# is there any other way to assemble A123 cylindrical cells then spot-welding?



## LiFe (May 24, 2010)

miernik said:


> In spot-welded packs will be a nightmare to replace cells.
> 
> Isn't there really any other way?


Yes. If your name is Rube Goldberg.

If spot welding cells is such an issue for you, then you should have purchased some Headway cells with studs instead...


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## miernik (Nov 28, 2009)

LiFe said:


> Yes. If your name is Rube Goldberg.
> 
> If spot welding cells is such an issue for you, then you should have purchased some Headway cells with studs instead...


Well, I only ordered a small amount of them so far, so I might still change to Headways, but I am not yet convinced that Headways will offer me as good economy on total kWh run though the cell over its lifetime. 

A123 you can do to DOD 100%, and Headways only 80%.

I'd have to take a bunch of B-grade A123s and a bunch of Headways, run a 4C charge/4C discharge on them continuously to 90% and sun up all the discharge kWh over the whole lifetime, up until the cells are unusable. And then divide the cell price shipped by that.

Any other cells I should consider for such test?

Or can someone already predict the result approximately?


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## JRP3 (Mar 7, 2008)

I'm not sure pressing the cells that way will damage them, but what it will do is prevent the ends from expanding as designed if pressure builds up. That means they will explode out the side instead of venting as they are supposed to. I think they really need to be welded.


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## piotrsko (Dec 9, 2007)

how about spot welding tabs with screw holes and assembling with discrete hardware either sheet metal screws or the old tried and true bolt and self-locking nut.


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## frodus (Apr 12, 2008)

You CANNOT compress the cells, they are not designed to be held together by pressure plates. It will interfere with the cell ends that are designed to "pop" in the event of failure. Weld or don't use them at all.

Why don't you get some A123 pouch cells if you want the performance of A123 but the ease of welding?



miernik said:


> A123 you can do to DOD 100%, and Headways only 80%.


Citation needed.


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## miernik (Nov 28, 2009)

frodus said:


> You CANNOT compress the cells, they are not designed to be held together by pressure plates. It will interfere with the cell ends that are designed to "pop" in the event of failure. Weld or don't use them at all.


OK, good to know, I am going to ask for them with spot-welded tabs, but to have a small hole on the other end of the tab to put a screw in there , so I can attach and detach it from a bar with a screw.



frodus said:


> Why don't you get some A123 pouch cells if you want the performance of A123 but the ease of welding?


I ordered one pouch to test it, but I have no idea how would I actually connect them together. And the requirement to have them in enclosed with pressure (opposite as with cylindrical cells) makes it even more complicated.



frodus said:


> Citation needed.


A123:

http://batteryworkshop.msfc.nasa.gov/presentations/11_Dev_Batt_Packs_Space_Appl_DCarmen.pdf
Page 9
From the graph: about 85% initial capacity after 5000 cycles charging and discharging both at 1C to 100% DOD (that is to 2.0V). 

Which gives 3% average capacity loss per 1000 cycles.

Headway:

http://www.kennedyalternativeenergy.com/38120sTechsheet.doc
70% initial capacity of 38120S after 2000 cycles, and that's charging at only 0.2C and discharging at 1C to 2.5V.

Which gives 15% average capacity loss per 1000 cycles. That's 5 times worse then A123, even with the test conditions being much lighter: 5 times slower charge and discharge only to 2.5V instead all the way to 2.0V.

That was all I could find of that type of tests. Does anyone know any more test results of capacity decrease after thousands of cycles?


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## rwaudio (May 22, 2008)

miernik said:


> OK, good to know, I am going to ask for them with spot-welded tabs, but to have a small hole on the other end of the tab to put a screw in there , so I can attach and detach it from a bar with a screw.
> 
> 
> 
> ...


You can't exactly compare those two sources, the headway version for example even states that is the best guess based on the data provided, not on testing.

The A123 results are going to be the best case results that look good in the brochure. They are probably real, but there's probably a reason that they didn't quote 2c, 5c, 10c, 30c or anything usable in that type of cell.

If you can find one person who tests the two types the same way under the same conditions then you have something worthy of talking about.

Since you are looking at the so called "B" grade A123's they may not perform as well for cycle life.

I like the idea of A123, and I ordered that same pouch cell and some 18650's to play with, but I have a feeling that headways will end up in my car.

Good luck with your search, keep digging for reliable info.


