Electronic – If I lower the volts on a computer fan will the needed amps increase? Im new too electrical engineering (updated)

amperagefanvoltage

I have a computer fan that I am using for a school competition. The rules state that voltage used can be no higher than 9 volts but most fans are 12 volts. The fan that I have is has a recommended 12 volt 4.5 amps. So if I used a 9 volt battery or 7.2 volt how many amps should that battery be? How do volts effect amps in motors? I am new to all this and so a simple answer would be appreciated. Also I need it only to run for about 10-15 minutes at most so if you have any battery recommendations that would also be helpful. The rules for batteries are no lithium or lead allowed. The rules are very prohibitive.

Newly Added Information

I am building a small scale hovercraft that has to be as light as possible. However I am awarded points for amount of weight it can carry. I am using this fan to fill the hovercrafts skirt. I have to use a computer fan because the rules state I can only use brushless motors if it is in a computer fan otherwise motors have to be brushed which I have had issues with. I found this fan in my house and found it very powerful. Here is a link https://www.digikey.com/product-detail/en/delta-electronics/PFR0912XHE-SP00/603-1707-ND/3078695 Here is a full copy of the rules its under hovercraft http://api-static.ctlglobalsolutions.com/science/SO_C_2018FINAL.pdf

Best Answer

a simple answer would be appreciated

Okay.

if I used a 9 volt battery or 7.2 volt how many amps should that battery be?

You clearly mean ampere hours.

If it uses 4.5 A when being fed 12 V, then you can assume that with 9 V battery that it will drain roughly \$4.5\text{ A}×\frac{9\text{ V}}{12\text{ V}}=3.375\text{A} = 3375\text{ mA}\$.

Let's assume you will run it for 15 minutes, then you will need a 9 V battery with at least \$3375\text{ mA}×\frac{15\text{ min}}{60\text{ min}}=843.75\text{ mAh}\$.

Considering that you will be discharging it at 4 times the capacity, then I'd aim for a little bit higher capacity, say 2000 mAh or even higher, or put several 9V batteries in parallel. Because high discharge (several amperes) will lower the capacity.

How do volts effect amps in motors?

If you increase the voltage, then the ampere will also increase.