# A123 20Ah pack configuration question



## frodus (Apr 12, 2008)

Use all cells or nothing. Having a range extending pack really complicates things, especially if they're not the same SOC. If you parallel them for range extension, the pack with lower SOC will cause an arc from the higher SOC pack. If you do things in series, you have to modify all of your controller parameters. If you use a BMS, it complicates things as well. If you use some sort of SOC meter, it can really complicate things.

Why wouldn't you do the large battery pack up front? Why redo it second phase and mix old with new?


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## rwaudio (May 22, 2008)

kakheath said:


> I need some advice from the pros .
> 
> More detail on my project can be found here: http://www.diyelectriccar.com/forums/showthread.php/tennessee-rx8-conversion-68311.html
> 
> ...


when you go with the dual motor set up are you putting the motors in series or parallel or doing series/parallel switching?

These A123's don't sag as much as prismatics so having a really high voltage pack doesn't make as big a difference. 

My logic could be wrong but I would guess that putting the extra range pack in series with the normal pack would allow you to keep things in better balanced. Putting another string in parallel should be fine in theory, but you wouldn't have the parallel cell connections between the two strings, they would be just tied at the +/- extremes. 

Another thing to consider (which is a big task for 500 cells) but I'm in the process of measuring the IR and capacity of every one of my cells (my pack will only be 288 of the 20ah A123's) that way I can group them into perfect parallel sets, in my case 3 parallel that total the same value for every single grouping. That way the series groups should all behave exactly the same, mine will be top balanced, but since they are all the same capacity they should behave like they are bottom balanced as well. So far I have been able to group them to within 0.01Ah.


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## kakheath (Jan 7, 2012)

rwaudio said:


> when you go with the dual motor set up are you putting the motors in series or parallel or doing series/parallel switching?
> 
> These A123's don't sag as much as prismatics so having a really high voltage pack doesn't make as big a difference.


I've been talking with John Metric from DC Plasma and his calculations show that if you have a high enough pack voltage (like 333V) the series/parallel switching isn't beneficial due to the electromagnetic field emf. So if I string enough together I could avoid all the additional contactors etc.



rwaudio said:


> Another thing to consider (which is a big task for 500 cells) but I'm in the process of measuring the IR and capacity of every one of my cells (my pack will only be 288 of the 20ah A123's) that way I can group them into perfect parallel sets, in my case 3 parallel that total the same value for every single grouping. That way the series groups should all behave exactly the same, mine will be top balanced, but since they are all the same capacity they should behave like they are bottom balanced as well. So far I have been able to group them to within 0.01Ah.


I'm very interested in learning more about this. How long does it take to test the capacity of each cell? What equipment do you use? Perhaps you can guide me on how to do it with a PL6.


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## rwaudio (May 22, 2008)

kakheath said:


> I've been talking with John Metric from DC Plasma and his calculations show that if you have a high enough pack voltage (like 333V) the series/parallel switching isn't beneficial due to the electromagnetic field emf. So if I string enough together I could avoid all the additional contactors etc.
> 
> 
> I'm very interested in learning more about this. How long does it take to test the capacity of each cell? What equipment do you use? Perhaps you can guide me on how to do it with a PL6.


Well since I'm using a PL6 to do it I'm sure I can help. There isn't much to it, I'm using a 4S3P pack of A123's to power the charger so that I can use regenerative discharge (up to 40A, I'm using 38A as a rough 2C discharge) then charge again at 38A (2C). I do have to recharge the pack powering the charger once in awhile but it works very well. I'm using the PC interface cable and the set up works great, everything is controlled from the software on the computer, the cells arrive around 50% SOC so I run "1 cycle" it's an option on the PL6, and basically it charges the cell, then discharges the cell and charges it again. You can choose to end on discharge if you like, if you wanted a bottom balanced pack. If you did the bottom balance method it would take about 15mins to top up the cell and 30 to discharge it, that's 45 mins per cell. I do the charge/discharge/charge so it's around an hour and 15 mins. I have a 2nd PL6 on order so that I can do two at a time (they connect together so it's all controlled through the single PC interface)

Below is the measured capacity of 76 cells.
17.76
17.78
17.82
17.84
17.89
17.95
17.99
18.06
18.08
18.11
18.13
18.15
18.25
18.26
18.27
18.28
18.33
18.33
18.34
18.34
18.35
18.36
18.39
18.40
18.41
18.41
18.44
18.44
18.47
18.49
18.50
18.50
18.51
18.51
18.51
18.52
18.54
18.55
18.55
18.56
18.56
18.56
18.56
18.57
18.59
18.59
18.60
18.61
18.61
18.62
18.62
18.62
18.63
18.64
18.65
18.67
18.69
18.69
18.70
18.70
18.71
18.72
18.73
18.73
18.75
18.77
18.78
18.79
18.81
18.81
18.83
18.84
18.88
18.90
18.92
18.93

Below are the groupings that I created based on this information (72 cells, 4 went back in the pool for grouping the next batch).
All groups total either 55.45Ah or 55.46Ah 

A	18.50	18.55	18.41	55.46
B	18.81	18.56	18.08	55.45
C	17.95	18.79	18.72	55.46
D	18.06	18.69	18.70	55.45
E	18.60	18.39	18.47	55.46
F	18.11	18.51	18.83	55.45
G	18.13	18.51	18.81	55.45
H	18.26	18.52	18.67	55.45
I	18.25	18.49	18.71	55.45
J	18.62	18.84	17.99	55.45
K	18.27	18.55	18.63	55.45
L	18.28	18.56	18.61	55.45
M	18.33	18.56	18.56	55.45
N	18.62	18.69	18.15	55.46
O	18.34	18.33	18.78	55.45
P	18.34	18.57	18.54	55.45
Q	18.35	18.59	18.51	55.45
R	18.36	18.59	18.50	55.45
S	18.44	18.62	18.40	55.46
T	18.41	18.61	18.44	55.46
U	17.84	18.73	18.88	55.45
V	17.82	18.73	18.90	55.45
W	17.78	18.75	18.92	55.45
X	17.76	18.77	18.93	55.46

The goal is that all cell groups behave exactly the same.
I didn't know this would actually work until fairly deep into the testing, so I've been topping up all the cells. I may switch to a charge/discharge cycle since the cells should behave basically the same regardless if they are top or bottom balanced. (this would save 30 mins per cell) Or at least allow me to bulk charge the cells in groups once assembled.


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## dladd (Jun 1, 2011)

just curious rwaudio, are you using the discharge or the charge capacity? Or are they the same? I'm doing similar cycling with CALB 130ah cells with my PL6 and I'm seeing about 2 more ah going in than come out on a cycle.

