How much is getting tested & matched A123 20ah cells worth?

[davec]

osn has decent cells but a bit expensive
vict ran out of the good cells
you know- now that a123 is a chinese brand - i wonder how long before they get things running again
i'm thinking they might even sell to us- so we can buy the cells legit- i don't know of any chinese vendors that will reject a customer who will pay for a product
out of all the vendors calb/headway/sinopoly/hipower their all open to selling lithium to the public - im sure the new a123 will be open to it as well

 

[999zip999]

Victpower has hit me up time to time With a batch of A123's and I was told they are the bottom of the batch ? I don't know ? Nancy at OSN is a friend. I like that they test the cell ? I got A123 20ah from JRHolmes 8 months ago I need One more as A cell is a little wacky. So this is the second cell to go a little under in my 24s pack. It's the end one on the pack.

 

[docnjoj]

My bad cell was also on the end of my 12S agniusm pack. Makes it much simpler to repair than one in the middle.
otherDoc

 

[Ykick]

I'm intrigued about the reports of end cell failure in your packs. While it may simply be "good" coincidence, is there anything about your mounting solution(s) that could be adding extra stress to end cells?

I sometimes strap RC Lipoly onto surfaces but always use a chunk of veneer or Masonite to prevent deformation cause by straps or other mounting apparatus. Particularly, exterior cells of the battery block.

 

[docnjoj]

I'm intrigued about the reports of end cell failure in your packs. While it may simply be "good" coincidence, is there anything about your mounting solution(s) that could be adding extra stress to end cells?

I sometimes strap RC Lipoly onto surfaces but always use a chunk of veneer or Masonite to prevent deformation cause by straps or other mounting apparatus. Particularly, exterior cells of the battery block.

Yes I do the same. My A123 6S packs have hardboard outer shell and are filament taped to avoid expansion. It just takes a slice or 2 with a sharp knofe to get through the tape (carefully I might add) and then the cells are exposed. Since they are bolted on the tabs removal is quite simple. I don't know why end cells fail more often (or even if they do) but I am grateful since it is much easier to work on them.
otherDoc

 

[whatever]

I've had two end cells fail on a 48v a123 20ahr pack, both on the positive end, positive end cell has alot more electricity flows through it than other cells, perhaps insufficient pressure on end cell was the cause, but has happened twice.

 

[amberwolf]

positive end cell has alot more electricity flows through it than other cells,

If it's a single series of cells, all of them have exactly the same amount of electricity (current) flowing thru them.

If you have multiple parallel strings of cells in series, *then* you might have one of them that has more current flow thru than others, if it has a lower resistance than the rest of the strings. It could also happen if you have all of the series strings paralleed at the cell level instead of just at the ends.



I'd guess that if you're having repetitive failures of a specific position in a pack, there's a mechanical issue at work (unless you have a BMS that has a design or manufacturing flaw that causes or allows that cell position to discharge or charge to an excessive level vs teh other cells).

 

[Doctorbass]

btw Ambrose have a pretty good deal on 28 of them right now.

http://endless-sphere.com/forums/viewtopic.php?f=31&t=65126

Doc

 

[amberwolf]

btw Ambrose have a pretty good deal on 28 of them right now.

http://endless-sphere.com/forums/viewtopic.php?f=31&t=65126

Um, I see only 12? :?

 

[whatever]

I will have to disagree with amberwolf that each cell in series 'sees' the same current. Lead acid batteries for example, its always the positive end cells that run out of water first ( same with agm type), the positive end cells are under more stress.
What is the correct explanation for this i'm not sure. Lets say we have 16 cells in series, each of those cells will provide current,
the current exits at the positive end of the pack, surely the current provided by the 15cells before the exit positive cell will go through the the last cell. The cell on the negative end will only have current provided by itself flowing through it during discharge.