Protected Li-Ions and over-discharge

[Syndil]

I have an unprotected Solarforce 18650 battery that I am fairly certain I have over-discharged, since I can't get it to charge to more than half a volt. At first I thought the battery was probably just low-quality junk, but then I started searching and reading in the forums and found that over-discharge can permanently damage a Li-Ion battery. Oops. I'm not a flashlight enthusiast, so I did not know anything about that, and frequently ran the battery all the way down, to where the bulb was extremely dim. So naturally I want to replace this battery.

From what I have read in the forums, some people claim that protected Li-Ion cells do not protect the cells from over-discharge, but only protect it from overheating, while others claim that protected means it will protect from over-discharge.

Which is it? I would like it if I didn't have to consciously worry about over-discharging my battery. These things aren't cheap!

 

[fivemega]

I have an unprotected Solarforce 18650 battery that I am fairly certain I have over-discharged, since I can't get it to charge to more than half a volt. At first I thought the battery was probably just low-quality junk, but then I started searching and reading in the forums and found that over-discharge can permanently damage a Li-Ion battery. Oops. I'm not a flashlight enthusiast, so I did not know anything about that, and frequently ran the battery all the way down, to where the bulb was extremely dim. So naturally I want to replace this battery.

From what I have read in the forums, some people claim that protected Li-Ion cells do not protect the cells from over-discharge, but only protect it from overheating, while others claim that protected means it will protect from over-discharge.

Which is it? I would like it if I didn't have to consciously worry about over-discharging my battery. These things aren't cheap!

When current draw is very low, protection circuit does not protect the cells from over-discharge but it does work well with normal or higher current draw.
BTW, never use unprotected cells if you are not familiar to li-ion cells.

 

[Justin Case]

When current draw is very low, protection circuit does not protect the cells from over-discharge but it does work well with normal or higher current draw.
BTW, never use unprotected cells if you are not familiar to li-ion cells.

My examinations are hardly exhaustive, but the Seiko and Texas Instruments Li-ion protection ICs I've examined don't seem to specify any sort of overdischarge protection limitation due to current draw. Either the voltage is ok, or it is too low.

 

[jasonck08]

My examinations are hardly exhaustive, but the Seiko and Texas Instruments Li-ion protection ICs I've examined don't seem to specify any sort of overdischarge protection limitation due to current draw. Either the voltage is ok, or it is too low.

I'm not electrical engineer, but as far as I know the IC doesn't directly provide the overcurrent protection. It's the mosfets on the PCB that do this.

 

[Quension]

Actually, what fivemega is getting at, is that the protection ICs are fine at cutting off discharge at a certain voltage threshold. The problem is that the voltage will naturally depress under high load, so the cutoff is tuned based on expected load in order to get the battery's full capacity. Under very low load, the battery will be discharged a lot more before it reaches that voltage, which may actually be too far.

 

[VidPro]

The problem is that the voltage will naturally depress under high load, so the cutoff is tuned based on expected load in order to get the battery's full capacity. Under very low load, the battery will be discharged a lot more before it reaches that voltage, which may actually be too far.

very well said.
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to the OP , i have very very slowly drained protected, to the 2.4v - 2.5V spec, and had them disconnect, and they STILL recharged everytime.
If the cell is properly protected, you can drain it down to this low spec level, and it should NOT DIE completly in that one occurance.
DEPENDING totally on the ammount of time it sits at that low level. And if other things are going ary, like internal self discharge, dipping it down even further.

frequently ran the battery all the way down, to where the bulb was extremely dim.
just very bad idea , if you had protected cells, especially with BULB items, that would be the minimum.

at any rate now you know, and you should also know that the li-ions do not live forever, one that self discharges, or doesnt hold a charge is bad anyways too.

there are single cell light items that will CUT-off either by default due to the drivers, or because they have built in cutoffs. In those a person might Get Away without protection, but an incan bulb will always destroy a Unprotected cell, unless the user intervenes quickly, and even then well . . ..

 

[Justin Case]

I'm not electrical engineer, but as far as I know the IC doesn't directly provide the overcurrent protection. It's the mosfets on the PCB that do this.

The Seiko IC, for example, has built-in FETs that shut down when an overdischarge condition is detected.

 

[Syndil]

Thank you for all the helpful replies, everyone. After some more forum-searching, I decided to order a pair of protected Trustfires to replace my Solarforce. Not the best, but a decent value.

This quote I found to be quite amusing:

BTW, never use unprotected cells if you are not familiar to li-ion cells.

A catch-22. I would have only known that if I had been familiar with Li-Ion cells in the first place.

