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Motor Current Requirement Calculator

Work out motor current requirement instantly with clear inputs, formula shown and shareable results.

About Motor Current Requirement Calculator

Torque is proportional to current through the torque constant, so current is torque divided by Kt. The supply voltage then splits between the resistive drop and the back-EMF, and whatever is left for back-EMF sets the maximum speed at that torque, since Ke in V per rad/s equals Kt numerically in SI units.

Formula

Motor current

I = T / Kt; available back-EMF = V - I R; speed = back-EMF / Ke

Worked example

With the default values below, Motor Current Requirement Calculator returns Current required of 7.06. Change any input above and every figure here is recalculated in your browser.

Inputs used

Required torque
0.6 N·m
Motor torque constant
0.085 N·m/A
Supply voltage
24 V
Winding resistance
1.8 Ω

Results

Current required
7.06 A
Winding dissipation
89.69 W
Voltage left for back-EMF
11.294 V
Approximate no-load speed limit
1,269 rpm

Step by step

  1. 1Values used
  2. 2Motor current
  3. 3Current required= 7.06 A
  4. 4Winding dissipation= 89.69 W
  5. 5Voltage left for back-EMF= 11.294 V
  6. 6Approximate no-load speed limit= 1,269 rpm

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why are Kt and Ke numerically equal?

Because of energy conservation: mechanical power out equals electrical power in for the ideal machine, which forces N·m/A and V·s/rad to be the same number in SI units.

What limits continuous current?

Winding temperature. Copper loss is I squared R, so the thermal path from winding to ambient sets the continuous rating.

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