# My DIY A123 modules ready to go



## kerrymann (Feb 17, 2011)

I have documenting my miata build in the "All Conversions and Builds" section and on my blog at:

http://electricmiata.blogspot.com/

I realized that my pack build up might be worth it's own post as a summary for others to build.



I went through at least a dozen design iterations and each time tried to simplify it and make it as DIY friendly as possible. I think the result is a pack that is about as light as you could possibly make it and you can still run max power without any additional life or performance hit. For my car I will only be driving in nice weather so cell cooling was my only concern. But it you wanted to put it in a insulated enclosure you could also heat the cells by circulating warm air.

The basic design end up being really just a DIY version of the A123 modules. 



​
The cells are stacked together with cooling fin sandwiched between every other cells. They are restrained by end places made of .120" aluminum sheet and 1" aluminum angle. The assembly is clamped together by 1/4" steel all thread.

For the electrical connections the tabs were bent and sandwiched together with 3 cells connected in parallel. 

I punch holes in the cells using a simple block I made that fit into a 3 hole punch.




​
The holes went very quickly but unfortunately removing the glue from the barcode stickers did not. You might have been able to leave it but adhesive is typically very non-conductive. To reduce the current density at the connections I interleaved the tabs. 


​

The pack was a little harder to assemble but the result was three times as much surface area for the current to flow through. The hardware was just zinc plated 1/4 bolts, washers and locking nuts. 







​
The BMS will connect to the extra threads on top of the nuts.


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## Jordysport (Mar 22, 2009)

Interesting design, But how are you allowing for the swelling of the cells? and what BMS system are you using? this appears to be what rwaudio wanted to do with his pack.

Edit, just noticed your bolted just the tabs together are you not worried about the Tabs failing when you've tightened them up (small surface area the bolt is acting on)? Maybe have a sandwich block on either side to clamp it up, maybe 2/3mm thick copper on each side with the same two bolts. 

What are the dimensions of the bolting face? as i am looking at making a 3P pack.


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## rwaudio (May 22, 2008)

Jordysport said:


> Interesting design, But how are you allowing for the swelling of the cells? and what BMS system are you using? this appears to be what rwaudio wanted to do with his pack.
> 
> Edit, just noticed your bolted just the tabs together are you not worried about the Tabs failing when you've tightened them up (small surface area the bolt is acting on)? Maybe have a sandwich block on either side to clamp it up, maybe 2/3mm thick copper on each side with the same two bolts.
> 
> What are the dimensions of the bolting face? as i am looking at making a 3P pack.


That is very similar to what I proposed but with the addition of clamping blocks like you mentioned. This should work well and the trade off for not using the clamping blocks is probably small with regard to voltage drop and does simplify the required hardware. I would speculate at the performance of the pack as slightly better than any pack using a separator block. (IE my pack or Jack R's design)

Well done Kerrymann!


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## Jordysport (Mar 22, 2009)

rwaudio said:


> That is very similar to what I proposed but with the addition of clamping blocks like you mentioned. This should work well and the trade off for not using the clamping blocks is probably small with regard to voltage drop and does simplify the required hardware. I would speculate at the performance of the pack as slightly better than any pack using a separator block. (IE my pack or Jack R's design)
> 
> Well done Kerrymann!


Less required hardware yes but the question of longevity on the tabs work hardening under vibrations etc combined with a small contact surface area from the clamping bolts. 

you would only need 2-4mm of copper/Al sandwich plates just to make the N/mm^2 less and to achieve a higher clamping force with less risk of failure. 

But those are minor details, Looks a great pack nice clean and tidy ready to drop in! will for sure be keeping an eye on your thread


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## NikiL (May 24, 2012)

Great job. Nice and smart designed A123 20Ah battery pack. In that way or similar I would build it also.


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## kerrymann (Feb 17, 2011)

rwaudio said:


> That is very similar to what I proposed but with the addition of clamping blocks like you mentioned. This should work well and the trade off for not using the clamping blocks is probably small with regard to voltage drop and does simplify the required hardware. I would speculate at the performance of the pack as slightly better than any pack using a separator block. (IE my pack or Jack R's design)
> 
> Well done Kerrymann!





Jordysport said:


> Less required hardware yes but the question of longevity on the tabs work hardening under vibrations etc combined with a small contact surface area from the clamping bolts.
> 
> you would only need 2-4mm of copper/Al sandwich plates just to make the N/mm^2 less and to achieve a higher clamping force with less risk of failure.
> 
> But those are minor details, Looks a great pack nice clean and tidy ready to drop in! will for sure be keeping an eye on your thread


Thanks to you both. I went back and forth on using plates and seperators even building a few cells up. I originally made Al plates to increase the surface area but I found washers gave almost the same area and when by interleaving the tabs the area was much greater:

*Plates*

My plates were 6mm thick and 45mm x 20mm giving 900mm^2. Neglecting current flow through the bolt area (12.5mm^2 *2 bolts) that gives you 875mm^2. Max current you can expect from these cells is 1200amps giving 1.37A/mm^2 which is an acceptable current density

*Washers*

The washers are 20mm OD and ~6mm ID giving each a area of 314mm^2-12.5mm^2. So each washer has ~300mm^2 of area so for two washers it is 600mm^2 total. This gives a current density of ~2A/mm^2 which is still acceptable but getting marginal. Now all this is assuming the current is just flowing through one face. So I interleaved the cell tabs so the current could flow through 5 faces. This gives me a surface area of 1500mm^2 and dropping the current density to a low 0.8A/mm^2

The clamping force is going to be constant based on the diameter and grade of the bolts. A higher clamping pressure is actually a good thing because it makes a better electrical connection. I am really not worried about fatigue in these tabs. Copper and aluminum are the most susceptible materials for fatigue but there is no really load on these tabs, road vibrations The shaker table we have the lab at my work is the size of a semi so it will be to sneak in some vibration testing.  It's not shown but there is a lexan cover that protects the terminals and you could put a bead of silicone down between the cover and the top of the tabs. It would restrain it but still peel off when you wanted to service the cells. In my opinion it isn't necessary but only time will tell. 

I am actually more worries about any potential internal damage to the cells from making the packs in the first place as some of these cells were removed and installed 3-4 times... 

I have shot video step by step for building the pack. If there are people that have cells and are really interested I can try to make up a tutorial and throw it on YouTube.


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## kerrymann (Feb 17, 2011)

I missed your question on the BMS. I am using a Lithiumate Lite system.


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## danh818 (Dec 14, 2011)

Great job Kerry! I think if you posted the video we would all appreciate it. 

Any worries about all that conductive metal surrounding the cells?


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## danh818 (Dec 14, 2011)

Also, what is supporting the bottom of your module? I have seen the picture on you build thread of the module in the stock fuel tank position; it seems to be hanging. What is keeping the cells from slipping out the bottom other than the tension of the cables?


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## Jordysport (Mar 22, 2009)

kerrymann said:


> I missed your question on the BMS. I am using a Lithiumate Lite system.


