A123 20AHr Pouch Cell Battery Build & Info Thread

[wb9k]

Well, if I'm confused at this point, so are the company's assembly specs and every engineer in the building responsible for them.

This leads me to believe there is still confusion.

OK, well mech stuff is not my forte. Apparently the verbiage comes from the air pressure driving the stack compressor, not the actual measurement of psi in the stack. My bad. So what's the proper verbiage...10 lbs of end-to-end pressure?

_10 lbs of end-to-end pressure?_ You say. 10 lbs is a measure of force, not pressure. Pressure is measured in pounds per square inch. Force is measured in pounds. See the difference?

Bigmoose helped clarify this for me a couple days ago. 10 lbs of end to end pressure was a misstatement by me. I have since spoken to the engineer responsible for this aspect and seen the spec. PSI was correct all along, I just didn't understand how much external pressure that equated to. I'm confident I'm stating things correctly now, and the verbiage of our specs says the same.

 

[wb9k]

If there is that much presure it's just going to pop out the sides.

Right ? where is the safety vent ?

The pouch seal and roll are the safety vent on the pouch cells.

 

[major]

Well, if I'm confused at this point, so are the company's assembly specs and every engineer in the building responsible for them.

This leads me to believe there is still confusion.

OK, well mech stuff is not my forte. Apparently the verbiage comes from the air pressure driving the stack compressor, not the actual measurement of psi in the stack. My bad. So what's the proper verbiage...10 lbs of end-to-end pressure?

_10 lbs of end-to-end pressure?_ You say. 10 lbs is a measure of force, not pressure. Pressure is measured in pounds per square inch. Force is measured in pounds. See the difference?

Bigmoose helped clarify this for me a couple days ago. 10 lbs of end to end pressure was a misstatement by me. I have since spoken to the engineer responsible for this aspect and seen the spec. PSI was correct all along, I just didn't understand how much external pressure that equated to. I'm confident I'm stating things correctly now, and the verbiage of our specs says the same.

So you are confirming you need to have almost 3/4 ton force on a cell?

So folks since a cell is 57 square inches in area that says that the A123 20 Ahr pouch cells want:
570 to 1425 lbs of compressive FORCE on the stack!

 

[etriker]

If there is that much presure it's just going to pop out the sides.

Only if you abuse the cell. Even then, there is room at the margins of the cell for some gas to go to before the pouch vents.

If you don't compress, the electrode stack develops uneven heating due to uneven distribution of electrolyte--even with "normal" use conditions. Hot spots result, which in turn results in gas generation and further delamination of the electrodes, and it just escalates from there. This is what we are trying to prevent with the pressure.

You can bet some ebikers will overcharge and abuse them. In the house, unattended. Then post the pictures online.

Thanks so much for your answers.

 

[wb9k]

So you are confirming you need to have almost 3/4 ton force on a cell?

As a max, yes.

 

[flexy]

Did anyone buy one of the 7S3P modules from victpower? https://www.youtube.com/watch?v=69JhQDmJALA
I notice they only have two steel bands for compression but the end plates are quite thick therefore spreading the force evenly over the cells.

There were also some much longer modules too 28S3P,

I tried to follow the band compression method with my build, the stainless steel cable ties I used have loosened slightly with vibration. I should have used the proper Band-it st/steel strap.

I also tried a nylon band strapping tool but it was difficult to attain good tension with a small diameter (under 500mm) loop of band.

The Band-it system seems the most accessible method but it is very expensive for a roll of stainless steel band, I picked up a used tensioning tool of ebay
https://www.youtube.com/watch?v=69JhQDmJALA

Got a pic of the 7S3P? Sounds like a Fisker module.

This thread has pics http://endless-sphere.com/forums/viewtopic.php?f=14&t=39320

 

[wb9k]

This thread has pics http://endless-sphere.com/forums/viewtopic.php?f=14&t=39320

Thanks. Yep, those are Fisker modules. We always have to clamp modules end to end with two bar clamps to keep the steel bands from flying all over when we cut them.

 

[megacycle]

Would'nt need to add weight, if it is possible to provide suitable force when the pack is in situ, designing the vehicle frame, or part of it, to enable it.
If you were removing it to work on it, maybe use clamping plates.
We just need to think around the box we're in.
Before i'd jump, i want to see those compartments that provide that equalised pressure at that force, because when there's mention of a 'can', it spunds like thin walled, unless it is squeezed, when in situ.

 

[wb9k]

Would'nt need to add weight, if it is possible to provide suitable force when the pack is in situ, designing the vehicle frame, or part of it, to enable it.
If you were removing it to work on it, maybe use clamping plates.
We just need to think around the box we're in.
Before i'd jump, i want to see those compartments that provide that equalised pressure at that force, because when there's mention of a 'can', it spunds like thin walled, unless it is squeezed, when in situ.

