A123 20Ah Pressure Thoughts--and bits for experiments.

Thats why i chose glass fiber resin reinforced board, working temp of 250C, doesn't flex too much compared to thermoplastics (i suppose A123 end plates are injection molded). http://en.wikipedia.org/wiki/FR-4
There you go if you missed:
a123%2520kit%25202.png

a123%2520kit%252022.png


P.S. This is not final
 
There's no doubting it's pretty, what i'm saying is that's where the concentration is on it's form.
 
megacycle said:
There's no doubting it's pretty, what i'm saying is that's where the concentration is on it's form.
Click to expand...

Can you elaborate more about this: "that's where the concentration is on it's form"

I can't follow what your point or meaning is about this. Please expand your thinking towards more understanding by writing about this more fully.

Thanks. :)
 
deVries said:
megacycle said:
There's no doubting it's pretty, what i'm saying is that's where the concentration is on it's form.
Click to expand...

Can you elaborate more about this: "that's where the concentration is on it's form"

I can't follow what your point or meaning is about this. Please expand your thinking towards more understanding by writing about this more fully.

Thanks. :)
Click to expand...

What i mean is, there's a lot of technical details in the materials used, forces that are going to be applied, etc etc then look at how you would want to put that into a design, not visa versa.
 
Looked up fiberglass resin board and first result was $103 for 3sq.ft. I wonder if it'd be crazy to use some ceramic tile as a substitute...? I've been shocked at how unbreakable some of those .25" and .50" tiles are. Box file notches in the side to keep the straps in place. Certainly wouldn't flex at all, but for some reason seems super ghetto. :)
 
the only problem i can see is if the tile does gets broken (say if your bike tips over) then ceramic tile shards may puncture the cells (not good).

though the tile may have a good heatsink value.

xenodius said:
Looked up fiberglass resin board and first result was $103 for 3sq.ft. I wonder if it'd be crazy to use some ceramic tile as a substitute...? I've been shocked at how unbreakable some of those .25" and .50" tiles are. Box file notches in the side to keep the straps in place. Certainly wouldn't flex at all, but for some reason seems super ghetto. :)
Click to expand...
 
xenodius said:
Looked up fiberglass resin board and first result was $103 for 3sq.ft. I wonder if it'd be crazy to use some ceramic tile as a substitute...? I've been shocked at how unbreakable some of those .25" and .50" tiles are. Box file notches in the side to keep the straps in place. Certainly wouldn't flex at all, but for some reason seems super ghetto. :)
Click to expand...
Not a bad idea at all! If it needs some ductility we could epoxy a 1 mm or so aluminum sheet to the backside of the ceramic or porcelain tile and make a "composite"
 
i am not sure but it may be a good idea to also have some http://mtg-technologies.com/zencart/index.php?main_page=index&cPath=8&zenid=nn7rndg7sqmi3onn3g3r6qk912 on the ends close to the electrical so the aluminum sheet does not short on the electrical bits.


bigmoose said:
xenodius said:
Looked up fiberglass resin board and first result was $103 for 3sq.ft. I wonder if it'd be crazy to use some ceramic tile as a substitute...? I've been shocked at how unbreakable some of those .25" and .50" tiles are. Box file notches in the side to keep the straps in place. Certainly wouldn't flex at all, but for some reason seems super ghetto. :)
Click to expand...
Not a bad idea at all! If it needs some ductility we could epoxy a 1 mm or so aluminum sheet to the backside of the ceramic or porcelain tile and make a "composite"
Click to expand...
 
you mention lipo a lot

arent a123'a lifepo4? so shouldnt lifepo4 not produce fire due to the bonding between the chemistry being stronger?



Doctorbass said:
I agree with the comporession 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 theu the layers.

Compressing pouches cells keep them in original shape and also keep layers closer wich help for the RI to stay low :wink:

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 wich is very bad.

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

The guy o fthe RIMAC car wich i consider as one of the genious in the high performance EV developpment also use that method and most o fthe EV manufacture are also using that method.
now..

As for the cylindrical cells, they dont need compression because they already are under compression!.. cylindrical shape is one of the shape that is the most strong to sustain pressure.

Layers expansion occur when cells are charged for the lipo and they also have an endothermic reaction wich 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 tickness is at his thinner state) then when they are installed in their battery box, if they try to inflate furing 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 :wink:

It is so constant than i just have to knock on the cell box and the sound pitch give me an idea of teh state of charge :wink:


What are you waiting for guys! :wink:

Doc
Click to expand...
 
ejonesss said:
i am not sure but it may be a good idea to also have some http://mtg-technologies.com/zencart/index.php?main_page=index&cPath=8&zenid=nn7rndg7sqmi3onn3g3r6qk912 on the ends close to the electrical so the aluminum sheet does not short on the electrical bits.
Click to expand...
I was thinking of putting the aluminum on the "outside" of the porcelain/ceramic tile. Away from the cells. I do use an insulating paper in my batteries, but the Nomex 410 is overkill. You don't need the superior abrasion resistance of the Nomex. I just use old fashioned "fish paper"
 
i was thinking having the metal plate between the pack and tile so if the tile broke it would not damage the cells.

