# Small cylindrical cell BMS?



## toddshotrods (Feb 10, 2009)

I tried searching but there are so many threads, and so many places this info could be inside a thread, that I just decided to ask. If this is a redundant question and someone knows where this has already been covered, please just point me there. Otherwise, how about a serious discussion about how to acheive effective BMS on a pack like I am planning to build.

My plan calls for 1800 A123 26650 M1 cells. 18 parallel strings of 100 cells in series, giving me 330 volts / 2070 amps. So how the heck do you do BMS for something like this?

I am planning to build six banana-shaped, CNC'd, cases that would put the batteries under the floor and rolling up behind the seats just a bit. 3 string sof 100 cells in series in each case. If I were to use Elithion systems the BMS would cost ($20-25K) more than the cells and cases, unless I am misunderstanding the info on their site. If this is the real cost and there is no other way, so be it, I'll have to work even harder, but I have no idea so I am asking.


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## major (Apr 4, 2008)

toddshotrods said:


> My plan calls for 1800 A123 26650 M1 cells. 18 parallel strings of 100 cells in series, giving me 330 volts / 2070 amps. So how the heck do you do BMS for something like this?


Todd,

You do 100 of the parallel (18 cell) sets in series. And use one BMS board for each parallel set. That way you need only 100 boards  Send me your email via PM.

major


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## toddshotrods (Feb 10, 2009)

major said:


> Todd,
> 
> You do 100 of the parallel (18 cell) sets in series. And use one BMS board for each parallel set. That way you need only 100 boards  Send me your email via PM.
> 
> major


PM sent.

Ahhh!  Gotta see how that fits under the floorboards. I need to quit working on this in my head and start modeling.


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## frodus (Apr 12, 2008)

where are you sourcing these A123 M1 cells anyway?


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## toddshotrods (Feb 10, 2009)

frodus said:


> where are you sourcing these A123 M1 cells anyway?


All other options failing, I will purchase and disassemble 180 36V DeWalt packs. I won't take a chance on the Ebay cells though, they have to be real. In an ideal world, I will score an inside connection. I have a possible option there, but it would probably mean a formal association that I am not sure I want to commit to.

Whatever it takes to reach the performance goals, and so far these are the _only_ cells that meet my requirements. Their new ones (32113) look interesting but they seem to be unobtainable other than some type of inside/sponsorship deal, so I can't count on them.


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## toddshotrods (Feb 10, 2009)

I think I can make 100 parallel sets in series work in my original case format. I think it will make the copper end plates for the cases much easier to model and cut was well. What BMS boards do you guys recommend to keep an eye on 18 M1 cells each?


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## frodus (Apr 12, 2008)

copper endplates?

how ya gonna weld that to the ends of the batteries? 

I really hope you're not planning on soldering them.......


Elithion has a board that is made for the 26650 cells. It'l do as many in parallel as you want. Manzanita Micro also makes one, 4 or 8 cells each board, so at least 13 8-cell boards.

The BMS won't come cheap, and I wouldn't cheap out on it.


And as far as the dewalt packs, you'd need what, 180 of them, at $120+ each, $21,000+ dollars.... good luck finding a supply of 180 packs.


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## toddshotrods (Feb 10, 2009)

frodus said:


> copper endplates?
> 
> how ya gonna weld that to the ends of the batteries?
> 
> I really hope you're not planning on soldering them...


I have few different ideas for that but haven't had time to purchase a pack yet and test any of them. I shouldn't have used the phrase "end plate". I'll dig into that later, I don't want to stray too far from the BMS discussion right now.





frodus said:


> ...Elithion has a board that is made for the 26650 cells. It'l do as many in parallel as you want...


Yeah that's what I was looking at when I posted this thread. I just wanted to see if anyone had comments, feedback, or any other suggestions on what boards they would use.





frodus said:


> ...The BMS won't come cheap, and I wouldn't cheap out on it...


