I would like to make battery pack for one of my M*glites. But there are a few things I need to understand first.
1. What is the "real" way packs are welded together? I know packs can be soldered together with braided wire and such but what other options are there?
As mentioned already, spot welding. They make small tool for this type of work, they aren't large and cumbersome like a regular welder because they are just charging up a capacitor and quickly discharging it for the weld.
2. What is the best thing to use for the ends, and where to get them? (like button tops etc). And what do I use to separate contacts between the button top and the cells that wont melt under heavy load?
If you get setup to do spot welds, then you'll just want to use flat top cells. You'll want some spare "tabs" to make connections at the ends of the "rows" of cells to other "rows" of cells.
3. Is it ok to use a NICAD charger like one from a dewalt or like tool pack on a NIMH pack if the voltage is the same? If not why?
General rule of thumb is "no," but it depends on the NiCD charger and depends on how "correct" you want your charging to be.
There's no 100% correct answer to this question, because it depends on how much imperfection in charge method you are willing to deal with. And it also depends on the specific charger in question.
many of them are simple timer based chargers that just charge at a given rate for an hour and then go to trickle charge, these won't really work right for NiMH since the capacity will be different. You could make it work with some fidlefartin around.
many of them use a simple voltage peak charge termination, where it's not looking for any voltage "dip" from the pack like a smart charger would, it just brings it up to some high voltage (usually over 1.5V per cell for the pack) and then terminates, this would be hard on a NiMH pack. Not good.
Some cheaper ones are just trickle chargers, these would be ok if you manually terminated the charger after the proper number of hours for a full charge.
Some chargers terminate based on temperature, again, not the best for NiMH cells but this would also work.
Most of the NiCD only chargers, take advantage of the fact that NiCD cells are very tolerant of abuse and don't really care HOW they are charged. NiMH is more sensitive to charging methods, and will wear out faster if you use a lousy charging method.
I'm sure I've missed some points to be made here, but you get the idea.
4. When building a pack sutch as a 13 cell, is it ok to use a sub c as the 13th if it is higher MAH than the AA cells like 12 2600mah AAs and 1 3000mah sub c?
Not a great idea. but it would work, but wouldn't be ideal for the pack, the pack would have trouble staying in balance properly, especially when you consider that most Sub-C high current cells are going to have lower resistance than most AA high current cells. Ideally speaking, if you want to use a different shape cell at the end of a pack, it would be best to match the capacity and internal resistance as closely as possible with that cell. Look at 4/5ths size sub-C cells for closer matches in capacity.
5. I also need recommendations on the highest mah AA cell that can be discharged at 10+ amps. So far the elite 1700mah is the only one I have found with a discharge graph, but I would really like to go with higher mah cells than that.
Thanks
The general rule of thumb is that as you increase in capacity, the tolerance to high current drops, as you build a cell for higher current capability, the maximum capacity is dropped.
Don't worry too much about label ratings as far as mAH is concerned. Look at actual discharge comparisons in the real world, under real loads, and see how various cells do.
Eneloops will handle 10 amps, and they are rated at 2000mAH. Does that mean they are a better cell for the job? Nope! At 10 amps they will not deliver 2000mAH of capacity and will suffer from significant voltage sag when compared to dedicated high current cells like the Elite 1700s.
Hope that helps
Eric
