Intel stock cooler into 9v battery fan

Thread Starter

s355

Joined Apr 13, 2021
32
I have a spare Intel E29477-002 stock cooler which I want to turn into a battery fan with a Low/Off/High SP3T switch. When lowering the voltage to 5v on the low setting, it makes a high pitched humming noise while it's spinning . On the high setting (9v) it spins at full speed w/o the hum. How do I fix the humming noise on the low setting?
 

Papabravo

Joined Feb 24, 2006
16,836
It sounds like it is not designed to run at a lower voltage.
EDIT: It looks like it wants +12V @ 300 mA and you're starving it.
Maybe try PWM
 
Last edited:

KeithWalker

Joined Jul 10, 2017
1,919
I can not find a data sheet for this fan. From your information it would seem that what you are hearing is the mechanical vibrations caused by the frequency of the switched voltage to the coils of the brushless DC motor at half speed. you can not change that.
 

Papabravo

Joined Feb 24, 2006
16,836
The diagram clearly shows that you are not controlling the fan correctly. It is designed to run from +12 Volts and be controlled with a PWM signal.
It works on 9 VDC, but so well a 5 VDC. You cannot wish things to work the way you want them to work you have work with them the way they were intended to work. You're wasting your time on this one.

Now you might be tempted to think that you just have a motor with a power and ground connection. 50 years ago that might have been correct. Today there is a sophisticated controller running the motor and it apparently is having trouble running on 5 VDC. You asked: "what can I do"? Answer, run the fan the proper way or don't run it at all.
 
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Thread Starter

s355

Joined Apr 13, 2021
32
The diagram clearly shows that you are not controlling the fan correctly. It is designed to run from +12 Volts and be controlled with a PWM signal.
It works on 9 VDC, but so well a 5 VDC. You cannot wish things to work the way you want them to work you have work with them the way they were intended to work. You're wasting your time on this one.

Now you might be tempted to think that you just have a motor with a power and ground connection. 50 years ago that might have been correct. Today there is a sophisticated controller running the motor and it apparently is having trouble running on 5 VDC. You asked: "what can I do"? Answer, run the fan the proper way or don't run it at all.
I connected the fan directly to a 5v dc power supply and it ran without humming.
 

Audioguru again

Joined Oct 21, 2019
3,550
Your 2N3906 has a maximum allowed current of 200mA but its datasheet shows it operates poorly at 50mA or more.
Your 100k base resistor provides a base current of 83mA and its datasheet shows that its output will be only 0.8mA which is almost nothing.
 

Thread Starter

s355

Joined Apr 13, 2021
32
Your 2N3906 has a maximum allowed current of 200mA but its datasheet shows it operates poorly at 50mA or more.
Your 100k base resistor provides a base current of 83mA and its datasheet shows that its output will be only 0.8mA which is almost nothing.
What about 10k ohms?
 

Audioguru again

Joined Oct 21, 2019
3,550
What about 10k ohms?
With a 10k resistor the base current will be 0.83mA and the saturated collector current will be 8.3mA which seems to be very low for a fan. The little 9V battery also has a low output current which might not drive a fan. Is it a tiny low power fan?
If Amazon is correct, they say the fan draws 300mA that will explode a little 2N3906 transistor and cook a little 9V battery..
 

Thread Starter

s355

Joined Apr 13, 2021
32
With a 10k resistor the base current will be 0.83mA and the saturated collector current will be 8.3mA which seems to be very low for a fan. The little 9V battery also has a low output current which might not drive a fan. Is it a tiny low power fan?
If Amazon is correct, they say the fan draws 300mA that will explode a little 2N3906 transistor and cook a little 9V battery..
What about 1k?
 

ElectricSpidey

Joined Dec 2, 2017
1,815
I would set the transistor up as a saturated switch, and place a resistor in series with the fan.

But you could just put the resistor in series with the fan without the transistor.

It's going to be very difficult to find the sweet spot with the current configuration.

Oh yea, change the transistor to a 907, that small signal one wont cut the mustard.
 
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