# how to get a balancing for a 64S pack?



## miernik (Nov 28, 2009)

If you build a 64S pack out of bare cells yourself, how do you get about balancing that?

Any commercially available chargers/balancers don't support anywhere near that amount, what solutions are commonly used for this by DIY battery builders here?


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## electricmobile.ru (Jan 14, 2011)

Did you mean 64 cells? What is the voltage of one cell?


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## miernik (Nov 28, 2009)

electricmobile.ru said:


> Did you mean 64 cells? What is the voltage of one cell?


Yes, 64 cells in series, like in "sixty four".

Nominal voltage of one cell is 3.3V.

64 * 3.3V = 211.2V

At full discharge to 0, the voltage of one cell is 2.0V, so that would make 128.0V at full discharge.

What's nice with such setup is that you can use pretty much any worldwide (with wide 100V-250V AC range) switch-mode power supply directly with the battery and it will work both for a fully charged battery and all the way down up to fully discharged.

That's why I want to use such setup - to be able to plug in most standard power supply's of electronic devices directly to the battery.

And for a 22kW charge from a standard European three-phase 400V 32A socket, only 100A of current goes between the charger and the battery - which is easier to manage then 400A for a 48V battery for example.


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## frodus (Apr 12, 2008)

miernik said:


> Any commercially available chargers/balancers don't support anywhere near that amount, what solutions are commonly used for this by DIY battery builders here?


There are actually a couple I know of off the top of my head:

Manzanita Micro
and
Elithion Lithiumate

If you have questions, let me know, I'm familiar with both systems.


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## pgt400 (Jul 12, 2008)

Whaty about the mini BMS? I don't think number of cells matters....check their site. Great product, price and they have a guy always on this site wanting to help.


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## frodus (Apr 12, 2008)

Yeah, MiniBMS like a nice product. Don't see what the max number of cells is anywhere, so check into it. It may be just what you need.


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## electricmobile.ru (Jan 14, 2011)

I had made separate balancers for 40..100Ah cell with 1.7A shunting current (actually any amp value is available). They have been designed to fit WB (Thunder sky) cells. But I think they should fit other cells, too. I need to know the size of your cells to make useful advice.
I'm sorry for advertisement, if not allowed.


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## miernik (Nov 28, 2009)

electricmobile.ru said:


> I need to know the size of your cells to make useful advice.


That will be only 3Ah (3 times 18650 1Ah parallel). Or maybe 4.

But I might be adding more cells in parallel as I gather more money, so the battery will grow, and the balancing circuit should be expandable too.

In parallel I don't need any balancing, they will self-balance, yes?


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## electricmobile.ru (Jan 14, 2011)

Sorry, my balalncers won't fit your cells. Only with additional wires&connectors.


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## frodus (Apr 12, 2008)

miernik said:


> In parallel I don't need any balancing, they will self-balance, yes?


They will self balance within that cell group of parallel cells. You still need to balance the pack. You might have one group at 3.1V and another at 3.3V. They all need to start at the same voltage.


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## brainzel (Jun 15, 2009)

So you got a 64S 3P out of 18650 cells, correct?
I think (no experience) it could be a little tricky to wire them up to a balancing system and let every connection be in place for a long time ... I will follow your thread to see it 
Good luck.

What kind of cells did you chosen? The NCR-18650A for example should be chargeed at 885mA, so three parallel would be 2,66A, not 4Amps ...


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## miernik (Nov 28, 2009)

brainzel said:


> So you got a 64S 3P out of 18650 cells, correct?
> I think (no experience) it could be a little tricky to wire them up to a balancing system and let every connection be in place for a long time ... I will follow your thread to see it
> Good luck.
> 
> What kind of cells did you chosen? The NCR-18650A for example should be chargeed at 885mA, so three parallel would be 2,66A, not 4Amps ...


Yes, 64S3P. Cells are A123 (cheap B-grade) of course (why does anyone buy anything else?), and each can be charged at 5A, so three in parallel makes 15A.