Thanks, looks a good setup, might consider it myself. just a few questions on it sorry to be a pain. I assume you have bottom balanced the 3 cells in parallel before assembling, then you can use the BMS to balance them in series? Do you have any more pics of the BMS system as this is one area i have no clue about atm (sorted controller, cells, motors, etc etc)

Thanks Again
Jordy


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## Jan (Oct 5, 2009)

Jordysport said:


> I assume you have bottom balanced the 3 cells in parallel before assembling...


Won't that happen automaticaly? I asume they are somewhat balanced from the factory. And if they are stressed they will balance prety quickly due to the deeper voltage sag at lower SOC.


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## kerrymann (Feb 17, 2011)

danh818 said:


> Also, what is supporting the bottom of your module? I have seen the picture on you build thread of the module in the stock fuel tank position; it seems to be hanging. What is keeping the cells from slipping out the bottom other than the tension of the cables?


They are completely supported by the tension. With a couple hundred pounds of force on each rod it will take well above 10gs for these cells to slip. I might add a bottom plate for splash protection though.



Jordysport said:


> Thanks, looks a good setup, might consider it myself. just a few questions on it sorry to be a pain. I assume you have bottom balanced the 3 cells in parallel before assembling, then you can use the BMS to balance them in series? Do you have any more pics of the BMS system as this is one area i have no clue about atm (sorted controller, cells, motors, etc etc)
> 
> Thanks Again
> Jordy


All the cells were drained down to the same level as part of the cell testing I did but it isn't necessary for cells in parallel anyway. They will find their own equilibrium. Originally I was going to skip BMS but I need cell monitoring to keep an eye on the gray market cells. 



danh818 said:


> Great job Kerry! I think if you posted the video we would all appreciate it.
> 
> Any worries about all that conductive metal surrounding the cells?


Thanks. I'll try to get around to it. I have zero video editing software and almost the same amount of time to do it.  

The only place where it is physically possible for a short to occur due to movement, is at the last cells. And I am insulating.


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## drgrieve (Apr 14, 2011)

This looks the easiest build I've seen around. I have a few questions if you don't mind:

1. I'm looking at 5p. Do you think that will still be doable with this design?
2. What is the weight of one of your modules (so I can see how much weight to plan for).
3. From others testing it seems that most of the heat manifests at the tabs. Perhaps allow room for a fan to be added later if needed.
4. Are the cooling fins structural or can they be replace by insulators

Cheers,

David.

PS Another vote for video. You might ask Jack Rickard if he is interested in the videos - not sure how turned off them he is after his mishaps.


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## kerrymann (Feb 17, 2011)

drgrieve said:


> This looks the easiest build I've seen around. I have a few questions if you don't mind:
> 
> 1. I'm looking at 5p. Do you think that will still be doable with this design?
> 2. What is the weight of one of your modules (so I can see how much weight to plan for).
> ...


No worries on the questions, by all means.

1) 4p would work but I am unsure about 5p as you would be distorting the top of the cells a lot. I would ask why do you need 5p? That is a lot of capacity. are you running max voltage of your controller? Even with my soliton1 and a ~250VDC pack I will only be pulling 680amps peak for my motor (170v max). I would try to maximize the voltage limit of your controller with cells in series and then add cells in parallel for capacity and current from there.

2) For 72cells it's about 34kg. The parts only weight ~2kg total so just add that to the weight of your cells. The pack system is insignificant to the weight of the actual batteries.

3)I'd be curious to see that data. I have a design that integrates to PC fans into the top cover but I haven't seen anything so far that would convince me I need to do it. There will be plenty of free airflow on it's own.

4) If you don't think you need cooling (say max of 3-4C) then just eliminate the fins all together. But everything I have seen and read shows that you want some cooling to maximize cycle life.

PS. I actually offered to Jack a couple weeks ago as it was the easiest way to share with people. Most of the video I shot 2 months ago but have been too busy to do anything with it. But Jack wasn't interested in the video and suggested I sign up for EVCON (too far of a drive and I have to work anyway).


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## MalcolmB (Jun 10, 2008)

Hi Kerrymann,

I really like the simplicity of your pack construction.



kerrymann said:


> 3)I'd be curious to see that data. I have a design that integrates to PC fans into the top cover but I haven't seen anything so far that would convince me I need to do it. There will be plenty of free airflow on it's own.


There are a few thermal images of these cells under load here: http://endless-sphere.com/forums/viewtopic.php?f=14&t=15093&hilit=A123+infrared&start=105


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## drgrieve (Apr 14, 2011)

kerrymann said:


> 1) 4p would work but I am unsure about 5p as you would be distorting the top of the cells a lot. I would ask why do you need 5p? That is a lot of capacity. are you running max voltage of your controller?
> 
> 2) For 72cells it's about 34kg. The parts only weight ~2kg total so just add that to the weight of your cells. The pack system is insignificant to the weight of the actual batteries.
> 
> ...


1. Ah well I'm trying to save up for an completely over the top build but an unplanned addition to the family and finishing an unnecessary expensive house build is getting in the way. 
Anyway the drive train I'm considering is dual Kostov 250v mated to a gear vendors overdrive connected to diff. 5P100S A123 (32 KWh) pack. Dual Soliton 1 controllers. Plan to run at 1800 amps (900 per motor) and over volt motors to 280v (RPM limited). Will charge pack to ~3.45v so under limit 350V Soliton limit. Aiming for peak battery output of 500KW.
If I was to go to 4P then I'd need to up the voltage but the only other option currently would be a Shiva. Which is even more over the top than I need.

2. Awesome! 

3. This is from evtv I think - I read a lot so forget the sources. No actual data that I recall, just from the commentary. My boxes will be enclosed so I'll probably need fans.

5. Thought as much. He's gone off A123. But nevertheless he has generated much interest even if he doesn't finished those side projects. 

Be sure to send him a spreadsheet of a power run when you get going. He should be jealous of your low voltage sag.

Cheers!


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## kerrymann (Feb 17, 2011)

drgrieve said:


> 1. Ah well I'm trying to save up for an completely over the top build but an unplanned addition to the family and finishing an unnecessary expensive house build is getting in the way.
> Anyway the drive train I'm considering is dual Kostov 250v mated to a gear vendors overdrive connected to diff. 5P100S A123 (32 KWh) pack. Dual Soliton 1 controllers. Plan to run at 1800 amps (900 per motor) and over volt motors to 280v (RPM limited). Will charge pack to ~3.45v so under limit 350V Soliton limit. Aiming for peak battery output of 500KW.
> If I was to go to 4P then I'd need to up the voltage but the only other option currently would be a Shiva. Which is even more over the top than I need.
> 
> ...


That is ambitious build! In that case just build 3p packs and connect half of the packs in parallel to get the equivalent of 6p. Or with 2 controllers you could even just run two separate packs so you would even get some redundantancy.


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## kerrymann (Feb 17, 2011)

MalcolmB said:


> Hi Kerrymann,
> 
> I really like the simplicity of your pack construction.
> 
> There are a few thermal images of these cells under load here: http://endless-sphere.com/forums/viewtopic.php?f=14&t=15093&hilit=A123+infrared&start=105


Thanks and thanks!


