3 x 5v fans hooked to a 9 volt?

[dog812]

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.

 

[Snaz]

are you hooking them up in series or parallel first?

 

[flat5]

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.

 

[dog812]

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?

 

[flat5]

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.

 

[audioguru]

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.

 

[dog812]

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

 

[audioguru]

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

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.