I am seriously thinking that instead of buying an expensive charger and complicated balancer, to hook up 64 different DC-DC converters - one for each group of 3 parallel cells. Like the guy here does: http://electricporsche.rwaudio.com/2010/11/electric-porsche-charger-design/

Do you think that's a good idea in my situation?


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## brainzel (Jun 15, 2009)

The theoretical idea is great. I thought about something similar a while ago, but the practical issue is a little bit "ugly" to me 

So many connections and electric components that could be fail ... and if you count every dollar (euro) you ivested, it could be easyer to get a charger of the shelf.


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## frodus (Apr 12, 2008)

That would create a very balanced pack, its a great idea, BUT, you still need LVC. If any cell goes too low, you need to know about it.

If one "charger" fails, you wouldn't know if it was only the DC-DC converter route. So maybe some cell-logs and that would be a great solution.

(note: I have a similar setup waiting to be put together, 32 3.7V DC-DC converters with 48V input and a couple 48V AC-DC power supplies)

Still a lot of work for that many cells in series.


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## miernik (Nov 28, 2009)

frodus said:


> I have a similar setup waiting to be put together, 32 3.7V DC-DC converters with 48V input and a couple 48V AC-DC power supplies


Can you provide a link or part number to the DC-DC converters you use? And how much they did cost you per piece?


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## rwaudio (May 22, 2008)

miernik said:


> Can you provide a link or part number to the DC-DC converters you use? And how much they did cost you per piece?


I'm doing the same thing with ~96 Syncor modules, they were under $5 each NOS from ebay. Unfortunatially the seller has now sold out of them but the model # is PQ48033QGA25NKS they turn up once in awhile as surplus.

Image below is using 4 of them to charge a 4S3P pack of headway cells.


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## miernik (Nov 28, 2009)

rwaudio: out of curiosity - is there a reason you don't use A123 here? Cause these blue cells don't look like A123, and I am curious are there any reasons to use anything else then A123 cells nowadays?


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## rwaudio (May 22, 2008)

miernik said:


> Yes, 64S3P. Cells are A123 (cheap B-grade) of course (why does anyone buy anything else?), and each can be charged at 5A, so three in parallel makes 15A.
> 
> I am seriously thinking that instead of buying an expensive charger and complicated balancer, to hook up 64 different DC-DC converters - one for each group of 3 parallel cells. Like the guy here does: http://electricporsche.rwaudio.com/2010/11/electric-porsche-charger-design/
> 
> Do you think that's a good idea in my situation?


 
lol, perhaps I should read back far enough in the thread. That's my blog, the PCB should make it a simple clean install without any messy wiring. I don't think I would try this setup without a pcb as there would be too much room for failure. This route is really only good if you can find the parts for the right price. In my setup I paid 500 shipped for 100 dc/dc converters and under 300 shipped for a pair of 1500w 48v supplies. So in the end I will have a 3kw charger that will self balance, the pcb's have voltage monitoring built in so that takes care of the LVC. The pcb's will cost a bit because of the low quantity, but easily worth it in terms of reliability and simplicity of assembly.

miernik, those are headway 10ah cells, however with the last few builders having quality issues with their headways I've ordered the same A123 20AH cell that you bought. I might change the battery, however the charger will work just as well.


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## frodus (Apr 12, 2008)

Miernik,

Mine are Vicor, custom model number and sold out. They were $10 each shipped. Found on ebay, seller has none left.

The MAIN reason people don't use A123, is they're expensive for a large pack with any sort of real range, and a REAL PAIN IN THE ASS to put a pack together. You cannot compress the ends, because it interferes with the pressure seal. You should NOT solder them, because it can lead to damage, so the only way you should put them together, is with a tab welder, which is an added expense.

Another HUGE reason, is that most of the "A123" B cells are unknown as to their authenticity. There are many conterfiet cells on the market, so its a crapshoot. Every chinese company is trying to make a buck.