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## kerrymann (Feb 17, 2011)

*Mark II module*

*Mark II module *



The original module design has undergone another change to improve the end plates. I went back to a previous design that uses nice thick 3/8" aluminium plates. I had originally try to keep things as DIY friendly as possible so I used .120" sheet and the L angles. The problems is the sheet is not stiff enough and doesn't do a very good job of distributing the force over the whole face of the cell and I worry if could lead to premature cell failure. Going to 3 channels makes it better but still not as good as I would like. So I am getting quotes on having the plates CNC'd. 





I hope to have the parts in a week or two and will update from there. If anyone else is interested in getting in on my CNC order let me know. 



In the mean time I am installing my BMS and should have pics of that tomorrow.


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## onegreenev (May 18, 2012)

*Re: Mark II module*

Just remember that keeping pressure on the plates does not keep them healthy. I had a set of cells that was happy and content visually in the case for the last 3 years and yesterday I decided to pull them out for charging. These had been drained slowly because of a failed BMS system. I am now thinking that the pack had been drained some initially and then driven not knowing that any cells were drained low. The balance was way off and the BMS failure failed to report low voltage cells. The vehicle was driven and then put up because of crappy performance and distance. Still not knowing what actually happened. Just before I pulled the cells they all looked perfect. All snug in a nice tight case. As soon as I pulled them they popped out like fat little pigs. So even after 3 years of being held tight the damage was done and the pressure remained. Pressure won't fix or prevent any thing from happening and only covers a problem. 

Don't put too much on clamping the cells. If I could have seen the cells puff from the damage from over discharging them while driving it would have been easy to diagnose a problem. 

Don't rely too much on the BMS system either. If you over discharge your cell while driving you WiLL kill the cell, clamped or not. 

Just thick flat aluminum ends would work. My idea will only be thick fiberglass reenforced with aluminum. No need for elaborate clamping except to hold them together lightly. I am including a bottom to hold them. 


Nice work but where is enough, enough?


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## kerrymann (Feb 17, 2011)

For those that had questions on the BMS (sorry for the overlap with my other post, it is a unintended consiquence of multiple posts):

BMS install 



I got all the BMS mid boards installed today. The Lithiumate Lite is about as simple a system to install as possible (short of not having a BMS . 

Some of the things I like about it so far is the board to board connection is realatively easy and the diagnostic light on the PCB that blinks 6 times to let you know you installed it correctly and that it is working. The boards are pretty small and fit well with 3 cells in parallel. Part of the way through I realized if I installed half of the boards upside down this gave you a bit of extra clearance.

​
Notice I said upside down NOT BACKWARDS! This brings me to one of the things I don't like on the system. If you install a cell backwards (i.e. wrong polarity) it is dead. Even for a millisecond. Elithion is very clear about this in their literature but it just seems like a diode to protect the boards would have been a easy fix. So with that in mind, I made sure I had a little installation procedure and followed it. Elithion manual seems very good along with some videos (with no audio for some reason) but for my application I set the pack on it's side and did half where the PCB would hang down to gravity. I was anal and checked every connection with the DMM first then verfied the LED blinked before tightening the nuts down. 

​
I did one full side then flipped the module and did the mid boards in the other direction.


​Cut then stripped all of the wires to the right length. 

​
I then made the connections, again one side at a time. 

​
This just helped to get in a pattern and ensure no mistakes.


​Just to reiterate what I said about the BMS earlier. If I had cells that I was 100% confident in then I would not have bothered. But being this is an experimental pack design I am far from it (not even close to 3 sigma . So I decided I needed to montior each cell. I looked into Battery Monitoring Systems and wasn't impressed. I found the Elithion system gave this functionality along with a management system for a very reasonable price and had a lot more features. I must say for someone that is skeptical of BMS I am preety impressed with the system so far. But I am not done yet either... 

I am also looking if I can use the lithiumlite system just for monitoring and keep my pack bottom balanced. 

BTW, Before I purchased I also found all the fabrication was done here in Colorado (Broomfield, CO). I am a big fan of buying locally so this was icing on the cake for what I already thought was the best system and best value.


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## kerrymann (Feb 17, 2011)

*Keeping cool*

*Keeping cool *

I have had a few people ask me about the cooling fins on the pack so I am posting so more info and hopefully the whole post will show up this time.

I know there is much debate whether thermal management is required for these batteries. Some say it is not required while others say it is essential for battery life. In reality they are both correct. If you are taking a leisurely cruise on a spring day then thermal management will not be a problem for you. The starting temperature of the pack and the low discharge rates don’t require it. However if you are driving in more extreme conditions or operating your batteries at a high discharge level then thermal management becomes much more important. For instance if you are doing laps +20 on a track on a hot summer day then your batteries will NEED cooling, not to mention every other system on your car:


​ 
The coolings fins placed between the cells are essential for getting the heat out of the cells. The fins are made from 8” wide aluminum flashing from Lowes. It comes in 25’ long rolls that are cut into squares. Since I don’t like making the same part more than once, I set-up a quick line to crank out a hundered in a matter of minutes using a $30 paper cutter from the office supply store.

​ 
The cutter comes with a simple fence and has no problems cutting the soft thin aluminum.







 
As you can see in the picture I setup the cutter and roll on a bench so I simply unroll it cut and repeat. For this pack I used one fin every other cell. This assures that each cell is in direct contact with a fin and should be minimum if your application requires cooling. Fewer fins will only cool some cells and result in potentially significant variations in cell temperatures. For very high power and ambient temperatures you can step up to a fin in between every cell for double the cooling. I used bare aluminum flashing for maximum heat transfer and it was the only finish I could find in 8” width. The flashing is also available in prepainted which could provide a thin barrier which could help with voltage leakage from the pouch casing but will decrease the effectiveness of the fin some amount. Whichever flashing you use make sure that the surface of the flashing and the cells are clean before assembly. Any dirt or debris that becomes trapped can potentially damage the cell during assembly and/or result in wear over time.


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## agniusm (Apr 30, 2012)

very nice battery indeed. What i would suggest is to put 4 springs under 4 nuts that titening the pack. This would allow for cell sweling.


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## kerrymann (Feb 17, 2011)

agniusm said:


> very nice battery indeed. What i would suggest is to put 4 springs under 4 nuts that titening the pack. This would allow for cell sweling.


Thanks, I have gotten that suggestion a few times but there are a few problems with that. I was originally thinking of belleville washers for that same reason but the threads get can get caught on the plates which is an easy problem to solve. But the main reason against any springs is the pack is mounted in the car by those end plates. So unless you make an odd connection to the car the end plates are held rigidly irregardless of the springs. Instead I prefer a .5" think sheet of elastic foam between the end plates and the first cells. It no only allows for swelling but also provides electrical isolation. 

I realize I have had my MkII pack built for over a month now and haven't posted the design. I'll try to get something up this weekend.


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## Stiive (Nov 22, 2008)

Hi there,
Was wondering if you get any problems with capacitance build up between the cell and the Aluminium? I guess it shouldn't matter too much if so, as the fins look like they are electrically isolated from the clamping rods and therefore the chassis, is this correct?

Also, do you get any leakage of voltage at the edge of the lamination of the cells?

We moved away from the aluminium between the cells, as in our experience it is mainly the tabs that heat up

Cheers


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## agniusm (Apr 30, 2012)

I am too thinking about making a pack for scirocco from these cells. I will weld up a box for cells with one side open to mount pressure plate on springs on one side. I got some .5mm aluminium sheets to heatsink each cell. This i how:








This will transfer heat to the walls of the box. Will be using 380 cells for 76S5P configuration.