Agreed.





frodus said:


> ...And as far as the dewalt packs, you'd need what, 180 of them, at $120+ each, $21,000+ dollars.... good luck finding a supply of 180 packs.


That's what distributors are for. 180 packs sounds like a lot when you're thinking about one EV, but when you consider all the possible 36 volt DeWalt tools that can be sold, and the contractors that might want extra/replacement packs, in a world with 6 billion people it's not so much. Ordering in bulk, from a distributor, would cut the costs significantly - especially if I can get that distributor to climb onboard as a sponsor and sell them to me for his cost. Win-win - he gets free advertising, and I get cells for a bargain.

Whatever they cost, and whatever it takes to get them, is what it is.


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## frodus (Apr 12, 2008)

I've got an elithion and I like what I've seen so far (not fully integrated yet, just testing). Its a very feature rich system, so your electrical skills should be a level 7+ out of 10 in my opinion.
More here:
http://blog.evfr.net/?p=312

I've seen first-hand the manzanita as well, and it seems like a great system. I've recieved some training on it and like what I see I may get one to use with my 12V aux battery.


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## Woodsmith (Jun 5, 2008)

I'm reading all this and all I am thinking is 'I could do with a cheap replacement battery pack for my DeWalt drill.'!

I am really going to have to get interested in the BMS side of things.


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## toddshotrods (Feb 10, 2009)

frodus said:


> ...Its a very feature rich system, so your electrical skills should be a level 7+ out of 10 in my opinion...





Woodsmith said:


> ...I am really going to have to get interested in the BMS side of things.


I will start bringing team members in when I reach that point, one specifically to handle the electrical/electronic side of things. I just want to learn enough about each area to know what's going on and be more focused in overall project design. Plus, the more cooks in the kitchen the more confusing the whole process gets. It's much easier to bring a team member in and say this is what we have to work with than sit down with six people and say what would do you want to do.


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## frodus (Apr 12, 2008)

I disagree somewhat.

If you don't have anyone on the team already that can accurately chose components based on requirements, then the design is destined to fail.

If you start with someone that knows a bit about the systems and go from there, you'll save a lot of time.


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## MalcolmB (Jun 10, 2008)

Hi Todd,
If you're thinking of buying a large number of A123 cells I can recommend the supplier on this thread on the Endless Sphere forum: http://endless-sphere.com/forums/viewtopic.php?f=31&t=19717
He's supplied several members of the forum in the past, some of them with large orders.

Personally, I would try to find a source of larger format cells such as Kokam that would require a much smaller number of connections. Building a large pack from cylindrical cells, especially untabbed cells, is a big undertaking. Just building a modest pack for my motorcycle has taken an inordinate amount of thought and time.


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## BMI/LiFeTech (Aug 12, 2009)

toddshotrods said:


> Whatever it takes to reach the performance goals, and so far these are the _only_ cells that meet my requirements.


So what are your performance goals exactly?


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## toddshotrods (Feb 10, 2009)

MalcolmB said:


> Hi Todd,
> If you're thinking of buying a large number of A123 cells I can recommend the supplier on this thread on the Endless Sphere forum: http://endless-sphere.com/forums/viewtopic.php?f=31&t=19717
> He's supplied several members of the forum in the past, some of them with large orders...


Thanks for the link. I will read through that thread later when I have more time. I have to admit though, I am so leary of purchasing these cells from anywhere but A123 or DeWalt packs. They seem to have tested well, from skimming through the thread, but I will be pushing them to their limits (50c). As I said, I'll look into that more later, and maybe get in touch with him.




MalcolmB said:


> ...Personally, I would try to find a source of larger format cells such as Kokam that would require a much smaller number of connections. Building a large pack from cylindrical cells, especially untabbed cells, is a big undertaking. Just building a modest pack for my motorcycle has taken an inordinate amount of thought and time.


I've been doing numbers on anything and everything out there and so far nothing has matched the energy density of the M1 cell. 300+ volts, 2000+ amps, and as light as possible are absolute musts for my plan - no wiggle room.
I don't care how much work is involved - whatever it takes.