They're also not very energy dense and can be heavy for a large pack, and have lots of connections. Its also very hard to replace a single cell if one goes bad.

Headway's are good for energy, decent for power and a hell of a lot easier to put together. I think rwaudio used them only for his 12V aux battery.


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## miernik (Nov 28, 2009)

frodus said:


> The MAIN reason people don't use A123, is they're expensive for a large pack with any sort of real range, and a REAL PAIN IN THE ASS to put a pack together. You cannot compress the ends, because it interferes with the pressure seal.


Wait, do you mean that this: http://www.tppacks.com/proddetail.asp?prod=Battery-Pack-Kit is not a good method to making an A123 pack?

I planned on doing something like that, will it damage the cell by pressure?

As for expense: if you divide the cell price not only by the capacity, but also by the number of cycles it will live, aren't A123s the cheapest cells there are? Especially B-grade 18650 1Ah for 2.05 USD a piece from A123RC.

I do plan to test a few thousand cycles on a few cells before buying a large amount of them, and I hope they'll still have about 50% capacity after 3000 cycles. If one 4C charge/discharge cycle takes half and hour, then after 1500 hours = 62.5 days, so after 2 months continuous test I will know what remains of them after 3000 cycles. Or did anyone do such a test already?


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## rwaudio (May 22, 2008)

miernik said:


> Wait, do you mean that this: http://www.tppacks.com/proddetail.asp?prod=Battery-Pack-Kit is not a good method to making an A123 pack?
> 
> I planned on doing something like that, will it damage the cell by pressure?
> 
> ...


The A123 cells you mentioned are $2.05 per AH, headways are less than that per AH and you could buy them from a reputable dealer that will have some sort of warranty or DOA policy for the cells. Plus they are much easier to assemble. Although I also made a very small order from A123RC it's a crap shoot for sure.
Something like Winston (was Thundersky) or CALB are more in the $1.20-$1.35 per AH range. 

So once you include the complexity of assembly and the sheer number of cells required they definatially are NOT the cheapest no matter how you look at it.

Real A123 cells have the benifit of being some of the highest power cells available, and even the "B" grade cells that you mentioned might give headway and others a run for their money but it's hard to tell.


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## frodus (Apr 12, 2008)

Nope, definately not a good method at all. Look up how an A123 cell is made. The ends are made to release if the cell goes pop. If you put any pressure on it, you can damage the cell. Kinda like opening a pop can, it tears a hole in the A123 cell. A123 specifically tells people NOT to assemble like that. Also, if you put pressure on it, it can't vent properly, so instead of blowing outward on the end, it will burst in the center, damaging other cells.

A123 are definately NOT the cheapest cells out there. And A123RC hasn't been proven to be selling legit cells, yet.


Compare cost for a 5kwh pack (in order of high to low power cells). These are just some examples of quick price-checks online.

A123:
1563 1Ah cells: 1563 * 2.05 = $3203.125
680 M1 2.3Ah cells: 680 * 76 per 10 cells = $5168
78 20Ah cells: 78 * 55 = $4290
plus tab welding, tab welder, nickel bussbar and that assumes they're legit

Headway:
156 10Ah cells: 156 * 18.50 = $2886
98 16Ah cells: 98 * 31.50 = $3087
plus: Buss bar and plastic holders

CALB:
16 100Ah cells: 16 * 137.50 = $2200 (about the same for all others)
plus bussbar

I sure as hell wouldn't want to put together a pack with anything more than a couple hundred cells.


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## miernik (Nov 28, 2009)

frodus said:


> Compare cost for a 5kwh pack (in order of high to low power cells). These are just some examples of quick price-checks online.
> 
> A123:
> 1563 1Ah cells: 1563 * 2.05 = $3203
> ...


Nice numbers, but now divide each one by the number of cycles of 4C charge + 4C discharge before the capacity drops below 50%, and what will be the result? Or even at 2C or 1C.