Granted my cells are a lot larger (and take more like 8 hours/cell to cycle) and 2ah on my cells is more like 0.3ah on yours, but was just wondering which number is considered the capacity of the cell.

I'd also be really curious to see if a single cell was cycled three times, how close are the three capacity values. In other words, how repeatable are the results with the PL6? I'm certainly not going to try and find out since it takes me 8 hours to cycle a single cell.


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## rwaudio (May 22, 2008)

dladd said:


> just curious rwaudio, are you using the discharge or the charge capacity? Or are they the same? I'm doing similar cycling with CALB 130ah cells with my PL6 and I'm seeing about 2 more ah going in than come out on a cycle.
> 
> Granted my cells are a lot larger (and take more like 8 hours/cell to cycle) and 2ah on my cells is more like 0.3ah on yours, but was just wondering which number is considered the capacity of the cell.
> 
> I'd also be really curious to see if a single cell was cycled three times, how close are the three capacity values. In other words, how repeatable are the results with the PL6? I'm certainly not going to try and find out since it takes me 8 hours to cycle a single cell.


I'm using the discharge cycle as the capacity (at 2C in my case which is somewhat close to or just above what the car should average), and you are close, I put in about 0.2Ah more than I get out. I did have a higher discrepancy 0.4 to 0.5Ah using the stock banana's and wires at 40A, I have since switched to a better banana and shorter 8awg cables. So a good portion of the loss was in heat, there is still some heat in the cables and connector so I believe actual losses in the cell to be very low. I have done some repetitive testing on a couple of cells and the results were within 0.01Ah (This isn't based on a very big sample though, one cell 3 times, and another cell twice). My testing is in a room with fairly constant temperature (basement with no outside doors that could be opened, and no sources of heat other than the furnace).


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## dladd (Jun 1, 2011)

rwaudio said:


> I'm using the discharge cycle as the capacity (at 2C in my case which is somewhat close to or just above what the car should average), and you are close, I put in about 0.2Ah more than I get out. I did have a higher discrepancy 0.4 to 0.5Ah using the stock banana's and wires at 40A, I have since switched to a better banana and shorter 8awg cables. So a good portion of the loss was in heat, there is still some heat in the cables and connector so I believe actual losses in the cell to be very low. I have done some repetitive testing on a couple of cells and the results were within 0.01Ah (This isn't based on a very big sample though, one cell 3 times, and another cell twice). My testing is in a room with fairly constant temperature (basement with no outside doors that could be opened, and no sources of heat other than the furnace).


Good info, thanks! I have noticed that my battery leads get VERY hot, I need to keep a fan on them. I'm using 10awg wire with screw on banana plugs. Not a big fan of the banana plugs, I'd sure rather see a screw terminal on the charger.


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## kakheath (Jan 7, 2012)

rwaudio said:


> Well since I'm using a PL6 to do it I'm sure I can help. There isn't much to it, I'm using a 4S3P pack of A123's to power the charger so that I can use regenerative discharge (up to 40A, I'm using 38A as a rough 2C discharge) then charge again at 38A (2C). I do have to recharge the pack powering the charger once in awhile but it works very well. I'm using the PC interface cable and the set up works great, everything is controlled from the software on the computer, the cells arrive around 50% SOC so I run "1 cycle" it's an option on the PL6, and basically it charges the cell, then discharges the cell and charges it again. You can choose to end on discharge if you like, if you wanted a bottom balanced pack. If you did the bottom balance method it would take about 15mins to top up the cell and 30 to discharge it, that's 45 mins per cell. I do the charge/discharge/charge so it's around an hour and 15 mins. I have a 2nd PL6 on order so that I can do two at a time (they connect together so it's all controlled through the single PC interface)
> 
> The goal is that all cell groups behave exactly the same.
> I didn't know this would actually work until fairly deep into the testing, so I've been topping up all the cells. I may switch to a charge/discharge cycle since the cells should behave basically the same regardless if they are top or bottom balanced. (this would save 30 mins per cell) Or at least allow me to bulk charge the cells in groups once assembled.


Since 500 would take forever, I definitely would leave them discharged. What voltage are you using for the cut offs? 3.65 & 2.0? Does the PL6 control this automatically or do you have to be present to stop it? How many PL6s can be connected together and controlled by the computer? I figure if I buy two more PL6s and end on discharge, maybe I could be done with them in about 3 weeks if I talked my wife into helping out with the swaps. I may regret that decision later though.


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## rwaudio (May 22, 2008)

kakheath said:


> Since 500 would take forever, I definitely would leave them discharged. What voltage are you using for the cut offs? 3.65 & 2.0? Does the PL6 control this automatically or do you have to be present to stop it? How many PL6s can be connected together and controlled by the computer? I figure if I buy two more PL6s and end on discharge, maybe I could be done with them in about 3 weeks if I talked my wife into helping out with the swaps. I may regret that decision later though.


I'm charging to 3.65 at 38A that terminates at 0.9A and discharging to 2.25v with a 38A constant current.
The PL6 will do everything automatically. You can actually hook up to 16 PL6's together and control them all from one PC interface. 

If you bought a few extra PL6's I'm sure you could sell them here or on the RC market for a reasonable loss that might be better worth your time.

I have a 2nd one coming for that purpose.

It's a good charger for the price, especially based on the software interface and data collection that you can do. I was going to save the log file for each cell as the cells serial number but never got around to bringing home a bar code scanner from work. That might be handy for the obsessive data collector though.


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## kakheath (Jan 7, 2012)

rwaudio said:


> I'm charging to 3.65 at 38A that terminates at 0.9A and discharging to 2.25v with a 38A constant current.
> The PL6 will do everything automatically. You can actually hook up to 16 PL6's together and control them all from one PC interface.


I think I'll order some additional ones like you say. How do they connect together and how does the interface on the computer change when you have several of them all hooked together? I'm thinking of getting 3 more to have 4 total.

Could you use a higher cut off voltage like 2.85V to save time, then correlate an average of the existing curves to predict the capacity instead of running it all the way to 2.25V? You may not save that much time, but times 500 it could add up.


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## DIYguy (Sep 18, 2008)

I didn't read all the details so excuse me if this has been covered but I just want to mention that you don't need multiple PL units to do more batteries. I have a PL 8 and I do 6 cells connected in series, at one time. With balance and charge leads connected, you can get individual IR readings and individual capacities. You can balance charge or not depending on settings. u can finish at top or bottom or anywhere u like . . on the voltage scale.


