18650 protection?

[TwinBlade]

I got some 18650's in today. After charging 2 of them, I threw one in my Fenix TK12 and turned it up to max and let it run. I just got done as far as I was concerned at about 2.25 hours (WOW!) (maybe had about 75-100 lumens output or comparable to my Inova T1) and I checked it on my volt meter. 2.25 volts seems like a pretty low number to me, but I have no idea what I am doing anyways.

Just curious if this low voltage protection goes lower than 2.25 or if the cell protection sucks...

TIA all. :thumbsup:

 

[jasonck08]

If they read 2.25v @ resting voltage then they have been way over discharged. The protection circuit did not kick in, and the cells are now permanently damaged.

For most LiCo cells, the protection circuit should kick in at ~2.75v under load. Once the cell goes that low, the voltage should rebound to around 3.2 or 3.3v and the cell should be recharged immediately.

 

[TwinBlade]

Ok, the cell has been resting for about 2 hours and reads 3.61v. I am very confused.

The high output is 280 lumens on max on that Fenix TK12. Very high drain on a battery. What am I being told when it shows 2.25v after immediately removing it and then showing 3.61v after 2 hours at rest? Is the cell ok?

I don;t have the first damn clue about anything regarding this, so start at the elementary level with me.

Would the high current draw on the battery affect the voltage protection?

I dunno nothing about any of this. I hate not knowing things...

 

[mvyrmnd]

It sounds like the voltage has rebounded OK, but the protection circuit should never have let it get that low under load.

What brand/capacity 18650's are they?

 

[jasonck08]

That's not a normal amount of voltage rebound for a cell. Are you sure your multimeter is accurate? Or maybe did you measured 3.25v then it rebounded to 3.61? That would be a lot more reasonable.

Secondly, the TK12 is only discharging the battery at about 1A. I wouldn't consider that a "very high drain" that's a pretty average current draw and any decent 18650 will handle that with ease.

 

[ateallthepies]

Is there a reason why the protection is not nearer 3 volts than 2.75? Then the rebound voltage would be higher and maybe more kind on the cell?

Steve.

 

[TwinBlade]

They are Ultrafire 3000 mAH batteries.

I am 100% positive my multi meter is dead nuts on the money. My other digital peak chargers that I can use as multi meters as well gave me the same identical readings.

I charged the one that I ran down to 2.25v last night and woke up and it had 4.19v of charge in it.

I guess I will have to treat these as unprotected cells and when the light gets noticeably dim, I will pull the battery.

Just irritating that you get something and it doesn't do what it is supposed to. I bought 4 cells and the ultrafire charger for like $38 from some dude in Hong Kong off ebay. It looked like a great deal to me. The runtime was certainly impressive at well over 2 hours, and up to 2 hours with no noticeable brightness decline.

 

[pae77]

It's frequently a crap shoot buying batteries on Ebay. There's lots of counterfeits out there.

In any case, the advice generally given is that it's not a good practice to rely on the protection circuitry to prevent over discharge. It's better to try not to over discharge Li-ion batteries and regard the protection circuitry as a backup fail-safe kind of safety system, but try to avoid actually triggering it. They tend to let the batteries get more discharged than is good for them and perhaps they can wear out or get damaged the more they are used and I get the impression they may not be all that reliable in the first place.

 

[TwinBlade]

It's frequently a crap shoot buying batteries on Ebay. There's lots of counterfeits out there.

In any case, the advice generally given is that it's not a good practice to rely on the protection circuitry to prevent over discharge. It's better to try not to over discharge Li-ion batteries and regard the protection circuitry as a backup fail-safe kind of safety system, but try to avoid actually triggering it. They tend to let the batteries get more discharged than is good for them and perhaps they can wear out or get damaged the more they are used and I get the impression they may not be all that reliable in the first place.

I am certainly inclined to believe everything you said having witnessed it first hand.

it was a very noticeable decrease in output to me even before it hit 2.25v. I will, as i stated, regard these batteries as unprotected. I cannot dispute a runtime on them. so far, 2 batteries put out 2 solid hours of output on my Fenix TK12. That is quite a bit of longevity as far as I am concerned.

I appreciate you confirming the knowledge and concerns regarding these batteries and counterfeits. I am of the opinion that the price was good enough to deal with it.:thumbsup::thumbsup: