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Author Topic: Need education on 18650 lithium cells TIA for any help!  (Read 3431 times)

Offline infringer

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    • mopowah
Need education on 18650 lithium cells TIA for any help!
« on: October 23, 2013, 06:04:19 AM »
Okay,
 
 I have read tons of info on these cells. And while there is an inherent danger to using different cells for different applications I am curious about something that really need to have some solid evidence on.
 
 I have a drill battery pack and it contains some INR high discharge cells which are "designed for power tools" and I have some laptop cells that are designed  more geared for capacity rather than high discharge.
 
 Are you supposed to use them no you are not according to what I have read and I am not telling anyone to do it either this is strictly theory.
 
 Now here is the other key element of the battery pack you have the battery control system.
 
 Is it not true that the battery control system is designed to monitor health of a battery while in use or while being charged in all cases?
 
 If this is so than would the odds be that explosions would not result from using this battery in my drill the BCS does not know chemistry it just knows battery voltages, and temps I know this is true.
 
 I have a feeling that someone will chime in and say something to the order of don't do it if the BCS fails than you are screwed or it's your life or whatever do not do it but the real question is if the BCS fails in any occasion I have seen the battery does not work and if there were some quirky thing that would go wrong and allow the battery to keep running it would do the same thing no matter which cell you put into the pack right?
 
 The IMR or INR based cells may be able to tolerate it a little better but in truth how much of a percentage safer would you be in that case using a high discharge or not my guess is your safety would be roughly the same in any case if all of the safety fails just enough to let this occur you may have a very small percentage of a chance that your battery being an imr/inr is going to save you because it all boils down to well boiling point the electrolyte is going to vent out no matter what at the same temps right?
 
 So would my theory be correct or is there something more to this that I am missing ? I am not asking for someone to tell me its OK I just want to know if I am understanding what I am reading correctly.
 
 DO NOT TRY THIS IT IS ONLY THEORY AND DISCUSSION!
 
 Results are pretty ugly when these things go.

Specs of drill battery are as follows:
 
 Nominal Capacity*1    1,300mAh / 18A
 Nominal Voltage*2    3.60V
 Charge Method    Constant Current Constant Voltage
 Charge Voltage (V)    4.20
 Charge Current(C)    0.5
 Discharge Voltage (V)    2.50
 Discharge Current (C)    0.2
 Dimension (mm)
 Thickness / Width / Length    18.0 / – / 65.0
 Max Weight (g)    43.5
 Remark    NCA

laptops batteries are rated at a 4amp discharge from what I am reading.

Little ohms law might be of the order here...
 
 Resistance calculation R = V/I
 
 Voltage calculation V = IR
 
 Current calculation I = V/R
 
 To me the discharge rate seems to be safe for operation unless my calculations are incorrect?

I'm going to go out on a limb here and suspect that a lot of the hazord may be hype from the rare instances of bad cells people are pushing the warnings as regurgetation to cover themselves from liability due the the over publicized events that took place during the explosive lithum summer resulting in lots of recalls. Which is fair I would do the same and adhere to the warnings but we are discussing theory here while use is likely impractical for the application and I would not use them I want some solidity and would like to know the error or holes in my theory? Please do help further my education on this subject.
 
 NOTE I STILL DO NOT SUGGEST USING IMPROPRER CELLS AS WELL THIS IS ALL JUST THEORY AND SPECULATION I AM NOT AN EXPERT AND ANY FURTHER OPINONS SHOULD BE TREATED AS THEORY AS WELL DO NOT USE IMPROPER CELLS IT IS DANGEROUS!

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Offline e2matrix

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Re: Need education on 18650 lithium cells TIA for any help!
« Reply #1 on: October 24, 2013, 08:49:22 PM »
After spending many years on a forum where Li-Ion cells were a big part of the discussion  and even the 18650's in particular I'll say it's not hype but it doesn't happen often.   But when they do explode or catch fire it's very very dangerous and the fumes are very bad.   And explosions in sealed containers can be very serious.   I saw enough personal experiences by members on those forums to know it does happen - just not that often.   The biggest problem would happen with 2 or more cells in series when one cell would go bad or get weak.   Unbalanced cells means one cell is pushing a lot of current through another one and that's when most problems happen.   I've heard of them blowing while charging, discharging or just sitting there turned off (although I suspect there may have been an accidental short or turn on that happened shortly before the problem).   I've used and abused some Li-Ions for years and have never had an explosion but be careful -especially in charging or high current discharging.   


 

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