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## kakheath (Jan 7, 2012)

DIYguy said:


> I didn't read all the details so excuse me if this has been covered but I just want to mention that you don't need multiple PL units to do more batteries. I have a PL 8 and I do 6 cells connected in series, at one time. With balance and charge leads connected, you can get individual IR readings and individual capacities. You can balance charge or not depending on settings. u can finish at top or bottom or anywhere u like . . on the voltage scale.


An important point for me would be to know the time it takes. I thought the PL6 could only deliver 40A max. If this is distributed over multiple batteries like 6 since that why it has its name that the amperage would go down and the whole process would take longer. 

I haven't used my PL6 yet so I'm not positive about this. My goal here is to measure the capacity while bottom balancing the pack. The idea of 6 batteries at once might be useful. Meaning instead of changing the batteries out every 45 minutes, I could change 6 batteries out every 270min (6*45min). This may be work investigating for working with a large number. I still think that I'll need multiple PL6s in order to complete 500 in a reasonable amount of time.


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## DIYguy (Sep 18, 2008)

kakheath said:


> An important point for me would be to know the time it takes. I thought the PL6 could only deliver 40A max. If this is distributed over multiple batteries like 6 since that why it has its name that the amperage would go down and the whole process would take longer.
> 
> I haven't used my PL6 yet so I'm not positive about this. My goal here is to measure the capacity while bottom balancing the pack. The idea of 6 batteries at once might be useful. Meaning instead of changing the batteries out every 45 minutes, I could change 6 batteries out every 270min (6*45min). This may be work investigating for working with a large number. I still think that I'll need multiple PL6s in order to complete 500 in a reasonable amount of time.


yes, your maximum current in and out is still the same. It's the repetitive set up time that may be reduced. It may depend on your connection method but for me, it was a huge improvement. I did 135 cells and let them cycle twice before ending at a specific voltage. 

One other thing I found very helpful was to pre-sort according to voltage. If you are doing in series set up. If they are fairly close in voltage, the whole process is shortened dramatically. This is because they must balance before the higher current charge/discharge cycle. I had cells that were in batches kind of and had several different voltage levels. When I grouped them accordingly the process was much quicker. I just went over them with a DVM and put piece of tape on each with the voltage. Then I would grab 6 that were close. At the end I had a handful that were all over the map and I would use a few resistors to bring them in line because I found it was worth the time.

I numbered each and noted IR and capacity in a log. I also saved the files on PC.


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## DIYguy (Sep 18, 2008)

thinking about it now, I may have led u a stray. I'm not sure if I got individual capacities or not. I was more interested in individual IR. . . That may be a problem for you if you are grouping according to capacity. Since mine is a high output application, I was grouping according to IR. I can go back and check or maybe RWAudio knows off top of his head since I think he was interested in grouping by capacity.


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## rwaudio (May 22, 2008)

DIYguy said:


> I didn't read all the details so excuse me if this has been covered but I just want to mention that you don't need multiple PL units to do more batteries. I have a PL 8 and I do 6 cells connected in series, at one time. With balance and charge leads connected, you can get individual IR readings and individual capacities. You can balance charge or not depending on settings. u can finish at top or bottom or anywhere u like . . on the voltage scale.


I did try that as well, and didn't get consistent results. During discharge it will stop the lowest cell and only discharge at 1A to the cut off point which is not the same as the 38A setting I was using. Perhaps I didn't have it configured properly to do it this way but that was just my experience. 

I would get a true capacity on the first cell to discharge but once the first cell hit the low cut off it messed up the results for the remaining cells. During charging it does work, but if the cells are very far off the whole balancing thing doesn't work very well with cells of this capacity. Shunting a maximum of 1A doesn't do much on a 38A charge if the cells aren't at the same SOC.

I gave up on that and went to a single cell, if you have any tips on how to do that better I would be happy to hear them. For me getting a capacity number under the same conditions every single time is more important than shaving off a bit of time.


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## kakheath (Jan 7, 2012)

rwaudio said:


> You can actually hook up to 16 PL6's together and control them all from one PC interface.


Is there a special cable that is used to connect multiple PL6s together? I have the USB interface for my first one. I'd like to order these cables with the extra units.


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## rwaudio (May 22, 2008)

kakheath said:


> Is there a special cable that is used to connect multiple PL6s together? I have the USB interface for my first one. I'd like to order these cables with the extra units.


servo extension and y cables.


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## kakheath (Jan 7, 2012)

rwaudio said:


> I did try that as well, and didn't get consistent results. During discharge it will stop the lowest cell and only discharge at 1A to the cut off point which is not the same as the 38A setting I was using. Perhaps I didn't have it configured properly to do it this way but that was just my experience.
> 
> I would get a true capacity on the first cell to discharge but once the first cell hit the low cut off it messed up the results for the remaining cells. During charging it does work, but if the cells are very far off the whole balancing thing doesn't work very well with cells of this capacity. Shunting a maximum of 1A doesn't do much on a 38A charge if the cells aren't at the same SOC.
> 
> I gave up on that and went to a single cell, if you have any tips on how to do that better I would be happy to hear them. For me getting a capacity number under the same conditions every single time is more important than shaving off a bit of time.


Well, my batteries arrived and they look great. They all have Made in USA on them and have brand new full size tabs. I'm not sure if I'm using the correct settings, but I managed to charge, discharge and charge again a single cell. I'm using a power supply instead of a 12V battery, so I appear to be limited to 10A up and down. This is terribly slow at about 2 hours each.









rwaudio, when you said you were using a block of A123s in 4s3p for a 12V power supply, how did you get started? Did you balance them individually first or just hook them up and charge them as a pack before balancing? I've measured the initial as-received battery votage of each one and they all appear to be at 3.27-3.28V consistently. Charging the first one up took about 10Ah, so mine appear to be half charged as well. The first cell capacity was 18233mAh. This was from 3.65 to 2.5V. I'm not sure if I'm doing this correctly. so if you have any tips on how to do this more efficiently, I would appreciate it greatly.