Our cans are not squeezed in situ. They can withstand quite a bit of internal pressure....far more than the pouches. The downsides are lower power density per volume, and cost--can cells are more expensive to make (at least theoretically).

 

[999zip999]

I don't think the number of 10psi. is easy to translate as with the math Bigmoose used it might just be a number on the machcine that is being used.

 

[wb9k]

I don't think the number of 10psi. is easy to translate as with the math Bigmoose used it might just be a number on the machcine that is being used.

That's not how the spec reads. The machine was set up around the spec, not the other way around.

 

[999zip999]

O.k. Just triing to get my head around it as I would like to get more then the yr. I have on them so far. Time for a ride or to drain 12ah off the pack. Good luck brainiacks. Just go for a ride.
Thanks for all the help. Now go for a ride. enjoy.

 

[whatever]

I can confirm one expanded cell in my 48v 20ahr a123 pack, which are sticky taped, my cells are stacked on their flat surfaces down,
the top cell with no pressure on it ( apart from some tape) expanded in a big way, the copper/aluminium sheets inside were quite warped also. Seems pressure on all cells is necessary.

 

[deVries]

Has anyone come-up with some good pressurization ideas to compress these light weight wise???

Also, can the wb9k A123 guy or someone with the Specs tell us what the minimum psi we might use instead of the maximum? Also, going with the minimum psi vs max is there any data about how much less lifespan or cycles we could expect? Obviously, there was a lot of Lab Testing done, so the data is 'there' somewhere.

Thanks.

 

[wb9k]

Has anyone come-up with some good pressurization ideas to compress these light weight wise???

Also, can the wb9k A123 guy or someone with the Specs tell us what the minimum psi we might use instead of the maximum? Also, going with the minimum psi vs max is there any data about how much less lifespan or cycles we could expect? Obviously, there was a lot of Lab Testing done, so the data is 'there' somewhere.

Thanks.

As I've stated before, this is a matter of debate and is at least partly application-dependent. The minimum I personally recommend is 10 psi, but there are those who believe as little as 5 psi is enough. My opinion is that the lower you go, the more critical it is that the pressure is applied as evenly as possible.

Lab testing....yes, lots of it, but it can only tell you so much so fast. That, and the data is proprietary so, sorry, I can't just reach into the server and post specs or test data here. Honestly I would be surprised if such testing had been done in a way that would be directly applicable to an e-bike application. It's not the target market. Existing test data is likely under much more brutal conditions--both environmentally and in terms of current flow. We're not in the business of finding what is the least possible we might be able to get away with if we really baby everything--you can't design like that in automotive.

 

[deVries]

[...] Lab testing....yes, lots of it, but it can only tell you so much so fast. That, and the data is proprietary so, sorry, I can't just reach into the server and post specs or test data here. Honestly I would be surprised if such testing had been done in a way that would be directly applicable to an e-bike application. It's not the target market. Existing test data is likely under much more brutal conditions--both environmentally and in terms of current flow. We're not in the business of finding what is the least possible we might be able to get away with if we really baby everything--you can't design like that in automotive.

Hi, thanks for your suggestions. I will note you have asked around for info before relating to this topic, and I was definitely not asking to publish test data. But I've worked in Lab settings before, and I know it's likely someone does know the range of PSI that one should consider using. Someone probably knows what effects will result if using a lower PSI too. So, there might be a known cut-off point to not go below. That helps customers design their products correctly, so this should not be considered "top secret". Imo.

Bikes without suspension will give a much rougher ride of vibrations and "shock-hits" vs automotive, so that's where to key-in on the PSI factor to prevent damage in that sense. Maybe that's not what the PSI factor is designed mostly for? Maybe for other reasons?

Again, thanks for your help regarding this matter. Anymore help about this is most appreciated. Thanks.

 

[xenodius]

deVries, I believe that wb9k already explained it's to keep the electrolyte evenly dispersed across the electrode, and prevent hot spots on the cells. Long term, that increases IR.

 

[deVries]

deVries, I believe that wb9k already explained it's to keep the electrolyte evenly dispersed across the electrode, and prevent hot spots on the cells. Long term, that increases IR.

Correct, but the point I was making too is how does this PSI rating relate to a static environment vs the hostile vibration and shock environment of riding by bicycle? Automobiles are Full Suspension and don't transmit the vibrations and shocks that bicycles do transmit over a larger variety of terrains.