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## kerrymann (Feb 17, 2011)

*Rev A and on to Rev B*

*Rev A and on to Rev B *



Here are some pictures of the Mark II pack. 







​
I have been having problems with one of my Mark I pack having leaking cells and I think it is due to uneven pressure on the cells. 

​
I pulled the pack and you can see the electrolyte on the cooling fin


​I am glad I made the pack easy to remove and replace cells. This is the third time I have had to R+R bad pouches.​

​The MkII has very stiff end plates which I think mitigates this problem. A couple of changes from the Rev - and Rev A design: I glued plastic plates over the inside of the end plate to prevent possible shorts to the end plates from the tabs. I also put a sheet of elastic foam between the end plates and the outer most cells. This foam sheet acts as as spring to control the pressure on the cells due temperature, cycling, etc. and insultation on the threaded rod to prevent a electrical pat from the fins that may be touching the rods.

I am considering adding insulation in between the cells. I haven't had a problem with it but others have:

http://www.diyelectriccar.com/forums/showthread.php/a123s-gone-bad-78971.html

The factory modules don't have any intracell insulation but obvious some people are having problems. I have to do some more head sratching as to what the root cause of the problem is first.


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## kerrymann (Feb 17, 2011)

agniusm said:


> I am too thinking about making a pack for scirocco from these cells. I will weld up a box for cells with one side open to mount pressure plate on springs on one side. I got some .5mm aluminium sheets to heatsink each cell. This i how:
> 
> 
> 
> ...


Looks like that should work. I think the rimac module uses a spring arangment similar to what you describe but haven't heard how well it works and no reason to think it won't. The .5mm is probably more then you need or want if you are putting it in a seperate box. I am using ~.15mm for mine to keep cost and weight low and it is plenty of heat transfer. It also allows me to make the parts much faster. Remember you will need to make hundreds of these fins for a pack that size.


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## onegreenev (May 18, 2012)

I really don't think you need to worry about cooling fins because the fins are actually against plastic anyway and won't wick away much of any heat. I would however suggest using TYVEK envelopes for each cell to prevent any of the mylar from touching any other cell. It is strong and breathable. Have a bottom support on the package and don't squeeze the cells. They are already tight due to the vacuum packing. Just make them snug. Make sure no terminal can short out and be sure you undercharge and underdischarge. 

Pete


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## onegreenev (May 18, 2012)

Don't forget to bottom balance all the cells first.


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## MalcolmB (Jun 10, 2008)

onegreenev said:


> Don't forget to bottom balance all the cells first.


Why would you bottom balance cells if using a BMS?


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## onegreenev (May 18, 2012)

Why use a BMS?


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## Ziggythewiz (May 16, 2010)

Pete is convinced that bottom balancing is so superior to top balancing that even if you are top balancing you should bottom balance first to be more better.


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## onegreenev (May 18, 2012)

Top balance if you must. I am not the only one here that thinks top balancing is a waste as well as using a BMS. So there is my stand from the horses mouth. 

Yes, I believe in bottom balancing and NO BS BMS. 

Yes, I believe in bottom balancing each pouch before being put in parallel. Then bottom balancing the whole thing with no BMS. Under charge and under discharge and you won't need a BMS.  A Proven Fact. These are LiFePO4 cells.


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## MalcolmB (Jun 10, 2008)

onegreenev said:


> Why use a BMS?


See post #21.


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## onegreenev (May 18, 2012)

I did have a look.


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## JRP3 (Mar 7, 2008)

onegreenev said:


> Why use a BMS?


How many A123 modules has Jack destroyed not using a BMS? Yes these are LiFePO4 cells, no these are not the large format CALB/TS/Winstons. These cells need monitoring, and if you're going to do that you may as well manage them too.


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## kerrymann (Feb 17, 2011)

Guys,
Let's defer on the subject of top balancing vs bottom balancing for this thread, please. There are already plenty of other threads already for that discussion where people have vastly different opinions and it's not particularly relevant here. I will say that with these gray market A123 cells that I believe you need active battery MONITORING.


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## onegreenev (May 18, 2012)

I'd love to see any BMS on the market prevent what happened with Jacks cells. A shorted cell is shorted. No BMS will fix that. A leaking cell is a leaking cell. No BMS will fix that. These are packaged in conductive Mylar which is pretty lame to begin with but you must take measures to prevent shorting. The thin plastic cover over the mylar is a problem. I proposed to use Tyvek covering over each cell to prevent direct contact to each cell and give the cell that much more protection. Hell you can scrape that covering off real easy. Those sides can touch and you can compress too much and get leakage. If you over charge them they will fail and if held too tightly they will split at the seam and leak. They can short if contact is made with another cell. Good luck with a BMS stopping that. 

No, these don't need a BMS. You can if you like but they are LiFePO4 in a mylar vacuum packed package. Aluminum plates between will not really remove much heat as the plastic covering is an insulator. LiFePO4 likes warm. 

Jack actually has two packs that have been done that have had no issues and NO BMS. I guess you don't pay much attention.


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## onegreenev (May 18, 2012)

Monitoring Yes. Management NO. Monitoring can be done manually.


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## Elithion (Oct 6, 2009)

MalcolmB said:


> Why would you bottom balance cells if using a BMS?


You wouldn't.

Despite all its disadvantages, bottom balancing admittedly does have one advantage in packs without a BMS.

But that one advantage is moot if you have a BMS. In that case, you would top balance an energy pack (e.g.: EVs) because top balancing has all the advantages and none of the disadvantages. You would mid balance a power packs (e.g.: HEVs).


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## onegreenev (May 18, 2012)

Don't need a BMS if you balance on the top either. Top balance and then undercharge to a specified voltage and your good to go as long as you stay well off the bottom so you don't drive any cell into reversal. You are ALWAYS limited to the lowest capacity cell in the pack BMS or not. I prefer to bottom balance because the pack is only full for a moment and beyond that moment it is on the way down. So down on the bottom is where I prefer to stay for the balancing portion. The amount of amp hours available above 3.5 volts any way and if you use a BMS to STUFF IN THAT LAST BIT you will get maybe a mile and a half at best before your well off that top anyway. So in reality there is no real need to top balance your pack. If you want to use a BMS of sorts to MONITOR your cells that is actually different than managing your cells. Those with LiPO cells may need a monitoring system and thermal management system to keep from frying a pack but still you won't need a system to keep them all topped off. Your only at the top for a moment. Why go there. If you have a cell or two that get to 3.7 volts during the charge cycle your still doing quite well. Yes there will be some with varying capacities but that should really be very small differences. If you happen to have a cell that is way off the mark of the others then just replace it with one that is within the capacity range of your other cells. Remembering that the lowest capacity cell IS your max you can put in or take out. Go beyond that and you kill a cell or more. 

Pete


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## MalcolmB (Jun 10, 2008)

Come on guys, kerrymann has already asked us nicely to take the BMS stuff elsewhere.


