My charger do not charge LiIon to 4.2V, is it faulty?
I see this question fairly often and most of the time the answer is: No, it works exactly as it is supposed to do.
Lets start with a typical battery datasheet:
It says the charging voltage must be 4.20 volt, it do not say anything about the battery voltage. It do also say what the standard charge current is (This is the charge current to use if you want the specified number of cycles, higher current will usual reduce the cycle life).
Further down in the datasheet there is a bit more explanation on how to do a standard charge. Cutoff means the current to stop charging at and C is the capacity of the cell, i.e. 0.02C is 0.02×3200 -> 64mA for this 3200mAh cell. I.e. when the charge current has dropped to 64mA, the charger must stop charging (Most chargers uses around 100mA as cutoff current, this means the cell with get slightly less filled and the charge will finish faster).
There is nothing about battery voltage in this, but the charger must supply the 64mA from 4.20 volt.
%202016-Charge.png)
Here is a real charge curve from one of my test stations. I have marked the constant current (CC) and constant voltage (CV). In the CV phase the charger will hold stable 4.20 volt and the current will drop until it is down to the cutoff value. I use the typical 100mA value.
%202016%20A-charge-1.0-Zoom.png)
Lets take a closer look on the voltage. The vertical yellow line indicates exactly where the charger stops charging.
As can be seen on the red voltage curve the voltage is 4.203 volt from the charger and the battery voltage is the same while charging in the CV phase. When the charger stops the voltage will drop immediately and continue to drop during the next hour. On this cell I measured 4.182 volt after one hour. Being a new cell in prime condition this is what can be expected, if the cell had been older or the charger had used a higher termination current the drop would have been larger.
%20%233.png)
The curve above is sort of ideal, here is a curve from a real charger with a used battery. The CV phase is not as flat (Due to resistance in the charger) and the voltage drop is larger, some of it is because the cell is older.
%20%233-Zoom.png)
Zooming in and the larger voltage drop is easy to see. This charger is charging with exactly 4.201 volt, but the battery will not measure more than 4.18 volt after the charger stops and after some minutes it will be 4.16 volt.
This is not a bad battery or nearly worn down battery, it is only about 10 months old.
What if my battery is above 4.20 volt?
If the battery after charging is 4.21 volt, does that mean the charger is defective?
Again the answer will often be no, there is some tolerances.
In the first datasheet there was an omission, usual the charge voltage includes a tolerance. The typical tolerance is +/- 0.05 volt, but other values are sometimes used (+/-1% or +/-0.03 volt). This means it is usual possible to add or subtract 0.05 volt to the above values and it is still correct.
If the battery comes out of the charger with 4.25 volt the charge is overcharging the battery, not enough to be dangerous, but the cell will have shorter cycle life.
If the voltage is below 4.10 volt the battery is probably worn down or the charger has a very low charge voltage and/or high termination current.
How do I check the charge voltage?
This requires a voltmeter and some metal foil strips. It can also requires some patience, depending on the meter.
I use copper foil, but aluminium foil from the kitchen can also be used. Be very careful if your use metal alligator clips like I do, the risk of shorts are fairly high and the result can be bad.
When the charger is nearly finished it is time to turn on the meter and read the voltage. This has to be done at regular intervals, like each 5 minutes. The highest value is the charge voltage.
My meter has a max function. Activate that and I can come back when the charger is finished and read the result.
Notes: The charger is not the same as from the curves above. A meter with peak capture cannot be used, it has to be maximum (Peak capture is very fast and will probably capture switching noise from the charger).
Disabling max again and the voltage is lower, due to the voltage drop when the charge current terminates (Not that much lower, this is a new battery).
It is also hopeless to measure later.
For the charger to be within specifications the charge voltage must be between 4.15 volt and 4.25 volt. Values below 4.15 volt will increase the lifetime of the battery and charge it to a lower capacity. Values above 4.25 volt will charge to a higher capacity and lower battery lifetime, getting much above 4.25 volt will also increase the danger.
Notes
Many cheap meter will show wrong voltage when the battery is about empty. If you charger suddenly overcharges or undercharges according to you meter, try replacing the battery in the meter.
My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/
great post to reffer to!
thanks for the restless work you do!
PLEASE NOTE
i do not work in "reviews, deals and codes" for the time being
maybe M4D M4X will return one day, but until then:
THANK YOU FOR YEARS OF YOUR SUPPORT AND FRIENDLY CONTACTS!
I’d rather err on the high side and end up with 4.2V after the battery settles than end up with 4.16-4.18V. I went through a couple chargers (xtar&nitecore) before I found a good one (liitokala) that would charge a cell the way I want it to.
You may like to charge that way, but it is not what the LiIon battery manufacturers recommends.
My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/
Nice explanation! Thanks.
link to djozz tests
Phew….that thread had be a little scared. When HKJ starts asking battery questions, the end is near
Good work as always!
Curiosity killed the cat……But I’m not a cat…..
Thank’s for this explanation. It is very much needed, I’m sure, judged from many posts from newbies (and also some old-timers).
I have a kind suggestion that you in the sentence:
“For the charger to be within specifications the voltage must be between 4.15 volt and 4.25 volt.”
change “voltage” to “charge voltage”, because some will refer to the picture just above (and then we have chaos again).
Thanks HKJ, I’ve been wondering why my hobby charger (Duratrax 235) stops before the battery reads 4.2. It must have a safer/long cell life type termination. I would have thought it could be adjusted but I don’t see a setting for it in the manual.
