Author Topic: EEVblog #515 - Battery Ionic Resistance Investigation  (Read 16196 times)

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Offline EEVblog

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EEVblog #515 - Battery Ionic Resistance Investigation
« on: September 04, 2013, 09:39:55 pm »
Dave investigates the ionic electro-chemical resistance of some Alkaline batteries under light multimeter input loading and an unusual physical battery phenomena, and explains how it differs drastically from the datasheet internal resistance value. He also finds a surprising result showing two types of Alkaline battery construction with different properties.
It demonstrates the usefulness of a high resolution bench multimeter.

« Last Edit: September 04, 2013, 09:45:03 pm by EEVblog »
 

Offline IanB

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #1 on: September 04, 2013, 10:24:06 pm »
Puzzled. I'm part way through the video, but when you switch the 10 M input impedance on and off, doesn't the trend look exactly like charging and discharging a capacitor? Curious why you are referring to it as an ionic resistance effect rather than an electrode capacitance effect?
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Offline EEVblog

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #2 on: September 04, 2013, 10:29:43 pm »
Curious why you are referring to it as an ionic resistance effect rather than an electrode capacitance effect?

Because that's the common encompassing industry terminology I am familiar with for the effect. I rarely recall ever having heard the term electrode capacitance used. Maybe in some more obscure research papers or something?

Also, pure capacitance alone would not explain some of the effects seen later in the video, like the full recovery and sudden drops.
« Last Edit: September 04, 2013, 10:47:41 pm by EEVblog »
 

Offline IanB

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #3 on: September 04, 2013, 10:46:52 pm »
There are obviously several complicated things going on there, but I think capacitance is part of it. I'm sure the equivalent circuit of an electrochemical cell includes capacitance as well as resistance and one or more sources of EMF.

What seems to happen when the cell is open circuit is that some chemical reaction charges up the battery an extra little bit, and when you apply the 10 M load this extra little bit of charge gets discharged through the meter.

Interestingly, I have read that in order to successfully use a Weston cell as a voltage reference you have to measure its voltage under null conditions to avoid disturbing the reading. This video clearly illustrates what can happen if you don't take care of such details  :)
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Offline CodeJunkie

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #4 on: September 04, 2013, 10:47:44 pm »
Long time viewer, first time commenter :)

You said in your video that the 9 volt batteries contained 6 “AAAA” batteries or cells. I know that some 9V batteries contain 4 “AAAA” cells but every time I have ripped one open it was six sort of blobs stacked on top of each other (see http://www.bristolwatch.com/ele/batt.htm for picture). Maybe a physical construction difference contributes to the different readings during the “squeeze” test. Would be curious to see the insides of each 9 volt.
 

Offline ejeffrey

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #5 on: September 05, 2013, 12:16:05 am »
There are obviously several complicated things going on there, but I think capacitance is part of it. I'm sure the equivalent circuit of an electrochemical cell includes capacitance as well as resistance and one or more sources of EMF.

Yes, to a point.  The chemical reactions are slow.  In an AC circuit model you would a phase delay as a capacitance.  However, the underlying mechanism in batteries is the diffusion of ions, not a physical capacitance.  Also, a (linear) AC circuit model does not describe the full behavior of a battery.
 

Offline Winston

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #6 on: September 05, 2013, 12:36:34 am »
Tear the four batteries apart to see if their internal construction explains the common pressure sensitivity between the Verta and Coles and the Energizer and Duracell.
 

Offline IanB

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #7 on: September 05, 2013, 12:37:39 am »
There are obviously several complicated things going on there, but I think capacitance is part of it. I'm sure the equivalent circuit of an electrochemical cell includes capacitance as well as resistance and one or more sources of EMF.

Yes, to a point.  The chemical reactions are slow.  In an AC circuit model you would a phase delay as a capacitance.  However, the underlying mechanism in batteries is the diffusion of ions, not a physical capacitance.  Also, a (linear) AC circuit model does not describe the full behavior of a battery.

