Not correct. An autotransformer absolutely does have a core. The
advantage of an autotransformer is in the size of the windings and core
for a given power level. For example:
1) Assume a standard 110V to 110V isolation transformer with a 1 amp
rating. So 110V/1A to 110V/1A rating.
2) A simple wiring connection of the two windings in series gives a
220V ability. At the junction of the windings is a 110V 2A connection!
3) To achieve this with a 220V/110V isolation transformer the windings
would be a 220V/1A winding plus a 110V/2A winding, requiring about twice
as much copper and a larger core to allow the larger size of the
windings. This is the economic reason for the auto-transformer
construction .
Regards,
Charles R. Patton
On 2/25/2016 7:39 AM, rolohar@... [Homebrew_PCBs] wrote:
>
> Variacs and autotransformers only have one winding. There is no
> primary/secondary winding
> configuration. There is no iron core to facilitate induction between
> the primary and the secondary
> windings.