Power in / power out for electric motor

In summary, electric motors are more efficient than internal combustion engines. It is not possible to use a smaller IC engine and generator to produce the same amount of power as a larger IC engine, but more efficiently. The advantage of using electric motors for propulsion on trains and large ships is the consistency of power delivery and the lack of need for a transmission. Additionally, electric motors do not suffer as much harm from sudden changes in load. Electric propulsion also allows for a flatter torque curve, making it more suitable for trains that take longer to reach their maximum speed. It is possible that diesel-electric drive may become more prevalent in off-highway construction equipment in the future.
  • #1
frogman
23
0
electric motors a far more efficeint than internal combustion. My question, could I not use a smaller IC engine & generator to power an electric motor and make the same amount of power as a larger IC engine. but a little more efficeintly.
 
Engineering news on Phys.org
  • #2
No. If you think about every stage of the process, you'll find losses that defeat the purpose.
 
  • #3
ok i'll buy that.

the reason for my question. They run electric motors on trains and lagre ships for propulsion. what is the advantage for them? they still produce the electricity by deisel or jet engine.
 
  • #4
It's primarily for the consistency of the power delivery from electric propulsion. It would be very difficult to shift gears on a train or ship, and electrics don't need a transmission. I'm not actually familiar with electric ships that much, though, except for submarines. I thought that most still use constant-geared Diesels.
 
  • #5
Very large internal combustion engines are most efficient when run at or close to a constant speed. By using the engine as a generator, they can run it at constant sped and instead add/remove fuel as needed based on the load placed on it.
 
  • #6
Also, electric motors don't suffer nearly as much harm if the load suddenly veries. The only ships I know of that use motors powered by an ICE are ice-cutters, and that is exeactly the reason. If a big chunk o fice suddenly stops the props, the electric motor will not experience the vibrational forces of impact that a mechanically-linked ICE would.
 
  • #7
frogman said:
electric motors a far more efficeint than internal combustion. My question, could I not use a smaller IC engine & generator to power an electric motor and make the same amount of power as a larger IC engine. but a little more efficeintly.
If the efficiency is a fixed-fraction of the capacity, you always lose the same fraction to inefficiency.
Example:
Gas motor: 35% efficiency
Generator: 95% efficiency
Electric motor: 95% efficiency

Input: 1 kW
Output: 1*.35*.95*.95=316W

Input: .5 kW
Output: .5*.35*.95*.95=158W

They run electric motors on trains and lagre ships for propulsion. what is the advantage for them? they still produce the electricity by deisel or jet engine.
In addition to what has already been said, the torque curve of an electric motor is pretty flat, but an ICE needs a certain rpm to run at all. So for for a train, which can take minutes to get up to speed, trying to use a clutch and gears to get it moving can be a nightmare. I actually wonder why they don't use diesel-electric for trucks, which have something like 18 gears.
 
Last edited:
  • #8
russ_watters said:
I actually wonder why they don't use diesel-electric for trucks, which have something like 18 gears.

You'll start to see diesel-electric drive for off-highway construction equipment (bulldozers) next year.
 

1. What is the difference between power in and power out for an electric motor?

Power in refers to the amount of electrical energy that is supplied to the motor, while power out refers to the amount of mechanical energy that is produced by the motor. In other words, power in is the electrical input and power out is the mechanical output.

2. How is power in calculated for an electric motor?

Power in can be calculated by multiplying the voltage and current supplied to the motor. This is known as the electrical power or wattage and is measured in watts (W).

3. How is power out measured for an electric motor?

Power out can be measured using a dynamometer, which is a device that measures the torque and rotational speed of the motor. The power out can then be calculated using the formula: Power out = (Torque x Rotational Speed) / 9.55. This will give the power output in units of horsepower (hp).

4. How does the efficiency of an electric motor affect power in and power out?

The efficiency of an electric motor is the ratio of power out to power in, expressed as a percentage. A more efficient motor will have a higher power out for the same amount of power in. This means that a higher percentage of the electrical energy is being converted into mechanical energy, resulting in a more powerful motor.

5. Can the power in and power out of an electric motor be increased?

Yes, the power in and power out of an electric motor can be increased by increasing the voltage or current supplied to the motor. This will result in a higher power input and therefore a higher power output. However, it is important to ensure that the motor is able to handle the increased power without overheating or damaging the motor.

Similar threads

Replies
3
Views
1K
Replies
3
Views
6K
  • General Engineering
4
Replies
139
Views
25K
Replies
8
Views
2K
  • General Engineering
3
Replies
72
Views
8K
Replies
6
Views
2K
  • General Engineering
Replies
32
Views
2K
  • Electrical Engineering
Replies
6
Views
778
  • General Engineering
Replies
5
Views
3K
  • Electrical Engineering
Replies
7
Views
191
Back
Top