I appreciate the kind of processes that happen inside a cell and how they are governed. Yet, in the search for a mechanism for what we observe we can make a hypothesis. My hypothesis is this: when the cell is resting, there is a process that moves ions towards the electrodes where they deposit their charge. The electrode voltage increases until the increased potential balances the driving force and the voltage plateaus. The accumulation of charge at the electrodes manifests as a tiny capacitance. As soon as the 10 M discharge path is applied through the meter the capacitance can discharge and the voltage can drop until the steady current flow is balanced by the electrochemical rate process that was driving the voltage up.

The part that is interesting is what this tiny charge accumulation process is? Clearly when a larger load is applied the cell can supply way more current and can manifest a DC internal resistance far lower than the 8.3k that Dave estimated. I observe the same with NiMH cells: there is a high internal resistance measured under very small loads, and a low internal resistance measured under large loads. I do not know the explanation, other than a commonly used term "surface charge".
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Offline EEVblog

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #8 on: September 05, 2013, 12:58:49 am »
What seems to happen when the cell is open circuit is that some chemical reaction charges up the battery an extra little bit, and when you apply the 10 M load this extra little bit of charge gets discharged through the meter.

Yes, but I showed a case where that voltage recovered to the original voltage over IIRC a 15min period.
Obviously lots of chemical and manufacturing voodoo going on here.
 

Offline robrenz

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #9 on: September 05, 2013, 12:59:16 am »
Interesting video, I would be very interested in the "measuring battery internal resistance video"

Maybe now that an Agilent bench meter has trend plot, people will accept how extremely useful it is.

Offline EEVblog

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #10 on: September 05, 2013, 01:10:28 am »
Maybe now that an Agilent bench meter has trend plot, people will accept how extremely useful it is.

and the fact that it allows greater than the nominal 6.5 digit resolution.
 

Offline robrenz

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #11 on: September 05, 2013, 01:24:01 am »
Maybe now that an Agilent bench meter has trend plot, people will accept how extremely useful it is.

and the fact that it allows greater than the nominal 6.5 digit resolution.

Yes, I use that extended resolution on my 8846A all the time. There are a lot of things on the Agilent trend chart that look more versatile than Flukes trend plot. Maybe its  time to push fluke for a firmware update to add some updated fuctionality ::)

Offline Psi

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #12 on: September 05, 2013, 01:44:16 am »
Back in the days of walkmans i remember it being common to squash the AA batteries to get a bit more life out of them when the walkman started to slow down.
The usual way was to gently bite them all over and put lots of dents into the metal case.  Used to get you 20min or so more music :)
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Offline redben

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #13 on: September 05, 2013, 08:14:45 am »
Hi, really nice video Dave.
I was wondering if measuring impute impedance of a multimeter with an other multimeter is possible ??
Or at least will not cause any trouble to the equipment ??
Thanks in advance for answers...
 

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #14 on: September 05, 2013, 09:32:33 am »
should be interesting to see what happens if you apply a negative pressure: in theory you should get the opposite trend plot, but you will need a vacuum pump or something like that.
 

Online Dr. Frank

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #15 on: September 05, 2013, 10:46:27 am »
I think, the voltage change by 'loading' the cell with 0.9µA (10MOhm) or +/- 25pA (hi ohm mode) has something to do with the ionic polarization effect.


That's a quasi static displacement of ionic charges to or apart from the electrodes by (small) electrical fields. This will change the EMK EMF, as this displacement is equivalent to the charging/discharging of a 'real' capacitor.
That's also one of the reasons, why the ESR is measured by AC fields, not by static DC measurements.

Ah, that will also explain the drastic decrease of the EMF when 10MOhm are attached.. this will "destroy" the Polarization in first order, not really discharge the cell noteworthy. And it's reversible, as the switching to hi ohm reveals

There's a lot of literature in wiki-land about that, but it's no easy read, and it has to be carefully analysed, how this effect can be explained in relationship with those small currents involved in Daves experiment.

Rem.: That effect also had to be observed, when measuring those good old Weston Standard Cells.
But I do not remember details, either.

