Testing 0V cells

Tostaki

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Hi there,

I have a doubt in mind when testing the 0v cells.

Some are beeping at the continuity test, some others are not. So far this is obvious.
But which ones need to be discarded rigth away ?

Thank you !
 

Korishan

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The ones that have no continuity at all toss. Something has caused the CID to pop and it is not safe to reset it.

As long as there is resistance, you can test the cell. But you don't want to have 0 resistance, either. I believe the resistance numbers are somewhere around 100mOhm, if I remember correctly (which is possibly not the case). I'm sure someone will give you the numbers in reply soon.

But no reading all, toss, definitely
 

DarkRaven

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Well, certainly the ones with continuity. But I would discard all of them right away.
 

Tostaki

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Thanks. I'll discard all those beeping

From my readings of datasheet, internal resistance is somewhere near 70 mOhms but at 1kHz.
 

DarkRaven

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Sorry, I've just realized that there is some confusion going on and probably on my behalf. How do you test the cells for continuity?
 

Korishan

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@DarkRaven: Some use the opus to test. Others, such as myself, use the MM and set it to Ohms and probe each end. That'll give you a pretty good indication of what the resistance is.

As Tostaki said, a lot of the IR's at time of manufacture is around 70 Ohms. But, different manufacturers vary depending on chemistry and process. So, I'd say, as high as 125, maybe 150 Ohm resistance. Stuff higher than that might be worth using only in single cell applications (ie, flashlights, etc).
 

DarkRaven

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I was wondering how Tostaki did it specifically. I've just tried a 0V cell with my MM, it says around 6000 Ohm and no continuity (both correct and reversed polarity). A charged cell however provides continuity when tested with reversed polarity and no measureable resistance.

I'm having a hard time to figure out how that fits together and whether my advice to discard the cell WITH continuity makes sense, especially without knowing how he did it. I'm blaming my tiredness, it is 02:40 AM :D
 

neilmc

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I'm not taking much notice of the resistance value on 0v cells until they have some charge in them (if they will take a slow charge at all without heating up).I do test to see if they are open circuit. If they are open circuit, they're trash.

On a normally working cell the resistance changesdepending on the state of charge/discharge. ( typically somewhere between 30 and 120 milliohms).

I have got some normally working cells from 0v cells with capacities over 2000ma, but it's not that common. They seem to yield good results much less often. As a time management thing, it might be worth putting them into a pile to maybe test one day when when you run out of other cells to process. They're more time consuming for less reward.

Really low voltage cells on the other hand often test really well (eg 0.1v and up). I give them an initial charge at about 50ma each before putting them through the test cycle.

My hobby charger just displays "connection break" on actual 0v cells, so I usually parallel the 0v cell with a 1v cell just long enough for the charger to be happy that I've got something connected. (there won't be much current flowing from a heavily discharged cell at 1v to a 0v cell). I then charge at 50ma NiMh manual mode until it's about 2.6v and then switch to lipo mode at about 50-100ma per cell until fully charged, and then into the Lii 500 for capacity testing.

Just for the time involved, 0v cells might not be worth it unless you're really short on cells. I'm probably getting only 20% of 0v cells working normally with capacities over 1600ma.

I had 6 dark blue LG cells come out of a battery this week all at 0v. One was open circuit. The other 5 all recovered ok, but with capacities onlybetween 1300 and 1700mah. (4 of them were 1600-1700)
 

Tostaki

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Sorry, I went to bed after my last reply.

To test the cells for continuity, I am using my multimeter in beeper / diode mode. It beeps when the circuit is closed.
Sometimes it displays a voltage, then not beeping, sometimes not.

I am using this mode ussually to find chip's leads connected together on a PCB.
At this time I did not tested any 0V cell. Only the ones above 1v for now. As the stock of 0v grows I was wondering which ones are safe to test and which ones must be avoided.
 

DarkRaven

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neilmc said:
I'm not taking much notice of the resistance value on 0v cells until they have some charge in them (if they will take a slow charge at all without heating up).I do test to see if they are open circuit. If they are open circuit, they're trash.

I always thought I knew what open circuit means. I never came across a german word for open circuit but I just found it: https://dict.leo.org/englisch-deutsch/Leerlauf
I never saw the word Leerlauf being used in this context, interesting. I guess hardly anyone here knows that Leerlauf applies here, unlike Kurzschluss which is german for short circuit.

You say you're not taking notice of the resistance, but isn't testing for open circuit exactly that? Isn't open circuit a high resistance connection up to a connection break (when the circuit is open, literally) with almost infinite resistance and the opposite to a short circuit?

The cell I tested yesterday, where I said it had a resistance of 6000 Ohm, actually has 6 MOhm, I've been reading this wrong. So it is 6.000.000 Ohm, that is a lot and definitely open circuit?

