INFO (not question) High Quality from street market

Hi Ruud,
Yes, you should check them. I was truly amazed at the bad design, all so save a few cents.
I HAD to spread a warning.

Hope yours are ok.

BR Harry - EA/SM0VPO

I have some AC adapters with selectable voltages between 3 and 9 Volts.
In fact, I never measured the voltage they produced.
But after reading this, I will!
(I use a voltage regulator in every piece of equipment I use those cheap AC adapters with. And usually I don't need a lot of current, so even if the adapter voltage is too high, dissipation in the voltage regulator is within safe margins.)

Ivan wrote:My sight was attracted by the words "MADE IN P.R.C" on the supply case.
"PRC" probably means "People's Republic of China"

Yes, Ivan, I believe that to be the case. But I did notice that the homepage is in Spain.

Ivan wrote:It expresses the quality of the
product perfectly, am I right?

Yes, Ivan, it does indeed express the quality.

I have now bought several of these unit while I have the opportunity. When dismantling them I always find other faults, such as 10mm component lead uncut, shorting to the switch chassis, or the odd plastic former wire guides broken off. Out of seven units I found only one that was without some form of construction quality error.

These units are certainly totally unuseable for the original purpose. They are dangerous to the equipment they power, and the design I believe to be un-serious.

Here are the pictures. As you can see, the top 4 settings of the selector switch are all connected to the 16v supply (12v, 9V, 7.5v and 6v).

BR Harry

Hi once more,
my sight was attracted by the words "MADE IN P.R.C" on the supply case.
"PRC" probably means "People's Republic of China" there, but in Czech "prc"
is a vulgarism, which means "fu.k". Literally. It expresses the quality of the
product perfectly, am I right?

VBR from Ivan

Hi all,
IMHO the manufacturer would perfectly take the dead bug attitude: no response and no resposibility.

BR from Ivan

I have just found yet another unit on the market, but a little cheaper.
This one also has no voltage regulator, and only TWO tappings on the mains transformer; 5V and 12V. It still has a 6-positions switch to select 6 different voltage, but it only gives out 16.8V (all 12v, 9v & 6v settings), and 7.5V (all 4.5V, 3V & 1.5V settings).

I think that the regulator must be your expensive 6V portable CD player. When you put 16.8V into it the excessive current drawn by the instrument sinks the voltage from the battery eliminator.

If anyone is interested I can supply an internal photo? (that was the question).

I wonder what would happen if I wrote to the PSU manufacturers and said the poor quality is responsible for the death od a $450 Samsung surf tablet?  

BR Harry

Hi all (There's four of you now :-)
I am presently building a PSU for my oscilloscope and I decided that the cheapest way was to get a couple of "cheap" transformers from a street market. They cost about $5 and give out DC 1.5v, 3.0v 4.5v 6.0v, 7,5v 9.0v and 12v, selectable with a switch. You know the beasties:



So I bought a few of them. They contain a lovely little transformer with seven different tapping   When I opened them up I found out just what bad quality they really are:

Measurements:
1.5v = 3.1v
3.0v = 3.1v
4.5v = 7.7v
6.0v = 7.7v
7.5v = 16.2v
9.0v = 16.2v
12.0v = 16.2v

It seemed like the switch had no effect at all for certain voltage settings.

When I opened up the PSU I found that the transformer did not have 7 different tappings, but ONLY 3 AC TAPPINGS.


If we take a closer look at the PCB and the 7-position switch tracks we see:



Notice how the 12v, 9v and 7.5v are deliberately bridged on the PCB itself. No wonder the switch had no effect.

But at least I have the transformer, 230v winding and a 12v winding (with some taps and magnet-wire I can re-use) so I can easily work with this. But it just goes to show the standard of workmanship, and the terrible design.

I wonder how many battery-operated domestic units have been blown up using this sort of bad design, just to save a few cents. I mean, how much extra can it cost to terminate 8 wires instead of 4 wires on the PCB and get a better quality product?

You get what you pay for!

I have now put two 230v windings (from two transformers) on the same former, and wound 95 turns of 0.4mm Dia. wire on one of them, so I have created a 230vAC to 230vAC 30mA + 6.3vAC (650mA) with minimum winding effort.

I re-built two transformers into one in three hours. Would have taken less time if I hadn't needed to varnish the laminations. The standing AC primary current was about 18mA with no load. After varnishing the laminations the no-load primary current dropped to less than 3mA.

I may be on holiday, but I can still do something technical

Very best regards from Harry - EA/SM0VPO
Nerja, Andalucia