[XCSSA] Can you break transformers?

[X-otic Computer Systems of San Antonio]

On Sep 5, 2008, at 3:14 PM, X-otic Computer Systems of San Antonio  
wrote:

>>
>>> 2) Use appropriate fuse on transformer secondary.  Generally slow-
>>> blow is OK for big transformers, but little transformers might need
>>> fast-blow and even that might not be fast enough.
>>
>> Secondary meaning the 12V side? I was thinking about that. Question
>> is, do I put it before or after the regulator and/or caps? Seems like
>> a requirement at this point :)
>
> Yes, secondary is the 12V side.
>
> Depends on what you want to protect from what.  If you're blowing
> your regulators, you want to put a fuse after the regulator.  If it's
> the transformer you want to protect, you can put it after the
> secondary.  (BTW, that's common practice in power amplifiers, or it
> used to be before they had computerized protection circuits).  Also
> fuses are often put on the primary side, that protects both the
> transformer and the house and the user (!) but problem with that is
> that primary side fuses generally won't be fast enough to protect the
> transformer secondary or anything else inside.  Legend is that fast
> blow fuse will always be protected by even faster blow transistors;
> that's not always true, but more true of primary side fuses than  
> others.
>
> With the way things are going for you, it sounds like you need fuses
> everywhere at least until you figure out what's going wrong.
>
> I though you had a tiny 100ma transformer or something, a sneeze will
> blow those, but blowing a 3 amp transformer?!!  That's a pretty big
> deal.  You must have a short somewhere, or maybe the rectifier or
> caps are wired backwards, something on that scale.  I'm surprised you
> haven't been seeing the blue smoke.  I'd check everything really
> carefully before plugging in again.

Oddly enough, I'm not blowing the caps, or regulators or anything  
really except the xformer. And yeah, no blue smoke. Not even a spark.  
No popping noises either. Of course, I bought it used to maybe it was  
just a bad wall-wart to begin with *shrug*

>>
>> Well, I'm thinking of just buying a new one of Allied and being done
>> with it. Not sure of those are fused or not though, but I'll go ahead
>> and just add a fuse the next time around and be done with it :)
>
> Big non-wallwart transformers aren't internally fused, or if they are
> it's at a much higher current.  The current specification for a
> transformer part is generally "working" rating which permits
> significantly higher peak currents.  It's intended that the circuit
> designer put in fuses and other design features (such as grounding or
> double insulation) as appropriate.  It's not a part that has to be
> safe for any
> dumb end user.

Well actually I mean a wall-wart from Allied, although they do sell  
the individual transformers. Might not be a bad idea one day (for  
cleaner power over voltage regulators), but I think, with enough  
filtering caps, the voltage regulators should work for the amps I'll  
need (less than 1A total with the synth fully built).

> But if you've got a bad enough short, you'll either kill the
> transformer, trip the breaker, or burn a wire or circuit board trace.

Yeah none of that happened. No clue what did occur though :P

> BTW, I think commodore external PSU's were not over-rated, and in
> I've seen dead ones before.  They just had barely enough output for
> use intended, and anything above that would blow them, just like
> cheap wall warts.

Well, that's why I'm trying to find an alternate solution. One,  
because it's fun, and two since it will hopefully give myself, and  
others, an option if they can't get a C64 PSU on-hand.

Thanks again Charles!

Tim