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## agniusm (Apr 30, 2012)

So come again, why all e-vehicle manufacturers without exception use battery management if they could make more profit by just bottom/top balancing cells? Perhaps it's a case of hiring incompetent engineers. To me not using BMS is the same as saying i don't trust the computers and will do math the old fashion way, using fingers. I have tested some top balanced in 6S config and its not pretty what it does. 
Sorry for trashing this thread.
What about using a solid aluminium box? I know that it adds to the cost but it would protect fragile cells and dissipate some heat. Crap was spieled here about plastic insulating these cells, cooling is necessary on high amp draw. At 200A they reach 50C in 5 mins and that is going towards hot NOT warm


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## MalcolmB (Jun 10, 2008)

The thermal images in the link I posted earlier from ES (http://endless-sphere.com/forums/viewtopic.php?f=14&t=15093&hilit=A123+infrared&start=105) show that most of the heat is generated close to the negative tab. Maybe it would be sufficient to concentrate on heat sinking the tab.


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## marc02228 (Jan 15, 2011)

agniusm said:


> So come again, why all e-vehicle manufacturers without exception use battery management if they could make more profit by just bottom/top balancing cells? Perhaps it's a case of hiring incompetent engineers. To me not using BMS is the same as saying i don't trust the computers and will do math the old fashion way, using fingers. I have tested some top balanced in 6S config and its not pretty what it does.
> Sorry for trashing this thread.
> What about using a solid aluminium box? I know that it adds to the cost but it would protect fragile cells and dissipate some heat. Crap was spieled here about plastic insulating these cells, cooling is necessary on high amp draw. At 200A they reach 50C in 5 mins and that is going towards hot NOT warm


Good to see, the thread is turning from the BMS rubbish (just for this thread, not in general) to the topic.

Do you think you will discharge the cell with 200A for 5 mins? That would be 600A for the entire pack. That's a huge amount of power and the pack would be empty after that time, anyway. 

I odered 300 A4 sheets of 0.2mm Mylar (actually used as airbrush stencil) to put between and wrap under the cells. Hopefully that prevents the Anode to cell body failures.


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## kerrymann (Feb 17, 2011)

onegreenev said:


> I proposed to use Tyvek covering over each cell to prevent direct contact to each cell and give the cell that much more protection. Hell you can scrape that covering off real easy. Those sides can touch and you can compress too much and get leakage. If you over charge them they will fail and if held too tightly they will split at the seam and leak.


I am thinking of electrically isolating my cells with sheets. Tyvec is a very durable material but I would advise against a pouch. The reason being if the cells do start to leak you won't be able to detect the failure



agniusm said:


> What about using a solid aluminium box? I know that it adds to the cost but it would protect fragile cells and dissipate some heat. Crap was spieled here about plastic insulating these cells, cooling is necessary on high amp draw. At 200A they reach 50C in 5 mins and that is going towards hot NOT warm


I am assuming you are talking about thermal insulation (as opposed to electrical). For fair weather driving insulation is a bad idea, but for cold weather it can be very important. Here in colorado my miata will not be outside in the cold. Charging very cold cells will lead to plating and greatly reduced cell life. What was your cell starting temp? Were the sides exposed or insulated.



MalcolmB said:


> The thermal images in the link I posted earlier from ES (http://endless-sphere.com/forums/viewtopic.php?f=14&t=15093&hilit=A123+infrared&start=105) show that most of the heat is generated close to the negative tab. Maybe it would be sufficient to concentrate on heat sinking the tab.


That is where you need it the most for sure but I didn't want any sharp edges against the pack that can damage the cell pouches. So the fin needs to be bigger then the whole cell. That and you aren't really saving much by trying to cool just the top.



marc02228 said:


> Do you think you will discharge the cell with 200A for 5 mins? That would be 600A for the entire pack. That's a huge amount of power and the pack would be empty after that time, anyway.
> 
> I odered 300 A4 sheets of 0.2mm Mylar (actually used as airbrush stencil) to put between and wrap under the cells. Hopefully that prevents the Anode to cell body failures.


You wouldn't be doing it for 5 minutes continuously but at a track you are going to be doing it 50-70% of the time. On the track you are either on the throttle or on the brakes, coasting doesn't cut it. Particularly at a track like Pueblo where the front straight used to be a 1/4mile drag strip...


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## kerrymann (Feb 17, 2011)

So I pulled my packs out last night and am giving them a complete inspection. The MarkII pack is great with no sign of damage, leaking or corrosion after a month. The MarkI has leaking cells and I will be pulling it apart tonight to determine the cause. Some of the leaking cells are in the middle of the pack which discounts the idea of it being due to unequal pressure. And the MkII had more compression then the MkI. All very curious...

For electric isolation I am considering sheets (material to be determined). I like the Marc's idea of using sheets because if you take a legal sized sheet and split it in half then it is perfect for the A123 cells. So I am debating 3 options:

#1 Leaving it with no insulation
#2 Adding insulation in-between every third cell since I have mine in 3p
#3 Insulation in between every cell

And I probably going to do #3.


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## agniusm (Apr 30, 2012)

I as talking about the enclosure to protect cells mechanically as well as help dissipating some of the heat. It would allow to think of a spring mechanism to allow cells to swell. I think this is what happened with one cell leaking on your mark1, at least it looks like that on the photo.


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## onegreenev (May 18, 2012)

agniusm said:


> I as talking about the enclosure to protect cells mechanically as well as help dissipating some of the heat. It would allow to think of a spring mechanism to allow cells to swell. I think this is what happened with one cell leaking on your mark1, at least it looks like that on the photo.


A cell that swells is a cell that has been overcharged or overdischarged. Usually the later because of an improperly bottom balanced pack. It can of course happen on the top because the charger failed because of a non working BMS. 

Can't say for sure about his leaky cell. If it was overcharged or overdischarged the cell because of the clamping pressure not allowed for swelling and caused it to pop a hole in the seam. Once that happens all the internal pressure would have been released and then electrolyte would leak out. Damage has been done. The pouch cells have no provision for pressure release so it is VERY VERY important to be sure you do not overcharge or overdischarge your cells. They must be balanced properly and if you have a BMS you must be sure it is working properly. Can/will the maker of the BMS guarantee his CELLS against FAILURE?

You all put to much on cooling or heating. LiFePO4 really don't need cooled. What they need is attention to proper balance.


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## jddcircuit (Mar 18, 2010)

onegreenev said:


> A cell that swells is a cell that has been overcharged or overdischarged. Usually the later because of an improperly bottom balanced pack. It can of course happen on the top because the charger failed because of a non working BMS.
> 
> Can't say for sure about his leaky cell. If it was overcharged or overdischarged the cell because of the clamping pressure not allowed for swelling and caused it to pop a hole in the seam. Once that happens all the internal pressure would have been released and then electrolyte would leak out. Damage has been done. The pouch cells have no provision for pressure release so it is VERY VERY important to be sure you do not overcharge or overdischarge your cells. They must be balanced properly and if you have a BMS you must be sure it is working properly. Can/will the maker of the BMS guarantee his CELLS against FAILURE?
> 
> You all put to much on cooling or heating. LiFePO4 really don't need cooled. What they need is attention to proper balance.


I have a very bloated and swollen cell that has never been charged or discharged by me. It did this by itself sitting on a shelf with only shipping and handling from CalibPower as far as I know. It is not a pouch cell but may have similar internal electrode and separator configuration.

