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

Thanks Bigmoose, so these are cut of tab cells then. I measured the plastic and it's the 225mm in your drawing, so it's not just extra long plastic. I'm trying to decide whether I think shortened tabs means anything good or bad. To me it at least means they're not factory rejects, since I think those would be tested and rejected still with full tabs. Do we have any info on those internal procedures?

The 2 I've run thru a cycle so far have in excess of 19.5ah . With my M1's I never saw end of discharge, but these larger capacity cells make it easier. It's pretty cool to see that flat discharge with voltage staying 3.3-3.1V for so long and stay above 3V all the way to 19ah of discharge.

I've got a friend with a shop who has an auto battery test machine. I'll have to take the 4 over there after coming up with a good connection to make them a 12V battery, and then go lean on them with a big discharge and see how voltage holds up when getting hit with hundreds of amps, maybe even 600A if my connections are good enough. It has something like a 10 second limit, but that's enough to confirm low IR for me. Add to capacity confirmation of a like-new cell, and the only other thing to make me happy enough to buy more is a lack of self discharge.

John
 
Take a look at this ES thread about standrdized tests for A123 cells
http://www.diyelectriccar.com/forums/showthread.php?t=71283

38A charge to 3.65v terminate C/20
38A discharge to 2.25v
 
EVPowers said:
Take a look at this ES thread about standrdized tests for A123 cells
http://www.diyelectriccar.com/forums/showthread.php?t=71283

38A charge to 3.65v terminate C/20
38A discharge to 2.25v
Click to expand...

I meant how A123 tests its cells. I can't do 38A amps, but I'm really just verifying the accuracy of the measurements done in China. After testing that the reported data is accurate, we don't have to test squat since we're paying for it.

BTW, no response back, so I guess he took the weekend off. Let's keep our fingers crossed that it's "thousands available and more in route" :D , and not "sorry, we have to wait for the next batch." :cry: Getting just 4 would almost be worse than any tease a girl ever pulled, though I'll have an awesome 12V battery. :mrgreen:

John
 
EVPower said:
38A charge to 3.65v terminate C/20
38A discharge to 2.25v
Click to expand...
I'm inspired to do a capacity test of my pack, something I haven't been particularly inspired to do as yet. Is that low voltage - 2.25V - an OK low? I mean, I'd have thought that too low, dangerously so. Don't want to damage the cell in the process of testing its capacity after all. :?:
 
arkmundi said:
EVPower said:
38A charge to 3.65v terminate C/20
38A discharge to 2.25v
Click to expand...
I'm inspired to do a capacity test of my pack, something I haven't been particularly inspired to do as yet. Is that low voltage - 2.25V - an OK low? I mean, I'd have thought that too low, dangerously so. Don't want to damage the cell in the process of testing its capacity after all. :?:
Click to expand...

2.5v, 2.4v, 2.25v are all essentially the same, ie the battery is essentially empty. At 38A it sagged so much that my discharge at 6.7A to 2.4A is actually a deeper discharge, so no that's not dangerously low, and as soon as the discharge turned off I'm sure they pop back up to an at rest voltage much higher than mine. Now if you see an at rest voltage of 2.25V, then the battery has less mah in it than you can count on 1 hand, but plenty of my M1's turned out fine after being even at 2V after sitting for multiple years.

In a pack with no BMS or a malfunctioning one the damaging thing is to continue to draw current through one that is empty. The other cells don't care and will keep sending, and when that one has nothing more to give then continued current thru it damages it, because it can't become just a piece of wire.

Hmmm, that tells me what an ideal BMS needs to be able to do, ie bypass the low cell(s) and keep going.

John
 
Oh well. This seems like a nice idea, but I'm not sure it's going to work. Those made in Korea cells are all gone. He bought a few from another source. They're also short tabbed and the negative tab has the small holes punched in it. Made in USA cells. He did the testing himself, not the source like the 4 I got, and the one sent sent a pic of has a capacity of 18.5ah and an IR of .9mOhm.

These have a used look to me, so I'm going to pass. He didn't mention price but I'm sure they're cheaper, but I'm passing anyway. I don't want used, and I'd rather pass on uncertainty of a 25% chance cells came off a bad machine and have an early failure risk unless they're somewhat cheaper.

John

Here's a pic of the latest.
A123 holes in tab.JPG
 
Any way to find out if that holey tab is Copper or Aluminum ??

I would still be interested for house batteries, after Jan., IF the total cost is significantly lower.
 
vict power is selling these as well for like 16/US per cell- these are used for sure- the ir seems ok they might be good for something lo key if you can work with the awkward tabs.

Vict seems to be buying these cells for 11US from some source and re-selling for a profit- the other vendors are probably doing the same thing
reading ark's thread about 3 of these cells going bad in his pack - yes i am a bit hesitant
 
I'm not sure about the safety thing. In my view, used cells are safer because they've proven not to be faulty. These aren't like the Konions where if you go soldering on the button end too much with the older versions before the extra ring of insulation where positive and negative are adjacent on the can, the thin green plastic gets melted and can short sometime in the future.

I'm waiting on the price. If the price is right, I may change my mind on that Sunday tabbed batch. A 5% reduction in capacity for a big discount could be interesting. Early on Jiang did mention that he saw some at $9/cell. He hadn't dealt in A123's at all a we both dismissed them as junk. It the 18.5ah/cell in the pic is at that kind of price, then I'm on it like white on rice.

John
 
Just saying I recently completed a second order with Victpower for those $16.50 per cell AMP20's and found it all kosher. Got the delivery no problems and all tested out at 3.3 volts on delivery. I've got one of those in my 12S pack now and its running fine. I'd suggest one of the uses of a group buy to Victpower would be to deliver a single cell into the hands of the wary, so as to prove out the authenticity of the offer. I still hold that these are not "used" cells, but essentially new cells from salvage of the Fisker pack bad welding machine fiasco .... the cells not shorted by the weld are fully up to spec. Understandably, the cheese grater short tabs scare a lot of folks away, but I've found them to not be a problem. :mrgreen:
 
Did all cells come with those small holes in the tab or also with full tabs ?
 
if you can get them for 9/a cell(same stuff vict is selling for16) the ir is good and capacity is a min 18ah - that's sounds like a deal to me.
 
arkmundi said:
All short cheese grater tabs.
Click to expand...
arkmundi,
Do you have info on how you put together a pack out of "cheese grater" tabs?

And by the way the "cheese grater" tabs actually have a name: "Zipper fuse"
Here are links to the patent drawing and overall pack explanation
http://www.faqs.org/patents/imgfull/20120196170_04
http://www.faqs.org/patents/app/20120196170#b
 
I got these.
Dear:Robert

Good news

Yesterday nite we arrivaled about more than 300PCS

Full tabs without hole(as same as before ) A123 20AH

If need,pls let me know today

If no need, i will sell to others ,coz rest of all are short tabs with hole

Price :18.0USD/pcs

Im gonna wait for your reply

Best Regards
 
999zip999:

Could you provide more information on these cells? Who to contact to purchase and cost of shipping. Any warranty? Thanks.
 
My live.com shut down and can't access my live.com email ? The contact is Victpower and asked them . Good luck. How about me getting off outlook and going back to live.com without paying 99 dollars good for 3 mos. than that;s it is that 99dollars a mo. for 3 mos ? Frouk it. Frozzooss my email is out that's out. Help.
 
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