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## kakheath (Jan 7, 2012)

rwaudio said:


> I did try that as well, and didn't get consistent results. During discharge it will stop the lowest cell and only discharge at 1A to the cut off point which is not the same as the 38A setting I was using. Perhaps I didn't have it configured properly to do it this way but that was just my experience.
> 
> I would get a true capacity on the first cell to discharge but once the first cell hit the low cut off it messed up the results for the remaining cells. During charging it does work, but if the cells are very far off the whole balancing thing doesn't work very well with cells of this capacity. Shunting a maximum of 1A doesn't do much on a 38A charge if the cells aren't at the same SOC.
> 
> I gave up on that and went to a single cell, if you have any tips on how to do that better I would be happy to hear them. For me getting a capacity number under the same conditions every single time is more important than shaving off a bit of time.


rwaudio, I assembled a 4s3p set of my batteries as a power supply and still seem limited to 10A charge and discharge. Can you tell me why I can't change the setting to 40A? Can you send me your pl6 file so I can check it out? I've been talking to a guy from Quantum Hobby, where I bought my PL6, and he seems convinced that I can do 6 at a time and get the individual capacities if I use his "special" connecter set. We'll see. So far I've tested about a half a dozen down to 2.5V and they ranged from 18.2 to 18.9Ah. I'm not sure how much extra will squeeze out if I go down to 2.25V or even 2.0V.


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## rwaudio (May 22, 2008)

kakheath said:


> rwaudio, I assembled a 4s3p set of my batteries as a power supply and still seem limited to 10A charge and discharge. Can you tell me why I can't change the setting to 40A? Can you send me your pl6 file so I can check it out? I've been talking to a guy from Quantum Hobby, where I bought my PL6, and he seems convinced that I can do 6 at a time and get the individual capacities if I use his "special" connecter set. We'll see. So far I've tested about a half a dozen down to 2.5V and they ranged from 18.2 to 18.9Ah. I'm not sure how much extra will squeeze out if I go down to 2.25V or even 2.0V.


My usual preset is attached, it's set to 38A charge/discharge but you can change it to 40A. Make sure that under the supply tab you have it set to battery power and not a power supply or it won't do regenerative discharge.

While your guy is technically correct, you can do 6 at a time. I didn't have consistent results doing so. There is a good 0.4ah left between 2.5 and 2.0v however 2.0 didn't let me charge again right away because it took awhile for the cell to recover above the 2.55 minimum voltage for this chemistry. That's why I chose 2.25v as my lower limit.

Be careful about what "special" connector set he tries to sell you and what he charges. This is all you need, and you simply wire it up with alligator clips or whatever method works for connecting to your cells. I use one of these with two clips when testing a single cell.
http://www.usastore.revolectrix.com/Products_2/Cellpro-PowerLab-6-EC5-version_2/Cellpro-JST-PA-Battery-Pigtail-10-9-Position

Also make sure you upgrade your stock cables if charging at 40A I switched to 8awg and still have some heat. I simply soldered 8awg car stereo power wire to some banana plugs I had laying around. On the cell end I have my aluminium bars set up with the 8awg clamped between two bars and another bar that I slide the tab between and tighten it up. I then attach the alligator clip to the remaining bare cell tab so that resistance in the connections doesn't mess with the voltage reading for the charger.

Hope that helps.


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## kakheath (Jan 7, 2012)

rwaudio said:


> My usual preset is attached, it's set to 38A charge/discharge but you can change it to 40A. Make sure that under the supply tab you have it set to battery power and not a power supply or it won't do regenerative discharge.
> 
> While your guy is technically correct, you can do 6 at a time. I didn't have consistent results doing so. There is a good 0.4ah left between 2.5 and 2.0v however 2.0 didn't let me charge again right away because it took awhile for the cell to recover above the 2.55 minimum voltage for this chemistry. That's why I chose 2.25v as my lower limit.
> 
> ...


I get "Safety Code 20: Bad Cell Count" when I use this setup. Any advice to correct this issue?

What do you use as the supply setting? I had it set on the last one (13.2V(4S)...A123...).


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## rwaudio (May 22, 2008)

kakheath said:


> I get "Safety Code 20: Bad Cell Count" when I use this setup. Any advice to correct this issue?
> 
> What do you use as the supply setting? I had it set on the last one (13.2V(4S)...A123...).


Do you have the balance plug wires hooked up? You need to use these wires or the charger can't measure voltage properly. I bought the balance board for my first PL6, but only the pigtail for the 2nd. 

Under "options" then "start setting" you have to pick one of the choices under "node wiring".
FMA would use the black and red wires for a single cell.
XH/EH would use the black wire and first white wire for a single cell.

For the supply I'm using 13.2v...A123..9200mah and it seems to work well.
Make sure you increase the battery amps in/out to 40.


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## kakheath (Jan 7, 2012)

rwaudio said:


> Do you have the balance plug wires hooked up? You need to use these wires or the charger can't measure voltage properly. I bought the balance board for my first PL6, but only the pigtail for the 2nd.
> 
> Under "options" then "start setting" you have to pick one of the choices under "node wiring".
> FMA would use the black and red wires for a single cell.
> ...


I got it working - finally. Thanks to your help. You're right about the stock output wires not liking the 38A current. They got very hot. I only did this once. I have since went to Home Depot and got some 6awg wire and some nice aluminum connectors for attaching to the cell. I also bought some nice banana clips that would accept the 6awg wire for connecting to the PL6. I just need to solder the 40A fuses to them I'll be set. I didn't want to work on it last night being Valentine's day and all . I will try to complete it tonight.

I think I'm gonna order the combo pack of two more PL6s. They come with the y harness and male2male connector.

I saw on your site that you are doing some interesting work on cell monitoring/balancing/charging involving PCBs. What is the latest on this work? I'd be interested in a simple and inexpensive cell level monitoring system.


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## rwaudio (May 22, 2008)

kakheath said:


> I got it working - finally. Thanks to your help. You're right about the stock output wires not liking the 38A current. They got very hot. I only did this once. I have since went to Home Depot and got some 6awg wire and some nice aluminum connectors for attaching to the cell. I also bought some nice banana clips that would accept the 6awg wire for connecting to the PL6. I just need to solder the 40A fuses to them I'll be set. I didn't want to work on it last night being Valentine's day and all . I will try to complete it tonight.
> 
> I think I'm gonna order the combo pack of two more PL6s. They come with the y harness and male2male connector.
> 
> I saw on your site that you are doing some interesting work on cell monitoring/balancing/charging involving PCBs. What is the latest on this work? I'd be interested in a simple and inexpensive cell level monitoring system.


According to FedEx both my PCB's and my parts from Digikey should arrive today, so if I have some time tonight (and everything arrives) I'll solder up the first boards and get ready for testing. I'll be posting the results.