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## toddshotrods (Feb 10, 2009)

BMI/LiFeTech said:


> So what are your performance goals exactly?


I'd rather not say because I am weary of arguing with people about whether or not I should be doing what I plan to do, whether it's possible to do what I plan to do, and why I won't just do something a little simpler, a little cheaper... 





I'll just give you the numbers that create the foundation:

330 volt/2070amp battery pack
400-500v/2400-2500amp controller
rewound, race-prepped, 11" series (dc) motor
direct-drive / nitrous-ready-style driveshaft
full-race Ford 9" based rear end
DOT race tires (separate autocross and drag race sets)
caged race chassis, built to NHRA specifications (8.50 and slower) with race-proven suspension geometry and parts
1200lbs total weight (+ me @ 125lbs)
My performance goals are the absolute maximum that combination is capable of.  

I probably shouldn't even post that much here, as this could end up in a stupid debate that totally kills the discussion about BMS but I think I have the information I need on that now.


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## JRP3 (Mar 7, 2008)

MalcolmB said:


> Hi Todd,
> If you're thinking of buying a large number of A123 cells I can recommend the supplier on this thread on the Endless Sphere forum: http://endless-sphere.com/forums/viewtopic.php?f=31&t=19717
> He's supplied several members of the forum in the past, some of them with large orders.


I too was going to recommend Paul, (cell_man). Everyone on ES who's purchased from him has been very satisfied with the cells as far as I know, and the ES guys know their A123's. He's spent a lot of time and money testing the cells as opposed to just shipping them out the door. The ES folks also have a lot of experience with BMS's for the A123 cells. Something else to look for, somewhere I saw a picture of an A123 cell with threaded stud terminals, which would make connections much easier if you could get them.


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## JRP3 (Mar 7, 2008)

Here's where I saw it: 
http://endless-sphere.com/forums/viewtopic.php?f=14&t=20591&start=0


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## frodus (Apr 12, 2008)

toddshotrods said:


> I've been doing numbers on anything and everything out there and so far nothing has matched the energy density of the M1 cell. 300+ volts, 2000+ amps, and as light as possible are absolute musts for my plan - no wiggle room.


you mean power density. For energy density, the M1's are pretty low. 

I'd concur with MalcomB. Look into Kokams. Higher energy and power density.

I'm skeptical about those threaded A123's being true A123 cells.


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## toddshotrods (Feb 10, 2009)

frodus said:


> you mean power density...


Yeah, I did mean power density.





frodus said:


> ...Look into Kokams. Higher energy and power density...


I don't get how Kokam has higher power density. I sized a Kokam pack as closely as I could to my proposed A123 pack.


Kokam SLBP 205130 SERIES & Here's the pdf.

12ah
3.7v nominal
354 ± 15
5(continuous) 20(pulse)
$73.88
*So:*

3.7 x 90 cells in series gives me *333 volts*.
240 x 9 cells paralleled = *2160 amps*.
9p x 90s = 810 cells x 354g = approx 287kg or *631lbs*
73.88 x 810 = *$59,842.80!!!*  *just for the cells*
By comparison


A123 26650 M1

2.3 ah
3.3v nominal
70g
10c continuous/ 50c pulse
*So:*

3.3V x 100 = *330 volts*
115A x 18 - *2070 amps*
18p x 100s = 1800 x 70g = 126kg or *278lbs*
$120 (price given in this thread for 10 cells in a DeWalt pack at retail) x 180 = *$21,600.*
No comparison. Or, am I missing something?