Maybe I buy a few of each brand and cycle them all for 2 months continuously. Or can you predict the result?

If Clabs would work out cheaper then A123 at such 4C cycle-life comparison test, I'd take them. But I doubt it.


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## frodus (Apr 12, 2008)

4C charge, thats nice, but do this for me. 4C * 2.3Ah = 9.2A. Multiply that by the number of cells in parallel 9.2*3 = 27.6A. Now, multiply that times the volts (64 * 3.2V = 204.8) which is 204.8 * 27.6A = 5652.48W. Do you actually have a feed that large (47A @120V, 24A @240V)? Great if you do. Do you have a charger that big? 

Discharge of 4C ain't no big thing. CALB are fine at 4C contuinuous. So are headway. Not sure what the CALB's do for peak, but headway will do 10C for over 30S, and will do 5C all day.

A123's drop quite a bit under a 10C load. I recently tested an A123 M1 at 5C, and it dropped to ~2.9V. At 20C (46A) it dropped to 2.25V, then as it heated up, it went to 2.5V... but it got to 150F. Headway 38120S cells at 5C dropped to 2.875V, never went above 127F.

The capacity of the cells was as follows:
A123 went for 640s, or 0.1777h at 11.5A, so capacity was roughly 2.044Ah (1C rating is 2.3Ah). 
Headway went for 672s or 0.1866h at 50A, so capacity was roughly 9.33Ah (1C rating is 10Ah). 

So, A123 is 0.255Ah lower at 5C, headway is 0.67. not a huge difference. I realize that's about 2.6 times the Ah rating loss in headway, but its not that far off. Not bad considering the cost and effort needed to build a pack. For the difference in cost, you could put a cell or two more cell in parallel and get the same results.

Those were just my preliminary tests with a couple cells, constant current and I monitored temp and voltage. Not as accurate as it is now, but its the data I've got.


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## rwaudio (May 22, 2008)

frodus said:


> 4C charge, thats nice, but do this for me. 4C * 2.3Ah = 9.2A. Multiply that by the number of cells in parallel 9.2*3 = 27.6A. Now, multiply that times the volts (64 * 3.2V = 204.8) which is 204.8 * 27.6A = 5652.48W. Do you actually have a feed that large (47A @120V, 24A @240V)? Great if you do. Do you have a charger that big?
> 
> Discharge of 4C ain't no big thing. CALB are fine at 4C contuinuous. So are headway. Not sure what the CALB's do for peak, but headway will do 10C for over 30S, and will do 5C all day.
> 
> ...


I'm with Travis on this one, unless you have equipment to properly weld the cells into packs it would be a massive effort with the 1ah or 2.3ah A123's, the 20ah pouches bring the cell count low enough that it is getting practical even if it's not easy. This is what drew me to the pouch cell.

I can see 4C peaks on discharge, but not continuous in anything practical. If you were racing the discharges would be higher, if it's your daily driver I would want a bit more than 15 minutes of driving time.

As for charging my headway 10ah cells are rated for 6c maximum, but I've only ever been able to do that one cell at a time on the bench. The pack I had planned for my Porsche would require a power generating station of my own. To expand on Travis's example with the exact pack I have planned for my Porsche.
768 10ah cells in a 96S8P configuration, lets use the 6C charge rate because that's what the data sheet says. I would need the following wall plug:
8 parallel cells x 10ah x 6c = 480 Amps
96 series cells x 3.5v = 336v (I could charge higher but I need to stay under the limit of the Soliton1)
So I need 161kw, given 90% charger efficiency that's 1475A @ 120V or 737A @ 240V

So unless you are building a pack for a pedal bike you are going to run into limits from the wall plug before you need to take advantage of high charging rates. My pack for example will be charging at 0.1C when I plug into a 240v line.

Perhaps if you explain more about the intended use and the type of conversion that you are doing we could give you more practical answers.

I don't want to discourage you from A123, but they are really only the best choice in certain applications.


