Does forcing a li-ion's protection circuit every time shorten it's lifespan?

[Paul520]

With an 18500 protected battery, does overcharging it every time so as to force it's protection to shut off the charging cause any harm, shorten it's life span, or cause any dangerous situation?

Thanks, Paul

 

[baterija]

With an 18500 protected battery, does overcharging it every time so as to force it's protection to shut off the charging cause any harm, shorten it's life span, or cause any dangerous situation?l

Here's a good link to answer your question. Typically the PCB will stop the over charging at a point that is already less than ideal for cell life span and safety. With a charger designed to stop before the fail safe of the PCB you have 2 safeties in place. Both have to fail for bad things to happen. If the PCB is bad and you are relying on it...

 

[Paul520]

Thanks for the link. I asked this because the wolf eyes charger (that I haven't yet bought) does just that and was trying to find out how long the WE batteries will last that way vs getting a Pila IBC charger and AW batts separately.

ps- that link didn't really answer that question.

 

[LuxLuthor]

Paul, the short answer to your question is "yes." baterija's link did answer your question, with relevant portions quoted with my red highlighting. Giving a precise % loss would require detailed testing, and would occur in proportion to the degree & frequency of overcharging. Also the exact PCB overcharge setting, and overall cell construction would impact results. (Violet highlighting also addresses impact of over-discharging which you did not ask about.)

[FONT=Verdana, Arial, Helvetica, sans-serif]No trickle charge is applied because lithium-ion is unable to absorb overcharge. A continuous trickle charge above 4.05V/cell would causes plating of metallic lithium that could lead to instabilities and compromise safety. Instead, a brief topping charge is provided to compensate for the small self-discharge the battery and its protective circuit consume. Depending on the battery, a topping charge may be repeated once every 20 days. Typically, the charge kicks in when the open terminal voltage drops to 4.05V/cell and turns off at a high 4.20V/cell.

What happens if a battery is inadvertently overcharged? lithium-ion is designed to operate safely within their normal operating voltage but become unstable if charged to higher voltages. When charging above 4.30V, the cell causes plating of metallic lithium on the anode; the cathode material becomes an oxidizing agent, loses stability and releases oxygen. Overcharging causes the cell to heat up. If left unattended, the cell could vent with flame.

Much attention is focused to avoid over-charging and over-discharging. Commercial lithium ion packs contain a protection circuits that limit the charge voltage to 4.30V/cell, 0.10 volts higher than the voltage threshold of the charger. Temperature sensing disconnects the charge if the cell temperature approaches 90°C (194°F), and a mechanical pressure switch on many cells permanently interrupt the current path if a safe pressure threshold is exceeded. Exceptions are made on some spinel (manganese) packs containing one or two small cells.

Extreme low voltage must also be prevented. The safety circuit is designed to cut off the current path if the battery is inadvertently discharged below 2.50V/cell. At this voltage, most circuits render the battery unserviceable and a recharge on a regular charger is not possible.
There are several safeguards to prevent excessive discharge. The equipment protects the battery by cutting off when the cell reaches 2.7 to 3.0V/cell. Battery manufacturers ship the batteries with a 40% charge to allow some self-discharge during storage. Advanced batteries contain a wake-up feature in which the protection circuit only starts to draw current after the battery has been activated with a brief charge. This allows prolonged storage.

In spite of these preventive measures, over-discharge does occur. Advanced battery analyzers (Cadex C7000 series) feature a 'boost' function that provides a gentle charge current to activate the safety circuit and re-energize the cells if discharged too deeply. A full charge and analysis follows.

If the cells have dwelled at 1.5V/cell and lower for a few days, however, a recharge should be avoided. Copper shunts may have formed inside the cells, leading a partial or total electrical short. The cell becomes unstable. Charging such a battery would cause excessive heat and safety could not be assured. [/FONT]

 

[Paul520]

Thanks. I'll have to get the Pila IBC and AW cells if I plan to start using any rechargeable system. Wonder how many ppl buy these lights and never think about charging dangers.

 

[Illum]

AW cells on DSD chargers by experience will turn the LED from red to green instead of red to alternating [indicating a cutoff]...but as the batteries age it becomes more and more likely that the charger will go from red to alternating indicating that the cell was full and the PCB cuts it off...so for now I have no way of knowing when to dump the cells out because it never tells me when it finished, only when it decides to cutoff

my AW cells:candle:
4x17670
4x14500
2xRCR123A