A123 20AHr Pouch Cell Battery Build & Info Thread

[Grinhill]

Great job, evb. This is my favorite A123 bike pack so far. Easy to build, readily available materials, cheap, good connections.

[liveforphysics]

Here are some interesting ones made of brass.
http://www.amazon.com/1-3-Cotter-Pin-pi ... 28&sr=1-16

A lot are stainless but there are some zinc plated ones in millions of sizes. Kool!
otherDoc

You do not want any conduction through the pin itself. For long-term function it would be best to even put a little layer of kapton where the pin sits just to avoid the chance of carrying any current through the pin itself.

The pin is there to make clamp load.

[999zip999]

So a steel pin would be better ? The brass pins could be squezzed with a vise grips then solder on each end. But solder isn't very strong.

[liveforphysics]

I think a spring-steel pin would be the optimal material.

[potatorage]

How strong are these pin connections? I'd like to find a relatively easy way to hook my batteries up.

[evb]

How strong are these pin connections? I'd like to find a relatively easy way to hook my batteries up.

I install washer 4mm to end of cotter pin and solder to fix it, I guess it's sufficiently reliable

[deVries]

Here are some interesting ones made of brass.
http://www.amazon.com/1-3-Cotter-Pin-pi ... 28&sr=1-16

A lot are stainless but there are some zinc plated ones in millions of sizes. Kool!
otherDoc

You do not want any conduction through the pin itself. For long-term function it would be best to even put a little layer of kapton where the pin sits just to avoid the chance of carrying any current through the pin itself.

The pin is there to make clamp load.

Please correct me where I'm misunderstanding this pin connection method.

1) The pin allows 2 tabs folded to slip between the pin slit-opening at one end. This applies some minimal contact "force" with the tab material, but I would think not much clamping force.

2) The clamping force shown by EVB's pic shows two 3mm thick aluminum plates that are somehow clamped against the pin.

3) No information is provided how EVB clamps the two 3mm plates to the pin, or how it is bonded to the pin lengthwise with some level of clamping force sustained against the pin. The pin is in the middle of the 3mm two plate "sandwich", so it is the aluminum plate that is somehow supposed to be providing, perhaps the main, clamping force too?

Does anyone understand how EVB is achieving this clamping force with the 3mm aluminum plates?

How are the two 3mm aluminum plates clamped & bonded to the pin?

I can't find any explanation how to do this...

This connection resistance is 0.06-0.08mOm

How did you measure this? What device or exact model of equipment? I'm just wondering about the accuracy of such a measurement based on the test method and equipment used.

[evb]

I will try to answer

I got an idea clamping aluminum plates from this video
http://youtu.be/GpQcrvRoigc

Somebody guess clamping cells are less resistance. I will test it soon.

Cotter pins idea is mine.
First assembled battery was not so good, it was longer, and with high resistance connections (0.25-1mOm).

I take into account the criticism of russian e-bike forum users and tried to reduce resistance.
I processed all tabs with white spirit for remove stickers adhesive residue and polished with sandpaper.
Then folding tabs several layers and strong press by jaw vice, and fix by cotter pins with washers.

For measure so low resistance I used a simple method:

Connect a battery to load.
Current was 16.2A. I measured voltage drop on place where tabs grow, it was 1-1.3mV.
V/I=R= 0.06-0.08mOm
Maybe it is not so accurate but I guess connection resistance is ok for my applications.

[deVries]

Then folding tabs several layers and strong press by jaw vice, and fix by cotter pins with washers.

Hi Evb, I watched your video. Thanks.

The video does not show what I quote above.

Can you make a video that shows how you clamp the tabs and the two 3mm aluminum plates to the cotter pins too?

Are you pressing in the vice only the layers of tabs? In other words, do you press the two 3mm aluminum plates and/or the cotter pin in the vise press too?

I still do not understand clearly. Thank you for your help.

You make good videos in English.

[evb]

Hi Evb, I watched your video. Thanks.
You make good videos in English.

It's not my video, I only catched an idea

Can you make a video that shows how you clamp the tabs and the two 3mm aluminum plates to the cotter pins too?

It's good idea, I will try to make video, but it will take some time.

The video does not show what I quote above.

I guess you dont realize because think that 3mm plates relate cotter pins, it's no relations or I don't understand you (my english is not so good)

Are you pressing in the vice only the layers of tabs? In other words, do you press the two 3mm aluminum plates and/or the cotter pin in the vise press too?