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## kakheath (Jan 7, 2012)

rwaudio said:


> I did try that as well, and didn't get consistent results. During discharge it will stop the lowest cell and only discharge at 1A to the cut off point which is not the same as the 38A setting I was using. Perhaps I didn't have it configured properly to do it this way but that was just my experience.
> 
> I would get a true capacity on the first cell to discharge but once the first cell hit the low cut off it messed up the results for the remaining cells. During charging it does work, but if the cells are very far off the whole balancing thing doesn't work very well with cells of this capacity. Shunting a maximum of 1A doesn't do much on a 38A charge if the cells aren't at the same SOC.
> 
> I gave up on that and went to a single cell, if you have any tips on how to do that better I would be happy to hear them. For me getting a capacity number under the same conditions every single time is more important than shaving off a bit of time.


rwaudio, did you test the same cell multiple times with different C ratings? I heard the spec capacity is based on 1C discharge. I'm wondering what the impact is of the 38/18 = 2.1C discharge is having on the capacity. Have you compared this to a 1C or 0.5C? 

I had been previously stuck in 10A or 0.5C mode, and am wondering what this impact will be when trying to be consistent with the cells. Now that I'm charging/discharging faster using 38A, will I need to go back and retest the 13 cells I already have data on? I suppose I could test a few of them and if the offset is consistent, just apply it to the rest. 

Also, my cutoff voltage has been 2.5V instead of your 2.25V. Do you think this is significant?


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## rwaudio (May 22, 2008)

kakheath said:


> rwaudio, did you test the same cell multiple times with different C ratings? I heard the spec capacity is based on 1C discharge. I'm wondering what the impact is of the 38/18 = 2.1C discharge is having on the capacity. Have you compared this to a 1C or 0.5C?
> 
> I had been previously stuck in 10A or 0.5C mode, and am wondering what this impact will be when trying to be consistent with the cells. Now that I'm charging/discharging faster using 38A, will I need to go back and retest the 13 cells I already have data on? I suppose I could test a few of them and if the offset is consistent, just apply it to the rest.
> 
> Also, my cutoff voltage has been 2.5V instead of your 2.25V. Do you think this is significant?


I have actually tested that. (thoroughly on one cell and more random testing on a few others) 
The capacity at 0.5C and 2C were virtually identical, 1C was actually slightly lower. In my testing the cells were cold at 0.5C and 1C and a tiny bit warm at 2C, I think this heating contributed to the better performance of 2C vs 1C in these cells. (just like drag racers that are faster the 2nd run because they heat up the cells the first run (with back to back runs)). I would say that if you are grouping the cells in a similar way to what I'm doing it really doesn't matter what voltage and C rate that you use as long as you do the same thing for every cell. Based on my experience you will probably have similar results with your 10A testing and 38/40A testing. I found ambient temperature played a bigger role in capacity variation than C rate. (I'm sure there is a limit though were very high or very low C rates would make this statement invalid).

I would say the difference between 2.5 and 2.25 is marginal and pretty consistent between cells, as long as you measure the same way every time it doesn't matter very much what voltage you choose. I picked 2.25 somewhat at random but I have to continue with that number since I've done it that way to start. I think in the real world there is no point trying to get anything below 2.5v on "average" to allow for a low group that might hit 2.0v. However with the tight capacity grouping that is possible when measuring them all the cells should be very close at the top and bottom.


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## kakheath (Jan 7, 2012)

rwaudio said:


> I have actually tested that. (thoroughly on one cell and more random testing on a few others)
> The capacity at 0.5C and 2C were virtually identical, 1C was actually slightly lower. In my testing the cells were cold at 0.5C and 1C and a tiny bit warm at 2C, I think this heating contributed to the better performance of 2C vs 1C in these cells. (just like drag racers that are faster the 2nd run because they heat up the cells the first run (with back to back runs)). I would say that if you are grouping the cells in a similar way to what I'm doing it really doesn't matter what voltage and C rate that you use as long as you do the same thing for every cell. Based on my experience you will probably have similar results with your 10A testing and 38/40A testing. I found ambient temperature played a bigger role in capacity variation than C rate. (I'm sure there is a limit though were very high or very low C rates would make this statement invalid).
> 
> I would say the difference between 2.5 and 2.25 is marginal and pretty consistent between cells, as long as you measure the same way every time it doesn't matter very much what voltage you choose. I picked 2.25 somewhat at random but I have to continue with that number since I've done it that way to start. I think in the real world there is no point trying to get anything below 2.5v on "average" to allow for a low group that might hit 2.0v. However with the tight capacity grouping that is possible when measuring them all the cells should be very close at the top and bottom.


What's your opinion on the top balance or bottom balance debate? It sounds like you are top balancing your cells. Is this correct?


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## rwaudio (May 22, 2008)

kakheath said:


> What's your opinion on the top balance or bottom balance debate? It sounds like you are top balancing your cells. Is this correct?


I'm in the boat that likes top balancing. Arguably the only time you can have complete failure causing fire or something like that is when charging, so I would prefer to have the cells top balanced for that reason only. 

However for cell safety I love the idea of bottom balancing, so that's where the careful measurements and obsessive grouping comes from in the 3P groups that I'm creating. In theory as long as I stay within a current range where small IR differences in the cells don't cause a difference in SOC over time then my cells should act like they are both top and bottom balanced. 

Only time will tell though and I'll have to see if that actually happens. 

I love the work that EMW is doing both on their display and charger. I will be going with the both of those products in the future. (hopefully the display sooner than later when the full featured version is available) Right now my charging system will be top balanced by default, however when I switch to the EMW charger I would have the option to top/bottom balance but I have a feeling (and hopes) that they will be virtually one in the same.


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## Nuts&Volts (Dec 20, 2011)

kakheath said:


> I got it working - finally. Thanks to your help. You're right about the stock output wires not liking the 38A current. They got very hot. I only did this once. I have since went to Home Depot and got some 6awg wire and some nice aluminum connectors for attaching to the cell. I also bought some nice banana clips that would accept the 6awg wire for connecting to the PL6. I just need to solder the 40A fuses to them I'll be set. I didn't want to work on it last night being Valentine's day and all . I will try to complete it tonight...


Got any pictures of your PL8 setup? I need to upgrade my output wires on my PL8, but haven't had the time to research a good solution. Links would be awesome too!

-Kyle


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## kakheath (Jan 7, 2012)

rwaudio said:


> I'm in the boat that likes top balancing. Arguably the only time you can have complete failure causing fire or something like that is when charging, so I would prefer to have the cells top balanced for that reason only.
> 
> However for cell safety I love the idea of bottom balancing, so that's where the careful measurements and obsessive grouping comes from in the 3P groups that I'm creating. In theory as long as I stay within a current range where small IR differences in the cells don't cause a difference in SOC over time then my cells should act like they are both top and bottom balanced.
> 
> ...