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## frodus (Apr 12, 2008)

Start at the cell level. Calculate power and energy density of the actual cell. Ignore cost because that wasn't my argument. I was saying that Kokams have a higher energy and power density. Let me show ya:
*
Kokam 4.8Ah Ultra High power battery*
http://www.dowkokam.com/resources/SLPB11043140H_4800mAh_Grade.pdf
3.7V * 4.8Ah = 17.76Wh
115g
*154wh/kg*
40C peak discharge
20C continuous
*6177W/kg*

*A123 2.3Ah M1 cell*
http://www.a123systems.com/cms/product/pdf/1/_ANR26650M1A.pdf
3.3V * 2.3Ah = 7.59Wh
70g
*108wh/kg*
52C peak
30C continuous
*5638W/kg*

*That's a difference of:
46Wh/kg energy density 
539W/kg*

You're right, No comparison. Kokam clearly wins.


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## JRP3 (Mar 7, 2008)

Just remember, not only do the Kokams cost a lot more to purchase, they also have much lower cycle life.


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## toddshotrods (Feb 10, 2009)

frodus said:


> ...You're right, No comparison. Kokam clearly wins.


I understood your point, I just did it my way to see what it would mean specifically for my project. The real difference is in the C-rates. I used 20C max (peak) and you have that for your continuous rate, with 40C for peak. Of course that tips the scales in the Kokam's favor. I was looking at a different cell. 500 cycles though! 





JRP3 said:


> Just remember, not only do the Kokams cost a lot more to purchase, they also have much lower cycle life.


Exactly. The up front purchase cost is enough by itself, but when you figure in more frequent replacement it just doesn't make sense - outside of full sponsorship. I still hold to my original conclusion that I have yet to see a battery that works better than M1s for my project. Maybe I should just leave out the terminology, and say they're the best for me (without explaining why), to avoid the endless debates.

Like I said, when you get too many cooks in the kitchen... This whole thread is turning into a discussion about batteries that I have had so many times before and it was supposed to be about BMS.


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## dimitri (May 16, 2008)

Todd,

I have a little experience in BMS world  and I must say that for your project I would recommend Elithion system.

I think they will be excited to give you a good deal in exchange for bragging rights.

CroDriver has Elithion in his BMW racer, I'm sure you have seen it. They developed nice GUI display around it too.

I am not ashamed to admit that my MiniBMS is probably too simplistic for your supercar, although it would still do the job, but Elithion would be a better match, IMHO.

Good luck with your project! It has to be the best I have seen so far, ever.


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## toddshotrods (Feb 10, 2009)

dimitri said:


> Todd,
> 
> I have a little experience in BMS world  and I must say that for your project I would recommend Elithion system.
> 
> ...


Wow dimitri, that's mighty high praise! Very humbling, and you are a very down-to-Earth guy yourself to openly recommend a competitor's product because you feel it's best for the application. I really appreciate that.

Now, what are you doing in my battery debate talking about BMS - oh wait, this _was_ a discussion about BMS! 

So my next steps will probably be to start talking with them to get some ideas on what specific components they recommend and how much I need to inflate the project budget to accomodate them. Talk about scope creep!


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## frodus (Apr 12, 2008)

Dimitri is stand up. He just wants to help people with their projects. Glad you're seeing things that way Todd. I've pointed customers towards his BMS plenty of times. All BMS have their application. 



toddshotrods said:


> Whatever it takes to reach the performance goals


I thought you said whatever it takes 

I do understand though. Cycle life is important as well as cost.

So in the end, cost/life/performance are all important. Realize that you may not have all three at once.


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## toddshotrods (Feb 10, 2009)

frodus said:


> ...I thought you said whatever it takes ...


Yup, and I mean it too. It's just a broad swipe coming from me. I am a big picture guy. Each tree is only meaningful it if contributes to the good of the whole forest. 





frodus said:


> ...So in the end, cost/life/performance are all important. Realize that you may not have all three at once.


It always comes back to "pick any two" huh? Seriously though, I'm not really sacrificing anything. If the using the A123s was really going to hurt the performance potential I would have to find a way to pay more, more frequently. Going back to the whole forest mentality, Big Sol is still under development and it still remains to be seen how much of its full megawatt I will actually be able to apply, and for how long. I have a while before I start purchasing batteries, and if it turns out Kokam or some other cell is the only way - whatever it takes...


