> Is Low Voltage Protection Necessary?
hope the OP also learned the answer to his question :student:
I’m not positive if a protected battery would be in any better shape, after sitting for a year or two. Protection circuits have a parasitic drain on the cell, in order to operate. Once the cell is down to 2.5v, and the protection kicks in, does the cell not continue to drain (albeit slowly)?
The danger is that you won’t know what the real voltage of the cell is. It reads 0v on your DMM, because the protection has tripped. But, does that mean the cell is 2.4v, and therefore safe to recharge? Or, does it mean the cell is 0.1v, and therefore unsafe to recharge? You won’t know. You could recharge a cell that has degraded, and has internal shorts. It could just catch fire at any time, and the protection circuit does nothing for internal shorts.
well
most chargers will not try to charge a cell under some minimum limit
the danger is that if they do, the cell may charge, but now it is a time bomb and may have internal shorts
or it may catch on fire while charging
it isn;t actually hazardous to overdischarge
just when you try to charge or use it later, do the problems occur
wle
Yeah, but a lot of chargers will try to charge a cell as low as 0v. Most good ones will at least do it slowly, which is better than just dumping 2 amps into it. Most of Xtar’s chargers do that. But, you really should measure a cell’s voltage yourself (with a DMM), if you’re at all unsure about its discharge state.
Or if you have a fancy charger that warns you about low voltage, that would be good too. Maybe something like the Skyray MC3000 does that? (I have no idea, since I don’t have one.)
i thought usually they would just sit there and not start a charge, if it is too low
may or may not read the volts for you
it just acts like ‘i do not see a cell here to charge’
wle
I can’t find an answer to whether or not protection circuits add parasitic drain after tripping. Sounds like the positive terminal is disconnected after tripping. The cell could still self discharge over time though.
Depends on the design, but the IC needs power if it’s still monitoring. They use very little, though, maybe less than self discharge. In any case, a cell that’s been drained for years below the trip… I’d want to know the real voltage.
Really?
That’s annoying. I hadn’t seen that mentioned in any reviews or anything… How long (roughly) do you think would it take to drain the 14500 below safe recharging levels?
it would be prudent to use Protected 14500 in the AA Tool, since the light itself has no built in LVP.
I would disable the tail LEDs.
or just use Eneloop
See post #12 for amp draw of tailcap;
Why are Protection Circuits Needed?
“Figure 1 illustrates the top of an 18650 cell for Li-ion with built-in safety features.”
Learn what causes Li-ion to fail and what to do in case of fire.
“A mild short will only cause elevated self-discharge and the heat buildup is minimal because the discharging power is very low. If enough microscopic metallic particles converge on one spot, a sizable current begins to flow between the electrodes of the cell, and the spot heats up and weakens. As a small water leak in a faulty hydro dam can develop into a torrent and take a structure down, so too can heat buildup damage the insulation layer in a cell and cause an electrical short. The temperature can quickly reach 500C (932F), at which point the cell catches fire or it explodes. This thermal runaway that occurs is known as “venting with flame.” “Rapid disassembly” is the preferred term by the battery industry.”
https://batteryuniversity.com/learn/article/premature_voltage_cut_off
“Most mobile phones, laptops and other portable devices turn off when the lithium-ion battery reaches 3.00V/cell on discharge. At this point the battery has about 5 percent capacity left. Manufacturers choose this voltage threshold to preserve some energy for housekeeping, as well as to reduce battery stress and allow for some self-discharge if the battery is not immediately recharged. This grace period in empty state can last several months until self-discharge lowers the voltage of Li-ion to about 2.50V/cell, at which point the protection circuit opens and most packs become unserviceable with a regular charger. ( See BU-808a: How to awaken Sleeping Li-ion )”
===
“Li-ion batteries contain a protection circuit that shields the battery against abuse. This important safeguard also turns the battery off and makes it unusable if over-discharged. Slipping into sleep mode can happen when storing a Li-ion pack in a discharged state for any length of time as self-discharge would gradually deplete the remaining charge. Depending on the manufacturer, the protection circuit of a Li-ion cuts off between 2.2 and 2.9V/cell. “
You could have it both ways if the charger gives the tripped cell a quick pulse to untrip the protection and then checks the real Voltage to make sure it’s not too low……don’t know if there are chargers that do it this way or not.
This is the way.
yes :+1:
If cells already have built in protection, why are add on protection circuits needed I’m wondering?
maybe I dont understand the question, but let me try and break it down for you
specific to LVP
1. Protected Cells have LVP
2. UnProtected Cells do not have LVP
3. Anduril lights have LVP in the driver, so they do not need to use Protected battery cells.
4. Most lights do not have LVP in the driver, and they should be used with battery cells that have LVP in the battery, since it is not in the driver.
make sense?
I guess I misunderstood the article to mean all LIs have protection circuits already built in.
they do, but they are overvoltage, overpressure, overheat protections in the cap
Low Voltage protection is a fourth type, that does not exist in all cells. They specify either Protected or UnProtected, depending on application.
High drain tends to be unprotected, and best used with drivers like Anduril that have LVP in the driver… and so on
So reports range from 5 days to a couple of months. Lumintop themselves claim “One month, in theory”. Not good, but not terrible…
I would generally recharge a cell after using it anyway, so it’d not likely go more than 48hrs and not be stored in the light.
Do the 14500s from Fenix have sufficient LVP?
I use the Fenix protected 14500s. They are a OK cell but I have not put the LVP to a test.