jaofos

Just curious if anybody here has dissected one of the 3s1p retail packs and re-arranged the cells in a different configuration. Depending on how the cells are connected I don't see it being a terribly difficult task.

The reason I want to do this is I only run the packs in my stampede with an FLM extended chassis and I'm wanting to fab an under-chassis battery mount, but the height of the pyramid pack configuration makes this extremely difficult. It would be much easier to make a flat lower deck if the cells are in a side-by-side configuration.

Brian, maybe you can chime in here. How difficult would it be to unwrap the cells and re-arrange them? I know the dev cells come with the tabs but I'm not sure what is hiding under the wrapping of the retail packs.

Thanks,

Steve

A123 Racing

Hey Steve,

It would be somewhat difficult to re-assemble a 3S1P pack into a flat pack because of the way it is built. It would be much easier to buy a developer kit and solder your flat pack together yourself with a little heat shrink to finish it off nicely.

Let me know if you have any more questions.

Brian

[link=http://www.a123racing.com][/link]

jaofos

Somewhat difficult is better than "impossible"

Can you give me a hint as to whats hiding under the wrapping of my 3s1p packs? How are the cells connected together? Are there tabs? Would I just melt the solder off, re-arrange and re-solder them?

Thanks!

jaofos

What exactly does twisting the cap the tabs are welded to do to the cell?

everydayflyer

Destroys the seal and can cuase the cell to go open.. Photos are not mine and I would gladly give credit if I could remember the source.

jaofos

Well I figured to get the configuration I wanted I would probably have to buy new cells, so I unwrapped the cells to take a peek and to flatten the pack out I just twisted one cell 1/3 a turn and then taped them back up in a flat configuration.

Nothing popped off and the battery ran fine for the two cycles I was able to test tonight. I won't be doing my other that way, since I have a feeling I got lucky not destroying mine.

I'll just wait and get some dev cells I guess.

klhoard

My Feedback: (10)

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Do you guys know that Tanic sells A123 packs now?
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Brian will solder them up however you want them. www.tanicpacks.com
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everydayflyer

I do but I am not going to pay $25per cell myself when my DeWalt cells cost me $10-$11 per cell. Let's see $35 for me to built a 3S from DeWalt cells or $75 for a premade. It takes me 15 minutes and I save $40.


Charles

dcheatwood

Hello Everydayflyer,
Please share info on how to go about doing this build from Dewalt cells or maybe a link to this info. Also which Dewalt power packs to purchase. I know that the packs have to be disassembled. The rest is knowledge that many of us could use.
Thanks Doug

everydayflyer

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

http://www.slkelectronics.com/DeWalt/packs.htm

Hope Brian does not get to upset with me. We think outside the box on RC Groups

Those interested in alternate A123 sources,packs,chargers,balancers relly should visit

http://www.rcgroups.com/batteries-and-chargers-129/

and do a Search on A123

There is a lot more going on over there.

Want to see a rather large A123 battey?


http://www.rcgroups.com/forums/showthread.php?t=623723

Charles

dcheatwood

Thanks for the info.
Doug

jaofos

Looking at that picture you posted, it seems like just turning what the tabs are welded to on the positive sites would just turn the rivet inside and not the whole cap that pops off.

Is that rivet sealed in some way that affects the cell? Just from looking at the pictures I can't see where turning that would damage the battery, as its just holding the little accordian connector to the cap.

everydayflyer

Well in the first place the cell is sealed I would think but perhaps not and twisting the end(s) can destroy the seal as I see it. Secondly the connectors from the cells matrix to the ends are not designed to be hinges.

Info sheet which comes with cells from A123 Racing.

"DO NOT rotate the negative tap (cap) relative to the can, this can cause internal damage to the cell"

Take it for what it's worth. They did not mention the positive cap nor did they mention damaging a seal.

jaofos

Well as soon as the weather wants to cooperate, I'm gonna put few more cycles through the pack I altered and see how it holds up. From the picture you posted I can't see where twisting that small cap on the positive side could damage the cell.

