Question Can you provide the formula I need?

[ReveurGAM]

I'm evaluating fans based on multiple factors, including how long it takes to spin down from max RPM.

I need to know how to calculate a result that will give a value for each fan's results based on the averaged: RPM of multiple tests and time to stop in seconds. It needs to even things out so that the RPM factor is equalized to account for differences in the max RPM.

Secondary to this, and not math, I currently do 5 quick tests, a 2-minute run before turning it off, and a 5-minute test, too. I plan to also do spin-up tests of similar duration. This is to see what kind of difference I can detect in performance between a cold and hot fan. How long do you think a LONG test should run? Is 30 minutes enough?

I was reminded that there's bearing friction, air resistance and blade design that affect the test results.

I hope that makes it clear.

 

[punkncat]

It would seem fairly easy in that you take the 5 tests results add them up and divide by 5 to get the average.

The thing I question is how are you going to make the shut down time the same across the tests?
Normal computer shutdown varies a bit from time to time according to what all needs closed before shutdown, any pending updates, things like this...so if just hitting the 'shutdown' command isn't going to be a reliable way to time spin down time. It would seem that part would be easiest using a power source which you can physically disconnect, but then makes the RPM readings useless.

Just curious, what is this for? Own edification?

 

[ReveurGAM]

It would seem fairly easy in that you take the 5 tests results add them up and divide by 5 to get the average.

The thing I question is how are you going to make the shut down time the same across the tests?
Normal computer shutdown varies a bit from time to time according to what all needs closed before shutdown, any pending updates, things like this...so if just hitting the 'shutdown' command isn't going to be a reliable way to time spin down time. It would seem that part would be easiest using a power source which you can physically disconnect, but then makes the RPM readings useless.

Just curious, what is this for? Own edification?

I've already done that. That cannot equalize the RPM issue, however. Since I'm testing a wide range of fans with many different RPM ranges, I need to be able to produce a score that handles that variable in such a way as to show how, if each one had the same range, which would perform the best in regards to this testing.

If I make the shut down time exactly the same, that defeats the purpose of my testing. I'm using a fan controller to control the speed (instant).

I'm a tester and reviewer.

 

[Ralston18]

Start here:

https://extension.sdstate.edu/understanding-fan-performance-metrics-and-variability

https://www.ferrariasiaventilation.com/performance-testing-of-industrial-fans/

https://www.aircontrolindustries.co...mance-testing-on-all-aci-manufacturered-fans/


Formulas:

https://calculator.academy/fan-effi...the fan flow rate,input, then multiply by 100.

https://www.linquip.com/blog/fan-efficiency/

You will probably need some formulas involving angular velocity, acceleration, and momentum.

https://lambdageeks.com/angular-acc...omentum and angular,of rotation of the object.

https://phys.libretexts.org/Courses...tional_Kinematics_Angular_Momentum_and_Energy

There are quite a number of online physic videos showing the formulas and demonstrating the mechanics involved.

You will have to select and apply the constants and the variables applicable to your tests and the calculated end results to evalutate.

Likely you will need a good stobe light and digital timer as well.

 

[ReveurGAM]

Start here:

https://extension.sdstate.edu/understanding-fan-performance-metrics-and-variability

https://www.ferrariasiaventilation.com/performance-testing-of-industrial-fans/

https://www.aircontrolindustries.co...mance-testing-on-all-aci-manufacturered-fans/


Formulas:

https://calculator.academy/fan-efficiency-calculator/#:~:text=Fan Efficiency Formula,to calculate the Fan Efficiency.&text=To calculate the Fan Efficiency, multiply the fan flow rate,input, then multiply by 100.

https://www.linquip.com/blog/fan-efficiency/

You will probably need some formulas involving angular velocity, acceleration, and momentum.

https://lambdageeks.com/angular-acceleration-and-angular-momentum/#:~:text=The angular momentum and angular,of rotation of the object.

https://phys.libretexts.org/Courses/Joliet_Junior_College/Physics_201_-_Fall_2019v2/Book:_Custom_Physics_textbook_for_JJC/11:_Rotational_Kinematics_Angular_Momentum_and_Energy

There are quite a number of online physic videos showing the formulas and demonstrating the mechanics involved.

You will have to select and apply the constants and the variables applicable to your tests and the calculated end results to evalutate.

Likely you will need a good stobe light and digital timer as well.

