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Old Jun 06, 2007, 06:21 AM
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Slovakia
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Right.
I would start with discharge 2s pack (with one of the cells charged much more) to 3.4V and carefully decrease the end voltage. Volts over tested cell could be measured by dvm.. I would be glad to know what value of reverse voltage kills the cell (approximate), I mean whether it could survive temporary reversal allowed by shottky diode in parallel..
However, if cutoff will occur, the time spent in reverse will be probably very short. The problem is that I suppose that cell may die few minutes later after cutoff.
Could You somehow simulate also low current consumed by servos and receiver?
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Old Jun 11, 2007, 07:02 AM
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Madrid (Spain)
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Hello again,
I've been out some days, but let the charger doing his homework (99cycles at once). The cell is over 250 cycles now, all of them discharging at 22A down to "zero" (0'2V). After a couple of discharge graphs on the CBA, everything looks as usual, maybe a bit down on capacity: 2050-2100mAhs delivered.
But no harm done, so tonight/tomorrow I'll upload some discharge graphs, and see how I manage to do "survival" tests putting the cell into reverse, as we agreed the only way to really kill them.
Regards
Josep
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Old Jun 11, 2007, 01:20 PM
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Airdrie, AB Canada
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Thanks for your testing done so far Josep. It's so nice to see a few more long term tests done.

I did manage to kill one of these the other day. It was a crashed pack, the bottom of one cell was slightly punched in. I couldn't see the slightly damaged bottom of the cell. I was doing some high rate test (30A) charging. Pack started with a normal discharged voltage around 11V (4s). I am using 3.75V cutoff to stay in CC longer. At the end of the charge one cell was noticably hotter than the others. I put it by the cooling fan, but it just stayed hot. All the other cells were cool, so I cut the shrinkwrap off to figure out what was going on.

The single cell went into some type of thermal runaway, I assume there was some type of internal short. It got fairly hot (168F), but not terrible. It stayed hot for around 10 minutes and drained to .012V. Of course I was in Lipo hyper alert mode expecting some type of venting even if not a ball of flame. The cell just self discharged and finished with a closed circuit. I was very pleased.

I was just cycling through them (4s packs) to see where they landed with some cycles at 30A in 40A out. Don't have the equipment to log 500 cycles, but they were perfectly happy in those circumstances.

The amount of punishment they will take is amazing. I don't mind significantly reduced cycle life, but truth is they don't seem to die quickly even when abused.

Thanks for your information and hard work.

Mike
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Old Jun 13, 2007, 03:50 AM
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Well, I am a bit uncertain about which graph belongs to which test..
Anyway, it seems to me that "survive" is not the same as "is happy" for tested cells.
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Old Jun 14, 2007, 04:40 AM
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Madrid (Spain)
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Hello again,
After 400 cycles, the cell discharged every time down to "zero" volts looks as happy as were the other A123 cells I tested after around the same amount of cycles.
So, to me, looks like discharging WELL DOWN the "official" 2'0 minimum volts DOES NOT harm them. Keep in mind what will happen to a lipo with the same treatement (discharging at high rate to 0 V)... I will for sure not do this test
Here you have three discharge graphs: new cell, after 250 cycles and after 400+ cycles. All cycles done charging at 3C (6'9A) up to 3'7V and discharging at -10C (22A, the graph shows wrongly 12C) down to 0'2V. The (small) differences involtage are more temp/connectors related than a real show of any change in the cell's status: as on previous tests, the cell gives good voltage, and has lost only capacity (now giving around 1950mAh).

Coro, you are right, this thread is now too long with graphs here and there. I will "recapitulate" as soon as I have some spare time to show more clearly the three long term tests and the results and conclusions.
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Old Jun 14, 2007, 04:43 AM
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Madrid (Spain)
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Now we know A123 cells are not damaged by dicharging them to zero.

We need to know what happens is they are maintaned at low voltages (near zero) for more time. I'll see that with this same cell.

And then, we want to know how much "reverse" voltage they can stand before going dead. This is what can happen in a medium/big pack ina a unbalanced status. I hope the cell will survive the above test to let me do this one as well.

Regards

Josep
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Old Jun 14, 2007, 10:14 AM
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Marshfield, Wisconsin, United States
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What connectors are folks using to carry these higher currents? I have a HOrizon HObby p51 at 65 inches and they recommend a eflite 60 motor and am thinking it would be perfect with a123 batteries at 7s. JUst trying to figure if I should make my own packs from ebay, or buy ready made packs from Maxamps. Thoughts?
Great and interesting thread. NIce of you to share your efforts with us. Thanks
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Old Jun 14, 2007, 10:33 AM
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We are using this, 3.5mm are mostly sufficient. : http://www.mpjet.com/news/index.php?...pper&Itemid=28

Soldering to A123 cell is not possible using small iron. You need heavy soldering tip (powerfull soldering staion), or You will not be able to reach necesary temperature for good join, without destroying the cell itself.
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Old Jun 14, 2007, 10:38 AM
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Thanks Coro, I have a 140 watt gun, would this be enough? IF not Ill bite th ebullet and purchase packs. Fact is I hate soldering, although the bigger stuff is easier than Dean's microsGeez!
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Old Jun 24, 2007, 08:23 PM
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So in a nutshell....I can set my LVC at 7.2 for a 4s123 and not worry that I am damaging my battery

That would be very nice indeed.
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Old Jun 25, 2007, 02:43 AM
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Quote:
Originally Posted by santeepat
So in a nutshell....I can set my LVC at 7.2 for a 4s123 and not worry that I am damaging my battery

That would be very nice indeed.
It is a pitty but this is not true.
7.2V may, and probably will, mean one cell reversed in 4s pack. E.g. 3.3V+3.3V+3.0V+ (-2.4V). Or 2.5+2.5+2.5+(-0.3)...
The cell that was reversed will go to short circuit very soon, rise to zero volts, and keep conduct current (that saves the plane by keeping receiver power).
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Old Jun 25, 2007, 11:21 AM
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Is a 60W iron with a hammer head tip enough to solder the A123's?
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Old Jun 25, 2007, 01:06 PM
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Quote:
Originally Posted by norbique
Is a 60W iron with a hammer head tip enough to solder the A123's?
I have not soldered too many of A123 cells, but as far as I know, I think that Yes.
Perhaps depend on maximum temperature, I have 85W lead free solderin station so I can select higher temperature than necesary..
of course DO NOT use lead-free Sn98Cu...., allways use Sn60Pb40 or Sn60Pb38Cu2 with quality flux.
Crystal505 / Kristal 505 flux (also available inside tube type solder) was loved one.

EDIT: Please excuse me for posting, and please stop hijacking this thread by off-topic questions. Soldering A123 has several another threads..
Overheating the A123 cell by soldering may be harmfull and degrade cell, so I will left this post here. But I will not respond anymore.
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Old Jul 26, 2007, 07:01 AM
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Hi Josep and thanks for the testing, it is really impressive! :-)

Laurent
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Last edited by orionRider; Jul 31, 2007 at 09:29 AM. Reason: removed question about overcharging, was already done earlier in the thread.
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Old Aug 27, 2007, 11:02 AM
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Do you have any other info about the EVList, it sounds interesting. I'd like to see the kokam video.


Quote:
Originally Posted by savuporo
In related news, this was posted to EVList just a day or so ago:


There is a explanation of why this took place posted as well:
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