How to select the right DC Power Supply for DC Motors?
Motors, solenoids and relay controls require higher levels of current on start up than they do for continuous operation.Mechanical failures such as motor stalls or sticky can increase the current draw dramatically. When designing or installing a DC motor supply, many factors such as back up, loading, speed variation, regenerative current and others should be considered. At Helios, we recommend that when selecting a power supply for your DC Motor, you should be aware at least of the following aspects:
- Maximum Current required: Amount of current the motor draws at stall, in this condition the motor draws maximum current, but the motor does not rotate.
- Constant Current limit: Not one that goes into hiccup mode this means that,should an overload occur, the output current stays at its limit point, and the output voltage reduces towards zero. Typically, the supply will automatically return to its normal output voltage when the overload condition is no longer present.ie when the motor is running normally.
- Output diode required: To prevent the power supply being damaged by reverse voltage spikes which occur when the supply is turned off and the motor is slowing down.
To illustrate, here are examples for brushed dc motor and a brushless dc motor
Brushed DC motors
With this type of motor, the magnets are stationary and the coil spins. Electricity is transferred to the spinning coil by the use of “brushes”. The advantages of this type of motor are low initial cost and easy speed control.
When the power is interrupted, the motor coil will act like an inductor and will try to continue to produce current, effectively becoming an inverted voltage source. This will apply a reverse polarity to the power supply and can cause damage. (Back EMF – Electro-Magnetic Flux)
By using a diode, as shown below, the diode provides a current path for the reverse motor current and will clamp the reverse voltage to a level no greater than the forward voltage drop of the diode. This protects the power supply’s output capacitors and other components from being stressed by the reverse voltage.
Brushless DC motors
Brushless DC motors, often referred to as BDCMs or BLDC motors, have permanent magnets that rotate and the armature is fixed.
Although more expensive, they are more reliable in the long term as there is no brush or commutator wear and position control is more accurate.
When the motor is turned off or reversed, it will act as a generator and produce a high voltage spike. This spike can cause the power supply’s overvoltage protection to trip, shutting down the unit.
By using a diode in series with the output, as shown below, the spike will be blocked from interfering with the power supply. 
Variable Speed – DC Motors
Changing the voltage applied to the armature of the motor is one of the ways of control DC Motor’s speed. We suggest for that specific application to use a power supply with a promogramable output voltage but as every application is different and many factors might affect the final design, contact Our Team of engineers if you require more information about how to power and backup your DC Motor.