3 x 5v fans hooked to a 9 volt?

D

dog812

New Member

• Nov 24, 2008

• #1

I am hooking 3 x 5v fans hooked to a 9 volt, What resistors should i use? should i put 1 in the main line or 3 , one to each fan?
Thanks in adavance.

 

S

Snaz

New Member

• Nov 24, 2008

• #2

are you hooking them up in series or parallel first?

 

F

flat5

Member

• Nov 24, 2008

• #3

You can do either. To calculate the resistor you want to find out the current or power rating of the fans. Then use Ohm's law.

 

D

dog812

New Member

• Nov 24, 2008

• #4

Parallel.
I think i have already calculated it correct but i am not sure..

9 volt to a switch
switch branches off to 3 resistors and the three resistors to the fans.
2 x 25 mm 5 volt .06 amp connected to 2 x 68 ohm resistors.
1 x 40 mm 5 volt .19 amp to 1 x 20 or 22 ohm resistor

Correct?

 

F

flat5

Member

• Nov 24, 2008

• #5

2 of your motors draw .06 amp each.
The resistors need to drop 4 volts.
You solve for the resistors. 68 ohms
Use 1/2 resistors.

I'd use a 2 watt for the other fan.

 

Last edited: Nov 24, 2008

audioguru

Well-Known Member

Most Helpful Member

• Nov 24, 2008

• #6

The fans might not start running since they need up to 10 times their running current to start.
With a load of 310mA, a little 9V battery will be 8V in a few minutes and will be 6V in less than 1 hour.

 

D

dog812

New Member

• Nov 24, 2008

• #7

I was running the 1 40 mm fan with no resistor on 9volt and it worked fine. Until someone told me about resistors..

 

Last edited: Nov 24, 2008

audioguru

Well-Known Member

Most Helpful Member

• Nov 24, 2008

• #8

dog812 said:

I was running the 1 40 mm fan with no resistor on 9volt and it worked fine. Until someone told me about resistors..

Click to expand...

Did you measure 9.0V with the 5V fan running? Or was it 5.5V because the little battery was overloaded?

If the supply was actually 9.0V then it might take half an hour for the little fan motor to burn out.