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Q & A: enhanced battery energy

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Most recent answer: 02/26/2012
Q:
I have made a little project with some flash light bulbs and have the problem that the 2AA's that run them tend to go out after about an hour. I was wondering if a more powerful battery such as a 9 volt with what I have been reading up on the net to be a "step down converter" would enable a system like that to run for longer. Ideally I need a system that can run for at least 4 hours without needing a battery change though 6 hours would be ideal. Is this concept of using a higher voltage system with a step down conversion feasable to get these results? And is there a governing principle or known equation by which such a prediction of battery life/power drain might be predicted?
- Matt (age 32)
Norwich, NY
A:
The 9V idea won't work. The key issue is that your circuit uses a certain amount of power, i.e. energy per time. A particular type of battery has some energy density per unit volume. It can vary a bit depending on the efficiency of the construction, but will be roughly the same for any standard alkaline cell.  The 9V batteries have more units in series, delivering higher voltage, but that doesn't raise their energy density. In fact, the extra construction probably lowers it. Hooking them to inverters and transformers to step that voltage down would just be awkward and waste some more power.

So what you need to do is either switch to some more expensive AA batteries with a higher energy density or simply switch to bigger batteries, such as C's.

Another possibility would be to replace the (incandecent?) bulbs with LED bulbs, which use much less power for a given light output.

Mike W.

(published on 02/26/2012)

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