[sdiy] Unmarked transformers

[Karl Ekdahl]

The problem is that they're totally encapsulated in
plastic, i just pryed one open but unfortuanley
they're totally covered in rubber as well and that
seems more or less impossible to remove. They only
clue i have is that on the inside of the plastic cover
it says "weisser", "wz.." and "7405". I did a google
search on it and came with nothing - as suspected.
These transformers (i've got a bunch of them) are
small 3x2.5x2.5 cm pcb mounted ones.

I thought there was some simple way of measuring the
resistance or something? I'm totally lost regarding
transformers (and most other electronic stuff so
far)...

What i actually want is to do a dual powersupply that
can take both 220v and 110v and i'm basically
wondering if something will blow up if i connect these
to 110v. 

Another thought has been to completely skip the
transformers, and put on an outlet for a common AC
adaptor instead. Then i could just buy a 12v AC
adapter in the country i currently am in. Since i need
+9 -9 and GND i used a half-wave rectifier, but
apparently the synthesizer - that i'm going to use the
powersupply for - didn't like that at all and started
doing loud bass tones that i'm fairly sure is the
50-60hz found in the wall. The thing is that i
measured the amp usage of the synthesizer while using
a "real" dual powersupply and it only measured up to
70mA use so i thought my little half-wave (7x09 based,
470uF filters + 1uF after) would be enough. 

Clearly, i do not possess the needed knowledge to do
this on my own. Enlighten me!

karl

 --- Ken Stone <sasami at hotkey.net.au> skrev: 
> Simple way to tell if a transformer is mains rated-
> The primary and secondary will be on different
> bobbins, sometimes one above
> the other, some times one inside the other. Not all
> mains transformers do
> this, but if you are smart, you won't use the ones
> that use the common bobbin.
> 
> Ken
> 
> >Hi, i've got a bunch of unmarked transformers that
> i
> >have used doing 220v -> 22v. I don't have a clue if
> >they're actually designed for 220v input so maybe,
> >there's a risk of fire or something equally
> >unpleasant. Question; how do i know how much a
> >transformer can take? Also, since i'm wondering
> what
> >would happend if i plugged this into a 110v outlet,
> it
> >just so happends i need to build a +-9v adaptor for
> >both 220v and 110v input.
> >
> >Karl
> >
>
_______________________________________________________________________
> Ken Stone   sasami at hotkey.net.au or
> sasami at cgs.synth.net
> Modular Synth PCBs for sale
> <http://www.blaze.net.au/~sasami/synth/>
> Australian Miniature Horses & Ponies
> <http://www.blaze.net.au/~sasami/>
> 
>