How to select the right DC Power Supply for DC Motors?
Motors, solenoids and relay controls require higher levels of current during start-up than they do for continuous operation.Mechanical failures such as motor stalls or due friction can increase the current draw dramatically. When designing or installing a DC motor supply, many factors need to be considered such as back up, loading, speed variation, regenerative current and others. 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: High currents drawn above the motor rating can cause motor seizures, overloads and motor failures causing heating and not rotating
- Constant Current limit: Has the ability to provide full current should any anomalies arise if for example any overloads occur. This enables the motor to still start because this type of power supply has the capability to provide full current in these types of conditions.
- 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 rotate. Electricity is transferred to the rotating 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 to the motor. (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 a fixed armature.
Although this option can be more expensive, providing higher reliability in the long term having no brushes or commutator wear plus enabling position control to be 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. 
 Posted by Power Guy http://power-topics.blogspot.com/
Variable Speed – DC Motors
Changing the voltage applied to the armature of the motor is one of the ways to better control the DC Motor’s speed. We suggest for a specific application to use a power supply with a programmable output voltage.As every application is different and there are many factors to be considered that can or might affect the final design. Contact Our Team of engineers if you require more information about how to power and backup your DC Motor.