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## pgt400 (Jul 12, 2008)

I've (as well as many others) solder M1 cells. Use a large iron, tin and don't over heat the cells. Some of my soldered RC packs are over 4 years old....still giving fully capacity (unlike many swollen lipo's).



miernik said:


> Soon my first A123 18650 cells will arrive. And I am thinking what method to use to assemble them into packs.
> 
> I thought of using two metal plates around each cell and a long screw to press it together. But then I read pressing the ends of A123 cells will damage them.
> 
> ...


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## LiFe (May 24, 2010)

rwaudio said:


> Since you are looking at the so called "B" grade A123's they may not perform as well for cycle life.


Unrelated to the OP's question, although has some merit;

There is no such product as an A123 "B grade" cell. 

I searched for the origin of this hogwash, and the closest I could find was something posted and quoted by both Don Harmon and Armin from '08 on EndlessSausageFest. And I doubt it originated from either of those characters. Maybe from one of the resellers? 

Following the ChinaBAK contract end, considerable materials inventory remained on site. And was used to assemble additional cells with. Paste was already a controlled inventory item. Meaning that few of the cells assembled after contract termination with branded shrinkwrap did not include A123 Systems chemistry. Maybe that's where the "B grade" definition had originated.
If your cell lots are date coded in the spring of '08 (as the OP's cells are), then you have legitimate, "A grade" cells.


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## frodus (Apr 12, 2008)

No one has proven if they effect the cell or not, but A123 themselves tell people that it can damage the cell, and to never solder them, and to weld only. No manufacturers solder, everything is welded for realiability, lifecycle and to protect from damage. 

Now, physically, yes, you can solder them, but with almost 200 connections (64s3p) I wouldn't recommend it for a pack he wants to last 11,000 cycles (as he seems to want). There's no way to tell if it does effect cycle life under the use he intends to use them.

I don't seen any quantifiable testing that has been done on soldering cells that can prove that soldering has no negative effects. If someone has it, please share, I'd like to see it. 

IF you do decide to do this, get a very large soldering iron that gets really hot, and solder very quickly. If you heat the cell too much (where the cell internals get warmer than 60C), you will probably damage that cell. After you're done soldering, consider holding a heatsink against it to wick the heat away from the solder joint.


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## miernik (Nov 28, 2009)

LiFe said:


> Following the ChinaBAK contract end, considerable materials inventory remained on site. And was used to assemble additional cells with. Paste was already a controlled inventory item. Meaning that few of the cells assembled after contract termination with branded shrinkwrap did not include A123 Systems chemistry. Maybe that's where the "B grade" definition had originated.
> If your cell lots are date coded in the spring of '08 (as the OP's cells are), then you have legitimate, "A grade" cells.


Are you talking about ANR26650M1, APR18650M1 or AMP20M1HD cells?

I just received a few APR18650M1's from http://stores.ebay.com/vpower-hk3 
Here is what's written on them:

APR18650M1A
EL0809035
00514ZZ

APR18650M1A
EL0809037
11065

APR18650M1A
EL0809043
17017

APR18650M1A
EL0807910
11243

Is the datecode in there?

Back to the assembly problem: these cells have the + (positive) end with a piece of metal about 2 mm above the rest of the inside of the cell. Maybe if I make cell-holders which just touch the metal, but not press it very hard, it will not prevent the pressure valve from working? 

In fact I have not had a ANR26650M1 in my hands, but from the pictures it seems that the end is built a bit differently.


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## pgt400 (Jul 12, 2008)

Yeah, those silly manufactures....most of what we do to thier batts they say not to do! Welding is better for sure...but most people don't have a welder while everyone has access to an iron. 64s3p...ugh, no thanks, Headways screwed end to end would build so fast.



frodus said:


> No one has proven if they effect the cell or not, but A123 themselves tell people that it can damage the cell, and to never solder them, and to weld only. No manufacturers solder, everything is welded for realiability, lifecycle and to protect from damage.
> 
> Now, physically, yes, you can solder them, but with almost 200 connections (64s3p) I wouldn't recommend it for a pack he wants to last 11,000 cycles (as he seems to want). There's no way to tell if it does effect cycle life under the use he intends to use them.
> 
> ...


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## frodus (Apr 12, 2008)

They are made different than the M1, you're right. Do you have pictures, that would help a ton. Is it possible to take the cover off of one cell to get more insight on how the ends are made? These may be separated from the cell, so they may not heat it as much if soldered.