Once you complete all your charge/discharge/charge cycles are you just going to assemble your cells like that or will you connect them all in parallel for a few days to guarantee they all have the same SOC? I read this trick on the Elithion site. http://lite.elithion.com/general_description_.php

What are you doing with the IR data you record? Are you going to pull out any of the cells due to higher than usual values? Are you only focusing on the total capacity? Mine have been from 0.6-0.8 mOhm.


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## rwaudio (May 22, 2008)

kakheath said:


> Once you complete all your charge/discharge/charge cycles are you just going to assemble your cells like that or will you connect them all in parallel for a few days to guarantee they all have the same SOC? I read this trick on the Elithion site. http://lite.elithion.com/general_description_.php
> 
> What are you doing with the IR data you record? Are you going to pull out any of the cells due to higher than usual values? Are you only focusing on the total capacity? Mine have been from 0.6-0.8 mOhm.


I'm going to assemble them as is and use my dc/dc charger to top them all up to 3.5v then run a full discharge/charge cycle to measure the capacity of the 4S3P pack and make sure the cells hit the top/bottom together. Once all is well with a module it will get get installed in the car.

If it was easy to hook up I would probably parallel them all for balancing, however I think my method should work pretty much the same.

As for IR, I am recording it, but virtually all cells have fallen in the 0.6-0.8mohm range just like you. I had a couple that were 1.0 and I kept those to the side and they went in the 12v battery I use to run the charger. That will eventually be the 12v battery in the car.


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## kakheath (Jan 7, 2012)

Nuts&Volts said:


> Got any pictures of your PL8 setup? I need to upgrade my output wires on my PL8, but haven't had the time to research a good solution. Links would be awesome too!
> 
> -Kyle


I finally got the 2 additional PL6s. I ordered 3 sets of jumper cables that connect on the input side. They only shipped 1, so only 1 PL6 is currently hooked up. I purchased the 6awg wire and the aluminum ends from home depot. I got the banana clip that's plugged into the PL6 from Radio Shack. 6awg is the max that will fit in the banana plug. The system gets only a little warm to the touch unlike when I used the stock cables. You could smell the cables burning when I tried to run them at 38A. Even though they come with a 40amp fuse, I wouldn't take them there regularly. 

Here's a few picks of the setup. I have configured a 4s3p 13.2V power supply out of A123s to take advantage of the full current in and out of the PL6. If you don't use a battery, it limits discharge to 10A. However, just to be safe I soldered in 40 amp fuses just like the stock cables. To distribute the heat better at the tabs, I'm using the same aluminum flat bar that I cut for the pack assembly. In this pick, I have one on each side of each tab and bolts clamping them together.

I'll probably go with some type of quick release built into a board to facilitate quick cell change-outs in the future. This is the first attempt so bare with me please.

I've already made a second gen version of a 13.2V pack that doesn't use the nylon all-thread. I'll post pictures of this later. I'm very proud of the 2nd version, but I already have plans for a 3rd gen. Right now, I believe the 3rd generation will be the one that goes into the car. I'll probably start a new thread for the car's actual pack design.


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## Nuts&Volts (Dec 20, 2011)

Very Cool. Thank you for sharing that stuff. Since I will probably not be drilling holes through my tabs I will most likely just get beefier alligator clips or clamps that will help lower the resistance. Additionally I will use some shorter 6or8AWG wire as well for the output leads. This should allow my error to drop below 5% or so hopefully


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## rwaudio (May 22, 2008)

kakheath said:


> I finally got the 2 additional PL6s. I ordered 3 sets of jumper cables that connect on the input side. They only shipped 1, so only 1 PL6 is currently hooked up. I purchased the 6awg wire and the aluminum ends from home depot. I got the banana clip that's plugged into the PL6 from Radio Shack. 6awg is the max that will fit in the banana plug. The system gets only a little warm to the touch unlike when I used the stock cables. You could smell the cables burning when I tried to run them at 38A. Even though they come with a 40amp fuse, I wouldn't take them there regularly.
> 
> Here's a few picks of the setup. I have configured a 4s3p 13.2V power supply out of A123s to take advantage of the full current in and out of the PL6. If you don't use a battery, it limits discharge to 10A. However, just to be safe I soldered in 40 amp fuses just like the stock cables. To distribute the heat better at the tabs, I'm using the same aluminum flat bar that I cut for the pack assembly. In this pick, I have one on each side of each tab and bolts clamping them together.
> 
> ...


That looks good, I like those banana plugs! I have half dozen of them left over from my audio stuff but didn't think the PL6/8 designers would have been kind enough to use the proper spacing so I never tried one. I think with some careful trimming of strands 4awg could be made to fit reasonably well and you would benefit from lower resistance in almost the whole cable except for the connection points which will have higher resistance anyway. Are you watching the SOC/balance on your 13.2v pack??

PS... You can export pictures directly from the "Graph" window if you want.


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## kakheath (Jan 7, 2012)

rwaudio said:


> That looks good, I like those banana plugs! I have half dozen of them left over from my audio stuff but didn't think the PL6/8 designers would have been kind enough to use the proper spacing so I never tried one. I think with some careful trimming of strands 4awg could be made to fit reasonably well and you would benefit from lower resistance in almost the whole cable except for the connection points which will have higher resistance anyway. Are you watching the SOC/balance on your 13.2v pack??
> 
> PS... You can export pictures directly from the "Graph" window if you want.


Yeah, the power supply pack SOC is an important issue. I discovered after reaching the 11V cutoff that my power supply pack was not balanced. Luckily, I already had a set of batteries from a previous design that had various SOCs from which to choose. I replaced the low V 5p group with a group similar to the rest of the module and now the total 4s5p module works pretty well together.

I've since then created 3 battery power supplies like this 4s5p module. This is consequently what I plan to use in the car. I'll have 16 of these (4s5p) modules in the trunk with 7-8 additional ones in the engine bay. I like their practical size for handling and maintenance.

I also bumped the current up to 40A and have charged and discharged all without issue at this rate even with the 40A fuses soldered in place. The wires only get slightly warm. Nothing is hot to the touch anymore. I have shortened the lead wires to match the first PL6, and I've mounted the test cell hookups on a board to facilitate quick change-outs. Now, I'm finally able to cycle up and down a set of 3 in 1 hr. 

I've been leaving them discharged for now to save overall time. I figured I would charge them in groups later once I knew all the capacities. I've measured 48 so far, but now I have an assembly-line to get it done more quickly.

Too bad it just sits there while I'm at work. I hope to get 12/day through he week. 3 in the morning, 3 when I first get home, 3 after an hour, and another 3 when I go to bed. At some point, I'll have to add some energy back into the power supply batteries. I'll let you know how it goes.

