Can I Run a 12V DC Motor on 24V?

In the fields of electronics and engineering, it is common to consider using components beyond their specified ratings to achieve higher performance. A frequent question that arises is whether a standard 12-volt DC motor can be safely operated on a 24-volt power supply. From a professional standpoint, the direct answer is: it is strongly discouraged for continuous operation and carries significant risks of immediate damage and catastrophic failure. While the motor will likely run, it will do so far outside its designed parameters, leading to a drastically reduced lifespan and potential safety hazards.

The Immediate Effects: Speed and Current

The operational characteristics of a DC motor are governed by fundamental electrical principles. The rotational speed of a DC motor is primarily proportional to the applied voltage, while the current draw is proportional to the torque load. When a 24V supply is connected to a 12V motor, the immediate and most noticeable effect will be a dramatic increase in speed.

• Massive Speed Increase: Neglecting load, the no-load speed of the motor will attempt to double. This is because the higher voltage overcomes the motor’s back electromotive force (Back EMF) more effectively, causing it to accelerate to a much higher rotational velocity. This excessive speed can exceed the mechanical limits of the motor’s components, particularly the bearings and brushes.
• Increased Inrush Current: Upon startup, the motor will draw a significantly higher inrush current than it would at 12V. This initial surge can potentially damage your power supply or blow fuses if they are not rated to handle it. The operating current under load will also be higher than designed.

The Primary Dangers: Heat and Component Failure

The most critical and destructive consequence of over-volting a DC motor is excessive heat generation. The power dissipated as heat in the motor’s windings increases exponentially with the current. This relationship can be expressed as:

Power Loss (Heat) = (Current squared) x Resistance

• Extreme Overheating (Thermal Runaway): Applying double the voltage leads to a substantial increase in current, which in turn causes a quadrupling (or more) of the power dissipated as heat. The motor’s armature windings are not designed to dissipate this level of thermal energy. The thin enamel insulation on the copper windings will quickly overheat, melt, and fail. This results in short circuits between windings, causing the motor to burn out and fail completely. This is the most common failure mode.
• Accelerated Brush and Commutator Wear: For brushed DC motors, the higher speed and increased current create excessive arcing between the brushes and the commutator segments. This process rapidly erodes both the carbon brushes and the copper commutator bars. The lifespan of these critical components can be reduced from thousands of hours to mere minutes under such conditions.
• Bearing Failure: Motor bearings are rated for specific maximum speeds and loads. Doubling the motor’s speed can push the bearings far beyond their operational limits, leading to rapid wear, overheating of the lubricant, and eventual mechanical seizure.

Controlled Scenarios: Pulse Width Modulation (PWM)

While connecting a 12V motor directly to a 24V source is dangerous, it is possible to use a 24V supply to control a 12V motor safely. This is achieved using a Pulse Width Modulation (PWM) controller. A PWM controller works by switching the 24V supply on and off very rapidly. By adjusting the duty cycle (the ratio of ‘on’ time to ‘off’ time), the controller can deliver an average voltage of 12V (or any other voltage up to 24V) to the motor. Using a PWM controller with a 50% duty cycle, for example, would allow you to power the 12V motor from a 24V source safely and efficiently, providing precise speed control without the destructive effects of constant over-voltage.

Conclusion

In summary, directly running a 12V DC motor on a 24V power supply is a recipe for rapid destruction. The resulting over-speed condition generates excessive heat that will quickly destroy the winding insulation, while also causing extreme wear on the brushes, commutator, and bearings. It is a practice that should be avoided unless you are prepared for the motor to fail. For applications requiring the use of a 24V source with a 12V motor, the only professionally acceptable method is to employ a suitable DC-DC converter or, more commonly, a PWM speed controller to safely regulate the voltage delivered to the motor.