On the A123 APR18650M1 graph for lifecycle, it doesn't mention how many C it's doing, and it says "over 1000 cycles". It drops to ~86% capacity after 1400 cycles, and the 38120S drops to ~84% after 1400 at 1C. Also, I don't know what we should consider useable. It could be that 80% capacity after 1500 cycles is acceptable for some people, but not for others. What is the consensus on how much of the pack should be useable after 1000, 2000, 3000 cycles?

Would be nice if A123 actually labelled the graphs correctly.


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## frodus (Apr 12, 2008)

pgt400 said:


> Yeah, those silly manufactures....most of what we do to thier batts they say not to do! Welding is better for sure...but most people don't have a welder while everyone has access to an iron. 64s3p...ugh, no thanks, Headways screwed end to end would build so fast.


I completely agree. I know most people don't have access to a welder, which is kinda why I do intervene for larger pack builds. I've welded 10 packs of 26650 sized cells, with ~120 cells each (two different motorcycle projects). It's not something I'd like to do again, and it made it a huge PITA to replace bad cells. So for a larger pack, consider the assembly of the pack and how important it is to have a low cost, when you'll spend more money and more time assembling a pack that works.


miernik, Can you get them with tabs welded on them? That would make things a ton easier if the company did it for you.


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## miernik (Nov 28, 2009)

frodus said:


> They are made different than the M1, you're right. Do you have pictures, that would help a ton. Is it possible to take the cover off of one cell to get more insight on how the ends are made? These may be separated from the cell, so they may not heat it as much if soldered.


I will try to make a picture, but I don't think it would be to clear, you have to hold the cell in your hands to really see what's there. Buy one, its just 2.18 USD with shipping at http://www.a123rc.com/

Is the pressure valve on an ANR26650M1 on the "-" or the "+" side?
All photos I can find show only the "-" side.



frodus said:


> On the A123 APR18650M1 graph for lifecycle, it doesn't mention how many C it's doing, and it says "over 1000 cycles". It drops to ~86% capacity after 1400 cycles, and the 38120S drops to ~84% after 1400 at 1C.
> 
> Would be nice if A123 actually labelled the graphs correctly.


But in the top part of the PDF it says:

Cycle life at 5C discharge, 100% DOD Over 1,000 cycles. We might assume that the graph is at 5C also. But better just run some cells though several thousand cycles and see.

For me the right measure is not really "how many cycles" but "how much kWh you can push through the cell throughout its whole lifetime. So I'd cycle them till they die and sum up all kWh that went out. With each cycle that would be less, so after 20000 cycles each cycle will add so little kWh that it would be irrelevant for the result.


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## frodus (Apr 12, 2008)

Pressure valve is on the - side.



I realize they say 5C, but does that go with the graph? It's hard to tell unless they label it, as most manufacturers DO NOT do. It's just a pet peeve. It may be ok to say 5C, but I'd like to see them spell it out. I don't trust manufacturers.

I hope you don't expect that much out of these cells, because you're not gonna get 20,000 cycles. I doubt it you could get above 5-6000 before they're basically unseable. Why would you want to drive a pack that gives you 1/2 capacity? And what does that do to the power available? 

Long and short, people haven't cycled them, and unless you buy a cycler, it's gonna be hard to tell. I know some chargers do it, but do they long that data too? Could, but I doubt they do 5C discharges AND charge AND log.


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## miernik (Nov 28, 2009)

frodus said:


> Pressure valve is on the - side.


Then if that's what I see on photos, then the APR18650M1A valve is different (besides being on the + side), it has a piece of metal 2 mm over the valve, and I think that piece of metal can be pressed without affecting the valve which would be well below and still have space to operate.

That would be amazing if that would be so, I wouldn't have to solder anything, just take bars of metal on both sides and fasten then with screws, like this: http://www.tppacks.com/proddetail.asp?prod=Battery-Pack-Kit

Only they do it for ANR26650M1 which should not be treated like this, but I'll do it with APR18650M1 which if what I see and judge how the valve works is right, would be OK with this.

Where is the primary source of the info that A123 cells should not be pressed? I'd like to dig weather that source has anything to say about pressing APR18650M1's.



frodus said:


> I hope you don't expect that much out of these cells, because you're not gonna get 20,000 cycles. I doubt it you could get above 5-6000 before they're basically unseable. Why would you want to drive a pack that gives you 1/2 capacity? And what does that do to the power available?
> 
> Long and short, people haven't cycled them, and unless you buy a cycler, it's gonna be hard to tell. I know some chargers do it, but do they long that data too? Could, but I doubt they do 5C discharges AND charge AND log.


