Efficiency of an electric motor

In summary, the conversation discusses the relationship between efficiency and load in an electric motor, as well as different equations and factors that affect power input and output. The formula for work input and output does not directly relate to efficiency, and efficiency can vary depending on the load and other factors. The conversation also touches on the use of power instead of work in calculating efficiency.
  • #1
JayCAquino#4
7
0
The motor runs on dc current. I understand efficiency is useful work/work input. It is attached to the pulley. I think efficiency will remain constant as long as voltage of mains and vertical height remain constant. Am I wrong? Other people claim efficiency increases with load
 
Physics news on Phys.org
  • #2
Usually, efficiency increases with load in an electric motor. Many motor manufacturers will provide spec sheets showing the efficiency vs load.
 
  • #3
Using the formula useful work/total work input. I use mg(delta)h/ivt and this suggests efficiency is constant because when mass increases so does time. But how come when you take into account torque efficiency increases with load?
 
  • #4
The formula for work input doesn't tell you anything about efficiency. Work input and output are mostly independent of each other, being driven by different factors.
 
  • #5
russ_watters said:
The formula for work input doesn't tell you anything about efficiency. Work input and output are mostly independent of each other, being driven by different factors.
Oh okay so I should use power instead of work. Thanks for the help. Much appreciated
 
  • #6
Right: work input is a combination of mechanical and electrical inefficiencies, which are functions of different things.
 
  • #7
JayCAquino#4 said:
Other people claim efficiency increases with load
What is efficiency when the load is zero? I.e. the motor is spinning freely at it's no load rpm? What about when the load is very large and the motor is stalled so not rotating?
 
  • #8
russ_watters said:
Right: work input is a combination of mechanical and electrical inefficiencies, which are functions of different things.

What equation do I use to calculate my power input if the motor is connected to a shaft which is lifting a load off the ground. I know the rpm and the radius I just don't know how to put it all together
 
  • #9
billy_joule said:
What is efficiency when the load is zero? I.e. the motor is spinning freely at it's no load rpm? What about when the load is very large and the motor is stalled so not rotating?
I don't know how to use rpm to calculate power
 
  • #10
JayCAquino#4 said:
What equation do I use to calculate my power input if the motor is connected to a shaft which is lifting a load off the ground. I know the rpm and the radius I just don't know how to put it all together

P = IV (electrical power)
P = Fv (mechanical power)

Efficiency:
η = P out / P in
JayCAquino#4 said:
I don't know how to use rpm to calculate power

It's P = Tω

My questions were somewhat rhetorical. The answer to both is 0% as there is no work being done so output power is 0 W.
 
  • Like
Likes jim hardy

Related to Efficiency of an electric motor

1. How is efficiency of an electric motor measured?

The efficiency of an electric motor is typically measured by dividing the output power (measured in watts) by the input power (measured in watts). This calculation results in a percentage, which represents the efficiency of the motor.

2. What factors affect the efficiency of an electric motor?

Several factors can affect the efficiency of an electric motor, including the design of the motor, the type of motor (such as AC or DC), the quality of the electrical components, and the operating conditions (such as temperature and load).

3. How can the efficiency of an electric motor be improved?

The efficiency of an electric motor can be improved by using high-quality materials, reducing friction and resistance within the motor, and optimizing the design for maximum performance. Regular maintenance and proper use can also help maintain and potentially improve the efficiency of a motor.

4. What is the average efficiency of an electric motor?

The average efficiency of an electric motor can vary depending on the type and design of the motor. However, most modern electric motors have an efficiency ranging from 75-95%, with some specialized motors reaching efficiencies as high as 98-99%.

5. How does the efficiency of an electric motor impact energy usage?

The higher the efficiency of an electric motor, the less energy it will consume to perform its intended function. This means that a more efficient motor will result in lower energy costs and potentially reduce overall energy usage in a given system.

Similar threads

I Electric motor with increased load
    • Electromagnetism
Replies
2
Views
738
Efficiency of a small electrical motor
    • Mechanical Engineering
Replies
8
Views
1K
Gravity Based Electricity Generator
    • Electrical Engineering
3
Replies
74
Views
1K
Calculating Motor Load Capacity for a 4kg Vehicle
    • Engineering and Comp Sci Homework Help
Replies
2
Views
1K
How to make an Electrical Diagram with added Steinmetz Circuit for a Delta 3 phase motor?
    • Electrical Engineering
Replies
0
Views
294
Engineering DC Shunt Motor: calculation of the efficiency
    • Engineering and Comp Sci Homework Help
Replies
4
Views
5K
Regenerating electricity on an e-bike
    • Electromagnetism
Replies
15
Views
1K
How can the output power of a motor be controlled using an inverter?
    • Electrical Engineering
Replies
6
Views
1K
Good energy efficient motor to use with 12 volt battery?
    • Electromagnetism
Replies
4
Views
2K
Sizing an Isolation Transformer for a DC Power Supply
    • Electrical Engineering
Replies
8
Views
1K

Hot Threads

Recent Insights

Back
Top