I am a keen fisherman and always looking for new projects to work on in my spare time.
My latest pet project is that I'm looking to increase the capacity of the batteries that power my 3W cree LED headlamp, by making a battery pack that clips to my belt.
The lamp currently runs off 3 x AAA 950mAh batteries, it has quite a long burn time but after the first hour there is a significant decrease in brightness, which continues to decrease throughout the night.
I have 8 Eneloop AA 2000mAh batteries lying around the house, and my first idea was to use 6 of these batteries by running two sets of 3 AA batteries in series and parallel giving me 4.5V and 4000mAh. But I was thinking I could also use the other spare 2 batteries.
My question is would there be any real benefit is using two sets of 4 AA batteries in series and parallel giving me 6V 4000mAh then reducing the voltage down to 4.5V using a regulator or am I just wasting 2 batteries doing this?
Any help appreciated. I also appreciate that it would probably be simpler just to buy a new lamp. But where's the fun in that?
Best Answer
First, I second the purchase (from ebay about $15) of a new headlamp that uses 18650 cells.
There are several one chip handful discrete components that would do the trick. HOWEVER, if you place the electronics at your belt (and even if you don't), there will be a significant current which will loose energy on the wires to your lamp. Most headlamps with larger battery packs, usually either place the pack at the back of the head, or up the voltage and buck the voltage at the light head. Unless you are completely rebuilding the head enclosure, that is probably not practical. Since you are wanting to use more capacity to achieve longer running time, I would place all the batteries in series at your belt and use a buck circuit to bring the voltage down to that compatible with your lamp head. If you are ambitious national & linear tech & microchip all have chips to help in this. If you want a nice circuit board and decent circuit low cost, ebay has numerous China vendors which sell small buck circuits to do exactly what you want.