Oh boy. I appreciate the links - I'll read them and see if I can understand and use what they have, though. Physics is way beyond my ability. 🙁 I really need some guidance to be able to make a spreadsheet formula.

 

[ex_bubblehead]

You'll also need to account for temperature as that will have an effect on the viscosity of any lubrication on the motor shaft and bushings/bearings.

 

[ReveurGAM]

You'll also need to account for temperature as that will have an effect on the viscosity of any lubrication on the motor shaft and bushings/bearings.

Which is why I'm doing testing while the fan is cold as well as when it has warmed up. Can you help me with the formula?

You forgot to mention that humidity affects pressure.

 

[punkncat]

I am curious to know what you hope to show or prove that would actually matter beyond actual cooling abilities and noise, which are both commonly available through the manufacturer spec page. The minute differences in fan spin because of temperatures or atmospheric pressures is digging down to a level that I cannot imagine make any real world differences.

I know you say you are a reviewer and want to perform these tests and have this formula to prove these seemingly insignificant details. What are you hoping to pass along to the average consumer that will matter to them, if I may ask?

If you are digging down that deep, are you going to take into account such things as humidity? Elevation?

Forgive me, but I am having a hard time seeing the point in the effort in such a way that you could pass along some significant reason to put in the work. What are you expecting to see? a 1% variance in stated performance? 10% (probably not going to happen)?

What one line would be your catch that you make this all matter to a consumer?

Whatever the end point, I would be interested in seeing you link back to the results of your review when completed.

 

[Ralston18]

Consider that there is no specific formula for your project.

Much of science depends on developing a formula and then doing experiments to determine if the experimental results match the formula's predicted results. If not then the formula may be wrong or there was some experimental issue that needs to be resolved.

FYI:

Scientific Method

There are many similar links and you should read several of them.

= = = =

Apply the scientific method to your fan project starting with a Hypothesis.

I suggest something simple such as "I predict that the higher the fan RPM the longer it will take for the fan to spin down and stop." ( A straight forward line on a graph.)

I.e. Gather data.

For example, simply record the fan rpms, the temperature, the humidity, the time to stop, etc. (what ever you want) for each tested fan some given number of times. Work up and down the RPM range.

Put the results in a spreadsheet to look for correlations. Graphical and calculated.

Very likely that you will quickly notice that one or more of the data variables do not make any significant difference and can thus be ignored. E.g., the room temperature and humidity.

Look for margins of error. For example there may be no notable stop time difference between X RPM and X + or - 100 RPM. Could be a measurement issue or that there is another variable involved.

You must then revise your experiment to determine what is happening. Maybe improve the accuracy of the RPM measurement and/or the timer.

And it is common to repeat any given test multiple times and average out the results as suggested by @punkncat.

What is your hypotheis, your predicted result, and what formula could be used to establish some relationship/ratio between stop time and RPM?

Hint: For starting purposes you only need three columns on the spreadsheet. One column for the variable, one column for a measurement, and the third column being the calculated result of your formula.

Results should graph out very nicely.

 

[ReveurGAM]

Consider that there is no specific formula for your project.

Much of science depends on developing a formula and then doing experiments to determine if the experimental results match the formula's predicted results. If not then the formula may be wrong or there was some experimental issue that needs to be resolved.

FYI:

Scientific Method

There are many similar links and you should read several of them.

= = = =

Apply the scientific method to your fan project starting with a Hypothesis.

I suggest something simple such as "I predict that the higher the fan RPM the longer it will take for the fan to spin down and stop." ( A straight forward line on a graph.)

I.e. Gather data.

For example, simply record the fan rpms, the temperature, the humidity, the time to stop, etc. (what ever you want) for each tested fan some given number of times. Work up and down the RPM range.

Put the results in a spreadsheet to look for correlations. Graphical and calculated.

Very likely that you will quickly notice that one or more of the data variables do not make any significant difference and can thus be ignored. E.g., the room temperature and humidity.

Look for margins of error. For example there may be no notable stop time difference between X RPM and X + or - 100 RPM. Could be a measurement issue or that there is another variable involved.

You must then revise your experiment to determine what is happening. Maybe improve the accuracy of the RPM measurement and/or the timer.

And it is common to repeat any given test multiple times and average out the results as suggested by @punkncat.