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## miernik (Nov 28, 2009)

rwaudio said:


> Perhaps if you explain more about the intended use and the type of conversion that you are doing we could give you more practical answers.


I want to have a high possible charging rage, because I want to divide the battery into removable modules, where 1 module weighs no more then 10 kg. Such single module I could remove, put in my backpack, and take to someone's flat to charge it - and I need it done in as little time as possible, 15 minutes is OK, but I don't want to have to sit there for hours. After 15 minutes, when it charges I can come back to my car, put it back in, and possibly take another module upstairs for charging.

Running a cable from someone's flat through the window down to the street is not an option in most places in the city. I will not even be able to park the car close enough!

So I want to be able, while I am on the road, to recharge the batteries at a random friendly stranger's place within 15 minutes - and get as much charge as I can in that time. And taking into account the 10 kg limit, otherwise it'll be too heavy to carry.

So my calculation is: how much energy I can put into a 10 kg battery in 15 minutes of charge. Of course the absolute maximum is 16A (max home socket rating) * 230V * 0.9 (charging efficiency) * 0.25 (quater of an hour) = 828 Wh. A123 18650 in 10 kg I can put 931 Wh - so thats about what I need, and even a bit more.

How much energy you can put into 10 kg of Headways in 15 minutes?


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## frodus (Apr 12, 2008)

At ~300grams each, you could fit about 32 of them into a 10kg package, 32Wh each cell, is about 1024kw. Lets Just say that's 102.4V nominal (3.2V each), so 1024/102.4=10A would charge this pack in 1 hour. The batteries can take 6C, which is 60A. If you did 60A and 102.4V, that'd be ~6kw. If you HAD a 6kw charger, you could charge in about 10 minutes. 

BUT, you stated the limit is 828Wh from the wall, and charging at 102.4V, you're not limited by the batteries, you're limited by the wall. They'd get the same amount of energy from the wall as the A123 batteries.

Feel free to keep tossing questions my way. I test/sell/build battery packs on the side..... specializing in Lithium Ion.




Now, concerning the "module" idea....

You want to charge individual modules. You want to take them out of series (64s3p right). Are you just going to charge each one up as needed?

That will create a very unbalanced pack, especially if one "module" is charged, and another is not fully charged. Your pack is only as "full" as the "most empty" group.

(I have experience with modular pack design if you feel like discussing that as well)


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## rwaudio (May 22, 2008)

miernik said:


> I want to have a high possible charging rage, because I want to divide the battery into removable modules, where 1 module weighs no more then 10 kg. Such single module I could remove, put in my backpack, and take to someone's flat to charge it - and I need it done in as little time as possible, 15 minutes is OK, but I don't want to have to sit there for hours. After 15 minutes, when it charges I can come back to my car, put it back in, and possibly take another module upstairs for charging.
> 
> Running a cable from someone's flat through the window down to the street is not an option in most places in the city. I will not even be able to park the car close enough!
> 
> ...


That is a much different problem and makes much more sense within the context you are talking about. I would recommend a different approach.
Slightly less efficient, but much safer and more practical in terms of having the pack stay balanced and last for years. Create the largest pack you are willing to carry, and use that pack to recharge the entire cars pack. Don't charge one module, putting the whole system out of balance. Charge a 48v pack from the wall for example and then plug that pack into the car to allow it to recharge the rest of the pack. Now you can use mainstream batteries for the car. Winston/CALB/Headway, and then find the the most practical battery for portable use. You will only be putting a small amount of energy in the pack each time, but you don't have the issues related to unbalancing the pack or even having the entire pack removable, just one small module would need to be removable.

Give it a thought.


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## miernik (Nov 28, 2009)

frodus said:


> You want to charge individual modules. You want to take them out of series (64s3p right). Are you just going to charge each one up as needed?
> 
> That will create a very unbalanced pack, especially if one "module" is charged, and another is not fully charged. Your pack is only as "full" as the "most empty" group.


