Using resistor and DC motor acting as generator as a brake

In summary, to calculate the resistance required for a resistor in series with a generator (DC motor in reverse) to achieve a certain torque, you need to consider the amount of work being done in running the generator circuit. This is a similar mechanism to that used in electric diesel locomotives for rheostatic braking. Additionally, it is important to ensure that the motor is suitable for use as a generator. Converting RPM to angular velocity and ensuring the torque is in the correct units is also necessary for accurate power calculations.
  • #1
Ry122
565
2
how would you calculate the resistance required for a resistor which is in series with a generator (DC motor in reverse) to achieve a certain torque from the generator?
Eg, there's a torque of 30kN acting on a 100kW generator while it moves at 50RPM.
The is the same mechanism as electric diesel locomotives use to brake that employ rheostatic braking.
 
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  • #2
You have to ask yourself how much work is being done to run the generator circuit.
 
  • #3
Ry122 said:
how would you calculate the resistance required for a resistor which is in series with a generator (DC motor in reverse) to achieve a certain torque from the generator?
Eg, there's a torque of 30kN acting on a 100kW generator while it moves at 50RPM.
The is the same mechanism as electric diesel locomotives use to brake that employ rheostatic braking.

If this is a real, practical problem then the motor would need to be a suitable one. Many motors will not work as generators, particularly not high power motors, with field windings.
Your suggested 100kW generator is quite a meaty piece of kit.

Note. If you want to calculate power (in Watts), as Simon B suggests, you will need to convert your RPM to angular velocity (and get your Torque in the right units, too - do you mean kNm?)
 

1. How does using a resistor and DC motor as a brake work?

When a DC motor is acting as a generator, it produces a back EMF (electromotive force) that opposes the current flow. This back EMF is directly proportional to the rotational speed of the motor. When a resistor is connected to the motor, it creates a circuit that allows the current to flow through the resistor, effectively slowing down the rotational speed of the motor. This process of converting kinetic energy into electrical energy through the back EMF is what allows the resistor and DC motor to act as a brake.

2. What are the benefits of using a resistor and DC motor as a brake?

Using a resistor and DC motor as a brake is a cost-effective and efficient way to slow down or stop the rotation of a motor. It does not require any additional mechanical parts and can be easily controlled by adjusting the resistance of the resistor. This method also generates electrical energy that can be used for other purposes, making it a more sustainable option.

3. Can any DC motor be used as a generator for braking?

Yes, any DC motor can be used as a generator for braking as long as it is connected to a circuit with a resistor. However, the efficiency of the braking will depend on the specifications of the motor, such as its voltage rating and maximum rotational speed.

4. Is there a limit to how much energy can be generated using a resistor and DC motor as a brake?

Yes, there is a limit to how much energy can be generated using this method as it is dependent on the motor's specifications and the resistance of the connected resistor. If the resistance is too high, it can cause the motor to stall and not generate any energy. It is important to carefully choose the resistance to ensure optimal braking and energy generation.

5. Are there any safety considerations when using a resistor and DC motor as a brake?

Yes, there are a few safety considerations to keep in mind when using this method. Firstly, the generated voltage can be high, so it is important to use appropriate safety measures, such as insulating gloves, when handling the circuit. Secondly, the resistor can become hot during braking, so it is important to use a resistor with a high enough power rating to prevent overheating. Lastly, it is important to have proper circuit protection, such as fuses, in case of any unexpected failures.

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