How to test computer case fan ?

[eyepea]

Can a computer case fan be tested with a ohm meter correctly ?

Fan not rotating.

Fan blades can be rotated by hand easily. The changes in magnetic poles felt. Can't notice any difference from a working fan. So no dust or anything obstructing fan rotation.

I connected fan to psu and checked voltage near connector. It is 12V.
So I assume fan getting power.

Next I want to check loose connection, coil burnt open or short circuit.

I disconnect fan and check resistance with a ohm meter (analog - I could not get hold of a digital one). It reads about 20 ohms.

Do I get a useful reading since am using an analog meter ?

I saw this in the web : http://www.ehow.com/how_7544128_test-computer-fan-ohmmeter.html

It says if resistance is greater than 10 ohms then fan is bad.

Is this information correct ?
So according to that ehow article, the fan is bad.

But I also want to know...

since ohm meter read 20 ohms, it means there is no broken wire, there is no burnt coil giving open circuit or no short circuit.
Is my assumption correct ?

so why fan not working ?

 

[eyepea]

any idea please ?

Mata danaganna oney, circuit eka short hari open hari nathnam, resistance tikak vadi unaama, ai fan not working ?

Also, resistance eka ehema wadi wanney kohomada ?

thanks!

 

[NB Diamonds]

no idea machan.

 

[eyepea]

looks like my idea of wires connecting to motor coil is not quite correct

found some idea of the internals of a pc case fan here -> http://prodmod.wordpress.com/2007/02/12/take-apart-that-pc-fan-see-whats-inside-brushless-dc-motor/

But my question still remains

why resistance increase ?
checked working fan in another comp. 4 ohms.
check in a new fan. less than 1 ohm.

so how exactly does a fan go "bad" ?

If anyone has more info please let me know. thanks

 

[eyepea]

another question

when cleaning computer and you hold vacuum close to fan, fan will rotate high speed, sometimes in opposite direction ?

Can this damage the fan ?

thank you weywa

 

[scylla1990]

If you PC fan doesn't start with the PC or it's rotating slowly you can do this.

http://www.techrepublic.com/article/quiet-noisy-computer-fans-with-a-drop-of-oil/5034842

Just put very small amount of oil and see first coz if you too much then it start rotating too fast and make so much damn noise. Tested and done successfully.

 

[eyepea]

Just put very small amount of oil and see.

useful info. Thanks!