overcharged 18650 at 4.24V?
- Thread starter 00birdy
- Start date
That's what your flashlight is for!
You'll probably be OK this time. Just don't do it again!
45/70
Flashlight Enthusiast
Hi birdy. The actual specification is 4.20 +/-0.05 Volts. We usually refer to "4.20" Volts, simply because that's the middle ground and considered "ideal". It's also the best compromise between cell longevity and maximum capacity.
Most protection circuits don't kick in until around 4.25 Volts. Anyway, I wouldn't worry about it too much. As long as you don't do that all the time, you'll be fine.:) It's when the voltage gets up around 4.35 Volts, that you should be seriously concerned. Of course, a better charger would help.
Dave
jasonck08
Flashlight Enthusiast
You are fine, that is still within spec, but does more damage to the cell vs 4.15 or 4.2v. 4.20v is the industry "standard" for rating most LiCo cells capacity and cycle life.
excellent thanks for the information. I also read on a good reference site that if you do not charge to maximum capacity it should improve longevity significantly. Around approximately what would this number be? 41.5V? something like that?
41.5V may end badly for you. :poke: 4.15 is the sweet spot for charge capacity and longevity.
fyrstormer
Banned
I've had batteries overcharge to 4.5V before, or at least that's what their voltage was after sitting on the shelf for a few days. Who knows why it happened, but they still work fine.
I was about to ask the same
5% is meaningless, as 4.2 could read as 4.41.
1% get you the +/- .05v, so 4.25 could be fine, or over charged
.1% is when you can start trusting the 1/100th digit to being right
HKJ
Flashaholic
Many cheap meters will show a high value when the battery needs to be replaced.
If you get a unlikely value from a DMM, it might a very good idea to check with another meter or replace the batteries in the meter.
If you get a unlikely value from a DMM, it might a very good idea to check with another meter or replace the batteries in the meter.
45/70
Flashlight Enthusiast
It's possible that fyrstormer actually did charge a cell to 4.50 Volts, but I agree it's more plausible that the reading was inaccurate for some reason. Just the same there is no guarantee that just because a LiCo Li-Ion cell is charged to 4.50 Volts that it will vent. It's been done before by members here on the Forum, on purpose, and the cell did not always vent.
The problem with charging LiCo cells to such a high voltage is it is very likely that plating out of metallic lithium will occur within the cell. Metallic lithium, once formed, can never be reconverted, cannot be removed, and the associated ill effects are cumulative over time, eventually resulting in cell instability.
The existence of metallic lithium in any Li-Ion cell, can and eventually does, cause the cell to become unstable. Interestingly, this instability can not only cause the cell to vent when charged, or discharged, but the cell could vent at any time, eg. while you're carrying a light in your pocket, or when the light is stored away in a drawer. Unstable Li-Ion cells are something you really don't want to have to deal with.
If a LiCo cell has been knowingly overcharged to a voltage greater than ~4.35 Volts, it's best to discharge the cell and dispose of, or recycle it. As I said, there is no real guarantee that the cell will ever "vent with flame", but a process has likely been started within the cell that is cumulative, and also irreversible. The cell can never again be trusted, so it's best to recycle and move on.
Dave
The problem with charging LiCo cells to such a high voltage is it is very likely that plating out of metallic lithium will occur within the cell. Metallic lithium, once formed, can never be reconverted, cannot be removed, and the associated ill effects are cumulative over time, eventually resulting in cell instability.
The existence of metallic lithium in any Li-Ion cell, can and eventually does, cause the cell to become unstable. Interestingly, this instability can not only cause the cell to vent when charged, or discharged, but the cell could vent at any time, eg. while you're carrying a light in your pocket, or when the light is stored away in a drawer. Unstable Li-Ion cells are something you really don't want to have to deal with.
If a LiCo cell has been knowingly overcharged to a voltage greater than ~4.35 Volts, it's best to discharge the cell and dispose of, or recycle it. As I said, there is no real guarantee that the cell will ever "vent with flame", but a process has likely been started within the cell that is cumulative, and also irreversible. The cell can never again be trusted, so it's best to recycle and move on.