Continuity then is a connection between two points and more like a short circuit than open circuit. The threshold for continuity on my MM is 20 Ohm. If you test the cell for continuity with a MM and put the negative probe to the cells negative terminal and the positive probe to the positive terminal and get continuity between them, the cell has shorted and can't be used anymore. So is testing for open circuit is done by testing for continuity or by testing the resistance? Continuity is more like a resistance quick check, so to say.

And is this comparable to a charged cell which should have a very low resistance? I'm not getting any continuity on a charged cell, which is good because if I did then there is a short circuit, but I do get continuity when the polarity is reversed, i.e. negative probe to positive terminal and positive probe to negative terminal. That doesn't happen with my 0V cell (of which I "sadly" only have one at the moment, quite s small sample size). And I never get any measurable resistance which probably makes sense as the internal + external resistance of the cell should barely reach the minimum the MM can measure which is 0.1 Ohm + margin of error so probably more like 0.2 Ohm.

So, with all that in mind, what are we looking for at a 0V cell?

Continuity is bad because the cell would be shorted, so low resistance between the terminals is bad. But open circuit, high resistance, is bad as well. Does this make any sense?
 

neilmc

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DarkRaven said:
neilmc said:
I'm not taking much notice of the resistance value on 0v cells until they have some charge in them (if they will take a slow charge at all without heating up).I do test to see if they are open circuit. If they are open circuit, they're trash.

I always thought I knew what open circuit means. I never came across a german word for open circuit but I just found it: https://dict.leo.org/englisch-deutsch/Leerlauf
I never saw the word Leerlauf being used in this context, interesting. I guess hardly anyone here knows that Leerlauf applies here, unlike Kurzschluss which is german for short circuit.

You say you're not taking notice of the resistance, but isn't testing for open circuit exactly that? Isn't open circuit a high resistance connection up to a connection break (when the circuit is open, literally) with almost infinite resistance and the opposite to a short circuit?

The cell I tested yesterday, where I said it had a resistance of 6000 Ohm, actually has 6 MOhm, I've been reading this wrong. So it is 6.000.000 Ohm, that is a lot and definitely open circuit?

Continuity then is a connection between two points and more like a short circuit than open circuit. The threshold for continuity on my MM is 20 Ohm. If you test the cell for continuity with a MM and put the negative probe to the cells negative terminal and the positive probe to the positive terminal and get continuity between them, the cell has shorted and can't be used anymore. So is testing for open circuit is done by testing for continuity or by testing the resistance? Continuity is more like a resistance quick check, so to say.

And is this comparable to a charged cell which should have a very low resistance? I'm not getting any continuity on a charged cell, which is good because if I did then there is a short circuit, but I do get continuity when the polarity is reversed, i.e. negative probe to positive terminal and positive probe to negative terminal. That doesn't happen with my 0V cell (of which I "sadly" only have one at the moment, quite s small sample size). And I never get any measurable resistance which probably makes sense as the internal + external resistance of the cell should barely reach the minimum the MM can measure which is 0.1 Ohm + margin of error so probably more like 0.2 Ohm.

So, with all that in mind, what are we looking for at a 0V cell?

Continuity is bad because the cell would be shorted, so low resistance between the terminals is bad. But open circuit, high resistance, is bad as well. Does this make any sense?
Terminology is fun :)

I take open circuit as no connection between the positive and negative end. Likely a popped CID. If testing for open circuit though, I would junk something that's extremely high resistance even before trying to revive it. I'd certainly count something as 6M ohm as extremely high.

Normal cells are well under 1 ohm in resistance. It changes a bit depending on the cell model and charge state, but generally something between about 30 milliohm and 130mohm

A milliohm is only one thousandth of an ohm, so we're talking a bit over one tenth of an ohm at the high end. On an auto-ranging digital multimeter, you should see a lower case m for milli and an upper case M for mega.

The reason I say that I don't take that much notice on a 0v cell is that 0v is so far out of its normal operating range. So if I saw 6 ohms, I'd still try to recover it even though it might be 60 times higher than typical. If it quickly heated up with under 100ma of charge current and wouldn't hold a voltage at all off the charger, I'd give up on it pretty quickly.

I had 12 2000mah samsung cells today out of an ancient looking HP brick of a battery. 9 of them were zero volts. 8 of those got hot at only 100ma of charge current and when they did get over 2v, they dropped back near zero in under a minute. I don't think they're ever coming back to life. One of the zero volt cells did hold at about 2.6v for half an hour, so it's still a maybe for testing. 3 out of the pack had about 0.3v. I don't know what they're like yet.

