• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Cheap wallwart? Beware.

Status
Not open for further replies.

audioguru

Well-Known Member
Most Helpful Member
I connected a cheap wallwart to my new project but it did not work properly. The DC voltage from the wallwart was a little low so maybe something in my circuit was drawing too much current? I 'scope'd it and found TONS of ripple coming from the wallwart.

I cut the wallwart apart expecting to see a swollen filter capacitor but the capacitor was missing. There was a symbol and two solder pads for an electrolytic capacitor but the capacitor was not there. The wallwart is labelled, "9VDC/280mA, made in (you know where)". I added a 470uF/16V capacitor and measured 19V with no load so I quickly removed my 16V capacitor and used a 220uF/25V one. The no load voltage is still 19V but is 16V with 100mA of load so I changed the marking on the label to 16V/100mA.
 

JLNY

Active Member
You never know what you might get sometimes with those cheap wall adapters. Where did you get it from? Did you get it recently enough that you might return it?

Another big danger to worry about is poor isolation between the primary and secondary, either due to poorly designed separation in the board layout or shoddy winding in the transformers. Apparently some have gotten mains shocks off of dodgy USB chargers and the like.
 
Last edited:

Willen

Well-Known Member
There was a symbol and two solder pads for an electrolytic capacitor but the capacitor was not there. The wallwart is labelled, "9VDC/280mA, made in (you know where)"
Of course my neighbour China, and sometime made in PRC (you know where is PRC). My wallwart have the output capacitor but still its output seems poor. When I use the wallwart to charge any android phone, the wallwart start to use the phone itself. It opens slide screen lock, opens menu, opens contacts and makes calls itself sometime. :)
 

spec

Well-Known Member
Most Helpful Member
I have had problems with products from all parts of the world, not just PRC.

spec
 

MrAl

Well-Known Member
Most Helpful Member
Hi,

What is PRC?

I can tell you first hand that there are many many types of wall warts made and back some 20 years ago or more there were some made in the US. One place that made them would get orders from other companies for a run of wall warts of a certain design. That design could be anything from an AC type with AC output only to a DC with regulation. The key to understanding the type was what the company that ordered the wall wart was going to use it for. Those other companies would create a design of some piece of equipment to sell themselves and ti would be designed to use a certain wall wart type (AC, DC, regulated DC) and so they would order lots of the same kind.
This means that there could be a lot of different kinds popping up here and there for sale because they probably sold their overrun to some other company for sale to the consumer. So we might end up seeing AC wall warts, DC with no capacitor, DC with little capacitor, DC with large capacitor, and of course regulated DC with different current ratings. For one example a while back i got a 24vac wall wart for something like $2 USD.
The real problem i think is that there seems to be no way to label them other than "DC" and because there are different variations like no capacitor, small capacitor, large capacitor, there is little way to know what you are getting beforehand unless you write to the seller first and hope they know. The only type i see with notes about it on sellers sites is the 'regulated' DC type which usually they state that it is regulated. I would not count on that either though.
 

spec

Well-Known Member
Most Helpful Member
Some of the most dangerous wall warts and leaded power supplies came from the UK in the days before switch mode techniques became common.

They were very poorly constructed and the workmanship was abysmal. Some of the problems were.
(1) Overheating causing the cheap plastic case to distort and sometimes catch fire.
(2) Bad regulation
(3) High ripple
(4) Components not tethered and inclined to move and fracture self leads or short to adjacent components.
(5) Poor quality mains leads which would fracture
(6) ...

And non Japanese TVs were nothing short of a disgrace at one time.

Even now some of the guitar amplifiers from the west are very poor.

And a certain car model catches fire because of poor electrical design.

You also hear unsubstantiated negative statements about the quality of cheap components on eBay for example. But, in most cases, they are fine, often they are just old stock. In one case, I got some 555 chips in the original RS packets- they probably dated to the 1990s. At the company I worked at when a production run had completed they would simply junk the complete stores content and order new components for the next batch.

I recently bought a load of components from cheap sources, mainly eBay. One item was a set of 2% metal oxide resistors, covering values between 1 ohm and 1 M ohm. So I decided to batch test the resistors. For a start you could not tell them apart from Allen Bradly, and in fact they looked like a famous brand item and, to top it all, the resistors I checked for resistance were in specification.

But there are blatant rip-offs: batteries being number one, but also power transistors, RF transistors, and high value electrolytic capacitors- you will always get rouges in any area of society. Why eBay and the Chinese government do not stop these forgeries in a mystery, because they tarnish the image of the whole electronics industry.

There is a lot of innuendo about Chinese electronic products, but the truth is that Chinese products have improved the quality of products radically and their low cost has opened up a whole new range of possibilities for home constructors.

spec
 
Last edited:

JimB

Super Moderator
Most Helpful Member
There is a lot of innuendo about Chinese electronic products, but the truth is that...
China makes what we ask them to make and pay for them to make.

If we ask for it dirt cheap, that is what we get.

If we ask for some quality, are prepared to pay for it, and just as with any western manufacturer do quality control, then China will make good stuff.

JimB
 

JonSea

Well-Known Member
Most Helpful Member
I recently had a batch of 60 audio oscillator boards assembled in China. The boards used an I2C square wave oscillator chip and an I2C digipot. when I received the boards back, I ran my test program that should produce a series of tones of increasing volume. Instead I got a series of random beeps and silence.

After some troubleshooting, I determined that the oscillator, an LTC6904, was responding erratically to everything on the bus, not just commands to it. I replaced the chip with a known good one and the board worked as expected. The LTC6904s my assembler got were counterfeit!