I am gonna hack something out of some chargers hooked up to a computer, but so far it needs to wait as I am out of money for more gear. 

I'd run then 5A in and 5A out continuously (possibly stopping if temperature increases over a certain value) and log all mAh, voltage and cell temperature every second, until the cell is nearly dead (say 50 mAh goes out instead of 1100 mAh).

Why would I want a pack with 1/2 capacity? Well, even an 1/2 capacity its still much better Wh/kg then lead-acid! I think a pack would be usable for me until its 10% capacity, then it'll be worse then lead-acid.

And as the old ones age, I'd add new packs, but still use together with the old ones which still give some useful extra range. Until they add more consumption because of their weight then they give energy.


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## frodus (Apr 12, 2008)

> Then if that's what I see on photos, then the APR18650M1A valve is different (besides being on the + side), it has a piece of metal 2 mm over the valve, and I think that piece of metal can be pressed without affecting the valve which would be well below and still have space to operate.


Just pressing cells together is a very high resistance connection. They WILL heat. Solder if you're gonna do anything besides weld. You're going to be discharging with high current. They're fine for low current when losses are low, but if you pull many amps out, you will get heating.




> Where is the primary source of the info that A123 cells should not be pressed? I'd like to dig weather that source has anything to say about pressing APR18650M1's.


direct from A123. Not sure if there's documentation anymore, I can't find the white papers.





> I am gonna hack something out of some chargers hooked up to a computer, but so far it needs to wait as I am out of money for more gear.


Sounds cool, thats what I did for discharging, but charging is a little more tricky. most chargers are CC/CV, you'd have to design something to maintain 5C charging.



> I'd run then 5A in and 5A out continuously (possibly stopping if temperature increases over a certain value) and log all mAh, voltage and cell temperature every second, until the cell is nearly dead (say 50 mAh goes out instead of 1100 mAh).


You'll have to build a constant current load. Just a resistor won't work if you want to be accurate. If you put a resistor on there, as voltage decreases, so does amps. You have to stay within spec, below 60C and above 2V for discharge, and below 60C and below 4.2V for charge. Don't go by Amps, you have to stop at 2V. 100% DOD is 2V.



> Why would I want a pack with 1/2 capacity? Well, even an 1/2 capacity its still much better Wh/kg then lead-acid! I think a pack would be usable for me until its 10% capacity, then it'll be worse then lead-acid.


1/2 capacity may also mean 1/2 power, or at a higher voltage drop at 5C. That graph doesn't tell us much about how amps and voltage is effected.



> And as the old ones age, I'd add new packs, but still use together with the old ones which still give some useful extra range. Until they add more consumption because of their weight then they give energy.


The pack is only as strong as your weakest battery. There's nothing there to control how much current you are drawing from each pack. They don't current share equally if paralleled. You will also need a BMS for each "pack". Better to get the right size pack now and let them age together equally.


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## miernik (Nov 28, 2009)

frodus said:


> Just pressing cells together is a very high resistance connection. They WILL heat. Solder if you're gonna do anything besides weld. You're going to be discharging with high current. They're fine for low current when losses are low, but if you pull many amps out, you will get heating.


Solder vs. weld is not much difference to me. If I am to solder, I can as well get welded tabs. What I want is removable cells. I can achieve that by having the welded tabs have a hole at the other end where I will insert a screw which will be screwed in to the bus bar. This way cells will be easily replaceable.

How come spot-welded tabs get much lower resistance then pressed? From what I imagine the spot-welding is just a tiny dot that the cell is welded to the tab, the rest just touches the cell just like if it would be pressed. That tiny dot makes all the difference?

Is this effect measurable by measuring the internal resistance of an assembled pack? Lets say I join two cells by just pressing them, measure the internal resistance of the 2S pack, and then I join the same two cells by a spot-welded tab, and measure the internal resistance. Will this tell me how much worse is the pressing vs. welding?



frodus said:


> Sounds cool, thats what I did for discharging, but charging is a little more tricky. most chargers are CC/CV, you'd have to design something to maintain 5C charging.
> 
> You'll have to build a constant current load. Just a resistor won't work if you want to be accurate. If you put a resistor on there, as voltage decreases, so does amps. You have to stay within spec, below 60C and above 2V for discharge, and below 60C and below 4.2V for charge. Don't go by Amps, you have to stop at 2V. 100% DOD is 2V.


