I think I let my A123's starve to death

[wb9k]

Hi all,

Haven't been around much lately, and haven't had time to read this thread thoroughly, but here is the LV bottom line for A123 cells.

They can go as low as .5 Volts essentially forever and suffer no ill effects. A cell that has been below 300 mV (call is 500 mV for some safety buffer) AT REST for any length of time should be scrapped. Don't even attempt to use it. It may charge up and even hold a charge reasonably well at first, but every charge cycle brings added risk of a catastrophic failure in the form of an internally shorted cell. I've explained the mechanism responsible here before elsewhere.

1 Volt? No worries AT ALL, you're perfectly fine. Charge and enjoy.

 

[ALLVLTS]

Sorry for the delayed reply, I got very busy at work.

wb9k, I see that you're a warranty analyst at A123. I read many of your posts. If there anyone who would know, it's probably you. That being said...
Awesome! I'm elated to know that I didn't waste over $1300, and that all of these should be just fine (maybe except that rogue cell that randomly went down to .4V)

I did get my iCharger 4010Duo yesterday (that was fast!). I am still going to cycle all of the cells and get all the data anyway, I've actually wanted to since I bought them un-used and was reasonably sure that they were good. If I do have any less-than-obvious duds for whatever reason, now I'll know for sure, and I'll know all of the cell's real-world specs based on my planned actual usage.
This thing is awesome! It can do everything but wash your dishes for you (though I wish it did that too). It really is a serious little machine, and I'd like to go on and on about it, but it would just take too long to describe the total epic-ness that is 4010Duo.

I haven't finished my 10S x2 cell-swappable setup yet, but I did throw a single cell on the iCharger just for the heck of it. It was cell T5, which is one of the several that sat at 3.2x this whole time, so was a known good one. I cycled it three times @ 2.3A charge (1C) and 4.6A discharge (2C), 3.6V to 2.00V. Each cycle, the capacity did go up by a tiny bit. The last and best one was 2209 mAh which is about 96% of rated capacity. I suppose that's good for a 2C discharge?
Voltage drop was horrible though (it held about 2.9V @ 4.6A), but I think it's because I'm using a very weak connection method (did that just to get it going because I wanted to play ). Consequently, measured IR was about 150 mOhm. I'm disregarding those numbers entirely until I get it set up for real.

Thanks again to everyone for all of your help.

 

[dnmun]

you will not have good handle on capacity until you cycle the cells a number of time to full charge and back.

it doesn't look like did any damage so it is reasonable to expect they will all be close to spec, with just normal manufacturing variations which seems to be really small on these.

 

[wb9k]

ALLVLTS, I'm glad to deliver good news! It would be interesting to compare the capacity of each individual cell against the voltage you found them settled to. I wouldn't expect to see much difference among them if their life histories are indeed otherwise similar. Everything the chemists tell me points to the idea that while in storage, lower voltage is better for a cell as long as it never goes critically low. Cool temps in storage are good too.

 

[arkmundi]

They can go as low as .5 Volts essentially forever and suffer no ill effects. A cell that has been below 300 mV (call is 500 mV for some safety buffer) AT REST for any length of time should be scrapped. Don't even attempt to use it. It may charge up and even hold a charge reasonably well at first, but every charge cycle brings added risk of a catastrophic failure in the form of an internally shorted cell. I've explained the mechanism responsible here before elsewhere.

1 Volt? No worries AT ALL, you're perfectly fine. Charge and enjoy.

Hey wb9k, thanks for posting, as we're on this learning curve. That is amazing, that these cells can undergo such a discharge and come back to life! FYI, I'm in process of building another 36V 12S8P with the 26650 cells. Chose this format over the AMP20's on your advise regarding pressure requirements for those cells. This time, also per your suggestion, new cells from http://www.buya123batteries.com/.

 

[wb9k]

Hi Ark,

Glad to see you're still in the game. You might want to take a peek at the Hymotion modules Sybesma's (under the user name mathorsby) has finally listed on the used items for sale board here. Those cells still have plenty of life in them and they are priced to sell. You could buy three modules, split them in half, and get TWO packs of 12S 11P for under $1500 delivered. Just a thought.

BTW, LFP in 12S has a nominal voltage of about 40V, not 36...fudge factor/rounding error?

 

[John in CR]

You got lucky and remembered them in time, and the vast majority will be fine.

Unless a 3s pack has a bad or weak cell, I'd suggest not breaking them up. Doing so will increase your work at least 5X, and you increase the risk of cell damage too.