Can a bucking transformer get "high on its own supply"?

There's a lot of industrial 277V in North America that's a few volts too hot to support level 2 EV charging. It just needs to be knocked down to roughly 240V, and that's not that hard to do with a small bucking transformer, thusly, outputting 241V (close enough).

For instance at 48A, the bucking transformer is 36V x 48A = 1.7 kVA. Not a big transformer. So this is pretty achievable.

simulate this circuit – Schematic created using CircuitLab

Note that the current economics are a little weird here - even though 48A is flowing through the outer ring circuit, giving 48A @ 241V (11.5 kW), and the transformer is drawing 6.2 amps, the 277V draw isn't 48A + 6.2A = 54.2A... it's actually 48A - 6.2A = 41.8A.

However, 277V-36V transformers are far less common than 240V-36V transformers. Is it possible to feed the bucking transformer from its own output? Like this

simulate this circuit

• This is called an autotransformer. Should work. Commented Sep 21, 2023 at 22:03
• Forgive my ignorance, but would it make more sense to just use a 12kVA 277V to 240V transformer? Commented Sep 21, 2023 at 22:03
• @TomCarpenter because 12 kVA transformers cost and weigh a lot more than 2 kVA ones. An EVSE with a 2 kVA transformer inside could be lifted without rigging and shipped UPS. Commented Sep 21, 2023 at 22:49
• @TomCarpenter - an autotransformer can be much smaller (cheaper) than an isolating transformer because the magnetic field only needs to transfer a small portion of the total power delivered to the load. Commented Sep 21, 2023 at 23:49
• @manassehkatz I suspect it's more because Tesla knows that "Tesla Taps" exist and that other cars don't support 277V. Which I think is more of an oversight than a masterplan to save \$2 a car. Commented Sep 22, 2023 at 18:24