I want to test all cells discharging them only to 2.5V not to 2.0V. Both charge and discharge at exactly 4C.

I am thinking of getting an FMA Cellpro PowerLab 8 (v2) for this purpose: http://www.revolectrix.com/pl8_specs_tab.htm
It is able to run charge and discharge up to 40A (even between two batteries back and forth). Has an RS232 port which I'd hook-up to computer to log everything continuously.

The only thing I miss, is I won't be able to test the A123 AMP20 pouch at 4C, because that would require 80A, twice the charger capability. So I'd have to test it at 2C so the results would be incomparable. I want to compare the AMP20 pouch with APR18650M1 cylindrical. 

However the charger is about 250 USD, and it'd need to be assigned only for this test for months! And I need one charger per battery, if I want to get the results in reasonable time for 4 types of cells, I'd need 4 such chargers (1000$).

And a single cell is not very statistically good, at least several of a single type of cells would need to be tested to see how they vary.

This charger supports charging up to 3A thought balancing leads (up to 8 cells), maybe I can use that to test 8 cells at once?

Or maybe someone knows another device with similar functionality needed here which would be cheaper per cell?



frodus said:


> The pack is only as strong as your weakest battery. There's nothing there to control how much current you are drawing from each pack. They don't current share equally if paralleled. You will also need a BMS for each "pack". Better to get the right size pack now and let them age together equally.


Getting the final desirable size pack initially will not work, as it will take me several years to save enough money. So I want to expand the battery every few months as I save-up more money. That way I can have a range of say 5 km in the first year, 10 km in the second year, 15 km in the third year and so on up to 50 km in 10 years. You can imagine that waiting 10 years before I can ride my EV is not a practical option... I won't be able to afford to spend more then 5 km worth of batteries per year. And a 5 km range EV is already useful for me. But a 10 km or 50 km much more useful.

I will need to deal with making the pack modular and expandable somehow. For example a current limiter for each sub-pack. Should be much easier then suddenly becoming 10 times richer in 1 year, LOL!


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## major (Apr 4, 2008)

miernik said:


> For example a current limiter for each sub-pack. Should be much easier then suddenly becoming 10 times richer in 1 year, LOL!


Hmmmm. Don't know about that  Guess it depends from where you start.

You know miernik, if you applied all the money you will spend buying the equipment and samples for these tests and applied it towards a decent battery pack, you might be better off.

But then I should talk  I hate to think of all the money (and time) I have spent over the past 20 years "testing" batteries. But a large portion (of the money at least) was somebody else's.

My opinion of an "add-on pack" for a 10 year (or even 2 year) duration is crazy. Chances are that same cell will not be available. Or if it is, something else will be out there at twice the performance or half the cost. I'm stuck with dying tool batteries and no place to go. Good tool, no battery. I'm now trying to convert NiMh tools to Lithium. Fun times 

But to everybody their own road. Good luck.

major


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## frodus (Apr 12, 2008)

> Solder vs. weld is not much difference to me. If I am to solder, I can as well get welded tabs. What I want is removable cells. I can achieve that by having the welded tabs have a hole at the other end where I will insert a screw which will be screwed in to the bus bar. This way cells will be easily replaceable.


So you're going to just "order" some custom tabs" with a welded end and a hole in the other? Good luck. I doubt they'll even entertain that idea unless your order is in the 10's of thousands.



> How come spot-welded tabs get much lower resistance then pressed? From what I imagine the spot-welding is just a tiny dot that the cell is welded to the tab, the rest just touches the cell just like if it would be pressed. That tiny dot makes all the difference?


because mechanical connections are not as low of a resistance of a welded connection, where the metal is actually now a part of the other metal, they've fused together. Mechanical connections corrode, get loose, get dirt in between and if loose enough, cause arcing, which can degrade the contacts.



> Is this effect measurable by measuring the internal resistance of an assembled pack? Lets say I join two cells by just pressing them, measure the internal resistance of the 2S pack, and then I join the same two cells by a spot-welded tab, and measure the internal resistance. Will this tell me how much worse is the pressing vs. welding?


Yes its measurable. And yes its worse for mechanical connections compared with a welded or soldered connection. 



> I want to test all cells discharging them only to 2.5V not to 2.0V. Both charge and discharge at exactly 4C.


at 4C you will be fine, but at 20C, it drops below 2.5V under load.