Need to fastforward to summer time again so it's not pitch black dark when I get home from work at 5:30pm, and if it would stop raining every single weekend this winter I could really start to enjoy these packs

everydayflyer

Perjhaps Brian will clear this up but .

The Positive end is the one which has what appears to be a gragile metal strip which when twisted could shear.

The negative end is the one with the folded braid material. The negative end has a blue bot in the center of ther vcap which is where the cell is sealed after assembley with UV activited sealeant.

It would seem to me to be a very bad idea to twist either end cap and risk damaging the seal.

93 cycles and still kicking Mule.

Charles

jaofos

OK, I got the ends confused then. I thought the positive end was the one with the blue dot and the rivet I'm talking about.

The smaller cap on the negative end is the only thing that turns when you twist it, and it looks like it's twisting on whatever holds that small cap to the end, which inside the cell holds the braid material, which should stay in place. I wouldn't think that turning the small cap would break the seal as it's inside the rivet, nor damage the braid inside.

But hey, if A123 says not to.. there's gotta be a reason.

Scower

Is it normal for the positive terminal of a cell to blow or "pop" open?
I just made a 3 cell pack, blanced and cycled it a few times and and after it was sitting in my room for a few days un-touched (with 3.35V a cell) I heard a pop from the battery. I examined the pack and found that the positive terminal on cell #2 was turn open at the crease. I quickly checked the voltages and they were all still 3.35V each. I also ran the pack for a bit (unwise I know...) and after the pack was still balanced. The only thing I am concered about is that I can smell lithium. I think I can also get you guys pictures if you want them.

Please let me know what you guys think about this.

SS Pede

Scower - it is never normal for batteries to make popping noises or for cells to change shape on their own. I'm not familiar enough with these particular cells to tell you exactly what went wrong, but I would treat that cell with extreme caution. These batteries are quite stable compared to other lithium types, but remember that even good old NiCd or NiMH cells can fail catastrophically in the right (or wrong) situation. You should probably salvage the good cells in that pack and buy a replacement pack or a replacement cell if you're comfortable with battery construction.

Scower

Thanks pede, I know that this is not a normal situation. I just wanted to get a handle on how critical this failure is, if it has ever happend to A123 or others before, the consequences of this type of event (just battery side, not "your house going to burn down" ), and what may have casued it. perhaps brian can shed some light on these questions.

Edit:
Had to edit out those damn auto smilies...

A123 Racing

Hello Jaofos,

I will be creating a separate post for this message, but you should NOT twist the negative terminal on the cell. Twisting the terminal on the cell can result in an internal short. If you cannot get the 3 cell pack into the configuration you need then you should definitely just buy some cells and make your own.

Scower,

It isn’t normal for the battery to pop open, no matter what end. Did you twist any of the ends like Jaofus did? You should definitely stop using the cell, even when our batteries are damaged they are still capable of providing power. Was this cell purchased from us or was it pulled out of a Dewalt pack?

Brian

[link=http://www.a123racing.com][/link]

Scower

I acquire these cells from a dewalt battery pack. I also made a considerable effort to prevent any damage to the cells when I constructed the pack. I did not directly solder the cells together (I used the existing tabs that were spot welded on the ends of each cell) , nor did I twist any of the ends like Jaofus did. Further, I used the ElectriFly Triton charger on the Li-ion setting. I am well aware that this setting will peek the cells at to high a voltage, and I therefore watched each battery charge carefully and removed the pack once it reached 3.7 volts per cell.
I hope this information helps.

dcheatwood

How long did it take you to charge the pack?

Scower

The ElectriFly Triton is a very delicate charger and maxes out at 2.5 amps. The pack therefor charged in approximately 45 to 60 minuets (it is not a CC charger). I don't believe that I could have damaged this cell by charging it too slowly. If I did, that would imply that the material on A123's website is misleading which I don't believe either.