What is your hypotheis, your predicted result, and what formula could be used to establish some relationship/ratio between stop time and RPM?

Hint: For starting purposes you only need three columns on the spreadsheet. One column for the variable, one column for a measurement, and the third column being the calculated result of your formula.

Results should graph out very nicely.

Yes, thank you, I am familiar with the process. I just do not have the mathematical ability to figure out the formula. Basic algebra is the highest I remember, although I went all the way through to advanced math with As and Bs - but only because I worked hard, not because I'm good at math.

 

[USAFRet]

If comparing spin down times of various fans, one would think a simple line or bar graph would be pretty easy.
Repeat multiple times for each fan and average.
Then repeat for each fan after it has been running for xx minutes, to compensate for internal heat.

Do this with the various fans spinning at the same RPM.

Fan A average 15 secs
Fan B averages 17 secs
Fan C averages 9 secs


If they are running at different RPM, no direct comparison can be made.
Fan A may slow from 1500RPM to 1100RPM faster than Fan B slows from 1800 to 1200, but slower spin down from 1100 to 0.
Too many variables for a simple comparison.


Unless of course I'm missing some deep detail.

 

[ReveurGAM]

If comparing spin down times of various fans, one would think a simple line or bar graph would be pretty easy.
Repeat multiple times for each fan and average.
Then repeat for each fan after it has been running for xx minutes, to compensate for internal heat.

Do this with the various fans spinning at the same RPM.

Fan A average 15 secs
Fan B averages 17 secs
Fan C averages 9 secs


If they are running at different RPM, no direct comparison can be made.
Fan A may slow from 1500RPM to 1100RPM faster than Fan B slows from 1800 to 1200, but slower spin down from 1100 to 0.
Too many variables for a simple comparison.


Unless of course I'm missing some deep detail.

Yes, I know, but that is what I need to do. I have fans that range from a max of <1,000 to up to 5,000, so it is not useful to limit all of the fans to <1,000 when some cannot even attain that speed, and the fan controller I'm currently testing with (Akasa FC.Trio) cannot go below about 1,140 RPM. That is why I need the equalization formula. Of course I will make graphs, too. Can you help?

 

[USAFRet]

Yes, I know, but that is what I need to do. I have fans that range from a max of <1,000 to up to 5,000, so it is not useful to limit all of the fans to <1,000 when some cannot even attain that speed, and the fan controller I'm currently testing with (Akasa FC.Trio) cannot go below about 1,140 RPM. That is why I need the equalization formula. Of course I will make graphs, too. Can you help?

You would have to accurately measure the spin down RPM vs time, and create a curve for each fan.

Either at a specified time interval. (Every 1 second ?)
Starting at X,XXX RPM
1 sec == 1400RPM
2 sec == 1280 RPM
3 sec == 1025 RPM
and so on until 0.

A line graph or curve for each fan.
Display on the same chart.

Or, note the time at each RPM interval. Every X00 RPM drop, at what exact elapsed time.

Gather the data first, then work on the graphs.

 

[ReveurGAM]

You would have to accurately measure the spin down RPM vs time, and create a curve for each fan.

Either at a specified time interval. (Every 1 second ?)
Starting at X,XXX RPM
1 sec == 1400RPM
2 sec == 1280 RPM
3 sec == 1025 RPM
and so on until 0.

A line graph or curve for each fan.
Display on the same chart.

Or, note the time at each RPM interval. Every X00 RPM drop, at what exact elapsed time.

Gather the data first, then work on the graphs.

In other words, I would need to do that by using my PC and HWInfo64, assuming it has those functions, to record that kind of data. Correct?

The problem there is that the Akasa FC.Trio isn't (cannot be) connected to my PC, except the PSU, and the other one, CopalFan FC works the same way. I would have to do this from BIOS. I'd have to make a video so I could get the data since I'm not the Flash. 😉 I think your second idea of "laps" would be easier since I could click the button each time except for the fact that there are numerous RPM changes that occur and I wouldn't have those numbers. 🙁

 

[ReveurGAM]

I am curious to know what you hope to show or prove that would actually matter beyond actual cooling abilities and noise, which are both commonly available through the manufacturer spec page. The minute differences in fan spin because of temperatures or atmospheric pressures is digging down to a level that I cannot imagine make any real world differences.

I know you say you are a reviewer and want to perform these tests and have this formula to prove these seemingly insignificant details. What are you hoping to pass along to the average consumer that will matter to them, if I may ask?

