help sizing toroidal PSU to stepper/drives

[irving2008]

Probably I'm wrong with my nema34 steppers but I've seen a lot of different Chinese specs and I do not trust them, and the ones sold in Europe and USA have the same Chinese specs sheet... and they are so optimistic compared to the good brands.
The 3.1Nm has too high inductance for my 42V drives.
I have missed the rotor inertia 560g·cm2 vs. 850g·cm2. High speeds without good acceleration are worthless. Will see them performing in real life... to many calculations for a hobby engineer.

yet we all use them because the inductance effect determines the corner speed of the motor, the speed where torque drops off, and a good mechanical design should never operate above the corner speed, at least not when cutting.

Any recommendation regarding the PSU power? I have read somewhere that 60% of the steppers/drives current is enough for a toroid. Is this true?
And another probably dumb question.. with 25A at 30V AC will I have 25A or 18A at 42V DC? .

Yes, it's generally true and often much less in practice. But you do need enough bulk smoothing capacitance to cope with the occasional peak demand.

25A @ 30V AC will give you 25A @ 42V DC

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