[sdiy] A transformer question.

Simon Brouwer simon.oo.o at xs4all.nl
Mon Nov 3 23:07:18 CET 2008

Bob Weigel schreef:
> Tom,
> Normally the variation in 20V around 230V divides to a variation of a 
> coule volts in the stepped down side... and in most circuitry that's a 
> tolerable variation.   And same percentage variation in the 110 to 
> 120...usually ok.  The 100V in Japan can cause some 'brown out' 
> simulation, but some things will also work just fine with it.  For 
> example a Siel DK80 I'm pretty sure wouldn't like the 100V without a 
> step up transformer because the headroom is too limited on the 
> regulators as I recall.  It'll buzz as the ripple drops below the 
> regulator's headroom requirement.
> You can get step up transformers for 100V to 120V.   For running 
> Russian gear here I had a good sized 2X transformer so I just wired it 
> up in a plastic box and made a simulation of the funny round pinned 
> outlets on the top of the plastic box :-).  Anytime you have to step 
> DOWN there are real cheap options out there.  Step up requires a more 
> expensive solution.  -Bob
I once had to deal with (very expensive) Japanese equipment that was 
expecting 200V and should be run on 220V. To reduce the mains voltage I 
used a standard 220 -> 20V transformer (connecting the primary to the 
mains, and the secondary in series with the mains input of the equipment).
Wiring the secondary in the reverse way, you can increase the mains 
voltage, e.g. from 100V to 110V. The secondary only needs a current 
rating to match the input current of the equipment, so this requires a 
relatively small transformer.

Vriendelijke groet, 
Simon Brouwer. 

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