I'll try to take a few pictures tonight.


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## rwaudio (May 22, 2008)

I'm glad to hear everything is working well.

I changed my set up slightly as well, I added a second PL6 and decided to leave the cells discharged just like you. I have found that by skipping the final charging phase it takes much longer for the supply pack to get drained since it basically gets the energy from the cells when they arrive to make up for some of the wasted power (heat, running the charger/fan etc.).

I got through 20 cells in a few batches over the weekend and I'm happy with the process now. The only "problem" I'm finding is that this new box of cells that I opened has a higher average capacity than the first 72 cells that I tested. Meaning that I may have a hard time getting low enough average groups to match the first 72. I haven't assembled those first 72 though, so I may start over and re-average the target capacity and re-group the cells before assembly. So it's really not bad news, but the most recent box of cells are almost all in the range of 19.1 -19.5Ah with a 2C discharge.

The one thing I'm noticing with two cells discharging side by side is two cells of the same capacity (virtually the same anyway) but different IR have much different terminal voltage once they dip below 3.2v so if possible when grouping cells for a street car capacity should be the first consideration but averaging the IR should also be in the back of your mind. 

The other thing to note is my 12v pack powering the charger now has well over 100 shallow cycles on it along with some 100% discharges and some high current bursts. I use the pack to move my Porsche in and out of the garage when I need to. This pack (12v 50.75Ah) and the Soliton1 work happily together to drive the car (slowly) I've also used it to jump start my Infiniti when it had a dead battery, and my F150 when it was too cold to start. This is a pack of my "defective" cells, IE low capacity, high IR, and or soft cell.

Basically if these reject cells that I won't be putting in my traction pack work this well I have high hopes for what the "good" cells can do and how they will perform.


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## kakheath (Jan 7, 2012)

rwaudio said:


> I got through 20 cells in a few batches over the weekend and I'm happy with the process now. The only "problem" I'm finding is that this new box of cells that I opened has a higher average capacity than the first 72 cells that I tested. Meaning that I may have a hard time getting low enough average groups to match the first 72. I haven't assembled those first 72 though, so I may start over and re-average the target capacity and re-group the cells before assembly. So it's really not bad news, but the most recent box of cells are almost all in the range of 19.1 -19.5Ah with a 2C discharge.
> 
> The one thing I'm noticing with two cells discharging side by side is two cells of the same capacity (virtually the same anyway) but different IR have much different terminal voltage once they dip below 3.2v so if possible when grouping cells for a street car capacity should be the first consideration but averaging the IR should also be in the back of your mind.


I had some time to kill last week and thought I would see how matching would work. I created a random set of 20 cell caps and tried to group them as if they were my actual cells. It worked out OK using the manual pick-and-choose method to match the averages. It didn't take as long as I thought either. I'm going to wait until I have all the caps before starting the real matching sudoku game.

Which IR measurment are you using for comparison? Sometimes the very first charge IR is higher like 1.4, then after I discharge, the next charge it's 0.8 on the same cell. This was more in the beginning, because now I'm stopping the cycle on discharge. When I was having supply issues and having to restart the whole cycle multiple times, I noticed that I would get different values. It seems you have to wait several minutes for the averaging to stabilize to give a consistent IR value. Have you seen this in your testing?


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## rwaudio (May 22, 2008)

kakheath said:


> I had some time to kill last week and thought I would see how matching would work. I created a random set of 20 cell caps and tried to group them as if they were my actual cells. It worked out OK using the manual pick-and-choose method to match the averages. It didn't take as long as I thought either. I'm going to wait until I have all the caps before starting the real matching sudoku game.
> 
> Which IR measurment are you using for comparison? Sometimes the very first charge IR is higher like 1.4, then after I discharge, the next charge it's 0.8 on the same cell. This was more in the beginning, because now I'm stopping the cycle on discharge. When I was having supply issues and having to restart the whole cycle multiple times, I noticed that I would get different values. It seems you have to wait several minutes for the averaging to stabilize to give a consistent IR value. Have you seen this in your testing?


I have seen that as well, so I use the final value, I typically leave the graph window on IR so I can see the trend during the charge cycle. If it was 0.7 for 90% then dropped to 0.6 at the end I'm going to use the 0.7


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## kakheath (Jan 7, 2012)

OK, so here are the pics from my latest setup. I have all 3 PL6s up and running . Each have independent power supplies made from a module of 4s5p A123 cells. I'm using a board that has bolts mounted from underneath that go through the output leads so that the cell change-outs can be quick. I crossed the output leads before connecting to the cells so that I could place the cells with their writing on top. 

I also made up a jig out of another board where I mounted the punches out of a hole puncher. This provided a very clean and consistent hole for all the cells. After you remove the label, there's always a glue residue left behind. I use lacquer thinner on a rag to wipe this off. Fortunately the labels always stay in one piece when you pull them off.

I'm quite proud of this second generation battery design . I first used the nylon all-thread concept, but it was a hassle weaving it through the tab holes and I didn't like how the rod would distort with any real amount of force applied. So, instead of a solid rod between all the cells, I used a rope. It's only job is to align the tabs and connectors so it didn't need to be special. I finally used a 5/16" all-thread steel rod in the center between the tabs with steel clamps on the ends in order to provide a good amount of clamping force to hold it all together. I have one of those black plastic wire looms around the all-thread to protect against any unwanted fireworks during installation. The rope consequently becomes a lifting handle for the module as well. Here are my latest pics:


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## kakheath (Jan 7, 2012)

Cell testing is progressing. I just pulled #258 off the bench. I thought I would update my car pack design ideas to hopefully get some feedback from the group.

Each 4s5p module would have 10 pieces of aluminum flashing cut to approximately 7" by 7" square and placed in between every other cell. So that every cell has one side contacting a piece of flashing. This is to provide about 0.25" fins on each cell edge for wicking away heat from the pack. Below is a top view of the design. The electrical connections on top would be made of 1/4" by 2" angle to provide a solid terminal for each module. To minimize the outer dimensions on the clamp side, I plan to weld one end of the all-thread to one end of the clamp and use a lock washer and lock nut on the other to hold the clamp in place. I will torque this lock nut several times between cycles to ensure that there's no thermal expansion problems.

Then I plan to construct a trunk pack out of 12 of these 4s5p modules in a design that minimizes the connection lengths on top - see attached top view. In addition, I will arrange the modules such that perforated air tubes can deliver air from the floor of the battery box. See the green line depicted below. The air inlets will be routed to a safe location to draw clean fresh air. A fan will be installed in the lid of the box to pull air across all the battery fins.