Edit: I see another thread is dealing with this "pressure debate" here:

A123 20Ah Pressure Thoughts--and bits for experiments

Doctorbass posted some excellent ideas and reasoning:

I agree with the compression method.

All the packs i built have compression on them,, LiPo, LiMn and LiFePo4. All are still 100% working today, none have puffed yet :wink: and RI always stay low. so i can charge them at nominal rate or more without problem :wink:

For the lipo i also think it help reduce the danger.

Like i explained many times on E-S in the past, problem with pouch is that once they inflate (puff), the corner and edges on the side will have deformation and this is what might cause them to catch fire if they puff too hard. When deformation occur the conductive anode and cathode layers inside might short together as well as when a cell have puncture thru the layers.

[...]

Most of the lipo fire occur with pack assembled together with ducktape or simple shrink and sometime just inside a nylon bag where they can move and hit edges of the bicycle frame which is very bad.

Building a case to protect them and hold the pouch together and keep them under pressure on the thickness axis is the key and it worked for me for many years.

Layers expansion occur when cells are charged for the lipo and they also have an endothermic reaction which make them to cool down!. once they are discharged they shrink a little bit.

TRICK:

One of the trick i have for pouch cells is to make the battery box with dimension of the cells in their discharged state ( when their thickness is at his thinner state) then when they are installed in their battery box, if they try to inflate during the charging process, this will make them to autocompress and will keep the RI low and keep them in original shape. then when they discharge, they recover their uncompressed original shape :wink: This cycle repeat over the lifetime of the cells

 

[Ypedal]

i just deleted a whole bunch of crap form this thread.... everyone.. and i mean EVERYONE stay on topic and keep the flame wars from past sales gone wrong out of this thread.

thank you.

 

[wb9k]

Correct, but the point I was making too is how does this PSI rating relate to a static environment vs the hostile vibration and shock environment of riding by bicycle? Automobiles are Full Suspension and don't transmit the vibrations and shocks that bicycles do transmit over a larger variety of terrains.

No test specs are more rigorous than automotive specs. Your bike application will not exceed what is tested for in a car, suspension or not. The mechanical shock testing these are subjected to is very intense. You will not have a greater pressure requirement due to the bike environment, I am quite confident of that.

 

[Ypedal]

i think it has to do with the over all mass, an EV sized pack is heavy and requires significant measures to keep it from shaking itself to bits ( if the cells move , at all, in relation to each other, the tabs would break obviously ) , a 15 lbs ebike pack on the other hand, can be strapped down solidly enough to prevent damage without going to extremes..

 

[oatnet]

This thread has pics http://endless-sphere.com/forums/viewtopic.php?f=14&t=39320

Thanks. Yep, those are Fisker modules. We always have to clamp modules end to end with two bar clamps to keep the steel bands from flying all over when we cut them.

IIRC before buying my stockpile of 7s and 28s modules, I saw several applications using the 7s3p configuration. How do you identify them as Fiskar modules, is it because the metal separator plates are black instead of beige?

-JD

 

[wb9k]

This thread has pics http://endless-sphere.com/forums/viewtopic.php?f=14&t=39320

Thanks. Yep, those are Fisker modules. We always have to clamp modules end to end with two bar clamps to keep the steel bands from flying all over when we cut them.

IIRC before buying my stockpile of 7s and 28s modules, I saw several applications using the 7s3p configuration. How do you identify them as Fiskar modules, is it because the metal separator plates are black instead of beige?

-JD

The only application I know of that 7S3P prismatic modules were built for was Fisker. A Fisker pack has 15 of those modules wired in series. That said, they're a handy surrogate for many 24V applications, so they have utility far beyond Fisker (note the spelling--Fiskars makes scissors). This is the main reason I have some. A couple years ago there were a plethora of pilot programs that have since fallen by the wayside and it could be there was one or a few that I was unaware of that used the same module. Can you be specific as to any other application?

(EDIT): As far as heatsinks go, all were changed from the grey paint to the black e-coat some time ago, so that is not a feature that signifies any specific program.

 

[deVries]

i think it has to do with the over all mass, an EV sized pack is heavy and requires significant measures to keep it from shaking itself to bits ( if the cells move , at all, in relation to each other, the tabs would break obviously ) , a 15 lbs ebike pack on the other hand, can be strapped down solidly enough to prevent damage without going to extremes..

This is good reasoning. Just combine this idea with Doctorbass suggestions about packaging/containing the cells and this probably will be more than "good enough". I hope so.

 

[ejonesss]

another thing i was wondering with compression is could i get an air tight box with pressure rated terminals like those used on refrigeration compressors and charge the box to the 15 to 25 psi of air or maybe even some inerting gas like nitrogen.