the battery could hit the ground if the bike fell over say the kickstand fails and i have had the kickstand fail

the bike i have right now only a rear kickstand will hold but the only rear kickstands are the bontrager brand one witch is all cast aluminum with a steel rivet and either the leg snaps or the front half of the c holder snaps off in half or the rivet wears out


for me the kickstand fails mostly because it is so easy to forget to put it up and when i corner it hits the ground stressing it and then eventually it fails.

not all of you use the battery for bike so the non bike applications i guess you are ok with the metal plate on the outside.



bigmoose said:
ejonesss said:
i am not sure but it may be a good idea to also have some http://mtg-technologies.com/zencart/index.php?main_page=index&cPath=8&zenid=nn7rndg7sqmi3onn3g3r6qk912 on the ends close to the electrical so the aluminum sheet does not short on the electrical bits.
Click to expand...
I was thinking of putting the aluminum on the "outside" of the porcelain/ceramic tile. Away from the cells. I do use an insulating paper in my batteries, but the Nomex 410 is overkill. You don't need the superior abrasion resistance of the Nomex. I just use old fashioned "fish paper"
Click to expand...
 
The ceramic tiles would be really cheap and strong, but yeh heavy and brittle.
I was looking at aluminium honeycomb panel, for strength and heatsinking
http://www.cooplex.com/product.php?Id=26
and
Kapton thermally conductive film between the cells and end plate.
 
Found some FR4 glass composite sheets on eplastics.com/G10_FR4_Glass_Epoxy_Sheet for quite reasonable prices. should be as flat, nearly as inflexible, and lighter than tile.

The aluminum honeycomb looks awesome though, if you can find a source I'm down. wonder if those air pockets will insulate?
 
That's the problem, i think most often the aluminium skin is bonded to the honeycomb during manafacture, so heat transfer beyond the skin would be affected, but the skin plate itself, i think, should heatsink well itself, with the right materials like the thermal transfer film.
A good aluminium honeycomb panel would be about 2.5x bending strength of the same solid aluminium, looks like you can get composite types, with hard laminate on one side, so the bending ( flex strength) should be a lot better than the 2.5x, depending on the laminate.
 
Actually thinking if the aluminium plate is anodised, which should be common for panel type sheet, then no insulating film is needed
 
megacycle said:
Actually thinking if the aluminium plate is anodised, which should be common for panel type sheet, then no insulating film is needed
Click to expand...

I would use the film anyway for redundancy if cost isn't onerous. Anodizing can be nicked or have flaws invisible to the naked eye.
 
Yes, trying to get that balance between, electrically insulating, thermally conducting, strength and cost, aluminium oxide is excellent for this.Its often used for this job.
The microscopicareas should be valleys in the surface, i would much doubt the foil bag surface would end up in those areas, it should bridge across those.
 
A purpose made, cast aluminium enclosure, maybe, would'nt be too hard to get done, could be sexy looking solution too.
The ends maybe looking like engine castings, not exactly sure how the mid section would look, if it was made for the same battery like a 24S1P, not a problem, dealing with multiple pack combo's, the mid section would have to be different, that not to hard though, when the ends are where the complexity would be and the mids could be same sized flanged rectangular tubes, coupled together maybe.
 
A question for WB9K...

How long ago did A123 publish information about using prismatic cell pouches properly by applying equal psi over the entire cell "stacked surface" area using some recommended range of psi? Was this published info available to anyone wanting to build batteries from these cells?

It seems there also could be established a gradient level of psi ranges to use based on the peak current draws for typical peak usage, and, also, typical constant current draws in typical use. In the extreme of automotive applications you have said 25psi is the typical design recommendation.

We know some people at A123 have said 5psi might be the minimum, but nothing is said relating to what this means in terms of peak current draws or constant current draws in typical use.

So, for design purposes it might be useful to add that "design by application" referencing the typical peak/constant current use TO the minimum psi design requirements too.

Any thoughts?
 
I'm still awaiting an answer from A123 too, emailed twice.
Can only conclude, email ( with receipt given) is not being forwarded, very slow in answering, bothering them, or maybe they don't know themseves.
 
The pressures on, to get an answer :wink:
Trying to stay happy today, downunder, a new far right goverment has snook in, effectively by default, setting policy back about 20 yrs and effectively cancelled our national fiber broadband rollout, neo luddite rule :cry:
 
OK, I've got a little new info.

The numbers I've already shared from the module build spec appears to be all the company presently has for a "pressure spec" for the 20 Ah pouch cell. The company has never really sourced pouch cells to nameless customers in any volume, and the gap in the cell level spec seems to have gone unnoticed until recently. I do expect this to change in the next couple of months.

I'm told there have been some studies recently done that show that at 1C or less, no compression is needed. However, cells have to be constrained somehow just to be usable, so some level of de facto compression will almost always be present.

Bottom line: I expect some official clarification from the company on this question will be coming for customers in the following months, and I expect the guidelines will be more or less what has already been spelled out in this thread. That is, compression is more important at higher C rates, at least a few psi is generally a good idea, and it should be as evenly distributed as is practicable.
 
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