On the webpage of the toroid manufacturer the calculations are slightly different, and I'm a bit confused, probably I should ask them.
Full wave bridge (FWB) With capacitor:
VAC = 0.8 x ( VDC +2 )
IAC = 1.8 x IDC
WATTS = VDC x IDC (output)
VA = 1.4 x ( WATTS + 2 IDC* )
Steppers are nothing like that, the duty cycle is nothing like steady state. I don't know why you have 6 motors but I'd be surprised if you need more than 60% of the total load and most of the peakiness is handled by the capacitors.
VAC = (VDC + 1.5)*0.7
IAC = IDC
VA = IAC * VAC, then chose next largest
for 2 parallel secondary windings each is rated at IAC/2
The 1.5 is voltage drop across rectifier, can be 1, 1.5 or 2 depending on product.
So 24A @ 60% = 15A approx. = IAC (or 2 windings @ 7.5A each)
VAC = (42+1.5)*0.7=30V
VA = 30*15=450 so use 500 or 625VA
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