Computer Fans and Battery Life

[motley man]

Want to put a couple computer fans in house, and run on locator size battery. How long does the battery last?

[Lusid]

Let's use a Vexilar battery as an example.

1amp = 1000 milliamps

Battery run time = Amps / current draw

Battery run time = 7amps / .275amps

Battery run time = 25 hours (Full to empty). But you have to factor the Voltage has to remain above 10volts if i recall correctly for the vex to run smoothly therefore the 16hrs is accurate.

The Vexilar typically consumes 275mA of power so on a 12v 7amp battery the Vexilar will be powered for around 16 hours.

Let's use this monster of a fan as an example:

APEVIA CF20SL-UBL 200mm Ultra violet LED Case Fan

newegg Item=N82E16835228028

Rated Current: 0.26 A = 260mA

Operation Voltage Range: 10.8 VDC ~ 13.2 VDC

So based on the data alone you should get approximately 16hrs on a fully charged battery, but conditions like temperature and age of battery make a difference.

Hopefully this makes sense.

Regards,

[Whoaru99]

Temperature and age make a difference and so does the discharge rate.

The rated capacity of 7AH is at a 20-hour discharge rate, which is equal to roughly 350mAH (0.350AH). If you pull more than 350mAH from the battery you effectively no longer have a 7AH battery.

For example, if load is

0.05 x AH rating, effective capacity = rated capacity = 100% (7AH in this example)

0.1 x AH rating, effective capacity = ~90%

0.25 x AH rating, effective capacity = ~75%

1 x AH rating, effective capacity = ~55%

So, in the last example, if the load on a 7AH battery was 7A, you would not get one hour of life you'd get roughly 33 minutes because at that load the battery's effective capacity is only 55% of 7AH rated capacity.

If you took the load of the Vex and two of the fans given in the previous example, you'd be at roughly 800mA load. This is load factor of about .11 (relative to battery's rated capacity) so you have in the ball park of 6.2AH effective, or roughly 7.75 hours run time. This is with battery at 68F, if colder and or battery is older it will be less.

[PierBridge]

Just bring a another battery and the fans will run for a day or more.

[Whoaru99]

Or use a bigger battery or use two 7AH in parallel.

With regard to 7AH batteries in this discussion, if the load is >350mA you will get longer total run time from two 7AH in parallel than using the two 7AH separately.

[Lusid]

Image of how to connect parallel. I had trouble picturing this so I used google and found an easy picture.