How to design a rpm and torque indicator from a fan?

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SUMMARY

This discussion focuses on designing a circuit to measure RPM and torque from a fan. Key methods include using external detectors for RPM measurement and calculating torque via power measurements, as expressed by the formula Power = Torque * RPM. The type of fan, its specifications, and the motor type (induction, universal brush, or IC engine) are crucial for determining the appropriate measurement techniques. Additionally, using strain gauges or spring balances to measure torque directly is suggested.

PREREQUISITES
  • Understanding of electrical circuits and power measurement
  • Familiarity with RPM measurement techniques, including optical devices
  • Knowledge of different motor types: induction motors, universal brush motors, and brushless motors
  • Experience with torque measurement methods, such as strain gauges and spring balances
NEXT STEPS
  • Research optical RPM measurement devices suitable for fans
  • Learn about power measurement techniques for calculating torque
  • Explore the use of strain gauges for torque measurement in rotating systems
  • Investigate the characteristics of brushless motors and their control systems
USEFUL FOR

Engineers, hobbyists, and students interested in fan design, motor control, and torque measurement techniques will benefit from this discussion.

dennis12
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how to design a circuit to determine the rpm and torque from a fan?
 
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Firstly, welcome to PF.

We need more information. It will be difficult to measure RPM without some form of external detector, but since Power = Torque * RPM, measuring the power, (or the current at a fixed voltage), will make it possible to calculate torque.

What type of fan are you using?
What is it's size and power?
What is it's rated RPM?
What is it used for? Ventilation? or engine cooling?
Is it 12VDC or AC?
Is the fan driven by an induction motor, a universal brush motor or an IC engine?
 
Another way is to measure the torque that the fan applies to it's mounts. Perhaps mount the fan on an arm that can pivot, use strain gauges or a spring balance etc

You can buy optical devices to measure propeller rpm from model aircraft shops. If the fan uses a brushless motor it might be possible to measure the rpm by tapping off the controller...but if you are able to do that you probably wouldn't be asking the question here.
 

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