[R-390] Bucking Transformer / Autotransformer Question

[Bob kb8tq]

Hi

The load current goes through the secondary. If you have a randomly chosen 12V filament transformer, it likely 
will do a fine job.

The math:

10A load current
10A secondary current (in the 12V winding)
1A primary current (to feed 10A at a 10:1 ratio into the 12V winding)

Obviously, 10A is a pretty big load ….

Bob

> On Jul 15, 2020, at 3:02 PM, Barry <n4buq at knology.net> wrote:
> 
> I'd like to employ a bucking transformer for some of my equipment - particularly a Fluke 760A calibrator.  I have a pretty hefty old transformer with two, separate 10V secondaries that can deliver 1.0A and 10.0A.  It also has a tapped primary with taps at 115V, 120V, 126V, and 132V (I think I'm remembering all those correctly).
> 
> I was thinking that since my mains voltage is right around 126V, then I could connect that to the mains and use the 115V tap in an autotransformer configuration.  I'm unsure, though, whether that is the best way to do this and whether the primary windings will have to carry more current than it's capable of supplying.
> 
> While I could connect one of the secondaries as a standard bucking configuration, I was thinking the autotransformer configuration might be better/simpler.
> 
> Any thoughts on this approach?  I'm just unsure of how much current that small section of primary would need to supply.  I think it would be the total current drawn by the load but I might be thinking of that incorrectly so thought I'd ask.
> 
> Thanks,
> Barry - N4BUQ
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