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DC Motor Protector - Voltage and Heat Protection

In this post we discuss a DC motor protector circuit from harmful over voltage and under voltage situations.

DC motor failures are commonly experienced by many of the users, especially in places where the relevant motor is run for many hours a day. Replacing motor parts or the motor itself after a failure can be pretty costly affair, something which nobody appreciates.

A request from one of my followers was made to me regarding solving the above issue, let's hear it from Mr.Gbenga Oyebanji, alias Big Joe.

Technical Specifications

"Seeing the harm our power supply has done to most of our electrical appliances, it is necessary to construct a protection module for our appliances that protects them against the fluctuations in power.

The objective of the project is to design and construct a protection module for DC motors. Therefore the aims of the project are

•    Design and construct an over voltage protection module for DC motors with indicator (LED).
•    Design and construct an under voltage protection module for DC motors with indicator (LED).
•    Design and construct a temperature protection module for the motor  (Thermistor) with indicator (LED).

The circuit protects the DC motor from over voltage and under voltage. A relay could be used for switching the load (12v dc motor) on and off. A comparator is used to detect if it’s either high or low. The over voltage should be 14V while the under voltage should be 10V.
The necessary rectification and filtering circuit should be constructed also. When any of the fault is detected the necessary indications should come up.
In addition when the field winding of the motor is open the circuit should be able to detect this and shut the motor down because when the field winding is open there is no longer magnetic flux within the motor and all the power is fed directly to the armature. This make the motor run until it breaks down. (I hope am right?). I would be grateful to get your response soon.

Thanks Swagatam. Cheers"

DC Motor Voltage Protection Module Circuit Diagram

The following high and a low voltage cut off which was earlier discussed by me in one of my posts, perfectly suits the above application for protecting DC motors from high and low voltage conditions.

voltage protection circuit for motors

The entire circuit explanation is provided over/under cut-off voltage circuit

DC Motor Over Heat Protection Module Circuit

The third problem involving temperature rise of the motor can be solved by integrating the following simple temperature indicator circuit.
This circuit was also covered in one of my earlier posts.

over heat thermal protection for motor with a simple circuit

The above over heat protector circuit will presumably never allow the field winding to fail, because any winding will heat up first before fusing. The above circuit will switch OFF the motor if it senses any abnormal heating up of the unit and thus avoid any such mishap.

The entire parts list and circuit explanation is provided HERE

Need Help? Please leave a comment, I'll get back soon with a reply!


  1. If we can use more then 12v. To conduct this test
    Like 220 v dc

  2. i did not understand your question.


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