More about XTAR chargers’ 0V activation function

4 posts / 0 new
Last post
xtarflashlight
xtarflashlight's picture
Offline
Last seen: 3 hours 57 min ago
Joined: 01/21/2013 - 21:25
Posts: 205
Location: Shenzhen
More about XTAR chargers’ 0V activation function

You may use xtar chargers’ 0V activation function to bring some over-discharged batteries back to life. So how does this 0V activation function work? Is it so powerful? More details as below.

A Li-ion battery might fall asleep due to over-discharge. And the sleep condition can occur when storing the battery in a discharged state, in which self-discharge brings the voltage to the cut-off point. The internal voltage of the battery is low enough so that the protection circuit won’t allow the battery to be charged. With the protection circuit tripped, it even reads 0 volts. Many chargers couldn’t charge this battery that is below a certain voltage, often in the 2.5V-2.8V range, because it will overheat the battery. It either further damages the battery or causes it to vent because of high internal resistance, and leading to overheating.

But some well designed smart chargers with 0V activation function, can revive the over-discharged batteries again. This kind of charger can gently charge the battery at a reduced rate, often 1/10th the charging rate, until the cell voltage has risen above a certain threshold. And the chance of overheating during this trickle charging is also reduced. Once above this threshold, often in the 2.5V-2.8V range, the cell will be charged at normal rate until it’s fully charged. In short, the trickle charge mode is engaged by the charger, so as to sneak the voltage higher till the protection circuit allows normal operation .

For most over-discharged batteries, it can be activated by the 0V activation function of the XTAR chargers. If it’s not activating, it’s because the cell may be faulty and cannot be repaired. This battery is not recommended to continue using it.

zoulas
zoulas's picture
Offline
Last seen: 6 hours 55 min ago
Joined: 06/01/2020 - 08:35
Posts: 1945

Nice explanation.

Lumeniac
Lumeniac's picture
Offline
Last seen: 5 days 23 hours ago
Joined: 12/19/2016 - 13:47
Posts: 795
Location: Russia

xtar charges helped me several times with baterries which were around 1v.

 

nbut they couldnt revive cells which were close to actual 0v

 

so calling it 0v charging is not that correct.

 

though, again, overall, xtar charged helps a lot with deeply discharged cells

 

 

def_nvar
Offline
Last seen: 1 day 18 hours ago
Joined: 11/01/2020 - 05:42
Posts: 75

there is a reason many chargers will not allow charging cells that have been depleted beyond 2.5V:

deep discharge -> copper cathode partially dissolves into electrolyte
“revive”-charge -> copper gets deposited back onto cathode again, but not evenly -> dendrides form, sticking out toward the separator
if you get lucky-> you notice high self-discharge, the cell gets warm
if you get unlucky -> thermal runaway, sometime in the (not so) far future, preferrably when least expected.

so unless the cell has its own protection, charging it after it dropped below 2.5V gives you a (time)bomb with thermite-like properties.
but if it is protected, then that will have prevented dangerous discharging, it just turned off the output.

If you want to dispose of it safely, attach to 100 Ohm resistor, leave them outside (keep dry!) for a few days.
Then recycle it (where you normally bring used-up batteries in your country).

I wouldn’t risk charging a cell below 2.5V.