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Change Direction of 12v DC Motor Rotation Using Relay

Abusair Agriculture Machinery

2021-09-23

![reversing a dc motor]This is a minimal reversing circuit for a dc motor. It is missing a stop button, start, and interlocks, and it can all be added to it. It does not start on it's own, one limit switch has to be pushed. The circuit has a dc motor, 2 relays, and 2 limit switches. The interlocks are important, because if the 2 relays are energized at the same time, it is a short circuit. As drawn, the whole circuit is on a same voltage (relay coils would be same voltage as the motor). The bottom part can be separated, and then the motor can be a different voltage than the relay coils. Normally a circuit like this also uses additional overtravel limit switches, in case the two fail.

1. VARIAC as DC motor speed controller from DC power source

I have consulted with my professors and they do not believe it would work.Professors are very, very clever people*. If they say it is not possible I would drop it. In fact I also believe it is not possible. Variacs are transformers and transformers are relying on inductance. That is : they need a continuous changing current. With DC you only get the resistance of the copper wire which is very low. Maybe your Chinese friend is using the Variac as a giant potentiometer. You do not want that as it will heat up!*Which also occasionally make errors

2. DC motor makes noise but does not rotate

analogWrite uses PWM. Is the motor you are using designed for pulsed operation? Try using

3. In starting a separately excited DC motor using initial resistors, what will happen if the field circuit is broken while the motor is running?

It depends on the loading of the motor. If it is unloaded or lightly loaded, the RPM is inversely proportional to the field current. Reducing the filed current increases the RPM. If the field current drops to zero, the maximum RPM theoretically goes to infinity. This is undesirable, because the rotor can fly apart at some high speed. A DC motor starter needs to have a mechanism to sense loss of field current and immediately cut power to the armature.In starting a separately excited DC motor using initial resistors, what will happen if the field circuit is broken while the motor is running?.

4. How can I develop a program to control the speed of a DC motor?

I will write the answer in brief.So the simplest way is to reduce the voltage supply, but that reduces the torque of the motor as well. But if you want to reduce just the speed at constant torque then use a motor driver, usually a dual H bridge or a H bridge IC (L293D or L298 ). So you can reffer to the datasheets of the IC's to know how and at what time delays to control it to achieve you r=desired speed reduction. And in the case of stepper motor you can just control the step angle wise rotation to get your speed control.You can also give the control inputs using a joystick/knob or a potentiometer etc at proportionate or PI or PD control to it . This increases the scope of your controls and precision can be decided by you. thanks for the A2A.

5. How do I control a DC motor using a switch in 8051 mc? What is the code for it in keil?

So the basic diagram for the above mentioned question can be drawn as follow:So the control switch is connected to P1.0 and the output of microcontroller is taken from P2.0 and P2.1. The IC ILQ74 is the optoisolator use to insolate the power circuit from the control circuit. And the IC L293D is the special functioning IC which helps in controlling the direction of rotation of the DC motor.#include#includesbit input1= P2^0;sbit input2= P2^1;sbit en= P2^2;sbit SW= P1^0;void main() SW=1; // declare as input// input1=0; // declare as output// input2=0; // declare as output// en=0; // declare as output// while(1) if(SW==1) en=1; input1=1; // for clockwise input2=0; // else en=1; input1=0; // for anticlockwise input2=1; // So you can implement this code in keil and check the output on porteus. The first statement in the if is for the clockwise rotation of motor and the later in the else is for anticlockwise rotation. Hope this will help you. What is the code for it in keil?

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