Therefore I assume there must be other mechanisms for cells to swell.

I have also heard of others with similar experience so I do not advise limiting the possible failure cause to out of range charging and discharging.

Regards
Jeff


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## onegreenev (May 18, 2012)

So as soon as you figure out any other mechanism that causes swelling it stands that overcharge/over discharge will and is what causes swelling. Out of range IS overcharge/discharge. Within range you get NO swelling. A shorted cell puts the cell out of range. Again overcharge/discharge. What ever the mechanism is it always goes to overcharge/discharge


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## onegreenev (May 18, 2012)

I know what caused this massive swelling in this cell. It was a failed BMS and the cell was overdischarged while driving because the BMS also failed to report that itself was damaged. This is an OEM BMS from Hi-Power Battery Company. Think I'd trust some back yard hack BMS? Not on your life. But the swelling did not just happen. It happened because of over discharge. I have also seen swelling on overcharge too. But NEVER within range.


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## kerrymann (Feb 17, 2011)

*2 month inspection of A123 cells*

*2 month inspection of A123 cells *




I wanted to give a update on my A123 module after a few months. There is good news and bad news. The bad news is that I have more bad cells, the good news is that there is a pattern to the failures. I have 4 modules in my car, 3 are the original Mark 1 design and the 4th is the Mark II with the much stiffer endplates. I did a pretty detailed inspection of all the cells. The pattern to the failures is cell pressure, either too much in the case of module 2 or uneven pressure at the thin end plates for all of the early Mark I designs.


​

*Module 1, Mark I, RevA*: 1 cell had signs of electrolyte leakage and 1 other cell had a little spot that looks like mold. 



http://2.bp.blogspot.com/-QRVyZXSaP0Q/UKvvayzDPgI/AAAAAAAAAow/brpS6Ve1-Mg/s1600/P1040924.JPG

​This spot is the start of corrosion in the pouch. The two cells were right next to the end plates. I am upgrading it to Rev B.


*Module 2, Mark I, RevA:* Numerous cells had signs of electrolyte leakage. Most of them were on the ends but some in the middle of the pack. This pack was also problematic last time I inspected it. My guess is that I over compressed the cells the first time I built it that caused undetectable damage. The second time I assembled it there was much less clamping force but I think the damage was already done. I am putting this pack aside for now until I have a had a chance to evaluate it further.












Here you can see several cells failed from the pack. In some the electrolyte is still trapped between the clear outer film and the silver inner layer.
http://1.bp.blogspot.com/-PGKCj6p4K1o/UKvwgaVeRLI/AAAAAAAAApw/nHq5UU75f6Y/s1600/P1040906.JPG




​*Module 3, Mark I, RevA:* 1 cell had signs of electrolyte leakage on one side. This cell was locate right next to the negative end plates. Failure looks like it was due to uneven pressure on the cell. I am upgrading it to Rev B.



​*Module 4, Mark II, RevB:* I actually had a leaking cell for the first time on the Mark II module. I didn't discover it until I checked each one separately. The cause was quite apparent, user error. 



​
When I had installed one of the cooling fins the sharp thin aluminum cut and tore the thin pouch material. I cannot over emphasize how gentle you need to be with these pouch cells. This is probably my biggest issue with using these cells. So I replaced the bad cell and also added electrical isolation using transparancies. I only did half of the pack. This way I will see the effect, if any. I also upgraded it to Rev B too.


​

As with all my other posted I wanted to post what I have found with testing so far. Hopefully it will save others some headaches if they decide to use the pouch cells, (or in some cases it might convince them it's too much work  I expected using these cells to be a learning experience, but this has been more work expected. I have spent more time and effort on the batteries then I have on the rest of the conversion but that is part of the fun of the project.


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## Ziggythewiz (May 16, 2010)

*Re: 2 month inspection of A123 cells*

Lots of great info! Thanks for sharing. What has your charge/discharge routine been?


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## rwaudio (May 22, 2008)

Good info, I've had similar "issues".

One thing you might consider adding to your design is kapton tape. I haven't done it yet but it does make sense.
http://randomev.wordpress.com/2012/01/21/pouch-cell-pack-building/


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## kerrymann (Feb 17, 2011)

rwaudio said:


> Good info, I've had similar "issues".
> 
> One thing you might consider adding to your design is kapton tape. I haven't done it yet but it does make sense.
> http://randomev.wordpress.com/2012/01/21/pouch-cell-pack-building/


Interesting. Honestly if it comes to that then I will be abandoning the cells but i am hopefully it won't come to that. Can you elaborate on the issues you have been having?


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## Stiive (Nov 22, 2008)

You _didn't_ tape the edge of the cells!? Rookie mistake.
_AND _you've got aluminium fins in there!

Get rid of the Aluminium, it is not needed.
Tape all around the edges with HV rated tape. 
Try get spacing between the cells to avoid capacitive coupling. 
Don't over clamp the cells.
Use a BMS.


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## rwaudio (May 22, 2008)

kerrymann said:


> Interesting. Honestly if it comes to that then I will be abandoning the cells but i am hopefully it won't come to that. Can you elaborate on the issues you have been having?


Same issues as you, I had a couple cells with larger corrosion spots, and a bunch with worse electrolyte leakage. 



Stiive said:


> You _didn't_ tape the edge of the cells!? Rookie mistake.
> _AND _you've got aluminium fins in there!
> 
> Get rid of the Aluminium, it is not needed.
> ...


I'm starting to think the tape is a necessary step, a BMS won't keep the cells from doing this but it should let you know that it's happened.


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## GizmoEV (Nov 28, 2009)

rwaudio said:


> I'm starting to think the tape is a necessary step, a BMS won't keep the cells from doing this but it should let you know that it's happened.


Every pouch cell I've seen in dissected electronics have the edges taped down. I'm sure there is a good reason.


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## marc02228 (Jan 15, 2011)

I had no problems, yet. 
But I only did a couple test drives without any pressure on the cells and max current of maybe 600A (3 cells in parallel) for a very very short period of time.

I'm gonna put a sheet of 0,2mm Mylar (A4 airbrush stencil cut to the correct size) between each cell and between the cells and the end plates. What do you think, do I still need the Kapton Tape when the sheets are larger than the cells?
Actually there should be no way to connect the separate cells to each other, then. Or is there some other reason for the Kapton?

How thick was your Mark 1 endplate? 2mm? That's, what my end plates are, too.

Even if I'm quite sure, that it's not the reason for the failure, could you post the parameters you set the BMS to? Just to compare...


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## kerrymann (Feb 17, 2011)

GizmoEV said:


> Every pouch cell I've seen in dissected electronics have the edges taped down. I'm sure there is a good reason.


That is actually the first time I have actually seen it done. Where have you seen it done? There are very few people using these cells in a car, and even fewer sharing there experiences so there isn't a great of deal of data that I have found. The A123 modules and the packs I saw at OSU didn't have tapped edges and they pulled some ridiculous amps from them.



Stiive said:


> You _didn't_ tape the edge of the cells!? Rookie mistake.
> _AND _you've got aluminium fins in there!
> 
> Get rid of the Aluminium, it is not needed.
> ...