Good suggestion.
My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/
You probably get about 2% more performance and 10% less battery life that way. Go for it!
but the concept is valid if not the specific amounts.
I made up those numbers…
To Air is Human, to Respire….Divine.
the difference is not detectable in real use and difficult to test with our equipment as there are too many variables.nit picking at its finest.
Thanks for this. Occasionally I will encounter a charger that charges slightly over 4.2, but never more than 4.25. I had wondered if this was a safe voltage. And on a side note… What is the lowest safe discharge level for a lithium ion. I’d thought it was around 2.7 for a lot of them. Is this right?
My YouTube Channel- Flashlight and Headlamp Reviews
Depends on what you mean by safe (There is no risk of explosion at 2.7 volt), maybe I ought to write an article about that.
My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/
Your expertise with LiIons is very much appreciated by all of us, so if you do a post on how low a cell should be allowed to go that will meet with an equally warm reception.
Phil
Ok so it’s safe, that’s good… But what is an ideal voltage. I test many lights, some of which do not have low voltage protection… And I often wonder what is an ideal voltage… What’s a safe voltage, what’s unsafe? Below 2.7? What is the lowest voltage that is best for the longevity and health of the cell… Or what is a dangerous voltage. There is such scattered and contradictory information out there, so I’d like to know.
But there definitely needs to be an article written on the subject.
My YouTube Channel- Flashlight and Headlamp Reviews
Then you aren’t going to be happy since there are many “opinions” on those numbers. IMO, and in my own practice, I try to keep the voltage above 3.0v at all times and generally above 3.2v. There is VERY little capacity under 3.0v and the volts drop precipitously after that making it a slippery slope. There just is not a lot of good reason to push that far unless you are in an emergency situation. Why bother?
Once you go under 2.5 it gets dicey. Below 2.0 you are likely getting into damage area.
You don’t get immediate problems from over discharge, you get problems from charging AFTER over discharge and the damage it may incur.
To Air is Human, to Respire….Divine.
I have tested a lot of lights and have found most commonly some cutoff point is around 2.6-2.8, which is why I was wondering. I often wonder why it’s usually about this voltage. I understand there isn’t a real consensus, but I wonder why that number is common.
My YouTube Channel- Flashlight and Headlamp Reviews
It’s probably/mostly ‘safe’. That does not mean it’s optimal. Just look at the voltage drop on HKJ’s discharge graphs. Your choice.
To Air is Human, to Respire….Divine.
Thanks HKJ for the effort put in here for us. Lets hope everyone’s DMM’s read accurately.
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I finally got a charger that charges to 4.2V, i suspect the ML-10X chargers are just made with components with loose tolerances because they finish charging from 4.04-4.11V, battery tested immediately off the charger.
Its interesting to note the voltage drops slightly as soon as removed, i suppose this is not well covered on BLF (add to the li ion thread
), so my 4.20V charger right off the charger must mean its charging to 4.22ish volts. I’m not going to complain, after living with 4.04V for years i’m happy to get a full charge.
Thanks for posting this thread HKJ
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I did some tests once with batteries that came of at around 4.2v versus 4.17v (Nitecore I2 and Opus 3100 respectively) and from memory the difference was about 1.8% when I discharged them on my Accucel 6. Wouldn’t be useful or noticeable in real life usage for me.
This thread needs to be sticky’ed…
I have created a setting for my MC3000, with termination at 4.25V and 50mA, newer batteries come out at 4.20V, and drops to ~4.17V a couple hours later. But I don’t think there is any real benefit by doing so other than pleasing the absurd need of achieving exactly 4.20V.
USB power meter/tester thread
It’s great to have articles written by someone that everyone trusts, keep going hkj, and thanks for the effort
homer
Another informative HKJ thread.
Opinions and metaphors can be interesting.
But it’s immensely more valuable to have conclusions that are supported by concrete facts and measurements.
Thanks for the excellent and informative write-up HKJ
very informative post, thanks HKJ for your effort
HKJ, thanks a lot for putting this down in a nice post for reference.
It was much needed. Ought to be stickied.
That would be good, and thanks for this one.
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So that’s how you test charging voltage. Thanks for doing this guide, I’m getting my Fluke out right now.
Thank you!
Hi again, HKJ.
As always, thanks for your posts. They are really interesting.
Keeping in mind the information shown on this post, and the information shown on this old post, ( http://budgetlightforum.com/node/5495 ), are these sentences right?
Please confirm them for clarity sake.
1) Charging Li-ion cells to 4,1V means cells will have more lifetime, but less energy.
2) Charging Li-ion cells to 4,25V means cells will have less lifetime, but more energy.
3) Termination current high will make voltage drop after termination high.
4) Termination current low will make voltage drop after termination low.
5) Charging a cell to 4,2V with low current termination will give more performance than charging the same cell to 4,2V with high current termination.
6) The best possible charge to obtain maximum performance from a Li-ion cell is to charge it to 4,25V, and a very low termination current. (Forget about cell lifetime).
And some questions:
It is really interesting to go to 0,025A termination current, or even lower in big capacity cells (forget about charge times) or it doesn´t worth it?
Do you recomend to modify termination current setting, depending on the capacity of the cell?
For example:
5000mAh cells -> 0,125A termination current.
4000mAh cells -> 0,1A termination current.
3000mAh cells -> 0,075A termination current.
2000mAh cells -> 0,05A termination current.
1000mAh cells -> 0,025A termination current.
Again, thank you very much for your work.
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