites (amongst countless others)
Tinytim, mine was not a "no-name" cheap product. It was CE, with instructions, a real physical company behind it, has its brand name on the case, has a serial number and all what you expect from a good quality product. It's only engineered with no overvoltage protection, so that if something fails, your phone can easily fry.