If you are digging down that deep, are you going to take into account such things as humidity? Elevation?

Forgive me, but I am having a hard time seeing the point in the effort in such a way that you could pass along some significant reason to put in the work. What are you expecting to see? a 1% variance in stated performance? 10% (probably not going to happen)?

What one line would be your catch that you make this all matter to a consumer?

Whatever the end point, I would be interested in seeing you link back to the results of your review when completed.

I will only say this: I will be looking for trends that are causal in nature.

 

[USAFRet]

In other words, I would need to do that by using my PC and HWInfo64, assuming it has those functions, to record that kind of data. Correct?

The problem there is that the Akasa FC.Trio isn't (cannot be) connected to my PC, except the PSU, and the other one, CopalFan FC works the same way. I would have to do this from BIOS. I'd have to make a video so I could get the data since I'm not the Flash. 😉 I think your second idea of "laps" would be easier since I could click the button each time except for the fact that there are numerous RPM changes that occur and I wouldn't have those numbers. 🙁

However you want to do it.

But in my estimation, there can be no direct equation or formula comparison, because the spin down rate of each fan is not linear from MAX to ZERO.

 

[ex_bubblehead]

Horizontal vs. Vertical orientation also plays a factor here, as well as bronze bushing vs. ball bearing. Type and amount of lubrication used (if any). There is no single formula for what you are attempting to accomplish.

 

[ReveurGAM]

Horizontal vs. Vertical orientation also plays a factor here, as well as bronze bushing vs. ball bearing. There is no single formula for what you are attempting to accomplish.

There are far more than two types of bearings but one of the things I'm hoping to see is a difference between them. For example, one fan I already did some testing of has the SSO2 bearing, whereas 2 others are FDB and one two ball bearing. I also have fans with sleeve, rifle, maglev, etc.

I test all fans standing up.

 

[USAFRet]

There are far more than two types of bearings but one of the things I'm hoping to see is a difference between them. For example, one fan I already did some testing of has the SSO2 bearing, whereas 2 others are FDB and one two ball bearing. I also have fans with sleeve, rifle, maglev, etc.

I test all fans standing up.

So then gather the data.

Spin down over time.

Then, you can compare and contrast various fan types, bearing types, etc, etc.
Maybe a trend will emerge.

But you need to gather some data first.

 

[ex_bubblehead]

As they may be installed horizontally you must also test in that orientation or your results are absolutely useless.

 

[punkncat]

I will only say this: I will be looking for trends that are causal in nature.

It does seem to be a subject of which I have not seen any other reviewer/influencer take a go at. This is very Steve/GN level of research, and if nothing else reviewers need something new to discuss rather than the next graphics card, CPU, or case.
If you can come up with a formula that gives repeatable results, make sure YOU (of all people) understand the why and what for, because the very next thing after posting will be 'peer review' as it were and you may need to explain the findings at a fundamental level. If someone else provides it, that could be problematic.

Good luck with your endeavor.

 

[ReveurGAM]

As they may be installed horizontally you must also test in that orientation or your results are absolutely useless.

"Absolutely" is a blanket statement, which makes your statement automatically false.

 

[ReveurGAM]

It does seem to be a subject of which I have not seen any other reviewer/influencer take a go at. This is very Steve/GN level of research, and if nothing else reviewers need something new to discuss rather than the next graphics card, CPU, or case.
If you can come up with a formula that gives repeatable results, make sure YOU (of all people) understand the why and what for, because the very next thing after posting will be 'peer review' as it were and you may need to explain the findings at a fundamental level. If someone else provides it, that could be problematic.

Good luck with your endeavor.

Thanks. I've encountered a setback because of the fan controller I have, the Akasa FC.Trio. The inductors and caps they used cause a significant delay in changing the RPM. I've just received my tachometer, so if I find that my EK Labs Copalfan FC will do a much better job then it should be okay, although it's not certain at this point. Testing will soon reveal the extent of the improvement.

I also got a 120mm rad for my pressure testing, so that's great!

 

[ReveurGAM]

I think the solution is to calculate the RPM/sec.

 

[USAFRet]

I think the solution is to calculate the RPM/sec.

"RPM/sec" is meaningless.

RPM already has the time value in it...Revolutions Per Minute.

In plain english, what are you trying to measure?