# Noobie question - battery life

#### Quixotic Rebel

Mar 22, 2015
1
Hi everyone,

So I'm a amature hobbiest that's trying to get back in to basic electronics. I'm starting building a small battery powered fan that I want to to be last longer than my 2 x AA cells powered portable fan.

So I built a simple circuit with:

• A 60mm 12v / 0.1a computer fan
• 8 x AA Energiser batteries
Connecting the batteries in series makes the 12v required to power the fan. What I was trying to figure out was, well how long will this fan be powered for, before the batteries die?

The data sheet for my battery suggests the power of the battery is 2000 mAh at 0.8v. However I doubt the fan would run at 6.4v (0.8v x 8 batteries) so am assuming the minum I'll need is 9.6v (or 1.2v x 8 batteries)

I found the data sheet for the battery and under the "Constant Power Performance" section on page 2 it shows the battery being able to deliver power at 100ma for about 20 hours.
http://data.energizer.com/PDFs/E91.pdf

So with 8 batteries should I assume that that means 20 x 8 batteries = 160 of run time? Is it that simple? 160 hours sounds too good to be true...

Last edited by a moderator:

#### tldelectronics

Mar 22, 2015
1
could you run the fan wires outside the chassis?

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
If the batteries are in series you don't multiply the number of hours by the number of batteries. If they were placed in parallel you would (but then the voltage would be the same as a single cell)

#### BobK

Jan 5, 2010
7,682
In other words, 8 2000maH 1.5V batteries in series make a 2000mAH 12V battery.

Bob

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