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## dimitri (May 16, 2008)

Todd,

since you already laid out desired battery specs, which calls for 100 series connected cells to get the voltage, I also wanted to comment as others have said already, smaller cells have to go in parallel to get desired AH capacity, THEN parallel groups go in SINGLE series string. This is most beneficial and most practical way to assemble the pack, as opposed to multiple strings of individual cells, which would end up as unmanageable mess. Since you get SINGLE string of 100 "supercells", where each "supercell" is treated as a single unit from BMS perspective, then you ONLY need 100 BMS module system, which is quite typical and should not cost any more than any other typical BMS package from same BMS vendor.

BMS module managing a parallel group of cells which I call "supercell" does not care how many individual cells there are in parallel, since they all become one unit of larger capacity and do not need to be managed individually any longer. Any individual cell failure in a parallel group results in reduced capacity of that group, which is no different than abused prismatic cell losing some capacity over time. This will simply result in overall reduction in pack's capacity, which will be shown by BMS and AH gauge. Once its pinpointed by BMS to a particular "supercell", then you have to take "supercell" apart and test each individual cell for failures.

Best way to avoid this situation is to test all new cells before grouping them and make sure all connections are solid. Any weak cell or weak connection will cause extra stress on that "supercell", which over time will damage other cells in that group.

Some of my BMS customers built similar packs from Headway cells and learned these things a hard way. Of course Headway cells aren't as good as M1's , but I would still do a load test and measure voltage sag on each cell before putting them in the pack.

Hope this helps.


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## toddshotrods (Feb 10, 2009)

dimitri said:


> Todd,
> 
> since you already laid out desired battery specs, which calls for 100 series connected cells to get the voltage, I also wanted to comment as others have said already, smaller cells have to go in parallel to get desired AH capacity, THEN parallel groups go in SINGLE series string. This is most beneficial and most practical way to assemble the pack, as opposed to multiple strings of individual cells, which would end up as unmanageable mess. Since you get SINGLE string of 100 "supercells", where each "supercell" is treated as a single unit from BMS perspective, then you ONLY need 100 BMS module system, which is quite typical and should not cost any more than any other typical BMS package from same BMS vendor.
> 
> ...


Helps a lot dimitri. I keep talking about the cells connected the crazy way because that's what I had in my head but you guys have gotten the point across about running them in parallel, then series. As I said, it actually makes my CAD/CNC case ideas work much better as well. It definitely makes the BMS system a sane proposition. I hear you guys loud and clear on that point.

I do have a question about connections though. Do the cells have to be connected via welding. In other words, could they be mounted in very precise cases with a screw in contact that maintained a specific pressure against the center of the cell's end cap? This contact could be torqued and locked to ensure proper pressure. All of this is outside the realm of practicality for the normal application these cells are used in, but for me modeling the system and having the CNC cut, drill, and tap, is nothing. Building the packs and carefully torquing 3600 contacts would be very time-consuming, but I don't mind that. It doesn't have to be done every other day...


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## JRP3 (Mar 7, 2008)

I don't think pressure contact is a good idea with the A123 cylindrical cells. The end caps are made to pop and vent if there is an over temp situation that over pressurizes the cells. If they are constrained the cell bursts out the side.


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## JRP3 (Mar 7, 2008)

Example: http://www.diyelectriccar.com/forums/showthread.php/solderless-framing-a123-26650-41240p3.html


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## toddshotrods (Feb 10, 2009)

JRP3 said:


> I don't think pressure contact is a good idea with the A123 cylindrical cells. The end caps are made to pop and vent if there is an over temp situation that over pressurizes the cells. If they are constrained the cell bursts out the side.


Yeah, I saw some posts concerning that. I was just taking a stab at whether the entire cap has to be unrestricted, or whether a small rigid contact can be made in the center and still have adequate burst room in the area surrounding it. In other words, would a rigid .250" contact point in the center provide enough energy flow and enough pressure relief area? If not, it's not a big deal - just an idea I always meant to ask...


