Transformer question (only slightly OT)

[Tony Duell]

> 
> On 9/2/2006 at 11:11 PM ard at p850ug1.demon.co.uk wrote:
> 
> >A useful trick is to connect a 100W mains light bulb in series with the 
> >input to the transformer when first applying power (and with the 
> >secondaries of the transformer unconnected). Such a bulb will easily 
> >handle the magnetising current of a small transformer, anf won't even 
> >glow (or drop much voltage), so you can check the output voltages, etc.
> 
> Hmmm, the way I'd do is to hook up one winding to the mains, then tie one
> lead of the second winding to either side of the mains supply and measure
> the voltage between the other lead and the other side of the mains supply.
> If correctly phased, the voltage difference will be closer to 0 than
> 2xmains.  

Sure. And you still use a series light bulb in case you get it wrong (or 
your meter is malfunctioning, or...). In fact you can use the bulb for 
the initial test, it'll drop almost no voltage so you'll get over 100V 
(from your mains) across the primary. Easily enough to see if you get 0 
or 200V between the free ends. 

No, I'm not afraid of the mains, but I do treat it with respsect.

-tony