I don't blame the assembler; I think their supplier ripped them off. The outside appearance of these chips was indistinguishable from the real thing. I returned the batch of boards with real parts and the reworked them. All of them worked properly when I got them back.
 

Willen

Well-Known Member
Once I damaged a telephone set when (not cellphone) while in charging because of overheat. 1 years later when I got a DMM then I knew that the walkwart I was using with the phone was giving double voltage than its rating. :)
 
Last edited:

KMoffett

Well-Known Member
Of....When I use the wallwart to charge any android phone, the wallwart start to use the phone itself. It opens slide screen lock, opens menu, opens contacts and makes calls itself sometime. :)
So, did you open the wall wart to see if there was a uC inside that somehow was controlling your phone?

Ken
 

Reloadron

Well-Known Member
Most Helpful Member
China makes what we ask them to make and pay for them to make.
Yeah, that sort of sums things up. They build to the specifications the buyer provides and label the same way. You want cheap they can make it happen, you want quality? They can make that happen too. The filter cap in Audio Guru's wall wart was not omitted by accident, the buyer likely choose to have it omitted as a cost reduction for their product which did not need clean DC.

Ron
 

spec

Well-Known Member
Most Helpful Member
One thing we do not know is if it was a one-off faulty unit. I don't believe there would be any point marketing a unit intentionally with over three times the specified output voltage- they simply would not sell many, especially as the vast majority of 5v wall warts are OK.

Practically all wall warts are made in China, including the wall warts supplied with mobile phones by the OEMs.

spec
 

audioguru

Well-Known Member
Most Helpful Member
You never know what you might get sometimes with those cheap wall adapters. Where did you get it from? Did you get it recently enough that you might return it?

Another big danger to worry about is poor isolation between the primary and secondary, either due to poorly designed separation in the board layout or shoddy winding in the transformers. Apparently some have gotten mains shocks off of dodgy USB chargers and the like.
I have a box full of wallwarts. This one also does not have any certification stamp to show that it is safe (or legal). It has good primary to secondary isolation and when plugged in for a while without a load it gets warm but not hot. Since I have many I should get rid of this one.
 

spec

Well-Known Member
Most Helpful Member
I have a box full of wallwarts. This one also does not have any certification stamp to show that it is safe (or legal). It has good primary to secondary isolation and when plugged in for a while without a load it gets warm but not hot. Since I have many I should get rid of this one.
Good move AG.

If you lived in the UK I could point you to a nice twin USB socket 5V, 2A wall wart for £3UK at your local Asda (Walmart).

spec
 

MaxHeadRoom78

Well-Known Member
I scanned the thread and did not see any mention of the two types of W.W.
Many early kinds had a voltage and current rating and were simple linear supply with a mains transformer, bridge and rectifier, the open circuit output was way higher than the specified as it would output the rated voltage when operating at the rated load.
Later, lighter versions used a SMPS P.S. and were/are regulated to output the rated voltage with all loads.
I suspect the OP has the first type.
Max.
 

spec

Well-Known Member
Most Helpful Member
I scanned the thread and did not see any mention of the two types of W.W.
Many early kinds had a voltage and current rating and were simple linear supply with a mains transformer, bridge and rectifier, the open circuit output was way higher than the specified as it would output the rated voltage when operating at the rated load.
Later, lighter versions used a SMPS P.S. and were/are regulated to output the rated voltage with all loads.
I suspect the OP has the first type.
Max.
To my knowledge there has always been two types of small low-cost power supplies, non regulated and regulated. The early supplies were linear with tiny mains frequency mains transformer which ran extremely hot, and had an embedded thermal fuse, and the latter, much improved power supplies, are switch mode, of course.

The only problem I have had with switch mode wall wart power supplies is that the stupid plastic earth pin snaps off so that you cannot plug the wall wart into the mains socket.:eek:

spec
 

MaxHeadRoom78

Well-Known Member
All the ones I have come across in N.A. only have 2 pins.
I prefer a linear supply, just that no regulation, I have added this to some.
Max.
 

Willen

Well-Known Member
So, did you open the wall wart to see if there was a uC inside that somehow was controlling your phone?

Ken
The wallwarts are $1 devices so who would use $2 uC inside? :)
Anyway that would be interesting!
I have few such poor Chinese or Chinese technology based Indian wallwarts which operates some android phones when charging. So I charge android phone with a pretty nice 1A wallwart made to power an external TV card.
 

spec

Well-Known Member
Most Helpful Member
The wallwarts are $1 devices so who would use $2 uC inside? :)
Anyway that would be interesting!
I have few such poor Chinese or Chinese technology based Indian wallwarts which operates some android phones when charging. So I charge android phone with a pretty nice 1A wallwart made to power an external TV card.
Hi Willen,

Although we may pay $2 for a micro controller, the price the wall wart manufacturer pays would be nothing like that, probably $0.20US would be closer.

I recon that one of the reasons why EBay etc components are relatively cheap is because the vendor has low overheads and does not take a large profit, also they deal in old/surplus stock.

It is an odd thing in retail that the distributor and retailer make a comparatively high profit, while the manufacturer who does all the innovation and actually produces the product makes a very small profit.

There is another odd aspect to semiconductor costing: the silicon chip with all the leading edge technology is relatively cheap- it is the packaging that costs the money. That is why the packaging is done in low cost labor areas: Philippines, Mexico, Malaysia... Then of course, in the UK especially, there are high taxes, 20% value added tax (VAT) for starters.

spec
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top