This is my first experience with lithium and as far as I am aware there are only a handful of DIY'ers in the world actually using these cells in a car so I'll certainly own up to any "rookie mistakes". Is this based off your experience with these cells? I have to ask because since I have started playing with these cells I have gotten lots of advice via the internet what to do or not do with these cells. Much of which is conflicting and coming from people who haven't actually used them. I am not saying yours (and the others) is not valid advice but I live by the phrase "One test is worth a thousand expert opinions". This is why I post my experiences here. The A123 module design uses fins and no tape (though that might have something to do with their recalls and bankruptcy  Pulling apart all the cells and taping is a lot of work and I run the rel risk of damaging the cells.



marc02228 said:


> I had no problems, yet.
> But I only did a couple test drives without any pressure on the cells and max current of maybe 600A (3 cells in parallel) for a very very short period of time.
> 
> I'm gonna put a sheet of 0,2mm Mylar (A4 airbrush stencil cut to the correct size) between each cell and between the cells and the end plates. What do you think, do I still need the Kapton Tape when the sheets are larger than the cells?
> ...


Marc,
My end plates are about 2mm. I put .008" (.02mm) PP film in between half of the cells in module #4 so we will see what happens. I don't think it will be very effective because of how close the cells edges get near the tabs.


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## Elithion (Oct 6, 2009)

Stiive said:


> Try get spacing between the cells to avoid capacitive coupling.


Please explain.

In my understanding:


 Capacity between cells is not an issue, because there is a minimal AC voltage between adjacent cells, so capacity has practically no effect
Capacity between the cells and chassis is an issue, but only to an isolation detector (it requires longer to detect a loss of isolation)
What am I missing?


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## powerhouse (Apr 1, 2011)

I thought I would share my modules
I designed and began building these about 1 month ago, and they have not shown any signs of damage or deterioration thus far*knock on wood*.
With that said, I have only charged / discharged each module once using the powerlab.
I have taped each and every cell I own using some 1" diameter kapton tape (about $4 a roll), I taped the top tabs to ensure I didn't get any shorting using 2" tape.
Thus far I have used about 4 or 5 rolls of 1" tape, and about 2 rolls of 2" for 250ish cells. 

In addition to kapton tape, I also began using some fish paper between every 4 cells (every parallel group). 

Lasering









More lasering









Came out okay 









Mock up 









Assembly..









Finished with one! Notice the dark blue fish paper between every cell group









Begin populating the rear battery box !









!!!


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## kerrymann (Feb 17, 2011)

powerhouse said:


> I thought I would share my modules
> I designed and began building these about 1 month ago......


Cool. I like it! 

I see you didn't put top on the pouch edge in-between the positive ab negative terminals. Is there a reason you taped the whole edge except for this spot? Also I added foam sheets in-between the end plates and the outer most cells. This accommodates any changes in pack length (due to temp, swelling, etc) and keeps the cell pressure in check.

BTW did you make the CNC laser yourself? That is definitely on my wish list.

Keep us posted,


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## ellweber (Jun 3, 2009)

kerrymann said:


> "One test is worth a thousand expert opinions".


I would like to see some discussion of the underlying problem that is causing these leakage and cell wall failures. Anectodal tales about "you have to do this" are not helping me to find a way to package my cells so they will survive and perform well.



Is it abrasion between the cell body and its mounting, aggravated by vehicle vibration?
Is it some sort of parasitic behavior between adjacent cells at different potentials (3+ volts at most!)?
Is it leakage at a weak point caused by poor handling practices or other damage to the surface of the cell?
Is it some sort of rupture caused by overpressure internally and, if so, what is causing the overpressure, ambient condition's, overcharge, overdischarge, overcurrent during charge, overcurrent during discharge or...?
Are there leprechauns from the PTO or competitors that are sabotaging these cells?
Other ideas?
Many of us that have bought these cells realize that they were rejected for some reason. If we can clearly understand the sensitivities and work around them then there is some hope for getting useful performance.

I am hopeful we can have an objective discussion about real data and experience.


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## GizmoEV (Nov 28, 2009)

kerrymann said:


> That is actually the first time I have actually seen it done. Where have you seen it done? There are very few people using these cells in a car, and even fewer sharing there experiences so there isn't a great of deal of data that I have found. The A123 modules and the packs I saw at OSU didn't have tapped edges and they pulled some ridiculous amps from them.


I have seen the edges taped down in the battery in a Compaq iPaq (PDA from ~2000), MacBook battery packs, IIRC, a Motorola cell phone battery I dissected, and several other devices I've seen pictures of. The MacBook pack I have open right now only has the sides of the pouch taped because of the way the pouch is constructed. The sides are just wrapped around the bottom of the cell. It looks like the A123 pouches' sides are constructed from two separate pieces.


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## Stiive (Nov 22, 2008)

Elithion said:


> Please explain.
> 
> In my understanding:
> 
> ...


Yes, this is vital in this design because of the Aluminium fins. Because the battery has only a thin lamination covering, this acts as a small spacer between the anode/cathode and the aluminium fin it sits on. Capacitance is obviously modelled on the surfaces area and distance between them, the smaller the distance the greater the capacitance. With many cells all contributing to the capacitance it can become a dangerous (very high potential can exist) and an electrically noisy environment. This as you say will also effect isolation unit as the capacitance is often more than the allowed coupling resistance can discharge. A small spacer will suffice and provide electrical insulation from the fins if the material is properly selected. With adequate spacing, this will make the fins basically useless as a method of extracting heat, and therefore should be removed. The vast majority of heat is built up in the tabs anyway as the current density is highest there.

If the fins are taken out, the effect of capacitance between cells can still be strong, however its effect isn't damning, perhaps can even provide benefit if correctly utilised. However I'd still recommend spacing for electrical isolation and to absorb some mechanical stress between cells.


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## Elithion (Oct 6, 2009)

Stiive said:


> Yes, this is vital in this design because of the Aluminium fins. ...


Thank you for describing why the capacitance is so high. 
You did answer that you're concerned about capacitance to ground (not capacitance between cells); thank you.

But what I was mainly asking was: "Why is a high capacitance to chassis a problem?".

Thanks.


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## Stiive (Nov 22, 2008)

kerrymann said:


> This is my first experience with lithium and as far as I am aware there are only a handful of DIY'ers in the world actually using these cells in a car so I'll certainly own up to any "rookie mistakes". Is this based off your experience with these cells? I have to ask because since I have started playing with these cells I have gotten lots of advice via the internet what to do or not do with these cells. Much of which is conflicting and coming from people who haven't actually used them. I am not saying yours (and the others) is not valid advice but I live by the phrase "One test is worth a thousand expert opinions". This is why I post my experiences here. The A123 module design uses fins and no tape (though that might have something to do with their recalls and bankruptcy  Pulling apart all the cells and taping is a lot of work and I run the rel risk of damaging the cells.


Yeh I have been working with these type of cells for a few years. I now have my whole garage full of them. Most solar racing and formula SAE teams use them, this is where I gained my experience. 
There are plenty of designs out there, _my _first design was early 2010 and used fins - back when I was a rookie  Pretty sure Kokam told us we needed it for heat dissipation, but I can assure you after many years of thrashing these type of batteries - it is not required.
I'm sure you'll find lots of designs to copy. Most new designs use laser cut tab holder (like powerhouses pictures) or a PCB arrangement. I'd be interested to see if anyone did this pre-2010, or maybe I was the first?

