help sizing toroidal PSU to stepper/drives

[irving2008]

When I'll need to reuse the toroid for 80V I'll take out some wire from the secondary.

Hmmm, have you ever tried it? I've done it and rewound them... not recommended, and very hard if you have multiple secondaries.

Not sure. I think it will give me more torque at high speeds (1.6mH nema34 vs. 3.5mH nema23). Plus the robust 14mm shaft.

Oh dear If they're the motors I think they are then you're starting at 2.2Nm rather than the 3.1Nm of a decent modern Nema23 and that 14mm shaft is just shed loads of inertia you dont need (as is the massive coupler) especially if you need to run it that fast. There are plenty of Nema23 with low inductance windings.

Actually I want to push the drive chip to the limits as the chip protections are quite good. But I'll probably go with 30V.

Not sure about the voltage drop on load. Will it be significant?

Depends on the spec of the toroid, but the load isn't constant... if only one stepper of the 4 is running then its driver could be more susceptible..