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Hi.
A lithium cell supposed to be limited in charging voltage to 4.2000 volts.
If 4.5V is applied to a charged cell, but the charging current limited to 1mA and for only a few hours; should it harm the cell ? Would the cell rise past its 4.2000V limit anyway ?
which in turn means that the accuracy of the charge current itself during the more or less constant current phase can be way off, even 20 percent is ok.
It can be a LOT further off than 20%, the constant current during charging is one of the things that determines how fast you charge it, with lower currents been 'nicer' to the battery - likewise the end cut-off current, for maximum charge you can take it down to 130MA for the 18650's I was using, but if you cut off earlier the batteries will last longer, but won't be as highly charged. Interestingly the protection board I've now fitted cuts off well above that.
The Battery University says that a Lithium-ion battery must not be overcharged or trickle charged because it causes metallic lithium to replace the ions and it shorts the cell. What happens when you short a fully charged lithium-ion cell? A nasty explosion and fire. Lithium burns very hot like titanium and magnesium metals. See the "ium"?
Why do you want to trickle charge a Lithium-ion battery? They hold a charge for many years. I have the Lithium-ion battery from my daughter's first cell phone. It still has the same charge it had about 20 years ago.
Hi there,
Well i would not go any higher than maybe 20 percent, but yes you can go lower than 20 percent as long as you stay above the min charge acceptance level.
20% of what?.
Charging currents can (and do) quite happily vary massively, 0.2c is the 'nice' charge, and what I aimed for as it gives maximum charge capacity, but as much as 2c is perfectly normal for a fast charge, but only gives 80% charge capacity. The minimum cut off current is usually 0.05c for the same maximum charge.
I've been testing a GPS / GSM tracking unit with a solar cell to charge the Li-Ion battery, instead of from the usual 12/24 V supply.
The solar cell voltage is only a bit more than the battery voltage, so I haven't bothered with MPPT, and all I have used is the normal charging IC, the L6924D (https://www.st.com/resource/en/datasheet/l6924d.pdf). I've increased the maximum charging time to around 12 hours.
Obviously the charge rate will often be very low. From the voltage graphs, there are no clear points where charging starts or stops each day as the sun gets round to the solar cell. The fastest charge is approximately C/10 but it could be anywhere from zero up to that.
The charging IC is happy to work with a current-limited supply which is what the solar cell is, and to limit the voltage. The IC has a constant voltage phase, at the maximum voltage, and it stops charging when the current taken by the battery falls below a preset level. When run off the solar cell, the charging doesn't seem to stop and the voltage is held at the maximum voltage for a couple of hours until the sunlight leaves the solar cell.
Will that harm the battery? Does limiting at 4.1 V rather than 4.2 V make it easier on the battery?
Hi,
I thought it was obvious that it means 20 percent of max charge current.
In my experience the max charge rate is not a function of C, but is a function of the manufacturer's data sheet. It states what the max charge current is and sometimes other interesting info.
Which you would define as what? - they don't actually usually give a 'maximum' value, just a range of values getting worse the higher they go.
The 'default' value, which I would imagine you were referring to, as you didn't specify anything else, is only 0.2C.
They normally specify it in terms of C, as it's then correct for all models.
Here's one datasheet - although it's a bit brief.
https://www.batteryspace.com/prod-specs/NCR18650B.pdf
It suggests a maximum charge of 0.5C, but this only allows 95% charge - dropping to 0.2C allows 100% charge, I suppose it depends if you're in a rush