That would be a problem only if the modules would be connected in series, but I'll connect them in parallel. When I'll connect a full module to an empty module in parallel, after a bit of time the charge will flow from the full battery to the full module to the empty module and both will become 50% full.

Each module will be 64s3p, if I connect three modules together that'll make 64s9p. Batteries connected in parallel self-balance, yes?

Concerning Headways, did you read this: http://www.zeva.com.au/tech/headway/
It suggests Headways don't perform too well.

Googling a bit I found many sources cite max charge of Headways at 2C, and some at 6C. I wonder why?

At 6C they would be better then A123s! And if it would be so, then everyone would be excited about Headways on forums and not about A123 as it is now. 

And what about cycle life? B-grade A123s can be bought at 2.05$ per Ah shipped, and what is the cheapest price you can get Headways (shipped) now? In quantities of up to 100Ah at a time?


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## frodus (Apr 12, 2008)

Whats this even going into anyway? 200+ volts and 9Ah? Is it going into a drag bicycle? Even at 20C with those batteries, that's only 180A and it'l sag so bad you'd be lucky to get 150VDC out of them under that load.



> That would be a problem only if the modules would be connected in series, but I'll connect them in parallel. When I'll connect a full module to an empty module in parallel, after a bit of time the charge will flow from the full battery to the full module to the empty module and both will become 50% full.


That would really complicate the design. You have to buss the first battery of the first module to the first battery of the second module. Then buss the second to the second, and so on. Just putting the "pack" in parallel with the other "pack" will not self balance. The packs will rest at the same voltage, but the cells will be all over the place. 

I'd kinda tend to agree with RWAudio on this one.




> Each module will be 64s3p, if I connect three modules together that'll make 64s9p. Batteries connected in parallel self-balance, yes?


so you want to connect 192 togther and have 3 modules? good luck. Its going to be a large task. I'm assuming you're using the 18650's. I've welded packs of 120 cells a piece, maybe 6 packs, and that was a REAL pain. Realize, you have 2 connections. that's 1280 welds, and you usually have to have 2 welding points, so 2560 welds. Forget about soldering.


> Concerning Headways, did you read this: http://www.zeva.com.au/tech/headway/
> It suggests Headways don't perform too well.


You realize that test was done 3 years ago, right? Those cells have come a LONG way since then, and I've tested them. I mean, its ok for companies to continuously improve products isn't it? Well good news, they have.



> Googling a bit I found many sources cite max charge of Headways at 2C, and some at 6C. I wonder why?


2C was 2 years ago. 6C is their current spec. Sometimes thats just how things are with China. The datasheets direct from headway state 6C max charge current on the newest cells. Some of the info is outdated because the "resellers" are lazy. I'll put that on my to do list of things to test. 



> At 6C they would be better then A123s! And if it would be so, then everyone would be excited about Headways on forums and not about A123 as it is now.


They're not BETTER for power, they're better for cost, ease of assembly, form factor, energy density and the ability to get legit cells with a WARRANTY. 

As far as people on the forums being excited about A123, Maybe in RC and the bicycle forums, but from what I have witnessed in the last year or two around here are more interested in TS, CALB, GBS and Headway. 



> And what about cycle life? B-grade A123s can be bought at 2.05$ per Ah shipped, and what is the cheapest price you can get Headways (shipped) now? In quantities of up to 100Ah at a time?


As with all batteries, lifecycle depends on their use. If they're used no more than 20% DOD, you can get well over 2000 cycles. 

As far as cost.... $2.05 an Ah shipped..... 100Ah is only 10 cells... so thats not really a very "large" quantity. Now, lets say you want the equivalent of 64S9p of the 1Ah cells, so about 64 cells of the 10Ah, thats something we stock, but its not a very large quantity of cells. Shipping wouldn't be that bad. I bet on 64 cells of 10Ah, they'd run about $18-19 + shipping, so lets say (worst case) $1216 + maybe $35 shipping + $25 hazmat = $1276. Now, compare that to buying the same thing 64s10p (equivalent pack), at 2.05. It works out to be just slightly more, $1312. Except you get no warranty, have to figure out how to weld 640 batteries, don't know if they're legit or not, and did I mention, its 640 frickin cells. 