Dave
brembo
Enlightened
- Joined
- Jun 14, 2011
- Messages
- 203
This is a handy thread, as I was wondering about my craptastic Ultrafire 2400 cells (18650). For whatever reason one of them likes to charge to 4.27v and the other 4.19 or 4.2, that is IF my mulitmeter is accurate. All my AW cells I yank off charge around 4.15, I still do not trust the WF-139 self termination with the spendy AW units.
Is there a way to test my MM to see how accurate it really is? Let me rephrase that, is there an EASY idiot=proof way to test my tester?
Is there a way to test my MM to see how accurate it really is? Let me rephrase that, is there an EASY idiot=proof way to test my tester?
HKJ
Flashaholic
A .01% resistor would work too, as the accuracy of measuring resistance depends on the current source in the meter, and the voltage measuring portion, so if you get a 10k .01% wire wound resistor ($6 or so on digikey) you can check your accuracy with that. However, the DMM check in the link by HKJ looks very nice especially for the cost.
But remember even if you can calibrate a $5 meter, it doesnt mean it wont drift horribly. If you can pick up a nice meter, even used, do a check with a resistor, and if its within the manufacturers claimed accuracy, you can probably call it good enough (and all the guys that work with metrology cringe... i know ;p ) . I.E. a fluke 87 is listed as 0.2% for resistance, so if you take your .01% resistor, and get within 0.2% of nominal, you could generally assume 0.2% accuracy of the voltage measurements too. The 87 is listed as 0.05% accurate on voltages, so you'd need at least a 0.005% reference (or calibrated meter) to truly calibrate it, the resistor would just be a check. Though if you get a fluke meter, the obvious thing would be to just send it back to fluke for calibration, and when it comes back, you can safely assume the factory stated specs for a year. (or more then a year, because its probably not gonna drift *that* much, but you cant play that game if you need to be traceable ;) ))
But like I said, the resistor should be good enough checking your DMM for metering cells, and low cost. The DMMcheck reference HKJ linked would be even better, at not much of an increase in cost, and best would be a shiny new benchtop DMM that comes with a silly amount of 0's in the accuracy ratings and the price tag.
But remember even if you can calibrate a $5 meter, it doesnt mean it wont drift horribly. If you can pick up a nice meter, even used, do a check with a resistor, and if its within the manufacturers claimed accuracy, you can probably call it good enough (and all the guys that work with metrology cringe... i know ;p ) . I.E. a fluke 87 is listed as 0.2% for resistance, so if you take your .01% resistor, and get within 0.2% of nominal, you could generally assume 0.2% accuracy of the voltage measurements too. The 87 is listed as 0.05% accurate on voltages, so you'd need at least a 0.005% reference (or calibrated meter) to truly calibrate it, the resistor would just be a check. Though if you get a fluke meter, the obvious thing would be to just send it back to fluke for calibration, and when it comes back, you can safely assume the factory stated specs for a year. (or more then a year, because its probably not gonna drift *that* much, but you cant play that game if you need to be traceable ;) ))
But like I said, the resistor should be good enough checking your DMM for metering cells, and low cost. The DMMcheck reference HKJ linked would be even better, at not much of an increase in cost, and best would be a shiny new benchtop DMM that comes with a silly amount of 0's in the accuracy ratings and the price tag.
HKJ
Flashaholic
I have not tested that, but I would be a bit suspicious about that kind of test. The current generator might also depend on the voltage reference and if the input voltage divider is damaged you would never detect it with a ohm measurement.
I builte a precision voltage reference based on the texas instruments 5045, http://focus.ti.com/docs/prod/folders/print/ref5045.html
It's pretty cool. Although it states low temperature drift, I try and run it for 5 minutes of so before using. I had access to a recently calibrated Fluke that measured to some ridicuosly low voltage for reference when building.
It's pretty cool. Although it states low temperature drift, I try and run it for 5 minutes of so before using. I had access to a recently calibrated Fluke that measured to some ridicuosly low voltage for reference when building.
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