> The only thing I miss, is I won't be able to test the A123 AMP20 pouch at 4C, because that would require 80A, twice the charger capability. So I'd have to test it at 2C so the results would be incomparable. I want to compare the AMP20 pouch with APR18650M1 cylindrical.


I can test up to 160A continuously if you want. Testing an A123 20Ah cell tomorrow night. I can do an A123 26650 cell too, but I'd need you to send me an 18650 to test on the same setup (I can send back). 



> However the charger is about 250 USD, and it'd need to be assigned only for this test for months! And I need one charger per battery, if I want to get the results in reasonable time for 4 types of cells, I'd need 4 such chargers (1000$).


Yup, if you want the data, we have to pay for it. if we want REAL lifecycle data, it can't be calculated, it has to be measured, and we'd have to actually cycle test them.



> And a single cell is not very statistically good, at least several of a single type of cells would need to be tested to see how they vary.


 yup. Battery manufacturers spend a lot on standalone battery discharge/charge units for multiple cells.



> This charger supports charging up to 3A thought balancing leads (up to 8 cells), maybe I can use that to test 8 cells at once?


 It charges at 40-60A, so at 8s1p, you could charge at up to 60A at 25.6V and test them all at the same time.



> Or maybe someone knows another device with similar functionality needed here which would be cheaper per cell?


Not cheaper than that. Not for charge and discharge.





> Getting the final desirable size pack initially will not work, as it will take me several years to save enough money. So I want to expand the battery every few months as I save-up more money. That way I can have a range of say 5 km in the first year, 10 km in the second year, 15 km in the third year and so on up to 50 km in 10 years. You can imagine that waiting 10 years before I can ride my EV is not a practical option... I won't be able to afford to spend more then 5 km worth of batteries per year. And a 5 km range EV is already useful for me. But a 10 km or 50 km much more useful.


Not a great aproach electrically though. The batteries will wear more the first year, and less the second, so you'll have these cells all over the place in their lifecycle. Your weakest link will always be the weakest pack.


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## rwaudio (May 22, 2008)

frodus said:


> Testing an A123 20Ah cell tomorrow night. I can do an A123 26650 cell too


I'm interested in those results, where was the 20ah cell sourced from? 
I'd love to know IR, can you do short term tests at 320A? I'd love to know voltage sag for a 5-10second load @320A hot and cold.


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## miernik (Nov 28, 2009)

frodus said:


> I can test up to 160A continuously if you want. Testing an A123 20Ah cell tomorrow night. I can do an A123 26650 cell too, but I'd need you to send me an 18650 to test on the same setup (I can send back).


But how many cycles are you willing to do?

What is interesting for me is after how many cycles the cell will have 50% of its original capacity, cycled at 4C charge. 4C discharge.

Or at least doing a 1000 cycles to 2.5V at 4C/4C with a AMP20M1HD-A, APR18650M1 and a Headway 38120P cell and comparing the % of initial capacity of each. That will already give me some idea which ones are worth investing in.

Load tests are interesting, but will not really answer my question with what cells to build my pack.


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## frodus (Apr 12, 2008)

rwaudio said:


> I'm interested in those results, where was the 20ah cell sourced from?
> I'd love to know IR, can you do short term tests at 320A? I'd love to know voltage sag for a 5-10second load @320A hot and cold.


I can test IR (using DeltaV/DeltaI = IR)
With respect to 320, 


rwaudio said:


> I can test up to 160A continuously


so, no. This is a very precise continuous current disharger for lab testing and capacity testing. If someone wants to pay me, I can buy an additional amp and test cells at a higher discharge.


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## frodus (Apr 12, 2008)

> But how many cycles are you willing to do?


I'll do a couple capacity and discharge tests, but not cycling. Do some cycles on them, come back when that is done and we can discharge again and compare.



> What is interesting for me is after how many cycles the cell will have 50% of its original capacity, cycled at 4C charge. 4C discharge.


I think to get that you'll have to buy a real battery tester. They're expensive but they'll do what you want, Over and over again, to batches of cells, at high discharge rates.



> Or at least doing a 1000 cycles to 2.5V at 4C/4C with a AMP20M1HD-A, APR18650M1 and a Headway 38120P cell and comparing the % of initial capacity of each. That will already give me some idea which ones are worth investing in.


You'll spend more hours, more money and more effort testing these cells than you would spend on your pack. Just get some A123's and be done with it. I mean, thats what you want to do anyway. 

