Force necessary to spin an alternator at the rated RPM?

Click For Summary

Discussion Overview

The discussion revolves around determining the force necessary to spin an alternator at its rated RPM, focusing on theoretical calculations, practical considerations, and specific examples related to alternators used in generators.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that the force required to spin an alternator depends on specific properties of the alternator, including internal friction and the time taken to reach the rated RPM.
  • Others note that the electrical load on the alternator also influences the force necessary to achieve the rated RPM.
  • One participant proposes a hypothetical scenario involving a 6000 watt generator head and questions whether it is possible to determine the necessary force without knowing specific details like mass and friction.
  • Another participant mentions that approximately 5 horsepower is needed for a 100 amp alternator.
  • A technical explanation is provided regarding the relationship between torque, angular speed, and power output, including a formula for calculating torque based on power and RPM.
  • One participant warns that real-world alternators typically operate at about 40% efficiency, indicating a discrepancy between calculated horsepower and the actual horsepower required to turn the alternator.

Areas of Agreement / Disagreement

Participants express differing views on the factors influencing the force necessary to spin an alternator, with no consensus reached on a definitive method or calculation. The discussion remains unresolved regarding the specific force requirements under varying conditions.

Contextual Notes

Limitations include the lack of specific details about the alternator's properties, such as mass and friction, which are necessary for accurate calculations. The discussion also highlights the dependence on efficiency ratings, which can significantly affect the required horsepower.

eli_lied
Messages
12
Reaction score
0
Can anyone tell me how to determine the force necessary to spin an alternator at the rated RPM?
 
Physics news on Phys.org


eli_lied said:
Can anyone tell me how to determine the force necessary to spin an alternator at the rated RPM?
No, because that depends upon properties of the specific alternator. In particular, the friction in the alternator itself and the time in which it is brought up to that RPM.
 


ok hypotheically then, let's say it's a 6000 watt generator head taken from a portable home backup generator. if i have 6400lbs-ft of constant force and the generator head operates at either 3600 rpm or 1800 rpm...without knowing the specific details such as mass(approx. 60-80lbs of rotational parts) or friction, is it possible to determine the force necessary? also does anyone know of a website that offers detailed information on alternators and/or suppliers that I could purchase one from?
 


about 5 horsepower for 100 amp alternator
 

Attachments

  • img304.gif
    img304.gif
    4.3 KB · Views: 757


Torque (Newton-meters) in angular rotation is the equivalent to force (Newtons) in linear motion. For an alternator, the power output (watts) is the product of the angular force times the angular speed. Specifically

T x 2 pi RPM/60 = W watts, where the torque T is in Newton-meters.

So for a 6000 watt alternator output (at 100% efficiency) at 3600 RPM, the torque is

T = 60 W/ 2 pi RPM = 15.9 Newton-meters.

6000 watts (at 100% efficiency) is equal to 8.04 HP

Bob S
 


be advised that in the real world alternators are 40% efficient which is why there is a difference between calculated HP and actual parasitic HP required to turn the Alt.
 

Similar threads

High School Centrifugal force spinning Basketball
  • · Replies 1 ·
Replies
1
Views
1K
Undergrad Changing the RPM of a frictionless spinning wheel in a box
  • · Replies 4 ·
Replies
4
Views
1K
Undergrad G-force centrifuge mounted on opposite rotating platform
  • · Replies 4 ·
Replies
4
Views
1K
Undergrad Reaction moment on I.C. engine when we increase RPM
  • · Replies 26 ·
Replies
26
Views
2K
Graduate How fast will two spinning weighted wheels propel a 7 lb cylinder?
  • · Replies 19 ·
Replies
19
Views
4K
High School The physics of flywheel launchers (like tennis ball shooters)
  • · Replies 60 ·
3
Replies
60
Views
6K
Undergrad Energy Transfer Between Inertia Wheels
  • · Replies 2 ·
Replies
2
Views
2K
High School Good equation for calculating RPM of a wheel?
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad Wondering how much thrust a drone propeller generates
  • · Replies 6 ·
Replies
6
Views
5K
Undergrad How will the final output here behave?
  • · Replies 3 ·
Replies
3
Views
1K