# Fan Needs 12V, only have 9V

I recently bought a 12V small computer fan(about 1"X1") and it was running rather slow when I checked it with a 9V. The package says that the fan requires 12V to run at an optimized speed, so is there a way/circuit that I can use/make that increases the voltage from 9 to 12?

• What you are looking for is a dc-dc step-up converter. I hope you don't try to feed your fan with a 9V block battery? – Botnic Nov 7 '15 at 17:27
• ebay.com/bhp/dc-dc-adjustable-step-up – Botnic Nov 7 '15 at 17:28
• @Botnic hehe at least it's cheap as dirt – Enthurzan Nov 7 '15 at 17:31
• The bigger bottleneck is the current that the 9V battery can provide. Boosting to 12V will only make that problem worse. – Passerby Nov 7 '15 at 18:47
• The battery is not going to stay at 9V either when under load. I'd estimate the fan will draw 0.1A @ 12 V (1.2W) and your 9V battery is unlikely to exceed 0.05A @ 8V (0.4W). 8xAA battery might be a better solution. A NiMH battery easily delivers that that 0.1A. – MSalters Nov 7 '15 at 19:45

Use an inverting buck regulator to create -3V and wire your fan between -3v and +9V. Maybe one of these: -

It's got a -5V output but that can be made -3V by choosing appropriate values for R3 and R4

As others have said, a 9V battery won't produce enough current to power a small computer fan. Using any type of step-up circuitry is only going to increase the current demand on the battery. Even if you could get it to work, you'd get only 3-4 hours runtime at most. The short answer is that a 9V battery just doesn't have enough juice to power a computer fan.

"Simple Switchers" (brand name) are easy to use, buck or boost, very efficient switch mode power supplies - boosting the output current should be easy, but I'll let the experts answer that, otherwise I'll get into hot water.

The simplest answer is to return the fan you bought, and get one intended to run from 9 V.

• This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. – jippie Nov 8 '15 at 15:29
• @Jip: Actually, it properly addresses the overall problem, just not the single solution the OP is envisioning. – Olin Lathrop Nov 8 '15 at 22:07

You can try putting the 9V battery and 2AA(1.5V) battery in series to produce 12V. Or you can try making a boost converter circuit which is a bit more complicated but will step-up or step-down your voltage in a circuit. You can learn more about boost-converters here.