The formula is correct. Most people say 80% of max. current is OK, but when your stepper already gets hot at 0.46V there is something wrong with the cooling
Is it a direct drive all_metall extruder? If so, make sure the heatsink has a good contact to the extruder without crunching the fan-mount. (Use extra M3 nuts)
Do you have a fan aimed to the drivers? A stepper can be very hot without failing, but the drivers have an overtemp protection.
When your z-steppers are connected in parallel you can double up the current, but with the leadscrews, this is usually not necessary.
It is much healthier and safer to wire the steppers in series.
Is it a direct drive all_metall extruder? If so, make sure the heatsink has a good contact to the extruder without crunching the fan-mount. (Use extra M3 nuts)
Do you have a fan aimed to the drivers? A stepper can be very hot without failing, but the drivers have an overtemp protection.
When your z-steppers are connected in parallel you can double up the current, but with the leadscrews, this is usually not necessary.
It is much healthier and safer to wire the steppers in series.