Vexta, powermax, stepper voltage question??????

Does anyone know why Vexta, powermax, ect. have such a high rated voltage? For an example, a Vexta #268-23B is rated at 24 volts and powermax are rated as high as 65 volts? Is this the maximum or average voltages for these steppers? I know one needs to supply at least 4 times the rated voltage, and not more than 25 times the rated voltage, but that would be a very expensive power supply!

Thanks,
Russ


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