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## JRP3 (Mar 7, 2008)

Honestly don't know  In that setup you'd be expecting the end cap to deform around the edges and vent before the sides blow out, seems unlikely but...


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## toddshotrods (Feb 10, 2009)

Too bad A123 is so averse to retail, it would be cool to be able to discuss stuff like this with their tech people.


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## JRP3 (Mar 7, 2008)

You could always do your own testing  Get an A123 cell, connect it the way you describe, hook it to a 12 volt charger, see what happens  Video camera on of course


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## toddshotrods (Feb 10, 2009)

JRP3 said:


> You could always do your own testing  Get an A123 cell, connect it the way you describe, hook it to a 12 volt charger, see what happens  Video camera on of course


I like that idea. When work resumes on the project, that will be on my to-do list. I like breaking stuff!


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## dimitri (May 16, 2008)

toddshotrods said:


> In other words, could they be mounted in very precise cases with a screw in contact that maintained a specific pressure against the center of the cell's end cap? This contact could be torqued and locked to ensure proper pressure. ...


The issue I see with this approach is that cell's end cap will give in to pressure over time and contact will get loose. I think connection has to be either welded or spring loaded, rigid mechanical connection will not stay rigid for long without spring action against it.


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## toddshotrods (Feb 10, 2009)

dimitri said:


> The issue I see with this approach is that cell's end cap will give in to pressure over time and contact will get loose. I think connection has to be either welded or spring loaded, rigid mechanical connection will not stay rigid for long without spring action against it.


Excellent point - especially in a rigid, jiggling, race car. Spring-loaded eh?


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## Bags (Jun 20, 2010)

dimitri said:


> BMS module managing a parallel group of cells which I call "supercell" does not care how many individual cells there are in parallel, since they all become one unit of larger capacity and do not need to be managed individually any longer. Any individual cell failure in a parallel group results in reduced capacity of that group, which is no different than abused prismatic cell losing some capacity over time. This will simply result in overall reduction in pack's capacity, which will be shown by BMS and AH gauge. Once its pinpointed by BMS to a particular "supercell", then you have to take "supercell" apart and test each individual cell for failures.


Does a larger number of cells in the supercell make it harder for the BMS to notice the overall reduction in pack capacity? I.e., from a BMS & cell-reliability perspective, is it better to have an 18-cell supercell vs. a 100-cell supercell? I.e., wouldn't the 100-cell supercell tend to "hide" a failing single cell, more than an 18-cell supercell?

--Jon
(planning an 1152-cell pack based on 96-cell sub-packs, trying to figure out the best configuration)


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## toddshotrods (Feb 10, 2009)

Bags said:


> Does a larger number of cells in the supercell make it harder for the BMS to notice the overall reduction in pack capacity? I.e., from a BMS & cell-reliability perspective, is it better to have an 18-cell supercell vs. a 100-cell supercell? I.e., wouldn't the 100-cell supercell tend to "hide" a failing single cell, more than an 18-cell supercell?
> 
> --Jon
> (planning an 1152-cell pack based on 96-cell sub-packs, trying to figure out the best configuration)


I've decided to boost my ultimate pack to 2992 cells, and I am heeding the advice given here. I will run 136 supercells of 22 cells in parallel, with a board on each one of these. That means 136 BMS boards.

If you do 96 cells in series (my original plan was similar with 100 in series) you're going to have a ridiculous amount of boards. One board can manage a supercell of *parallel*-wired cells. It sounds like you need to change the configuration like they told me to do. What cells, at what voltage, amps, etc are you shooting for?


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## Bags (Jun 20, 2010)

toddshotrods said:


> If you do 96 cells in series (my original plan was similar with 100 in series) you're going to have a ridiculous amount of boards. One board can manage a sub-pack of *parallel*-wired cells. It sounds like you need to change the configuration like they told me to do. What cells, at what voltage, amps, etc are you shooting for?


