inductor in series with transformer primary to reduce secondary voltage?

[infinia]

Wiring 120v-to-12v transformer like a *step-down* autotransformer is suboptimal: it reduces voltage applied to its primary and reduces voltage at its secondary, that makes output voltage regulation worse than it could be. Is there a point of doing that?

most certainly to fine tune the secondary voltage closer to "optimum", just like the OP is wanting to do. Like anything it does have some draw backs . the VA of the main transformer is reduced by approx. the same percentage as the primary voltage. as an example, operate a 220V mains XFMR at 110V and the specified VA is cut in half. the secondary VA of auto-transformer used needs to be rated > than or equal to the percentage dropped as well. If the OP uses a 12V transformer wired in post 24 to his 500VA 120-12 ~108VAC or 10% reduction he should only expect to have 450VA output capability. the auto transformer secondary 12V should be rated at 50VA minimum or 4.2A on the secondary. using engineering practice he should overate 50VA by 20%-50% not to impact regulation.

 

[jcx]

One does not use a step up auto-transformer to overdrive the load as suggested in this reply

sorry Andrew but you are being tendentious

it was already clear inthis thread that some have very low knowledge of xfmrs and even mains safety

my post spelled out the reason why it can be a bad idea to boost - didn't rule out your "proper use" idea