Headways are down below $1.80/Ah in quantity and TS and CALB are around $1.25/Ah in quantity. Shipping depends on how many you buy, cost goes down the more you order.


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## rwaudio (May 22, 2008)

They will only self balance if you connect each module together with 65 wires, IE you actually tie each of the cells together at the cell level. Are you going to use some type of BMS? How are you going to restrict current flow (and keep your charge/discharge rate in check) from a charged module to a partially discharged module?

It's not a bad idea given your situation but it's far from ideal.

As for the headways I have personally tested 12 of the 10AH 38120S cells. They all do 5C with virtually no heating, they do 10C for the entire discharge cycle without getting too hot to hold. I've done 15C for brief periods, however after about 45-60 seconds they are as hot as I'm willing to take them (but I can still hold the cell) I've done 25C tests for 3-4 seconds and the voltage is stable and consistent and there is no noticable heating (not that gets to the case anyways, they might be warm on the inside).

So from personal testing that I've done with my own two hands, I'm 100% confident in headway cells for my application, I am a bit worried about the mechanical issues that others have had but it's not a deal breaker. I would peak at 12.5C in my setup, which I've confirmed that the cells do without a problem, my normal discharge would ideally be between 0.5-1C because that's what I need to get the range I want. I do want a cell that can handle those small peaks though, and the prismatics just can't do the current I want in the pack size I need for my fairly small range requirements. I'm barely willing to assemble a pack with 768 cells, there is no way I would be willing to create a pack from smaller cells regardless of price.

You will find all sorts of different ratings on headways cells depending on where you look, there's no definitive answer there because if you get the info from headway directly it doesn't always match the resellers. However the conspiricy theorist in me says that these resellers "under rate" the cells because they will never fail, they will never have to deal with warranty or possible liability. And if something does happen it's not hard to say the customer used them beyond what we rate them to do regardless of what others say.

Attached is one of the documents I got directly from Headway, I'm sorry I was mistaken they rate the continuous charge at 5C, the 6C rating is on Manzanita's website, the charge rate for the "P" cell is 10C though which is the same as listed on Manzanita's website.

Headways might not be as good as real A123 cells but they are available and they are cheaper. If a reliable source of real A123 cells appears (I hope the cell I bought from A123RC isn't a dud) then things might change, but I bought one cell because I'm willing to lose that amount of money, I wouldn't be willing to buy a pack from them without lots of testing as well as more information about the source of the cells, any warranty etc.

Good luck with your project, your charging idea is quite unique.




miernik said:


> That would be a problem only if the modules would be connected in series, but I'll connect them in parallel. When I'll connect a full module to an empty module in parallel, after a bit of time the charge will flow from the full battery to the full module to the empty module and both will become 50% full.
> 
> Each module will be 64s3p, if I connect three modules together that'll make 64s9p. Batteries connected in parallel self-balance, yes?
> 
> ...


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## miernik (Nov 28, 2009)

frodus said:


> Whats this even going into anyway? 200+ volts and 9Ah? Is it going into a drag bicycle? Even at 20C with those batteries, that's only 180A and it'l sag so bad you'd be lucky to get 150VDC out of them under that load.


No, its a 2035 kg van.

Even 180A x 150V that is 27kW power and about 5kW, maybe max 10kW is enough to keep the van rolling at 30 km/h. I will only use batteries for city driving, and the speed limit is 30 km/h in most places here anyway. The diesel engine will stay, this is supposed to be a hybrid. The batteries are for short trips in the city.

Also the 9Ah is what I want to put at first, will allow me to travel several km at small city speed on batteries. I will increase the battery size once I get it all working and see that it all makes sense. It'll take me a year or two to convert anyway, so no sense buying more batteries earlier and just have them age.

