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I was buying DC motors for making robots. I wanted to ask whether the voltage written on the motor, e.g. 12V or 24V, matters. Whether a 100 RPM 5kg/cm torque 12V DC motor is any different from a 100 RPM 5kg/cm torque 24V DC motor. If I give 24V to a 12V motor, then would it be a problem, or would it not accommodate 24V and finally perform as it would have performed on a 12V power supply? Or would a 12V motor perform better on 24V than it does on 12V?

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  • \$\begingroup\$ At the most fundamental level, is the difference the gauge and length of wire used to wind the armature? So wouldn't the 24 volt motor use larger-gauge wire with the ability to carry more current (and thus a lower resistance)? Or have i got it back to front? \$\endgroup\$ – Ryan Griggs Feb 6 '14 at 22:05
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    \$\begingroup\$ Back to front. For the same power if voltage goes up then current goes down. P = V * I. \$\endgroup\$ – Transistor Nov 18 '15 at 23:45
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On their respective power supplies both motors should perform identically but the 12V motor would draw twice as much current from its 12V supply compared to the 24V motor on a 24V supply.

In other words power supplied to both motors should be quite similar for a given mechanical load. Mechanical load power is defined as \$2\pi n T\$ where n is speed in revs per second and T is torque is newton-metres. And if the 12V motor took 4 Amps to supply a certain mechanical power output then the 24V motor would take 2A to perform identically.

DC motors of the simple type (trying not to generalize here) will rotate at full speed on no-load and this speed is mainly determined by the applied voltage. Putting 24V on a 12V motor may wreck it. Conversely, on heavy loads, the speed normally reduces fairly linearly with torque but on a 24V supply there may be enough potential for the motor to fry due to it being able to supply more torque and speed. Don't do it is my advice.

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  • \$\begingroup\$ Thank you! I was restricted to a 12v 2aH power supply. I wanted to fit a boost converter into the 12v motor's case. This will step up the current before it reaches the terminals of the motor. So if I put a boost converter to a 12v motor that gives 5kg/cm torque and step it up to 24v, according to you, the motor would most probably blast? Am I right? \$\endgroup\$ – Ishpreet Feb 6 '14 at 14:35
  • \$\begingroup\$ You could probably take it up to 14V for medium periods of time but the 12V rating is what the manufacturer recommends and if you need more torque you probably be best to look for a different motor and power supply. \$\endgroup\$ – Andy aka Feb 6 '14 at 15:19
  • \$\begingroup\$ If we use the same logic, then would it be possible to get same motor characteristics (eg : torque) but using a 1V motor taking 48A ? where is the limit? \$\endgroup\$ – tigrou Feb 6 '14 at 21:15
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    \$\begingroup\$ @tigrou: you are correct, and this is fine in the world of spherical cows on frictionless ramps. In the real world, resistive losses will dominate. \$\endgroup\$ – Bryan Boettcher Feb 6 '14 at 22:22
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If i give 24v to a 12v motor, then would it be a problem

Yes, there will very likely be smoke and possibly fire.

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Your solution may be gearing and not power, because adding more power to or potential to your motor will not end well. Volts is a measurement of potential difference if the engineers and manufacture intended to make your motor a 24 volts they would have changed the design and materials. Amps are the amount of flow so adding more flow is not going to help it perform.

Think of your car or truck, you have a 4 cylinder motor and a transmission. Your transmission helps give your car more or less torque depending on how fast wheels are turning or you are trying to accelerate. If you were able to add a fuel pump that is double of your 4 cylinder, you are not going to make an 8 cylinder motor, the motor may not be able to even hold all the gasoline and you have a big fire on your hands. Because your 4 cylinder motor can only hold so much gas and burn so much safely no matter the amount you try to add to it.

If you are restricted to a 12 volt 2amp motor, look for a gear box that make be able to work with your requirements. You may have to redesign your device so a lower motor will work.

Hope this helps.

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Amongst the hazards of over-volting a permanent magnet motor are

a) overspeed - will only 2x overspeed burst the armature? Probably not, but the centripetal force is 4x rated, so it is possible.

b) excess current taken at standstill - the heating effect of this is the least of your worries. Most PM motors are designed so the magnetic field the armature generates when supplied with rated voltage and stationary, that is the conditions you'd get starting at full volts from standstill, will not be sufficient to demagnetise the field magnets. The margin for error is not large, double the rated standstill current may be enough to demagnetise, and therefore ruin, your motor.

As a robot builder, I often overvolted my 24v motors to 36v for a bit of extra speed, and used a current limited controller which was set to not exceed the rated standstill current.

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One important point - most often, higher voltage is given to the motor to get higher torque. Torque of a DC motor is dependent on the voltage. Motor being inductive load, the current rise is not as soon as the voltage is applied by gradually builds-up (in milsec).However, important point is to make sure that there is proper circuit to monitor the current and cut it off when it reaches the threshold. Most dot-matrix printer stepper motor circuit used to provide 24V to 12V Stepper motor - but nothing happens as the design takes care of the current limiting. However, when the transistor / circuit that is used to limit the current short-circuits for whatever reason, the entire PCB get sort of burnt.

If you are a beginner, better to stay with 12V for 12V DC motor and not fry the circuit.

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