Numb battery question: How do you make a small battery pack
First off, these questions are directly for my bicycle light project which will be a 12.8V 3.3Ah 4s1p pack. I am looking to sort out the LSDs (Little ****ty Details) so that as I hopefully one day move on to a bigger project I'm not asking the same numb questions.
So here it is, how do you build a battery pack? Ok, so my old NiMH 5s2p pack has thin flat metal "bars" connecting them, then there was a paper cover over the ends, a bit of saran wrap, and then 2 layers of heat shrink, and maybe some sort of voltage/current protector in there (little white rectangular do-dad in series with the batteries. And the "bars" don't look to be soldered but tapped in in place with a fine point. I'd rather solder something for a greater contact surface. The batteries I am looking at using are basically long C cells (26650).
So what is the best way to connect my batteries? Do I buy or make these nice little flat bars, or is good old wire acceptable? If so, what gauge? I know there is a calculation for this, but I don't remember it. I can also get them with with tabs added for 25 cents a battery. Would that do? I can get those nice square plastic battery holders for these, just like the ones you can get for the headways. How do I wrap these up, or protect them from the elements? I have a nice case that will be sealed, but this light is for my MTB, so better safe then sorry. Also, what kind of voltage/current protector should I use to protect the LiFePo4 batteries? I will use a charger specifically for those, so I am not as concerned about charging as I am worried about excessive discharging from a wire shorting out or something. And, how do you balance batteries that are in series? More importantly, for a max of 18 watts worth of LED draw from LiFePo4 with a charger designed to work with a battery pack that size, do I really need to worry about it?
Also, does anyone know about the Battery space website? Do they sell good stuff?
A gentleman on the MTBR DIY light forum was helpful when choosing LiFePo4 batteries, but suggested I leave soldering a pack to the professionals. I replied, but it would have been better off sending him a resume. Someday I'll grow up. There is also quite a bit on the candlepower forum on bicycle lights. But I have yet to take the time to sign up to ask questions, and I saw nothing on building packs there, at least for bicycle lights.
Well, I've already figured out the protection part. The same site sells a little PCB with circuitry just for this very pack, for $9. So now I guess I'm going to need wire. Just have to figure out what gauge now.
Those indentions are probably electric spot welds. Battery tabs often don't take solder. Can't remember what metal it is (aluminum?) but that might be a frustrating experiment.
Originally Posted by jazclrint
Spot welders are expensive lil buggers, even the tiny ones. When I replaced a bad cell in a power tool's battery pack, I took it to Batteries Plus and they spot welded the replacement cell for free. I bought the cell from them and the welding service is complimentary with it.