# DC Motor Field Current Speed Control

• OvaR8ed
In summary, a user is asking for advice on using a 12V, 0.6A, 180RPM, 3kg.cm, 66% efficiency geared DC motor with a 12V 1A DC power supply in a field current control circuit. They ask for theoretical resistance values for R1 and the potentiometer, as well as the wattage rating for the resistor and POT to handle the currents correctly. Another user suggests using a 555 pulse width modulation circuit instead of a potentiometer, as well as using switches instead of transistors for high amps. They also point out that the circuit in the attached diagram is not suitable as it would only add more load to the power supply.
OvaR8ed
I have a Geared DC Motor rated 12V, 0.6A, 180RPM, 3kg.cm, 66% Efficiency. I measured the impedance of the disconnected motor at 45 Ohm.

I want to use it with a with a simple 12V 1A DC Power Supply in a Field Current Control Circuit to be able to dial in variable speeds.

Will the circuit in the attached diagram work?

What are good Theoretical Resistance values to start with for R1 and the Potentiometer to give me a wide range of speeds with no load on the motor?

For which Wattage should the Resistor and POT be rated to deal with the currents correctly?

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That circuit won't do anything. The resistors are simply another load on the 12 volt supply.

Yeah, I realized that. It could work if you limit your current at the power source, but that will over complicate things.

I'm rather going with a simple 555 Pulse Width Modulation circuit...

first of all yes for high amps a pot will be a waste of enrgy you have to use switches like transistors, the other thing the device needs to be in series with the motor , you circuit as you probably realized by now is in parallel with the motor so the motor would still go full speed.

I cannot provide a definitive answer without further information and testing. However, I can offer some suggestions and considerations.

Firstly, the circuit in the attached diagram appears to be a simple voltage divider. This may work for basic speed control, but it may not provide precise or stable control. Additionally, the use of a 12V 1A power supply may not be sufficient for the motor's rated 0.6A current. It may be better to use a power supply with a higher current rating, closer to the motor's requirements.

As for the theoretical resistance values for R1 and the potentiometer, it would depend on the motor's characteristics and the desired range of speeds. It would be best to consult the motor's datasheet or conduct experiments to determine the appropriate values.

In terms of wattage, the resistor and potentiometer should be rated to handle the maximum current that will flow through them. In this case, it would be best to use components with a wattage rating higher than 1W.

Overall, it is important to carefully consider the components and design of the circuit to ensure safe and effective speed control for the motor.

## 1. What is DC motor field current speed control?

DC motor field current speed control is a method of regulating the speed of a DC motor by adjusting the amount of current in its field winding. This allows the motor to maintain a constant speed, even under varying load conditions.

## 2. How does DC motor field current speed control work?

The speed of a DC motor is directly proportional to the strength of the magnetic field created by its field winding. By adjusting the current in the field winding, the strength of the magnetic field can be controlled, which in turn controls the speed of the motor.

## 3. What are the advantages of DC motor field current speed control?

DC motor field current speed control offers several advantages, including precise speed control, constant speed under varying loads, and the ability to reverse the direction of the motor's rotation.

## 4. How is the field current of a DC motor controlled?

The field current of a DC motor can be controlled using a variable resistor, also known as a rheostat, or by using electronic circuits such as a pulse width modulation (PWM) controller. These methods allow for precise and efficient control of the field current.

## 5. What are some applications of DC motor field current speed control?

DC motor field current speed control is commonly used in industrial applications, such as conveyor systems, cranes, and machine tools. It is also used in household appliances, such as washing machines and electric fans, to control the speed of motors.

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