I still do not understand clearly. Thank you for your help.

no problem, I will try to explain you by picture

[deVries]

The video does not show what I quote above.

I guess you dont realize because think that 3mm plates relate cotter pins, it's no relations or I don't understand you (my english is not so good)

Yes, I was mistaken by the photo & by something you wrote too.

No problem now. I understand thanks to your new diagram.

The 3mm aluminum plate is for the battery box or container for the cells.

Thank you for your excellent diagram.

[deVries]

Hi Evb,

I have a question for you...

IF you have to replace a (bad) cell because it fails, then do you think the crushed tabs from the vise pressure can "unfold" & come apart to free the bad cell to replace it? Do you think replacing a failed cell is possible?

It seems it would be very difficult to replace a bad cell and do a repair with all the cell tabs in series and every tab is folded/crushed together?

Or, could you add a new cell to the end of the stack of cells, and, then, somehow bypass the failed cell leaving it in series too?

Thanks!

[evb]

Do you think replacing a failed cell is possible?

Yes. When I assembled this battery, one cell (4th) was bad and I changed it for 30 mins.
unfolded tabs by screwdriver difficult

I guess if change one of cells more 3-5 times, tabs can break

[oatnet]

Do you think replacing a failed cell is possible?

Yes. When I assembled this battery, one cell (4th) was bad and I changed it for 30 mins.
unfolded tabs by screwdriver difficult

I guess if change one of cells more 3-5 times, tabs can break

I agree, it is very hard to unfold the tabs once they have been crimped, but it is doable at least once.

I am so glad to see other people demonstrating success with the crimping method. I pioneered the crimping method for these cells in 2010: http://endless-sphere.com/forums/viewtopic.php?f=6&t=12461&start=60#p281360
But my implementation was met with criticism and skepticism, and I was really frustrated by comments from certain "experts" that such a join was resistive enough to heat up when loaded with an "ebike-significant" load, and the tabs would quickly come loose. I proved to myself that a crimped joint could handle the load without heating up - I mean heck both sides of the entire tab is in contact - and two years later those packs are still going strong, so in-your-face to my critics . If you are building an ebike pack, you don't need a fancy heavy rig to hold it all together, save yourself a ton of hassle and just crimp the cells together.

If you want to put 600a through the cell, a little spot-weld will help:
http://endless-sphere.com/forums/viewto ... 14&t=29959

I like the cotter pin idea for spot-welding (unnecessary for crimping), because it makes the external clamps I used unnecessary. I can see putting a cotter pin over the end of a pair of tabs instead of the steel strips I used, spot welding through the cotter pin to melt the tabs together, then roll it up and crimp it together. The crimp would carry the load, and the cotter-pin weld would guarantee a weld no matter what happens to the crimp. If you have to replace a cell, unroll the crimp, cut off the cotter pin, and there will still be plenty of tab to spot-weld a new cotter pin.

You do not want any conduction through the pin itself. For long-term function it would be best to even put a little layer of kapton where the pin sits just to avoid the chance of carrying any current through the pin itself.

Luke, you always seem to see an angle I miss, but I don't understand this issue. Since this pin is external to the interface between the tabs, isolated from the pack and outside air with heatshrink, what is the risk here?

-JD

[dnmun]

it was my fault for mentioning the idea of a brass split pin, cotter key. i was thinking of the difficulty soldering to the steel, and was thinking brass would make it easier. i had totally missed how ebv rolled this and clamped it in the vise and put the washer on it when i first saw the pictures. now i like JD's idea about using a spot welder first and rolling it up after. just am thinking of the sense wire all the time.

[oatnet]

it was my fault for mentioning the idea of a brass split pin, cotter key. i was thinking of the difficulty soldering to the steel, and was thinking brass would make it easier. i had totally missed how ebv rolled this and clamped it in the vise and put the washer on it when i first saw the pictures. now i like JD's idea about using a spot welder first and rolling it up after. just am thinking of the sense wire all the time.

I was able to roll the balance wire into the crimp, although it was a challenge, and thicker strands worked better than fine strands. Since the balance wire only sees a handful of amps instead of 100's, it needs very little contact area, and the risk from doing it badly is having resistance cause an inefficient balance charge (not regular bulk charges) for that cell, very little wasted current.

