Hello All,
I am completely new do anything electronic but i want to slow down an 80mm computer fan and power it with a 9v battery.
A bit of background of the project. I am making some terrain piece for a wargame (warhammer 40k) and i want these to spin SUPER SLOW. My friend said i would need to put a resister in so they would do that and not kill the battery. What sort of resistor would i need for the 12v 80mm fan?
Also i plan i putting a switch in so i am assuming it would be batterr --> switch ---> resistor ---Fan
A 12V fan does run slower when the voltage is only 9V from a brand new 9V alkaline battery. The battery develops an internal series resistance as it runs down which also slows down the fan.
If you add a series resistor then the fan might not start running, especially when the battery is running down.
You need gears or a pulley to make an electric motor run SUPER SLOW.
A 12V fan does run slower when the voltage is only 9V from a brand new 9V alkaline battery. The battery develops an internal series resistance as it runs down which also slows down the fan.
If you add a series resistor then the fan might not start running, especially when the battery is running down.
You need gears or a pulley to make an electric motor run SUPER SLOW.
A 9v alkaline battery can put out about 500mAh, so if your fan draws 500mA that means it will run for an hour. It probably draws a little less than that, like 400mA or maybe even 300mA, so it may last an hour or a little longer.
9v batteries dont hold much energy. It's always better to use AA's or lead acid for longer run time. AA's hold about 4 times as much energy with the same number of cells as a 9v has.
The current of the fan is much too high for a potentiometer. The pot will get much too hot then fail.
A pot is a resistor and will not work anyway.
A pot can slow down the fan if the pot adjusts the pulse widths in a Pulse Width Modulation motor speed control circuit. Then the pulses are full power but the reduced duty-cycle slows the speed.
I agree that a little 9V battery is too weak to power a fan.
We don't know how much current the fan needs. Its current draw is less at 9V than it is at 12V.
A battery is rated to deliver a certain amount of current. Its voltage drops as it runs down.
I showed that if the fan draws 400mA then a brand new 9V alkaline battery voltage drops to less than 7V in 15 minutes when the fan might stop or will not start running.
I think it's better to fix the problem at the source, by using a more suitable motor for your "SUPER SLOW" rotation.
Ebay has small stepper motors with driver PCBs that will rotate at a fixed speed. All you really need to do is hook up the power.
Or if you must have a DC motor solution, you can get cheap DC toy gearmotors with plastic gearboxes quite cheap. They will probably make more noise than the stepper motor due to the cheap plastic gears.