TBH the best method would be to ditch the plastic and make a large PCB for tab holder that also incorporates the BMS. I've yet to see this, but this is what i'd do next if I was making another pack.


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## Elithion (Oct 6, 2009)

Stiive said:


> TBH the best method would be to ditch the plastic and make a large PCB for tab holder that also incorporates the BMS. I've yet to see this, but this is what i'd do next if I was making another pack.


Did it in 2009.


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## Stiive (Nov 22, 2008)

Elithion said:


> Thank you for describing why the capacitance is so high.
> You did answer that you're concerned about capacitance to ground (not capacitance between cells); thank you.
> 
> But what I was mainly asking was: "Why is a high capacitance to chassis a problem?".
> ...


High voltage potential which can possibly be lethal. When we had aluminium fins, you could get a massive kick from the chassis if you were also touching any HV potential. Even leaning over the car to tighten a bolt on a battery you can get you a kick through the pants - not nice  well... sometimes.

This HV can also exceed isolation in your controller / dc/dc / other HV electronics and cause failure. 

Most (all?) standards require a certain amount of isolation between HV and LV systems. Capacitance will likely make you fail this criteria.

Capacitance can also couple your chassis to your charger potential when charging your batteries, which can either trip earth leakage protection, or give you a kick just by touching the frame if you have connection with ground.


Probably more problems.... I think its safe to say its *not *a good thing. I've been advocating people to take the fins out of their designs since my mistake in 2010 - even had to tell powerhouse quite sternly on his s2000 thread  Glad he didn't go through with using them.


Removing these fins will also stop the batteries from shorting and less likely for them to die. They can still short on each other, and should be taped and spaced if allowed.


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## Stiive (Nov 22, 2008)

Elithion said:


> Did it in 2009.



Nice one. You need to market these better, cant say i've ever seen anyone use it. 
Though its probably more of a custom design type of thing depending on the batteries - you'd want to sell pre-made modules I think.


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## Elithion (Oct 6, 2009)

Stiive said:


> you'd want to sell pre-made modules.


That too. 

(dummy extra characters so that message will be accepted, please ignore)


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## Stiive (Nov 22, 2008)

Elithion said:


> That too.
> 
> (dummy extra characters so that message will be accepted, please ignore)


Cool.
While we're on the topic; Do you use "fins" in any of your designs? Have you in the past?


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## Elithion (Oct 6, 2009)

Stiive said:


> can ...trip earth leakage protection


Thanks. Of all the things you mention, I agree that this is one is an issue. Thanks!

My back of the envelope calculations tell me that a capacity of 140 nF to chassis will trip a GFI at 120 Vac charging. That can't be right! Too low!



Stiive said:


> Do you use "fins" in any of your designs? Have you in the past?


Yes: the Enerdel stock battery modules. The water cooling uses cold plates pressed against the Enerdel fins. This pack is 98 % efficient at 4 C discharge and runs really cool when discharged in 15 minutes. 

The capacity to chassis is about 20 uF, which will definitely trip a GFI. 
But the chargers are 240 V and do not use GFI protection. 

I *do* share your concerns about fins between pouch cells.


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## GeoMetric (Aug 13, 2010)

Very cool thread, I hope you don't mind if I ask a few questions I might have missed. Did anyone here mention the problem Victor had when he built his Dow Kokam pack? The pouch cell sides conducted electricity. And the most important question to the cell's health, were these cells purchased from Mavizan? or A123? or were these Chinese market products?


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## kerrymann (Feb 17, 2011)

GeoMetric said:


> Very cool thread, I hope you don't mind if I ask a few questions I might have missed. Did anyone here mention the problem Victor had when he built his Dow Kokam pack? The pouch cell sides conducted electricity. And the most important question to the cell's health, were these cells purchased from Mavizan? or A123? or were these Chinese market products?


That is part of the thinking for taping the edges of the cell. There is a NASA paper that the found they could greatly accelerate manufacturing defects by applying a relativity small voltage to the pouch. IIRC they were able to get corrosion in a week or two. They recommended it as part of the receiving inspection as a way to weed out cells that would corrode own there own given enough time. It's been a while since I read the report, I need to find where I put it and re-read.

And these were gray market cells for china. Mavizan wanted $60-70/cell and that wasn't worth it by a long shot. Of course these at $19/cell might not have been worth it either...


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## marc02228 (Jan 15, 2011)

Hey A123 pouch users,

how are your A123 modules doing?
Mine are pretty well, actually. But they have only 20 cycles or so.
What's your voltage sag and at what current?

Mine sag to about 280V (for 96s) at something around 800A.
I charge them to 3.5V and get a warning, as soon as some cells voltage drops below 3V and the BMS turns off the controller when some cell reaches 2.8V (but I am not sure for this value).

I once discharged 3 cells (it's a 3p pack) down to 1.7V, because my BMS wasn't wired at that time, yet. Then charged it seperate with 5A back to 3.2V. These cells seem to be as good as the others... still.


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## ev99saturn (May 5, 2009)

Marc, mine are doing very well also. I built 12S4P packs, and also have only a few cycles, about the same as you. The car is parked for the the winter for more build-up; but there is no self-discharge after a few months sitting in the cold.

At 1014A, (253A/cell) cells sag is to 2.95V (10.6%) at about 50-55 degrees F. I found in testing that sag is deeper as the cells get colder. 

Very satisfied with the cells so far.




marc02228 said:


> Hey A123 pouch users,
> 
> how are your A123 modules doing?
> Mine are pretty well, actually. But they have only 20 cycles or so.
> ...


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## kerrymann (Feb 17, 2011)

marc02228 said:


> Hey A123 pouch users,
> 
> how are your A123 modules doing?
> Mine are pretty well, actually. But they have only 20 cycles or so.
> ...


No new issues with the pack as of yet but I am having problems with my charger that have prevent me driving it much at all this year. Glad to hear your is coming along. The new parts are on there way and hopefully I can charge back up next week and get back on the road.


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## kerrymann (Feb 17, 2011)

FYI marc, I got the fuse replaced in my PFC20 and it's working fine now but after a couple hours of charging a 12amps the BMS is showing that last cell in the string is still down at ~3.1V while the others are up to 3.45V. I am going to check it manually before I do any more charging and let you know what I find.

Kerry


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## marc02228 (Jan 15, 2011)

kerrymann said:


> FYI marc, I got the fuse replaced in my PFC20 and it's working fine now but after a couple hours of charging a 12amps the BMS is showing that last cell in the string is still down at ~3.1V while the others are up to 3.45V. I am going to check it manually before I do any more charging and let you know what I find.
> 
> Kerry


Hmm.. I had a bad BMS cell module, once. When it started balancing, it couldn't stop anymore. It always stuck at 19% balancing current. But I think it's something else in your case, because there's to much energy in the cell from 3.1V to 3.45V.
Maybe I should have added a some heating for my batterie boxes. It's below 0°C since a week or so and my pack doesn't get charged at these temperatures.


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