I've built packs, for both commuter and for racing. They were all using welded 26650 cells, 120 each pack, 2 welds each side of each battery, and I built 6 for one company and 2 for another (3840 welds), as well as several headway packs. Wanna know what I figured out for my build? Unless you're racing, Headway did the job I needed when I designed around the limitations. They're also MUCH easier to assemble. I would NEVER build an a123 pack unless it was given to me. They took me HOURS upon HOURS, and the bussbar and enclosures were designed for me. If I had to do the design, I would estimate it'd take twice the amount of time, amounting to over a month of nights and weekends.

But feel free, I mean, your time is free, right?


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## steven4601 (Nov 11, 2010)

Hi Travis,

What kind of welder setup where you using? A press-type or hand-probes ?
IF id be to use the 26650 cells id need about 1900 cells, that would be around 7400 welds. ouch


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## frodus (Apr 12, 2008)

It's not my welder, so I'm not sure what brand, but the heads on it say Myachi (i think).

Its a press type, foot actuated pneumatic.

But yeah, its a lot of welding.


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## taken by aliens (May 26, 2011)

Seems like the best thing to do is build a welder that does 100 welds at one time. Maybe a big capacitive discharge welder with 100 carefully calculated weld sites is an answer... but you want to be able to quick swap dead or depleated cells... 
I see where you are going with this, but why not just have 2 different battery packs? That way you can just quick swap them and take the time you need to replace the bad cells on the pack you removed, and your EV will still be driveable.

Finding out which cell in the pack is running low seems like you would have to take a DMM to each cell and record the voltage you saw. I dont know if you have some smart BMS that tells you what number cell is running low or not but if you dont its going to take some time to take the voltage readings of 100 different cells in your battery pack (probably 30 min). 

Im sure if you harass the right people at the battery manufacture company you can get them to make those tabs you want. You just have to clearly show them their is a unique marketing foothole they can capitalize on.


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## MitchJi (Dec 14, 2007)

Hi,


frodus said:


> Weld or don't use them at all.


One word, springs (good method using spring clips):
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=17912&start=0

Some examples in this thread of using spring clips and normal spiral springs, with more spring travel. Spiral springs required more labor but the labor saving techniques of the first method could be combined with the normal springs:
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=2498&p=137198








http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=2498&p=141973


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## MitchJi (Dec 14, 2007)

Hi,

Good info on testing the A123 15AH and 20AH prismatic cells here (the seller referred to can't get the prismatic's now so is selling the 26650's):
http://endless-sphere.com/forums/viewtopic.php?f=14&t=15093


> So, I've been doing cell testing on the cells sent to me by Cell_man. They are 15Ah and 20Ah cells rated for 30C discharge.
> 
> I badly underestimated the amount of work it would be to test these cells.
> 
> ...


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## frodus (Apr 12, 2008)

Two words "High resistance".

It's not bad with 1C, but try to pump 5-10C out of those connections and let me know how hot things get. Spring connections are a high resistance connection, you might as well tape a wire on the top.

Also, how do you expect for the valves to release if they have to vent if you're pushing on them inward? They're designed to blow outwards, on the ends of the cells. Pushing them inwards prevents that.

These cells are meant to be welded, that is how they're designed. Small packs this may be ok, but I'd suggest a different aproach with a car or even a motorcycle with a high quantity of cells.


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## MitchJi (Dec 14, 2007)

Hi,


frodus said:


> Two words "High resistance".
> 
> It's not bad with 1C, but try to pump 5-10C out of those connections and let me know how hot things get.


Do you really want to know (it doesn't sound like it)? If so you can read the original thread where the OP responded to that question.


frodus said:


> Two words "High resistance".
> Spring connections are a high resistance connection, you might as well tape a wire on the top.


Do you really believe that? Hopefully you are more intelligent than that.



frodus said:


> Also, how do you expect for the valves to release if they have to vent if you're pushing on them inward? They're designed to blow outwards, on the ends of the cells. Pushing them inwards prevents that.


Given that many cells function better with either compression or an enclosure that prevents expansion springs might work better (preventing low pressure venting but allowing high pressure venting). 

Do you expect your packs to continue to function properly if the cells vent?

Unless you start responding in a polite and constructive tone I'm going to stop responding in this thread. The question was is there a method of connecting these cells other than spot welding. You said to forget it. I thought an example to the contrary might be helpful. I'm sorry that implying that you might not always be 100% correct in all of your opinions seems to be hard for you to deal with.