But these 9Ah will also allow me to use a computer in the van so that will be an important purpose of the batteries even before I get any electric motor attached to it. I would be cool that this will start to get sold: http://www.poulsenhybrid.com/ so I could convert it to a hybrid quite easily then.

Anyway, I'll now be silent for some time, as I have to concentrate on work otherwise I'll never have money to buy more batteries.


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## frodus (Apr 12, 2008)

Ok, now more details of the actual build come out..... Temporary pack, not a long range and .....It's a hybrid. And it sounds doable if you can get the mechanicals worked out.

You want to put a 1.8kwh pack of A123 cells, and draw 10kw continuous off it, so lets say ~5C (~45-50A) which would maybe drop to 2.9V and give you ~10kw. Thats doable, but from my testing I did, it'l only give about 10 minutes or so of runtime, if that.

The devil is in the details, it'd have helped if the details were more up front.

You've got lots to work out, but it sounds like a fun project, good luck!


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## miernik (Nov 28, 2009)

frodus said:


> As with all batteries, lifecycle depends on their use. If they're used no more than 20% DOD, you can get well over 2000 cycles.


What exactly do you mean by 2000 cycles?
What I am interested in, is by how much the capacity decreases for each 1000 cycles.

And "well over 2000 cycles at 20% DOD" is nowhere near the cycle life of A123.

A123 charged/discharged at 1C loses only 5% capacity per each 1000 cycles, and that is more or less linear, even the loss % decreases a bit with cycles.

Which means it will reach 50% of its initial capacity at a 11000 cycles!
And what's more: all that at 100% DOD!

Talking about cycle life at 20% DOD is useless, because the cells are 5 times more expensive then.

What I want to compare is the cell price divided by usable capacity (DOD*nominal capacity), divided by the number of cycles it takes for the cell to degrade to 50% capacity.

For A123 that is 2.05 USD/(1.1Ah*3.3V/1k)/11000 cycles = 0.05 USD/kWh over the lifetime of the cell. 

If Headways are going to come close, I'll buy them, but I'd need to run a few thousand cycles on them and B-grade A123 to make a decision. I am a bit skeptical that Headways will come out cheaper then B-grade A123s in that calculation.

What do you suspect the most economical DOD to discharge Headways?
I.e. how many more cycles (until the capacity drops to 50%) I am gonna get for each 10% less DOD?

Anyway, I'll probably have to run tests-till-cell-death at DOD 100%, 90%, 80%, 70% and 50%, and at charge/discharge rate of 1C, 2C and 4C of a bunch of B-grade A123s and a bunch of Headways to get an answer.

Or did someone already done that?

As for warranty, factory, etc, it doesn't matter to me, what matters is real-life test results of a statistically significant number of cells. 

Screws at the ends, and the cells being larger 10 times are tempting, but if they are gonna be half-dead at cycle 2000 and A123 at cycle 11000 in the same conditions, then sorry - I will not pay 5 times much per kWh because they have screws and size.


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## frodus (Apr 12, 2008)

well, good luck on your pack then. If they're so great then get em, but have fun assembling all of those cells, you'll need a tab welder. 

I'm not going to argue the SOC, DOD and cycle life of A123 or Headway, mostly because the data isn't out there, and what info is out there, you can research it yourself.


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## nimblemotors (Oct 1, 2010)

A123 was quoted as saying packs used in buses were only expected 3x lifetime over AGM lead batteries. This is real world use, not a lab test.
Lab test is often a best-case result. 

I've seen the A123 cells with tabs connected with screws and nuts.
That's a lot of nuts, time consuming, probably adds a lot of weight too.
But you can replace and reconfigure them easily in the future.
welding is pretty much a permanent pack.



miernik said:


> What exactly do you mean by 2000 cycles?
> What I am interested in, is by how much the capacity decreases for each 1000 cycles.
> 
> And "well over 2000 cycles at 20% DOD" is nowhere near the cycle life of A123.
> ...


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