[sdiy] A transformer question.

Tom Bugs admin at bugbrand.co.uk
Mon Nov 3 22:18:29 CET 2008

Thanks Bob - that makes a lot of sense and, I think, gives me the 
direction to figure things for the most part.

I'd already been planning to use 18v secondary outputs to feed v-regs 
for 15volts (LM317/337)- I'll do some calculations to check whether it'd 
be worth heading up to 24v secondaries to cover the potential 100v 
situation. Making sure that the V-regs will receive happy operating 
- that'd be right, right?!


Bob Weigel wrote:
> 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
> Tom Bugs wrote:
>> Hi,
>> A quick question about twin primary transformers for which I've not 
>> been able to find answers...
>> If there are twin 115v primaries.. (ie series for 230v and parallel 
>> for 115v)
>> - should this be able to cover Euro vs UK ranges of c.220v to 240v?
>> - and would it cover US 120vAC and 110vAC in places like Cuba?
>> - how can one deal with the 100v in Japan (other than replacing the 
>> trafo with a different spec one?)
>> I'd guess there's a bit more to it too - dependent on current draw, 
>> trafo type & spec, etc..
>> Any help greatly appreciated!
>> Ta,
>> Tom
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