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## frodus (Apr 12, 2008)

> Do you really want to know (it doesn't sound like it)? If so you can read the original thread where the OP responded to that question.


Yes actually, thanks. If you could, post some quotes of what you've found relating to resistance of these connections and the venting issue, it would be much appreciated. I don't feel like sorting through 37+ pages of comments.



> Do you really believe that? Hopefully you are more intelligent than that.


Hopefully you're more intelligent than that.... and won't use springs to put together a large pack of A123 cells. High resistance in this case is higher than soldering or welding. Sure, it's a small resistance, but the more you add current, the more heat you get. It is far from an ideal connection. Add to that the fact that you can, and will, get some sort of corrosion buildup over time between the two dissimilar metals. You want these connections to have as low resistance as possible. Ever seen a loose connection on a car battery melt the battery case because it wasn't bolted down all the way and caused so much heat that it actually melted the case? It happens all the time.



> Do you expect your packs to continue to function properly if the cells vent?


No, not at all, but I'd rather have the weaker part of the cell (the ends made to vent) vent properly, rather than explode through the stronger part of the cell because the vent is blocked. If it goes out the sides, it damages other cells next to it and then things just compound and snowball.



> Unless you start responding in a polite and constructive tone I'm going to stop responding in this thread. The question was is there a method of connecting these cells other than spot welding. You said to forget it. I thought an example to the contrary might be helpful. I'm sorry that implying that you might not always be 100% correct in all of your opinions seems to be hard for you to deal with.


You can get a tissue and cry in the corner. I'm TRYING to be constructive and keep people from making the same mistakes that me and others have. I was polite. I just said "high resistance" and asked you constructive questions about how you plan for venting and gave you info on the higher resistance of this type of connection.

It sounds like you just don't like me pointing out the flaws in the design very much, that's not my problem, it's yours. I'm an engineer, it's my nature to look at all of the parts of a system and identify problems that could cause issues. Heat buildup is one problem, which I'm trying to point out is a problem for high discharge packs. Another is safety of a venting cell, when if the vent is blocked, it has to vent elsewhere, enough pressure builds up and you explode out the sides. I don't really want to be sitting on a motorcycle on a pack of exploding A123 cells under my "sensitive parts", or in a car driving down the highway.

I've got a little bit of experience building 26650 packs, both soldering and welding (I've welded over 1200 26650 sized cells, 2 welds each end, total of 4800 welds, this was after looking at other methods, believe me, I didn't want to weld all those). I'm just sharing what I've learned.


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## JRP3 (Mar 7, 2008)

frodus said:


> You can get a tissue and cry in the corner.


 We seem to have a recent trend of people getting upset if their ideas are contradicted. Sack up people, we're all here to learn, we all make mistakes, and sometimes the correct information doesn't come with flowers and a bow.


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## EVMAN (Jul 26, 2007)

Try conductive epoxy.
Time-consuming, but U could do groups for each mix.


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## DavidDymaxion (Dec 1, 2008)

They weren't A123 batteries, but I stressed tested some China High Power 10 Ahr batteries. Some cells did leak about a drop of electrolyte, and continued to function normally (lifetime might have been hurt, but they would deliver full power and capacity still). The cell that spit out a tablespoon of electrolyte was dead.

From this, it's my belief it would be best to mount cells with the vents upwards, that way a cell could vent a little pressure by venting steam rather than squirting out electrolyte. Obviously it is better to monitor temperatures and not vent in the first place!

FWIW I did pressure connects on the cells (used a racheting strap to push them together in a split PVC pipe). They would run at spec'd max continuous current just fine.

Note there is a difference between a pressure connection, and a spring connection. A spring is not designed for low resistance, it is designed for, well, you know, springiness. I would put the preferred metal directly on the battery contact, and use a spring to create pressure on that metal, but not to make the electrical connection directly.

I have only seen spring connects in things like flash lights and radios, but can't think of any examples of using springs for high currents. A contactor, OTOH, does use a spring to push the contacts together, but the spring's function is purely mechanical and not electrical.

Final thought: I have been making educated guesses here, but it would be easy enough to test. Do a spring connection and measure the temperature rise, and repeat the test with a pressure connection, and then repeat with a welded connection, etc.


MitchJi said:


> ... Do you expect your packs to continue to function properly if the cells vent? ...


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