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# How to stop a motor in this circuit?

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#### unleashed

##### Newbie level 4
hi there.

i have a project..and i have to ask something about how to stop the motor

let consider we have a motor (dc) .producing temperature..and a thermistor (ntc) is there...if the temperature is increased another motor(fan) is running to cool the system...
my aim is how to stop the running(dc motor ..first one..that produces temperature)
automatically means that fan is in working conditon and the same time the first motor stops..

Re: HOW TO STOP A MOTOR

You can switch the first motor from the power source to a resistor which dissipates the back EMF energy of the motor.

Another way is to use a PWM speed control system and slowly narrow the duty factor.

Re: HOW TO STOP A MOTOR

Is there any time you will need to run the motor(m1) while the other motor(m2) is running...

Re: HOW TO STOP A MOTOR

What is the load of your main motor m1? Depending on the load features, you will decide the proper means to stop the motor, there is not universal way for all cases.

Re: HOW TO STOP A MOTOR

well the simplest ways is that get a zener diode of the voltage which would be equivalent to the output of the thermistor at temperature at which you want to stop that motor then connect the cathode of the zener to the output of thermistor and the anode to a base of NPN the collector has to be connected to the vcc of the dc and the emitter have to be at ground...
now what happends is that when the specified temperature is approached then the zener will start opearting and switch the NPN on and the entire vcc will go towards the ground and will make the dc motor off...

Best Regards

Re: HOW TO STOP A MOTOR

Do you know some small fan like the one we use for cooling the cpu in computer graphics card? it has 3 cable instead of two. the fan has a temperature sensor in it, once it gets hot it will turn on the fan. to turn off the first motor you just have to sense if the fan is on, then turn off the motor. i hope this will help, i do not know the size of cooling you need.

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