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

[megacycle]

8) thanks

 

[IamIan]

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.

A study I found a bit ago that kind of goes into some of the technical side of the gas formation itself.

Link

 

[ejonesss]

can someone post a copy that does not require payment and registration?

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.

A study I found a bit ago that kind of goes into some of the technical side of the gas formation itself.

Link

 

[wb9k]

can someone post a copy that does not require payment and registration?

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.

A study I found a bit ago that kind of goes into some of the technical side of the gas formation itself.

Link

I haven't tried yet, but probably not. Welcome to life on the bleeding edge.

 

[ejonesss]

here is the text of the document

http://pastebin.com/SbCKAUru


no login required

 

[ambroseliao]

can someone post a copy that does not require payment and registration?

This link will start the download for the PDF file...
http://goo.gl/Yr8Njr
or
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&ved=0CEIQFjAC&url=http%3A%2F%2Fceder.mit.edu%2Fgetpaper.php%3Fid%3D196&ei=g3pAUqPiIYXs8QSKtYGwCA&usg=AFQjCNHaAt3U6qYI0NzgpCqa5ktPnQphxg&sig2=jev7oyGNO2-iFbFFFaytLw&bvm=bv.52434380,d.eWU

 

[h0tr0d]

Have you seen this?
http://www.rimac-automobili.com/upload/tbl_clanci/battery_pack_3_165528.jpg

http://www.rimac-automobili.com/upload/tbl_clanci/battery_pack_4_165533.jpg

 

[999zip999]

Hello Hotr0d ?

 

[h0tr0d]

hello!

Hello Hotr0d ?

 

[powersupply]

Have you seen this?
http://www.rimac-automobili.com/upload/tbl_clanci/battery_pack_3_165528.jpg

http://www.rimac-automobili.com/upload/tbl_clanci/battery_pack_4_165533.jpg

Spring loaded, very Interesting.
So how are the tabs connected then?
Is there a (cooling?) fluid flowing through?
Thanks!

 

[h0tr0d]

Spring loaded, very Interesting.
So how are the tabs connected then?
Is there a (cooling?) fluid flowing through?
Thanks!

I don't work at Rimac (yet), I don't know...

Cooling yes, you can see the channels and the wholes in the aluminium

Another idea, with springs or spring washers:

 

[bigmoose]

Rimac uses recognizable springs, A123 uses thin stainless bands. To me they are both "springs." The bands are cheaper and package better.

 

[agniusm]

Rimac uses recognizable springs, A123 uses thin stainless bands. To me they are both "springs." The bands are cheaper and package better.

... and weigh less.

 

[h0tr0d]

I agree with "bands as springs" but they act very non linear with displacement...

How to proper tension the bands is another question, for me anyway.

 

[agniusm]

I like what Rimac does. Great stuff but i still look at a top of the class DIY, not a production stuff with custom aluminum milling etc. . I bet A123 looked into strapping these cells and confirmed that it is working the way it should. Looking at Rimac battery design and then adjusting it for e-bike stuff is a bit off the line, first and most important - cost, second - weight (cells are heavy enough), third, size.
No one needs liquid cooling for these cells on a bike. I am starting to fade towards 18650-26650 being most acceptable option for e-bikes regarding size, arrangement capabilities, cost. Even more so for larger flatbed cargo bikes where battery compartment area in of no issue. You could probably get 60AH pack on a bike with 100A continues for a lot less money, perhaps same weight and without dangers damaging these cells mechanically.

 

[h0tr0d]

This geometry is awesome for perfect pressure distribution. Bit bulky...

 

[whatever]

Just an idea for even pressure distribution and lightweight.
Why not use the atmospheres' pressure to give even distribution, use vacuum bag around the cells and suck the air out.
Variations in air pressure of atmosphere might change pressure on cells a bit, I'm guessing wouldn't be a major issue.

 

[whatever]

diy vacuum pump from tyre pump
http://www.instructables.com/id/convert-a-tire-inflator-type-air-compressor-into-a/?lang=pt

 

[whatever]

diy vacuum bag connector
http://www.instructables.com/id/10-Vacuum-Bag-Stem-breach-valve-with-hardware-s/?lang=pt

 

[whatever]

1 atm = 760 Torr = 29,92 "Hg = 14.7 psi = 101.3 kN/m2 = 1013 mbar = 1013 hPa

so 1013mbar outside air pressure gives about 14.7psi right in the ball park.

 

[whatever]

a few issues though with all the wiring inside the bag, and how it comes out of the vacuum bag.

 

[CaptainKlapton]

Looked through this thread and didn't see this document yet: View attachment b24d4f5b63934c59d43e93b3bb4db60a.pdf
I just found it a few weeks back, there is information on mechanical support starting on pg.32

From what I have read, there is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi.

 

[wb9k]

Looked through this thread and didn't see this document yet:
I just found it a few weeks back, there is information on mechanical support starting on pg.32

From what I have read, there is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi.

Whoah, where did you get that? Good document, but I'm not sure how it got on the internet :?

 

[CaptainKlapton]

I didn't expect it either
https://www.buya123products.com/
They have a couple of them.
But more often than not, if you know the name of a document you can search it directly on google and bypass many of the pay walls and other blocks by clicking on the PDF button next to the link.

 

[wb9k]

I didn't expect it either
https://www.buya123products.com/
They have a couple of them.
But more often than not, if you know the name of a document you can search it directly on google and bypass many of the pay walls and other blocks by clicking on the PDF button next to the link.

Well then, that's a pleasant surprise. Looks like the company is getting a little less protective of this kind of data, which is good. Carry on!