0v cells are a lot of effort for usually not a lot of return, but there are some rare nicesurprises. I'm processing some zero cells for fun at the moment, but I have got a 0v box sat aside for testing later when I've worked my way through the better prospects and I've got time to deal with them. It might only be a 10% useful return on them.
 

DarkRaven

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Yeah I'm not going to bother with 0V cells anyway, just trying to figure if we are giving the right advice to people who want to try and, like in this case, try to pre-select the cells that may be worth testing.
 

DCkiwi

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neilmc said:
[...]
Just for the time involved, 0v cells might not be worth it unless you're really short on cells. I'm probably getting only 20% of 0v cells working normally with capacities over 1600ma.
[...]

I totally agree.

As the quote from 'the princess bride' goes ... there's a big difference between dead and mostly dead. My Xtar queen ant charger does a nice job of distinguishing, without any 'bump charging' (which I used to do with my hobby chargers).

And I think it worthwhile noting here, especially for all you 0v nay sayers ... there is a MASSIVE difference in finding a three four five year old cell with dust on that is 0v than even a brand new cell that has been thrashed (actively discharged) down that low. The former often is ok, the later is almost always wrecked.
 

Korishan

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sil5er said:
And I think it worthwhile noting here, especially for all you 0v nay sayers ... there is a MASSIVE difference in finding a three four five year old cell with dust on that is 0v than even a brand new cell that has been thrashed (actively discharged) down that low. The former often is ok, the later is almost always wrecked.

Most of us are grabbing used stock. So most likely, the 0V cells have been abused. If we know that the packs are new-old stock and haven't been used, then that's a different story all together.
 

jdeadman

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sil5er said:
neilmc said:
[...]
Just for the time involved, 0v cells might not be worth it unless you're really short on cells. I'm probably getting only 20% of 0v cells working normally with capacities over 1600ma.
[...]

I totally agree.

As the quote from 'the princess bride' goes ... there's a big difference between dead and mostly dead. My Xtar queen ant charger does a nice job of distinguishing, without any 'bump charging' (which I used to do with my hobby chargers).

And I think it worthwhile noting here, especially for all you 0v nay sayers ... there is a MASSIVE difference in finding a three four five year old cell with dust on that is 0v than even a brand new cell that has been thrashed (actively discharged) down that low. The former often is ok, the later is almost always wrecked.

lol on the princess bride quote!!! And yes I always try and force the dead cells back to life. After a charge/ discharge/Charge cycle if they do not hang onto their voltage they go in the bin. But I am always looking for cells as my supply is really slow
 

Oderus420

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I find a high percentage of 0V cells are bad so while I will test them, I have little to no hope that they'll test OK.

Most are heaters which means they self-discharge to 0V pretty quick and that's not good.
 

jdeadman

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I have about a 30% return rate so far with my <.05V cells. Anything above that I'm at 80% return to good operating use.
 

DCkiwi

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Korishan said:
@DarkRaven: Some use the opus to test. Others, such as myself, use the MM and set it to Ohms and probe each end. That'll give you a pretty good indication of what the resistance is.

something doesnt sound right about this.

if i attach my DMM probes to a cell/battery, plugged into the ohms/mA port, it blows a fuse.

and i thought there were actual special machines dedicated to IR measurement ...

and i thought Internal 'Resistance' was different from resistance in some important way... and there was ongoing discussion (lack of concensus) about how to even measure it 'the best' ...

is it really true that they are the same and can be measured on a regular multimeter set to resistance?

without a wheatstone bridge even?

Im confused.
 

Bubba

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if i attach my DMM probes to a cell/battery, plugged into the ohms/mA port, it blows a fuse.


Strange your meter has ohms and mA on the same port. Normally they are separate since to measure Current such as mA it is a short.

That's why you blew the fuse.

Also using a Multimeter to measure resistance doesn't work. When you measure resistance using a MM, the meter applies a voltage across the leads (they actually apply a constant current to the leads). So for measuring cells this is a no-no. Don't do it.
 

DarkRaven

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The DMM should have a separate port for current and a "main" port for everything else. Good way to blow the fuse: Forget to put the probe back to the other port after you've measured current and before measuring voltage of a cell next time.

The resistance of a cell is the internal resistance + external resistance. The internal resistance can't be measured with a meter. The IR is usually far too small to measure with a usual DMM since its resolution will not be good enough. IR is usually calculated by applying a known load and observing the voltage. If it's a really bad cell I guess you can measure it with a good DMM though because the IR will be so high that it actually matters.

I've never tested this though if it's really viable nor do I even know if my meter would be good enough. I usually don't care about the IR. Capacity and IR are causally connected to each other, if you know one then you get a good indication of what the other is. Combined with the capacity spec of the cell there is no more need to know the IR as far as evalutating the condition of a cell goes.
 
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