Frank
« Last Edit: September 05, 2013, 11:25:24 am by Dr. Frank »
 

Offline PA4TIM

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #16 on: September 05, 2013, 12:12:02 pm »
Nice to play with a meter but like you said, it is not a scientific test. Though, some things are easy to exclude by doing the right measurements. For instance use a DC source and a nulldetector (indeed like the standard cells) Some spectroscope meters also use a DC bias.
The pressure can be EMF, warmth of your hand, increasing the leakage current  by sweat ect. But the test is simple. Just put it on the bench en press with a piece of teflon on it instead with your fingers.

An other very interesting thing you can do with that trendplot. Put it in 10G mode. Put it in the shadow and in such a way the sun will shine through a small hole and travels in time over the battery. For instance when the suns goes down. We do not want to fry it. You will the the voltage climb and go down. Eveb indoors inspring and a late evening sun that little bit of light was enough. Very funny. But you can use that oven you made too.
 
After 5 minutes, Dave talks about the 1 kHz impedance. But that is not even close to be correct. The impedance is measured by a 1kHz sinewave and not using a pulse during a very small time. Also R does not allways stay constant. It changes with current and charge. Enigizer has a pdf over impedance of their batteries.

Impedance is made out or a pure resistive part ( materials like metal, and other stuff used) and an ionic part. The chemical proces ( electrolyte conduction, ion mobility, electrode surface area)

There are several tests:

DC resistance, first load the battery with a very small current and let it stabilize (the chemical proces), Then load it with a larger current and measure the voltdrop. The best way is to do the loadpart with a pulse during  100 ms and a longer recovery so deeper layers have some time to distribute charge to the surface layers again

There are two subvariants. One is repeating pulses (100 ms) that load it and pull a "normal" current. The other is shorting the battery 1 time with something like 0.1 Ohm and measure the Voltdrop but this is very hard to measure. This is also called a flash amp test.

AC resistance, for those small batteries this is most times done at 1 kHz. It measures |Z| and that will be lower as the DC resistance. Sometimes much lower. DC resistance varies with load (and current) and charge left . That also explains the behaviour in the video. With such a small load, resistance will be much higher so the voltdrop higher as expected. ( Think of it as the the ESR of a ceramic capacitor, very low at 100 kHz upto 100KOhms's at 50 Hz )  For instance an AA cel I tested (varta) had 6 Ohms DC resistance when (pulse) loaded with 100 Ohm but it droped to 0.9 Ohm when loaded with 15 Ohm (and inbetween with a very light stabilizing load) So loaded with 10M it will be higher than 6 Ohm. (at 10GOhm ther leakage from battery plus to minus pole over the dirty fingerprints, dust etc on the outside can be higher as the meter loading it)

Spectroscopy, here they measure all parts of the impedance and split them up in Z = ( R+jX ) and it tells you something about the charge or health too.  I allready measured this before I knew that name. It was strange I could not find anything about the way I measured and the results that give you an indication of the health of the cell.  But this week I found out they do it but it is called spectroscopy in the battery world.

I used an impedance bridge and a VNA. However both methodes give the same parameters. It   measures  magnitude and phase.
Randles model of a battery gives two resistors in series and a capacitance parallel over one resistor. A charged battery or new battery has a certain Rs and allmost no capacitance. It is a even a tiny bit inductive if it is a larger cell. If charge drops the Rs increases and the imaginair part becomes more capacitive. A bad rechargable battery will show more capacitance as a good discharged one. But capacitance of a disharged one is always higher as when charged. I read somewhere a rule of tumb would be 1F per 100 Ah for Randles model.


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Offline saturation

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #17 on: September 05, 2013, 03:32:54 pm »
... also how you can use low cost alkaline batteries, even NiMH as a 'transfer reference' when comparing 2 meters against each other, say doing poor man's voltage calibration.  With good DMMs and very high input impedance, the battery's  Vout is stable for minutes at ~ 1 ppm as clearly shown in the videos.

One thing I've tried is you can series connect those 9V together to get higher voltages for comparison, but as the batteries equalize among themselves, you'll get about 10ppm stability or less.

