Continuous Stall Current Interactive Calculator

When a motor isn't turning but is still powered, it'll draw its full stall current. There's zero back-EMF—so the only thing limiting current is the resistance of the wire in the windings. Use this calculator to find stall current, heat generated, and how much the windings will heat up, based input voltage, winding resistance, and motor thermal resistance. This is important for situations like linear actuators holding position, robotic arms that must 'freeze' under load, and damper motors in HVAC—essentially, any place where the motor is asked to hold against a force for long periods. Below you'll find formulas, an example, theory, practical advice, and a FAQ.

What is motor stall current?

Stall current is the amount of current a motor will draw if you keep it powered but physically prevent it from turning. With no motion, there's no back-EMF, so the only thing slowing current down is the resistance of the coil. This is the maximum current you’ll ever see from the motor.

Simple Explanation

If you’ve ever kinked a garden hose, you know what happens—normally, water flow (like current) is kept in check by the pressure pushing back (in a motor, that's the back-EMF created by spinning). But stall a motor—stop the shaft—and all that back-pressure is gone. The full line voltage pushes current through just the resistance of the copper. The result: a big surge of current, and that turns into heat very quickly. Too much heat and the motor is finished.

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📹 Video Walkthrough — How to Use This Calculator

How to Use This Calculator

1. Enter your supply voltage in volts — this is the DC voltage applied to the motor terminals.
2. Enter the motor's winding resistance in ohms — check your motor's datasheet for this value.
3. Enter the thermal resistance (°C/W) and ambient temperature (°C), then set the maximum allowable winding temperature for your motor's insulation class.
4. Click Calculate to see your result.

Mathematical Equations

Simple Example

Given: 12V supply, 4Ω winding resistance, 8°C/W thermal resistance, 25°C ambient.

Stall current: 12 / 4 = 3A

Power dissipation: 3² × 4 = 36W

Temperature rise: 36 × 8 = 288°C above ambient — well over any safe winding limit. Current limiting is required.

Engineering Theory Behind Motor Stall Current

If you prevent a motor from turning but keep it powered, you're dealing with a pure resistance load—no back-EMF in play. The current is just V divided by R, and you'll usually get numbers much higher than what you see when the motor spins normally.

For a running motor, back-EMF is proportional to speed and acts to cut the current down. The formula is I = (V - E_back) / R, where E_back is zero when stalled. That’s why the current is only limited by the resistance in stall.

Stall current is usually 5-8 times a motor’s rated running current. This leads to a massive jump in heating, since heat is proportional to I squared. Leave a motor stalled without protection, and it will cook the windings in short order. This is particularly true in actuators holding load or similar applications.

Practical Applications

Stall current calculations matter wherever you might need a motor to hold a load for any noticeable length of time. Linear actuators in positioning systems are a common case: ask the actuator to “hold” and you may be running at stall. Without current limiting or a way to break the circuit, the motor can quickly fail.

Robotics is another area—servos holding an arm in place need to be checked for safe temperature rise at stall current. The same idea applies in CNC and automation: holding torque comes from current, but so does heat, so you have to size motors and electronics for the worst case, not just running conditions.

In HVAC, damper or valve actuators often end up holding pressure in one spot. If a motor ends up at stall too long without protection, repeated overheating will eventually destroy it.

Worked Example

Design Considerations and Best Practices

If there's any chance your motor might stall and stay that way, you need to plan for it. The most straightforward option is a current limit—good for the motor's safety, but it’ll also reduce how much load it can actually hold. Another method is using thermal switches so power is cut when the windings get too hot.

Duty cycle limits (powering motor only part of the time) can let the motor cool between bursts. If your design demands reliable holding for long periods, mechanical solutions like spring brakes or worm gear self-locks are more robust—these take the job of holding away from the motor windings entirely.

The choice of motor (and its resistance) also makes a difference. Higher resistance means a lower stall current but, usually, less torque per unit size. For thermal management, look at mounting options, cooling, and actual expected ambients. Sometimes the best solution is to re-design the mechanism so the actuator never has to hold much force at all.

Newer motor controllers can estimate winding temperature based on measured current, ambient, and history—which is much smarter than just using a timer. This lets you run closer to the real limits of the hardware, but it's still only as good as your input parameters.

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