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Old Aug 08, 2009, 09:28 PM
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Thin tabs, spot welds --bad???

Three questions.
1) A123 -- Cells removed from Dewalt packs have thin tabs that are spot welded. Are those four wimpy contact points enough to deliver the massive current these cells are capable of? Seems not, so why did A123 use such a method? Wis they had doubled the welds. I guess the power tools don't draw as much current as RC.

2) A123 -- If spot welds are wimpy, then we should solder, right? But soldering is bad, right? Is there any definitive verdict about soldering to A123 and long-term damage or loss of performance? Is special solder necessary? I have soldered dozens of NIMH packs with my 80w iron that has a HUGE tip. Pre-tinned cells and bars are heated for less than a second, so is that fast enough for A123?

3) Lipo -- I may be wrong, but lipo cells appear to have thin, wimpy tabs sticking out of them as well. I have never assembled a pack, just going on what I have seen in pics. Is this true? If so, then isn't that a bottleneck for current as well?
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Old Aug 08, 2009, 11:02 PM
Frankenstein recycled packs
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USA, AZ, Gilbert
Joined Jan 2006
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1) The DeWalt packs deliver what is needed. A123 did all they were asked to do.

2) I use homemade solder bars made out of copper on my high amp 123 cells. I use a high watt soldering iron, get in, get er done, and get out. Only ruined one cell and like a nicad, you will hear a pop when they vent.

3) Newer higher C cells have thicker and wider taps. I built some year 2005 Thunder Power 10S5P 10,000mah last year and the tabs were paper thin.
I feel many of the low cost lipos of today still have tabs that are too thin but high end packs are quite thick. I have salvaged several cells from HC packs that had a temp short across the discharge leads and this overheated the tabs to the point that they lost the seal between the tabs and cells.

Rick
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Old Aug 08, 2009, 11:56 PM
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I was thinking of banging 10ga solid copper wire flat to make bars. Either that or using copper pipe straps cut with a dremel. Would that work? What do you use for homemade bars on these cells? Regular battery bars are not the right size (I think)

You say you solder for high amp apps. How many amps do you think the welded tab cells could safely/efficiently push out?
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Old Aug 09, 2009, 04:32 AM
Southern Pride
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Haralson County GA. USA
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Quote:
How many amps do you think the welded tab cells could safely/efficiently push out?

http://www.rcgroups.com/forums/showp...1&postcount=18

Charles
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Old Aug 09, 2009, 12:12 PM
Jack
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I read somewhere that some of the buss bars between cells are engineered to act as fusible links. That they will melt and open the pack at a discharge rate that is grossly in excess of the intended maximum rate, like a dead short anywhere in the pack.

I can seem to remember where I read that though...

I like the buss bars on the A123 18650 cells I'm using. They are easily and quickly tinned (I use some paste flux) and allow for quick soldering. I not found the cell ends to get any hotter than the rest of the pack when I was testing them so I think the they can handle realistic discharge rates fine.

nikg,

Using flexible metallic braid bot buss bars might be a better choice than hammering copper flat. It will have some flexibility and I think it will solder quicker too. You can buy that at some of the battery building supply places, battlepacks.com comes to mind.

Jack
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Old Aug 09, 2009, 12:24 PM
Southern Pride
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Haralson County GA. USA
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Quote:
I read somewhere that some of the buss bars between cells are engineered to act as fusible links. That they will melt and open the pack at a discharge rate that is grossly in excess of the intended maximum rate, like a dead short anywhere in the pack.

I can seem to remember where I read that though...
It is in the post that I provided the link to.
Use the link Luke , or Jack as the case may be..

Charles
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Old Aug 09, 2009, 08:44 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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I had already used that link. And it is not there in that post. But it is in post #1 in the thread that post was in.

http://www.rcgroups.com/forums/showthread.php?t=599316




Jack
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