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## kerrymann (Feb 17, 2011)

kakheath said:


> Cell testing is progressing. I just pulled #258 off the bench. I thought I would update my car pack design ideas to hopefully get some feedback from the group.
> 
> Each 4s5p module would have 10 pieces of aluminum flashing cut to approximately 7" by 7" square and placed in between every other cell. So that every cell has one side contacting a piece of flashing. This is to provide about 0.25" fins on each cell edge for wicking away heat from the pack. Below is a top view of the design. The electrical connections on top would be made of 1/4" by 2" angle to provide a solid terminal for each module. To minimize the outer dimensions on the clamp side, I plan to weld one end of the all-thread to one end of the clamp and use a lock washer and lock nut on the other to hold the clamp in place. I will torque this lock nut several times between cycles to ensure that there's no thermal expansion problems.
> 
> Then I plan to construct a trunk pack out of 12 of these 4s5p modules in a design that minimizes the connection lengths on top - see attached top view. In addition, I will arrange the modules such that perforated air tubes can deliver air from the floor of the battery box. See the green line depicted below. The air inlets will be routed to a safe location to draw clean fresh air. A fan will be installed in the lid of the box to pull air across all the battery fins.


I am contemplating the same but do you think you will need the cooling? From bench testing these cells at 2C continuous for 30 minutes I only get a rise of 10°F. And if I do another cycle with little to now cool down, I get a lower IR and a percent or two higher capacity. After 1.5 hours at 2C of charging and discharging, it was only at 98°.


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## kakheath (Jan 7, 2012)

kerrymann said:


> I am contemplating the same but do you think you will need the cooling? From bench testing these cells at 2C continuous for 30 minutes I only get a rise of 10°F. And if I do another cycle with little to now cool down, I get a lower IR and a percent or two higher capacity. After 1.5 hours at 2C of charging and discharging, it was only at 98°.


I think it all depends on how many amps you plan to draw at use. What controller and number of cells in parallel do you plan to have? 

I had planned my conversion for performance and thought I would get a Z2K, but have decided to go with a Soliton 1 instead. This will limit me to 1000 Amps, but should be more versatile for everyday driving. Since I don't really plan to drag race the car, I thought it would be the best choice for me. I do however, plan to add a second motor to take advantage of the full controller voltage (~350V). I don't know if I will really need the cooling, but it doesn't add much cost to build it into the design at this point. In fact, I may find that heating the cells will be as important as cooling them. The air flow and fins will allow me both options if I install some kind of inline heater for the inlet air flow. Depending on how well it can control the temperature, it may be feasible to install some sort of thermostat control depending on what the ideal temperature should be. Remember this is my first conversion. I don't claim to know anything about this subject. So I'm way over-thinking everything, but that's part of the enjoyment for me.


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## kerrymann (Feb 17, 2011)

kakheath said:


> I think it all depends on how many amps you plan to draw at use. What controller and number of cells in parallel do you plan to have?
> 
> I had planned my conversion for performance and thought I would get a Z2K, but have decided to go with a Soliton 1 instead. This will limit me to 1000 Amps, but should be more versatile for everyday driving. Since I don't really plan to drag race the car, I thought it would be the best choice for me. I do however, plan to add a second motor to take advantage of the full controller voltage (~350V). I don't know if I will really need the cooling, but it doesn't add much cost to build it into the design at this point. In fact, I may find that heating the cells will be as important as cooling them. The air flow and fins will allow me both options if I install some kind of inline heater for the inlet air flow. Depending on how well it can control the temperature, it may be feasible to install some sort of thermostat control depending on what the ideal temperature should be. Remember this is my first conversion. I don't claim to know anything about this subject. So I'm way over-thinking everything, but that's part of the enjoyment for me.


Yep I wasn't trying to talk you about of it. This is my first time using these cells too. I had been going back and forth on it and ultimately decided to put in the fins. Everything I have seen and read shows that keeping the cells at a comfortable temperature is key to cycle life. Especially at high C rates. I have been thinking the same thing on my motor situation and going to dual later to replace by ADC. For the heating are you going to insulate your boxes?

BTW, you conversion is looking nice. Sorry to hear you had the same problems I had with Electric Car Company and it's adapter and hub but glad it didn't set you back too much.


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## EVPowers (May 17, 2012)

A friend of mine is posting data points from his testing of cells from a group buy of 500 cells we did earlier this month.

He recently bought an infrared camera so he can measure the thermal qualities when charging/discharging. Without any cooling, he did a 103 amp discharge and saw a max temp of 105 degrees Fahrenheit.


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## kakheath (Jan 7, 2012)

EVPowers said:


> A friend of mine is posting data points from his testing of cells from a group buy of 500 cells we did earlier this month.
> 
> He recently bought an infrared camera so he can measure the thermal qualities when charging/discharging. Without any cooling, he did a 103 amp discharge and saw a max temp of 105 degrees Fahrenheit.


That's great. How many cells in parallel was he using when he discharged at 103 amps and for how long was he discharging the cell?


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## marc02228 (Jan 15, 2011)

I took another way to assemble the cells. 
The attached image is a PCB for a 9s3p module.
You put the tabs of three cells in parallel through one slot, fold them to the soldering pad and fasten them with two screws to the next three cells in series.
It will be a 3.2mm thick PCB, that should be solid enough.
Each terminal has a trace to the BMS connector.

I am still waiting for the produced PCB's. Actually it should take 10 working days. But I am waiting since 11th of June, now.

I will get double the number of PCB's I need, because it was almost the same price.


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## kerrymann (Feb 17, 2011)

EVPowers said:


> A friend of mine is posting data points from his testing of cells from a group buy of 500 cells we did earlier this month.
> 
> He recently bought an infrared camera so he can measure the thermal qualities when charging/discharging. Without any cooling, he did a 103 amp discharge and saw a max temp of 105 degrees Fahrenheit.


Interesting. One question is did you insulate the sides of the cell? When I tested mine I had similar results on single cells (just using a thermocouple) when I didn't cover them. But when you stack the cells into a module the heat can no longer escape the large flat sides of the pouch because it's covered by another cell. If you insulate both sides of the cells with some low density foam you'll get a much higher temperature.

Kerry


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## EVPowers (May 17, 2012)

kakheath said:


> That's great. How many cells in parallel was he using when he discharged at 103 amps and for how long was he discharging the cell?


He was simply bench testing two cells.

He has done testing with and without insulation.

Here is a link to his testing page.
http://99mpg.com/workshops/designingandbuildi/


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