peterperkins wrote:I'm starting to assemble my cell and wonder if insulating sheets between the cells in the stack is a good idea?
With any pouch cell it's a good idea, even something simple like a layer of wide double side tape is enough.
Is there a current/voltage leakage issue through the pouches?
Every pouch cell, Kokams, RC LiPo, and these A123's can and normally do develop some weak connection to the foil pouch over time, so if you've got them stacked touching other foil pouches and things, then you can get current leakage (the reason to insulate).
I was thinking that very thin plastic A4 stuff used in files/folders. With cutouts so the alternate tabs can be soldered.
That would work fine, but it would be slippery. Something adhesive would make for a strong pack.
It will insulate the tabs from one another as well which will be required anyway.#
Also thinking about temperature sensing in the middle of a stack. It would be nice to put a thermistor in the middle, but a thermistor bead sandwiched between two cells will deform them creating an indentation and possible problems internally. Like BigMoose said, check my thermal pics.
How about a thermistor on the copper tab. Will the heat conduction to the tab from inside the cell be suffcient to gauge the internal temp?
cell_man wrote:As was mentioned I'm kind of sold out of 20Ah cells. That's not strictly true, I have a customer that has already purchased a big quantity who is due to take most of the remaining 20Ah cells. With what's left I could probably do some smaller packs but not sure I'd have enough for a bigger pack. Situation on the 15Ah cells is similar but have a few more 15Ah cells to spare. There's no news on more batches of cells at the moment.
nerk wrote:they are Lipo 3.7v at 1.3aH, and for a dollar how can you beat that?
patrickza wrote:nerk wrote:they are Lipo 3.7v at 1.3aH, and for a dollar how can you beat that?
Hmm, that works out to 4.81wh per dollar or $0.21/wh. Good price but not all lipo is equal. It might have an exagerated ah rating, lousy C rating, or a lousy number of cycles. Best bet would be to buy one or two and hook them up to a cell tester and get some real figures.
cell_man wrote:Good work Peter, it looks really nice. Don't know how I missed your post previously. How long would you estimate it took to put it together?
Doesn't sound like you had a bad time soldering them, I found them very difficult. It seems fairly common practice to spot weld a nickel tab to the alloy tab of pouch cells but I think it requires a special spot welder. If that's done it's very simple to solder them together. If I'm able to get some more cells I'll see if I can get them prepared in this way. The mechanical method is pretty good but it is a lot of work.
Where are they available and what's the price?jimw1960 wrote:This thread has been dead awhile, but with the recent availability of a123 prismatic cells...
Asking Ping seems like a good place to start.jimw1960 wrote: In regards to terminating these prismatic cells, one thing that occurred to me is that prismatic cells are in widespread use for lipo and low-c lifepo4 packs like ping. So, why reinvent the wheel? Looking at the previous threads on how those packs are built, it looks like the proven cell termination method is to use a solder connection to a simple fiberboard with copper substrate. Since these are in widespread use, my question is whether anyone knows where one could buy circuit boards like they use to make lipo packs.
Where are they available and what's the price?
MitchJi wrote: Asking Ping seems like a good place to start.
MitchJi wrote:Would clamping or bolting to the circuit boards work equally well?