Tesla 18650 question

avoleoo

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Feb 12, 2014
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West Palm Beach, FL
Hi guys, got a tesla module and took it apart, measured some cells, comes up at 3000 - 3050mah - good, however, when discharging at 1A, which is what, like 0.3C, cells do get hot.

Does anyone has experience with these cells?

I had an impression that I could do at least 1.5C to 2C without them being too hot.
 
avoleoo said:
Does anyone has experience with these cells?
Yes, there are lots of threads about them, if you look around. Most have Tesla in teh title.

As for heat, well, remember these cells are cooled in the car they come from.

Plus, what rate are they used at in that car?

And how are you measuring the discharge current?
 
Okey, discharged another one at 3A and did not noticed any difference in heat. I'm assuming that it's just a working temperature. I can keep my fingers on it as long as I want, it's hot but not burning. Too bad i don't have a IR temp meter.
 
I've discharged Sanyo NCR18650GA cells at 1.5 C and they got to 80'C. I discharged a Tesla module at a little over 1 C with water coolant flowing through the pack, and the cells still got to about 46'C.

18650s just love getting hot...
 
This is a reputable test (Lygte) of a Sanyo (Panasonic) 18650BF,..very close to a Tesla spec cell...discharged at 5.0 amps.
Even at that rate (1.6 C) it only increases 25-30 deg over the complete discharge..
9tnFYW.png
 
Amberwolf: I am using Opus BT-C3400 to discharge them at 1A and for more discharging power I use iCharger 206B, so current and capacity measures comes from these chargers.

Hillhater: Assuming my inside temperature is 25C and your chart data, by the end of the discharge cycle I would get 55C which is very hot to touch, 60C is about where your fingers start to burn and you cant keep them on. So data seems to be in line with what I am getting. Discharging at 3A they do get hot, but never to the point where I cant keep my fingers on, feels hot but not burning.

I have some good Samsung 18650-26C that I have also tested and temperatures do feel the same. So maybe Tesla chemistry is not for high discharge rates, but is kind of slower discharge rate cells with good cooling system?

The whole reason I bought Tesla module was to eliminate heat, but it turns out they heat up as well. I am using Samsung cells for my pack and discharge them at 3A per cell, which is about 1.2C, pack is usually warm but never uncomfortable to touch and I'm in Florida so It's 28 - 30C outside. I'm starting to think that I worry too much about them being warm or slightly hot. It's just the way it should be.
 
If you can cool the cells in any way, they will last longer. You won't get any more energy out of them, nor will their efficiency change, but they will last longer.
The only cells which don't get as hot under discharge are things like the VTC6 and LG HG2 cells, which are rated for 30 amps per cell or something. Their internal resistance is lower, so less voltage drop, and therefore more amps - i.e. more efficiency.
But if yuo can keep them cool, even if it's by potting them in some thermally conductive epoxy with a short path to the aluminium enclosure, they will last longer.
 
Dude non-proper charging and discharging battery cells are not noticeable in short term other than making heat or reduced capacity.
Its better to use them with tesla bms itself.
 
avoleoo said:
..... Assuming my inside temperature is 25C and your chart data, by the end of the discharge cycle I would get 55C which is very hot to touch, 60C is about where your fingers start to burn and you cant keep them on. So data seems to be in line with what I am getting. ...
....i. Doubt it , that is a 5 amp discharge campared to your 1 amp, so the heat generated would be 25 times as much .
Tesla allow discharge rates up to 6-7C (15+ amps) ..in bursts.
 
I think there should be problem with your charger/tester. Because my Tesla 85kWh battery cell samples do not get significantly hot at 1C discharge rate. In fact thru my hands got a lot of 18650 cells and I cannot remember if at least one of them was significantly hot at 1C discharge rate.

Also I have already done some comparsion of Tesla 85kWh cell with Panasonic NCR18650BM (successor of BE cell) cells and after discharge tests up to 3C and more than 200 cycles at 100% and 50% DoD I can say that those cells are almost identical.

My conclusion, based on my long term tests in my own "lab" is that 85kWh battery Tesla cells are well balanced between the energy and power density in the current Panasonic 18650 NCA chemistry cells production line available on the market. But their cycle life and capacity fade course under my standard cycle life test condition 100% DoD* is pretty the same as on another Panasonic NCA chemistries, particularly NCR18650B, NCR18650BM, and NCR18650PF. I have tested all of those Panasonic NCA cells and all of them have after 1000 cycles at 100% DoD* nominal capacity slightly above 70% with almost identical capacity fade course.

*charge 0.5C to 4.2V@100mAh cut-off -- 10minut rest time -- 1C discharge to 2.5V -- 10min rest time. After each 50 cycles is inserted one nominal capacity test. Average ambient temperature ca 23°C
 
H8hErJ0.png


Allright, managed to hook up 206B to the laptop and attach the temp sensor. The only 18650 holder I had was cheap chinese one with thin wires, that explains the voltage sag, however, my goal was to check the temperature. So here is the discharge graph at 3.5A.

Ambient temperature 28C.
Max temp reached exactly 40C.
So 12C increase at 3.5A.

And Pajda, you were right, BT-C3400 was generating excessive heat, no heat issues using 206B, problem solved !

Be careful guys when taking apart tesla modules, I managed to damage one cell which resulted in thermal runaway today, luckily I was able to carry module outside of the garage and thanks god it did not triggered other cells. Made me rethink my safety procedures. Lot's of smoke and about 30inch high fireworks. Scared the @#$%@ out of me !!! Damaged corner which resulted in negative side venting.

H8hM2ww.jpg
 
avoleoo: Nice graph and good to hear that you found the problem.

In past I try lots of battery chargers as a battery testers and I was disappointend with most of them, even with FMA Powerlabs which measures significantly lower capacity. Now I am looking at BT-C3400 and that's the certainty of measuring nonsenses. Before I switched to ZKE TECH testers (also with minor problems) I found that Junsi iCharger series works relatively good as battery testers.
 
Right BT-C3400 is all over the place with results, very unreliable and heats up the batteries even at 0.5A disharge. Would not suggest to anyone. Yes iChargers are awesome !
 
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