-JD

[liveforphysics]

Luke, you always seem to see an angle I miss, but I don't understand this issue. Since this pin is external to the interface between the tabs, isolated from the pack and outside air with heatshrink, what is the risk here?

-JD

A steel cotter pin has the resistance of something like a 18awg copper wire. If you conduct through the pin, it's going to be hot in a second, and release it's clamp load. The clamp load is what provides all the desired electrical connection.

[oatnet]

Luke, you always seem to see an angle I miss, but I don't understand this issue. Since this pin is external to the interface between the tabs, isolated from the pack and outside air with heatshrink, what is the risk here?

-JD

A steel cotter pin has the resistance of something like a 18awg copper wire. If you conduct through the pin, it's going to be hot in a second, and release it's clamp load. The clamp load is what provides all the desired electrical connection.

OK, I see where you are going, thanks Luke!

I think in this application the welded tabs will be inside the cotter pin, so while it is part of the conductive package, there is a huge low-resistance pathway through the welded tabs, so it does not carry the load. If the tabs are rolled up and crimped, then the entire surface on both sides of each tab make a low resistance pathway, so it won't matter if there is a steel cotter in the middle.

I'm going to try this on my next 1p pack-build, a cotter pin should be much easier to work with than clamps. EVB thanks for the cotter pin idea, and Dnmum thanks for the idea of spot-welding the cotter pin.

-JD

[deVries]

I am so glad to see other people demonstrating success with the crimping method. I pioneered the crimping method for these cells in 2010: http://endless-sphere.com/forums/viewtopic.php?f=6&t=12461&start=60#p281360

It's a good read with lots of pics, so I'd recommend checking these posts if doing "the crimp".

[potatorage]

Luke, you always seem to see an angle I miss, but I don't understand this issue. Since this pin is external to the interface between the tabs, isolated from the pack and outside air with heatshrink, what is the risk here?

-JD

A steel cotter pin has the resistance of something like a 18awg copper wire. If you conduct through the pin, it's going to be hot in a second, and release it's clamp load. The clamp load is what provides all the desired electrical connection.

OK, I see where you are going, thanks Luke!

I think in this application the welded tabs will be inside the cotter pin, so while it is part of the conductive package, there is a huge low-resistance pathway through the welded tabs, so it does not carry the load. If the tabs are rolled up and crimped, then the entire surface on both sides of each tab make a low resistance pathway, so it won't matter if there is a steel cotter in the middle.

I'm going to try this on my next 1p pack-build, a cotter pin should be much easier to work with than clamps. EVB thanks for the cotter pin idea, and Dnmum thanks for the idea of spot-welding the cotter pin.

-JD

So what tool are you using to crimp the tabs?

[deVries]

So what tool are you using to crimp the tabs?

Evb uses a vise. His diagram...

Evb Uses Vice to Crimp

assemble.jpg (38.6 KiB) Viewed 733 times

[potatorage]

So what tool are you using to crimp the tabs?

Evb uses a vise. His diagram...

assemble.jpg

I meant these :

[oatnet]

Those are mine, more description on this build thread:
viewtopic.php?f=6&t=12461&start=60#p281360

I used a set of wide-jawed vice grips to hold the tabs together, as well as the straight edge for the first bend in the tab. It usually took me a couple of trys to get everything lined up just so, but it was nice to be able to release the clamp and do-over, because the first bend dicatates how the rest of the roll will go.

Once I had the bend as far as the Vice-Grips can go before interfering, I used a pair of large electrician's pliers to crimp it down. The pattern in the jaws formed indentations that really lock the tabs together, stretching the metal and expanding the contact surface even further. That first fold was always tough, because the tabs can still move around, and the balance wire wants to pop out.

I think I used my hands to roll the soft tabs together, and crimped with the same pliers after each fold. The indentations also are what made it hard for me to seperate the tabs later.

-JD

[ohzee]

So last night made a 12s pack using drutledge's method of compression of the tabs.

Got my cell_man 12s 80amp BMS and am about to put it on the pack.. had a question and I know this is BMS related , but
it's in regard to my build. I have never used a BMS before and the diagram makes what goes where pretty obvious.

One question I have is how much current can I send into the charge plug ?

I charge with 2 modded 12V HP supplies into a icharger 306b on my lipo currently.

Thanks - looked around , but did not find any obvious answers must be buried or I am blind.

[999zip999]

Hang the bms sense wires plug or board up in the air like a parachute. I found it easier to work from. So you can get the wires right.