Woops, sorry Russel I didn't see the second drawing.
I aggree though that a switch to parrallel the windings would be 
a much better idea.
In the simple circuit there is also the possibility someone sees 
the empty spot for a fuse and inserts one.

Peter

----- Original Message ----- 
From: "Russell McMahon" <apptech@paradise.net.nz>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Tuesday, January 18, 2005 10:53 PM
Subject: Re: [EE] Mains voltage selection for transformer


>> It doesnt have to be complicated at all
>
> Indeed.
> The example you gave was electrically identical to my second 
> one.
>
>> you dont HAVE to have two windings in parallel as long as one 
>> of the windings can handle the additional current at 110 volt
>
> Indeed. But in any "serious" application attempts are made to 
> optimise the winding windows used by primatries and 
> secondaries. By not using one winding at 110v you are using the 
> resource less effcieintly. In many cases this will be an 
> acceptable tradeoff with simplicity.
>
>
>        RM
>
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