Enter the stepper motor phase current (amps) and the phase resistance (ohms) into the calculator to determine the stepper motor winding (phase) voltage drop at that current (often called the motor’s “rated voltage”).

Stepper Motor Winding (Phase) Voltage Drop Calculator

Calculates the winding (phase) DC voltage drop using V = I × R (often called “rated voltage”). Not the recommended driver supply voltage.

Enter any 2 values to calculate the missing variable

Stepper Motor Voltage Formula

The stepper motor voltage calculator estimates the voltage dropped across a single motor phase when the phase current and phase resistance are known. This is the winding voltage predicted by Ohm’s law and is useful for checking datasheet ratings, confirming coil behavior, and understanding how much voltage appears across the phase at a given current.

V_{sm} = I_{sm} \times PR
Variable Meaning Typical Unit
Vsm Stepper motor phase voltage volts
Ism Stepper motor phase current amps
PR Phase resistance of one winding ohms

If you already know the voltage and want to solve for current or resistance instead, the same relationship can be rearranged as follows:

I_{sm} = \frac{V_{sm}}{PR}
PR = \frac{V_{sm}}{I_{sm}}

How to Calculate Stepper Motor Voltage

  1. Determine the phase current for the motor winding in amps.
  2. Determine the phase resistance of that same winding in ohms.
  3. Multiply current by resistance.
  4. The result is the voltage across the winding at that current.

This calculation assumes you are evaluating a single phase of the motor. For motors that can be wired in different configurations, make sure the current and resistance values match the exact wiring method being used.

What the Result Means

The value produced by this calculator is the winding voltage, not necessarily the same as the external power supply voltage feeding the stepper driver. In many real stepper systems, the driver uses current limiting and may run from a supply voltage that is much higher than the coil’s calculated winding voltage.

  • Winding voltage: the voltage dropped across one motor phase at the selected current.
  • Driver supply voltage: the voltage feeding the controller or driver electronics.
  • Current limit: the setting that keeps the motor phase from exceeding its intended current and overheating.

This distinction matters because a higher driver supply voltage can improve current rise time and high-speed performance, while the driver still controls the actual coil current seen by the motor.

Example 1

A stepper motor phase draws 2.8 amps and has a phase resistance of 1.1 ohms.

V_{sm} = 2.8 \times 1.1 = 3.08 \text{ V}

The phase voltage is 3.08 volts. This means the winding itself drops about 3.08 volts when carrying 2.8 amps.

Example 2

A smaller stepper motor phase operates at 1.2 amps with a phase resistance of 8 ohms.

V_{sm} = 1.2 \times 8 = 9.6 \text{ V}

The phase voltage is 9.6 volts. Motors with higher resistance generally need more winding voltage for the same current than low-resistance windings do.

Related Winding Power Relationship

If you want to estimate heat generated in the winding, power dissipation is also helpful:

P = I_{sm}^2 \times PR

This relationship shows why current settings matter so much. Winding heating rises with the square of the current, so even a modest increase in current can significantly increase motor temperature.

Common Input Notes

  • Use phase resistance, not total driver or cable resistance.
  • Use phase current for one winding, not the total current drawn by the whole system.
  • Make sure units are consistent before calculating. For example, convert milliamps to amps when needed.
  • Motor resistance changes slightly with temperature, so hot winding voltage may be somewhat different from cold measurements.
  • If the motor supports series, parallel, or half-coil wiring, each configuration can change the effective resistance and current rating.

Frequently Asked Questions

Is the calculated voltage the same as the motor supply voltage?

No. The calculated value is the voltage across a motor phase at the specified current. The driver supply voltage may be higher, especially in current-limited stepper systems.

Why can a stepper system use a supply voltage higher than the coil voltage?

The driver rapidly switches the supply and limits current electronically. This helps the phase current build faster, which improves torque retention as speed increases.

What resistance should be entered into the calculator?

Enter the resistance of a single motor phase for the actual wiring configuration being used. Datasheets often list this as phase resistance or winding resistance.

When is this calculator most useful?

It is most useful for validating motor specs, comparing winding behavior, estimating voltage drop across a phase, and checking whether a chosen current setting is reasonable for the winding resistance.