[sdiy] Toroidal Transformer considerations

[Jim Patchell]

Keith Winstanley wrote:

> I am putting together a couple of +-15V PSU for my
> modular, the digisound design and I am using 20VA
> toroidal transformers. Now I am sure there are some
> considerations when mounting these transformers?
> My cabinet is wood and I am thinking of mounting
> the PSUs inside an aluminium chasis. Are there
> problems using ferrous bolts through the toroid?

    No, there is not.  The big thing you need to be careful of is that
you do NOT have a complete electrical circuit.  So, if you bolt the
transformer down to the chassis, that is OK.  But you do not want to
have the chassis touch the "top" of the bolt in any way, as this will
make a complete secondary winding that is shorted, and current will
flow.  If you use a non-metalic bolt to fasten down the transformer,
they you don't have to worry about this accidently happening.  I use a
lot of 500VA torroids at work, and I have been using 1/4" steel bolts to
hold them down with no problem.

    By the way, you can get center potted torroids made by Amveco from
Digikey, in sizes up to 50VA.  The center potting makes mounting these
suckers a lot easier.

>
> The hold in the middle is threaded and I am sure that using
> a brass threaded bold will be fine but could someone give
> me a quick safety lecture? Induction etc??

    Sounds like a potted transformer already.  You should have no
problem using any screw you choose.

>
>
> TIA
>
> Cheers...
>
> Keith
>
> http://home.freeuk.net/lowpass