HP or PWOER Loss between 2 different sized Pulleys?

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Discussion Overview

The discussion revolves around the power loss or horsepower (Hp) loss when using two different sized pulleys, specifically an 8" driver pulley and a 10" driven pulley, driven by a 2Hp motor. Participants explore the implications of pulley size on power, torque, and load capacity, with a focus on real-world applications and calculations.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Exploratory

Main Points Raised

  • Some participants suggest that in an ideal scenario, there is no power loss, while others emphasize that real-world conditions introduce some percentage of loss.
  • One participant proposes that a larger pulley might result in a 25% decrease in horsepower, but this is contested by others who argue that power remains constant while torque and RPM change.
  • It is noted that power losses are primarily due to factors like bearing friction and belt interactions, rather than pulley size alone.
  • Participants express a desire to quantify the power loss, indicating that it depends on various factors beyond just pulley size, including the type of bearings and belts used.
  • There is a discussion about whether a 10" pulley can drive a 2Hp load effectively, with some suggesting that the output could be less than 2Hp in practical scenarios, while others caution that exact calculations are not possible and only estimates can be made.
  • One participant acknowledges the significance of power loss, while another clarifies that trading torque for RPM does not necessarily indicate a loss of power.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the extent of power loss or the implications of pulley size on horsepower. Multiple competing views remain regarding the significance of losses and the factors influencing them.

Contextual Notes

The discussion highlights limitations in calculating power loss accurately, as it depends on various factors such as the configuration of the system, the type of bearings, and the belt or cable used. There is also ambiguity regarding the definitions of power loss versus torque and RPM trade-offs.

trillionex
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hello guys..!
i have one pulley of 8" (Driver) and another one 10" (Driven) he driver pulley is driven by 2Hp motor, so is there any equation or formula to calculate the Hp loss or power loss from 2Hp?
 
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In the ideal case, there is no power loss. For a real situation, you'd need to know more to be able to figure out what the power loss was.
 
so if 10' pulley is kept on load then it would get 25% less Hp then the input Hp at 8"pulley as it is 25% bigger in size?
 
Pulley size will affect torque and rate of rotation (trading one for the other), but will have little effect on power. Power losses are due to losses in the pulley bearings and friction with the belt.
 
trillionex said:
so if 10' pulley is kept on load then it would get 25% less Hp then the input Hp at 8"pulley as it is 25% bigger in size?

Nope. The power would be the same, but the torque and rpm would change.
 
As said, ideally the power loss is zero regardless of the pulley size. Realistically, it is a few percent, depending on the configuration.
 
Yaa russ the change is few percent but i wana calculate that few percent..
 
Then you need to know more than just the size difference. That will depend on the bearings and belt or cable used.
 
Ok so suppose if 8" pulley is driven by 2 hp and 10" pulley has to also drive 2hp load then would 10" pulley will be able to drive that load with full 2hp or 1.75hp or 1.5hp?
 
  • #10
trillionex said:
Ok so suppose if 8" pulley is driven by 2 hp and 10" pulley has to also drive 2hp load then would 10" pulley will be able to drive that load with full 2hp or 1.75hp or 1.5hp?
You're not understanding: it could literally be anything below 2 hp in a real-world situation and it can't be calculated exactly, only estimated. If you have a real-world application and you need to know so you can select a motor, use 10% to be safe...and then increase the motor size by another 20% to be safer.
 
  • #11
russ_watters said:
You're not understanding: it could literally be anything below 2 hp in a real-world situation and it can't be calculated exactly, only estimated. If you have a real-world application and you need to know so you can select a motor, use 10% to be safe...and then increase the motor size by another 20% to be safer.

ok got it...i just needed to confirm that loss does occur and that also quite significant one...as u said it trades torque for rpm...others were saying that there is so little loss that it wuldnt even matter but i think that loss count matters
 
  • #12
trillionex said:
ok got it...i just needed to confirm that loss does occur and that also quite significant one...as u said it trades torque for rpm...others were saying that there is so little loss that it wuldnt even matter but i think that loss count matters
Right, but just so we're clear, trading torque for rpm is not loss.
 
  • #13
Yaa russ, thnx fr the help, appreciate it
 
  • #14
trillionex said:
ok got it...i just needed to confirm that loss does occur and that also quite significant one...as u said it trades torque for rpm...others were saying that there is so little loss that it wuldnt even matter but i think that loss count matters

What you don't seem to be understanding is that trading torque for RPM does not necessarily indicate a loss.
 

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