Old 04-08-2010, 12:42 AM #1
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Default Will they explode?

I have a collection of unprotected li-ion cells from a laptop battery, with voltages ranging from 2.8v to 1.9v. However, I've heard that these batteries can go open-circuit with copper build-up on the electrodes below a certain voltage, and are at risk of causing fire, but is there any limit below which I shouldn't dare charging? Or should I just give them a go but watch and measure temperature carefully? I've tried 2 of the 2.8V cells and they're barely warm after about 5 minutes of charging, now with around 3.8V across them in charger (getting into the "main cycle" of charging, I think?).

Any battery experts to offer their suggestions? I think I read 2.7v somewhere as the lowest before damage.


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Old 04-08-2010, 12:44 AM #2
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Default Re: Will they explode?

IIRC, a lith-ion rated for 3.6v should not be discharged below 2.4 or 2.7v..

Me thinks...
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Old 04-08-2010, 01:01 AM #3
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Default Re: Will they explode?

charliebruce;

I have used hundreds of "unprotected" lithium-ion cells.

1st question concerns the brand of the cells.

Name brands are much safer and durable.

2nd question is the application:

Single cell or multiple cell ?

If they are "name brand" and used in single cell application,
the ones with over 2 VDC should be OK.

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Old 04-08-2010, 01:04 AM #4
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Default Re: Will they explode?

Sony Fukushima 18650 cells labelled "G40" and "US17670GR", then stamped on "SET RKC250" - used in 3 sets of parallel in the battery I took them from, being charged in individually-regulated charger. Is that what you mean by "single cell"?

EDIT: if you mean each battery uses a single cell, then yes, it's an 18650.
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Old 04-08-2010, 01:11 AM #5
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Default Re: Will they explode?

They can explode,(more like catch fire) I've heard of very few violent "explosions". two, to be exact.
It is usually from overcharging IE: Putting a 3.0V in a 3.8V charger.
Just to be safe, you can put them in a old metal box, filing cabinet, etc. while charging.
Most often, it just ruins the mAh capacity of the batteries to let them become undercharged. <2.5.
I have never heard of one "exploding" from being undercharged. If they don't charge in 4-6 hours or they charge up in 5 minutes (correct V, but no A), it's time to buy new ones.
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Old 04-08-2010, 01:14 AM #6
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Default Re: Will they explode?

They're salvage so anything from them would be good - just so long as they don't damage my charger (or me) then I'm fine...

EDIT: at 3.9V, vaguely warm to the touch, on the cells that started at 2.8V. I haven't tried any of the worse ones yet. I'm thinking that I'll try anything greater than 2V (bin the 1.9V cells?).

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Old 04-08-2010, 02:33 AM #7
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Default Re: Will they explode?

Once a lithium cell is below 2 volts you can consider it a write off really. On rare occasions they can revive with a charge, but don't count on it.

As far as exploding goes: that's actually very rare unless you do physical damage to the cells. Such scenarios are possible when grossly overcharging or short circuiting cells, but the most common failure mode is that batteries simply don't hold sufficient charge.
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Old 04-08-2010, 03:15 AM #8
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Default Re: Will they explode?

charlie;

The good news is they are quality cells.

The bad news is they aren't #18650 cells.

The "US17670GR" denote 17mm by 67mm size with a capacity of only 1500mah.

They are a few years old, but you can still get some useful life from them.

By single cell, I mean is your final application a single cell.

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Old 04-08-2010, 03:28 AM #9
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Default Re: Will they explode?

Hi Charlie,

i think it's important how you charge the cells too. IIRC a battery like this shouldn't be charged for more than it's, "C", value. I.e. if the cell is rated 3.7V 1500mAh, it should only be charged at 3.7V at 1500mA for 1 hr. It can be charged at higher voltage for shorter time or higher mA for shorter time etc. I'll try and dig up a link for you and come back on this one but it's useful to know when your battery should be fully charged if your charger doesn't have an auto cutoff.

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Old 04-08-2010, 10:33 PM #10
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Default Re: Will they explode?

Quote:
Originally Posted by Morgan View Post
if the cell is rated 3.7V 1500mAh, it should only be charged at 3.7V
So you're saying all the chargers that charge the batteries to 4.2V are broken?

Quote:
Originally Posted by Benm View Post
Once a lithium cell is below 2 volts you can consider it a write off really. On rare occasions they can revive with a charge, but don't count on it.
It's still worth a try. Just watch it for the first few minutes to be sure it doesn't over-heat. Take it out after a few minutes and take a reading. If when you take it out the voltage of the battery falls dramatically, it's dead.

Sometimes the charger senses that it is too low of a voltage and doesn't attempt charging it. But if you have a charger that can charge two in parallel, you can try placing a good one in parallel with the bad. Again, do NOT leave this unattended and check the temp. Sometimes the good battery will jump start the bad one enough that the charger recognizes the pair as good and attempts a charge.

I've revived some from 0.1V before using this method.
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Old 04-08-2010, 10:52 PM #11
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Default Re: Will they explode?

Thanks for the advice everyone, the ones starting at 2.8 appear to have made a full recovery, a couple at 2.4 are charging fine with normal temperatures (no capacity test yet). I'm going to test-charge the really-low ones now, and I'll post back with my results.

@Larry, I didn't notice the size difference, I'd presumed from their overall similarity to DX 18650s that they actually were the same. Thanks for your research.

@Morgan, I'm happy with my charger, though I wasn't sure if it had an under-voltage protection. I believe that the charger I'm using handles each cell individually, but I'll test one by one, and if it doesn't charge, I'll try to use the parallel trick as suggested.

EDIT:
Cell 1/3: Started 2.044v, after 3min charging 3.43v, but is dropping by maybe 1mV every few seconds. Might be useable after full cycle.
Cell 2/3: Started 2.084v, after 3min charging 3.44v, same as above - though rate of voltage drop seems to tail off, so is this normal after removing it from the charger? I guess so.
Cell 3/3: Started 2.065v, same deal as above.

It's possibly because they were left to self-discharge naturally over time, rather than "forcibly" discharged by shorting or whatever, that I've been so lucky in getting them to come back to what seems a full recovery - is there any merit behind that theory?

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Old 04-09-2010, 07:34 PM #12
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Default Re: Will they explode?

If you have a Surefire, you've noticed 18650's don't fit the body tube. Your 17670's will, though. Just FYI...

And those cells that were below 2.6V? they might not hold as much, but they will be usable. If you have others, though, use those and just recycle these. I've noticed my older cells discharge on the shelf faster, and I'm getting ready to get rid of some of them purely because the shrink wrap is wearing out. I believe Radioshack recycles li-ion...
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