RadioBanter - View Single Post - What's in a "wall wart" so-called "transformer"?

PhattyMo · September 24th 06, 10:29 PM posted to rec.radio.amateur.homebrew

wrote:
I have a collection of "wall wart" (others may call them "transformers")
and I'd like to use one to cobble a little power supply. I've never
opened any to see what's really in them (and suspect it'll be quite a
chore), but I'm quite sure they are not ALL "transformers", because some
claim AC and some claim DC output, yet the first I grabbed out of the
junkbox claimed DC AND ALSO provided a HEALTHY AC output on the same
two wires! Furthermore, NONE of them seem to be voltage regulated!
(But if one says "X volts at Y milliamps", then loading it to Y mils
usually gives an output close to X volts.)

So what IS in them? Do the really light-weight ones, for example,
use a capacitor for relatively low-loss voltage dropping? And
why would one give *BOTH* AC and DC? Bad diode(s)?

Uhh,why a Transformer,of course..
The ones with the DC output will have a rectifier diode or two (or maybe
even a FWB,if you're lucky) and usually a filter cap,but not always,IME.

The AC ones are usually just the transformer,and that's it.

Some "wall warts" I've come across were actually really tiny SMPS's,you
can usually identify these fairly easily,they're really light compared
to the "iron core transformer" type.. These may be regulated,the
iron-core types above almost never are.

AC and DC output?
Are you sure you're not measuring the ripple? They usually have very
poor filtering,plus after time the cap(s) dry out,and make it even worse.
Or,it could be the diode(s),they've been known to fail aswell.