[chbot] Power supply

[Volker Kuhlmann]

On Mon 20 Jan 2014 14:57:22 NZDT +1300, Andrew Errington wrote:

> This any good? Free shipping from China:
> 
> http://dx.com/p/50w-5v-10a-led-switching-power-supply-adapter-280077

Ouch.

The only things between you and the grim reaper are things like

* A capacitor with films a few micrometer apart; one film connected to
the mains, the other to your fingertips.

* A small transformer with lacquer-insulated copper wires, in theory
something like half a millimetre apart; one connected to ...

* An opto-coupler, i.e. LED and phototransistor, facing each other in a
small plastic case, with the gods knowing how far apart. One is
connected to your fingertips, ...

Or a combination of the above. Welcome to the principle construction of
a switch-mode power supply.

Obviously it is possible to manufacture these components to be safe -
but their manufacturers have their heads on the block and know this, and
therefore can supply appropriate documentation to support their claims.
The same goes for the manufacturer of the power supply unit, who will
have to supply this documentation together with unit samples to a test
lab for independent verification of safety rules. The lab then issues a
certificate and the manufacturer is permitted to print the usual safety
symbols onto the units.

The importer of this kind of equipment into New Zealand is responsible
for ensuring that safety standards are met. Jaycar etc. know this, buy
by the container, and I suspect give some samples a once-over
themselves each time. That's what you pay for. Trademe is full of
clueless gits who don't know any of their obligations and make a bomb
re-selling dx.com junk. I asked a few, their answer is typically a
moronic "sold over 500 and no deaths yet".

Now it's well known that faking it is a Chinese national passtime.
People have died in China (not that long ago) because some contract
manufacturer for Apple used fakes (probablky unknowingly) of the parts
above. Keep firmly in mind that anyone in China can print a safety
symbol on anything, afterall they know well that you aren't going to be
kicking their bums (and neither will anyone else). So of course the
above dx.com item will have a safety symbol. But is it worth more than
the printer's ink?

I would definitely favour buying from aliexpress than dx for things like
these, they just give a more solid impression (and things arrive twice
as fast). However if you want at least some level of certainty you
probably have to buy commercial quantities and be prepared to pay for
it. In one case the fully-certified option from the same supplier I
asked about this was 3 times the price as the cheap one. One can expect
that there are sellers on aliexpress who sell good quality certified
power supplies, but finding them for a once-off seems to be impossible.
Do you like to go to the casino Nick? Like playing Russian roulette?

I've been looking for 5V 10A supplies too (and 32V 3A) that are
affordable and don't suddenly put out 240Vac just because they can, and
haven't found anything good. There are LED lighting constant voltage
supplies around the 35V mark, but they're a bit rare (constant current
is more likely) and LED lighting accessories are priced at the rip-off
level anyway.

Putting two switchmode units in series is not really satisfatory, PC
supplies are too noisy and clunky (probably lose efficiency too if the
12V output is unloaded).

I'd be very interested to hear more suggestions too, or if anyone has a
certified source for power brick type supplies. Otherwise the type of
semi-open supply Andrew linked to above is available from element14.com,
but not for cheap.

Nicegear might be prepared to add some items to their next order (if
they have one), to bring the shipping more into acceptable ranges. Or
can you obtain something similar from other sources Hads (time is not
much of an issue)?

Greetings,

Volker

-- 
Volker Kuhlmann
http://volker.top.geek.nz/	Please do not CC list postings to me.