Trend plot  :-+  I wish I had it, didn't realize I use it so often as I use graphs for monitoring and stat functions for looking at variations quickly :palm: but it was cheaper to get multiple 3456a and plot with a PC than a single new DMM.


Maybe now that an Agilent bench meter has trend plot, people will accept how extremely useful it is.

and the fact that it allows greater than the nominal 6.5 digit resolution.
« Last Edit: September 05, 2013, 03:36:36 pm by saturation »
Best Wishes,

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Offline 99tito99

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #18 on: September 05, 2013, 09:45:53 pm »
It's Time For A Battery Teardown

   

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Offline PA4TIM

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #19 on: September 05, 2013, 10:09:08 pm »
http://www.wisebread.com/the-40-hidden-inside-a-12v-battery Funny, a 9V battery is made out of AAA cells, and on it's turn a AAA (or AA, do not know for sure) is made out of button cells. So what' s inside a button cel ? :-) (look the top video, after a minute or soo you see the AA/AAA
Not much, this is an empty one. It was allready switched polarity. After more as a day, just resting on a shelf I heard a bang anf found this.



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Offline Dread

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #20 on: September 06, 2013, 06:34:25 am »
Loved the video Dave.  I am looking forward to a part 2 which would be great if it focuses on what happens when a battery dies and how it behaves when the load is removed and then put back on.  We know they recover but by how much and another question is how much extra power do you get on recovery and how much more by heating them up a bit.

Just last week I needed to label 10 wires with (1-10).  As Murphy would have it I could not find the needed 4x AAA batteries to power my label machine anywhere in the house (I always remove the batteries from seldom used equipment) so I ended up trying to scavenge them from one of my sons toys and of course those were dead.
So I heated them a little with a lighter held a few inches below them so they got about 30 deg hotter than room temp and quickly put them in the machine. The batteries easily powered it up and printed out the labels with power to spare.
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Offline Harvs

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #21 on: September 06, 2013, 09:29:13 am »
I was wondering if measuring impute impedance of a multimeter with an other multimeter is possible ??
Or at least will not cause any trouble to the equipment ??

If it's a standard 10M handheld DMM then this isn't a problem and is easy to measure.  Just put the DMM under test into voltage mode, where the input op-amp will hold the opposite end of the input resistor to the same potential as the other jack, then use you're second meter to measure it's resistance.  You also get to see what voltage your second DMM is measure resistance at.

Whilst not wanting to plug my own stuff, I used this principle for reverse leakage testing here which you may want to look at.
 

Offline PA4TIM

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #22 on: September 06, 2013, 10:51:23 am »
Harvs, great piece about that leakage current measurement. It is so simple that I wonder why I never tought about it. I have done such tests by measuring the voltage over a 10M resistor, never thinking about the fact that resistance is allready inside most meters (but you must know the Rin of the meter ( read manual or use an other  meter indeed)  and use the manual range switching as Rin is different between ranges. (btw: I have the agilent U1252A, also in blue great meter,)
www.pa4tim.nl my collection measurement gear and experiments Also lots of info about network analyse
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Offline saturation

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #23 on: September 06, 2013, 04:56:32 pm »
FWIW that's one of the few HH DMMs I know that have ~> 1 gigaohm input impedance at <= 1V range.  Its a reason I got one too when it was dumped 2-3 years ago in the USA.


Harvs, great piece about that leakage current measurement. It is so simple that I wonder why I never tought about it. I have done such tests by measuring the voltage over a 10M resistor, never thinking about the fact that resistance is allready inside most meters (but you must know the Rin of the meter ( read manual or use an other  meter indeed)  and use the manual range switching as Rin is different between ranges. (btw: I have the agilent U1252A, also in blue great meter,)
Best Wishes,

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alm

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Re: EEVblog #515 - Battery Ionic Resistance Investigation
« Reply #24 on: September 06, 2013, 05:34:13 pm »
Several cheap handheld DMMs have >> 10 MOhm input impedance for the mV ranges. I believe the Uni-T UT-61E is one such meter.
 


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