This is for A123 M1's. I am shooting for a balance of power, range (energy) and cost. Heavy on the power and cost, light on the range. Also favoring low weight (for autocross).

Current thoughts are either 16s6p or 4s24p within each sub-pack. The sub-packs will be connected to give about 158V & 55Ah (twelve sub-packs). Of course, inter-sub-pack configuration will be different depending on the intra-sub-pack configuration. 16s6p will need sub-packs in 3s4p configuration. 4s24p will need packs in 12s1p. 

So that's either 1152/6 or 1152/24 "supercells".

Until reading this thread, I was assuming I would need either 3 or 12 MiniBMS boards. Now I guess I'll re-examine that... any advice/comments welcome.


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## Duncan (Dec 8, 2008)

Hi Todd

Any bolted joint relies on the "spring" in the bolt to prevent it from relaxing and losing clamp load (and torque)

If you are going to stack a mess of cylindrical cells together and clamp them you can use the compression stiffness of the cells and the stretch in the clamping system to give yourself the required "spring"

I am thinking about a rigid tube that locates the cells but the clamping being by means of long small diameter rods - possibly waisted in the middle to give greater stretch

This also puts the highest stresses into the nice plain diameter in the middle and away from the nasty stress raisers at the bottom of the threads

With a bit of design and appropriate material selection I would expect to be able to get several centimeters stretch on your clamping rods - enough stretch so that any settling does not massively reduce the clamp loads


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## toddshotrods (Feb 10, 2009)

Bags said:


> This is for A123 M1's. I am shooting for a balance of power, range (energy) and cost. Heavy on the power and cost, light on the range. Also favoring low weight (for autocross).
> 
> Current thoughts are either 16s6p or 4s24p within each sub-pack. The sub-packs will be connected to give about 158V & 55Ah (twelve sub-packs). Of course, inter-sub-pack configuration will be different depending on the intra-sub-pack configuration. 16s6p will need sub-packs in 3s4p configuration. 4s24p will need packs in 12s1p.
> 
> ...


 

I posted my response last night after working all day and my mind was only halfway here. I changed the terminology in my post, but it remains uncorrected in the quote of it in your post. Let's see if I am using the terms right, and if everyone here is thinking the same:

*Supercell* = a group of cells wired together *IN PARALLEL* within a pack or sub-pack of cells.
*Sub-pack* = groups of supercells wired together *IN SERIES* and banded, boxed, or encased to form a physical battery pack; but not constituting the vehicle's entire battery pack.
*Battery Pack* = the whole system, of sub-packs, supercells, connections, cases, wiring, etc.
Bags, IMO it looks like you should do 48 supercells of 24 cells wired in parallel. You would then need 48 BMS boards.


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## toddshotrods (Feb 10, 2009)

Duncan said:


> Hi Todd
> 
> Any bolted joint relies on the "spring" in the bolt to prevent it from relaxing and losing clamp load (and torque)
> 
> ...


That may have worked with my original plan to run 100 cells in series, but now that I will be doing 22p x 136s, the setup will be much different. Well, actually my cases will be the same, but the conductive plates that go in them will be much different.

Interesting concept though...


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## dimitri (May 16, 2008)

I think its important to clarify HOW cells are wired together to avoid confusion.



toddshotrods said:


> *Supercell* = a group of cells wired together *IN PARALLEL* within a pack or sub-pack of cells.
> *Sub-pack* = groups of supercells wired together* IN SERIES* and banded, boxed, or encased to form a physical battery pack; but not constituting the vehicle's entire battery pack.
> *Battery Pack* = the whole system, of sub-packs, supercells, connections, cases, wiring, etc.


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## toddshotrods (Feb 10, 2009)

dimitri said:


> I think its important to clarify HOW cells are wired together to avoid confusion.


Agreed, good point. I'll edit my post accordingly for people who skim.


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