 

[Syndil]

So I got my Trustfires finally. Took almost a month for them to get here! Guess I shouldn't be surprised.

Anyway, I tested the voltage when they arrived, and they were both around 4 volts. So I put them in the charger, one at a time, charged them up till the light turned green, and now they both read 4.21 volts. I assume that's a good thing.

However, when I put them in my Solarforce L600 and click the switch, nothing happens. After reading through the forums, I'm not really surprised at this. Anything I can do to make it work? Or should I just replace the halogen bulb in this with an LED thingy?

 

[MikeAusC]

Halogen bulbs when switched on draw ten times their normal current for a fraction of a second.

This trips the protection circuit on the battery.

LEDs don't have this current surge.

 

[ASheep]

Syndil, as MikeAusC said, Halogens and most other incans draw a higher current than the protection circuit can handle at startup.
It is recommended to use IMR safe chemistry cells in high powered incandescents, as they can handle a far higher current than standard li-ions. IMR's are more resistant to over-discharge, but are not indestructible.
They also have a far lower chance of a vent with flame failure, which is far safer for someone who isn't familiar with li-ions.

 

[Syndil]

I can get it to turn on if I rapidly click the switch a few times. However, the thought of it burning up on me is not appealing. If I had known about all this beforehand, I would have never purchased the thing. Who knew something as mundane as a flashlight--two batteries and a bulb--could be this much hassle.

 

[radellaf]

I'm with you there. Given that digital camera packs, for instance, are the same type of battery, with pretty much the same protection circuits, and often charged on cheap knock-off chargers...it seems ... like something, somewhere, is being done wrong if 18650s aren't just as trustworthy.

Problem #1 is that most of the chargers out there overcharge, and there's really no engineering excuse for making a charger that does that.
Problem #2 is that a light without built-in low-battery-shutoff is a pretty dicey proposition, and it seems like most lights don't have it. Combine that with easy availability of unprotected cells and, well... I hope the lights and/or batteries at least come with warnings/instructions. Can't think of anything we could do to make the situation better, though, other than what CPF already does, which is make all this stuff pretty high up on any google search.
Excuse there I assume is cost. It's not more expensive to make a charger that doesn't overcharge. It is very much more expensive to put electronics in an incandescent light. For LED lights, maybe a small cost savings in some cases.

---

looking on lighthound I see this in a solarforce review:
"I bought new Ultrafire batteries but the draw from the bulb is so high that the protection circuit of the batteries would kick in. I could rapid click the tailcap several times and it would fire up but thats hardly a tactical solution. I read on Candle Power Forums that this light works best with AW 18650 batteries."

Maybe try some of those? You'd be another in a long line of Trust/Ultra-fire buyers who aren't happy with the product and end up replacing them with "good" cells. Whether AW's cells would have a protection circuit compatible with your particular light is probably on these forums somewhere... as would be the current the light draws. If it's over 3 amps continuous then, yeah, IMR cells are looking like a better idea as that's over the safe rate for even the new 2900mAh regular cells.

 

[Syndil]

Thanks so much for that detailed reply. I think I will just use my L600 as is until it refuses to work any more. I only hope that when it fails, it is not catastrophic. But I have no interest in becoming a flashlight enthusiast, so I will not be spending any more money on this light. I doubt I will get my money's worth out of the light, and that is upsetting to someone like me. The Trustfires are protected, so they probably won't blow up, right?

 

[radellaf]

I don't know any actual probabilities, but "probably" they won't

From what I've read the usual way *fire cells fail is they just die. The protection should keep them from getting damaged by over-discharge. The weakest cell should cut out rather than getting too low. Best for your batteries not to run them down all the way like that, but if you do, yes, they are _supposed_ to stay safe. Were it me, I'd check with a voltmeter if that happens just to be sure.

The one thing they're not effectively protected against leaving them in a charger that trickle charges them. Dunno what charger you use, but basic safety would be: don't leave them in there 6+ hours, don't leave them unattended, and pull them out right when it says they're done. Lots of advice on here about charging and chargers. Would be a good idea to read some guidelines and maybe specifics about your particular charger.

They should protect themselves if the charger has a major fault and tries to seriously overcharge them.

Sorry you ended up with a light like that. It's really "for" enthusiasts. Any 18650 setup other than AW cells and a Pila charger, I consider "enthusiast".

At least give a thought to selling it on the buy/sell/trade part of this board and using the proceeds to get some 500+ lumen LED light you'll like better. Maybe a polestar A6 or Fenix TK40, both run off AAs. If it's working well enough, cool, but us enthusiasts just hate to see someone not enjoying their light when we _know_ there's the perfect one out there for you