EEVblog #515 - Battery Ionic Resistance Investigation - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: September 04, 2013, 09:39:55 pm
content: 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.

author: IanB
author_rank: Super Contributor
timestamp: September 04, 2013, 10:24:06 pm
content: 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?

author: EEVblog
author_rank: Unknown
timestamp: September 04, 2013, 10:29:43 pm
content: Quote from: IanB on September 04, 2013, 10:24:06 pmBecause 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.

author: IanB
author_rank: Super Contributor
timestamp: September 04, 2013, 10:46:52 pm
content: 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

author: CodeJunkie
author_rank: Newbie
timestamp: September 04, 2013, 10:47:44 pm
content: Long time viewer, first time commenterYou 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 (seehttp://www.bristolwatch.com/ele/batt.htmfor 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.

author: ejeffrey
author_rank: Super Contributor
timestamp: September 05, 2013, 12:16:05 am
content: Quote from: IanB on September 04, 2013, 10:46:52 pmYes, 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.

author: Winston
author_rank: Regular Contributor
timestamp: September 05, 2013, 12:36:34 am
content: 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.

author: IanB
author_rank: Super Contributor
timestamp: September 05, 2013, 12:37:39 am
content: Quote from: ejeffrey on September 05, 2013, 12:16:05 amI 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".

author: EEVblog
author_rank: Unknown
timestamp: September 05, 2013, 12:58:49 am
content: Quote from: IanB on September 04, 2013, 10:46:52 pmYes, 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.

author: robrenz
author_rank: Super Contributor
timestamp: September 05, 2013, 12:59:16 am
content: 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.

author: EEVblog
author_rank: Unknown
timestamp: September 05, 2013, 01:10:28 am
content: Quote from: robrenz on September 05, 2013, 12:59:16 amand the fact that it allows greater than the nominal 6.5 digit resolution.

author: robrenz
author_rank: Super Contributor
timestamp: September 05, 2013, 01:24:01 am
content: Quote from: EEVblog on September 05, 2013, 01:10:28 amYes, 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

author: Psi
author_rank: Super Contributor
timestamp: September 05, 2013, 01:44:16 am
content: 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

author: redben
author_rank: Contributor
timestamp: September 05, 2013, 08:14:45 am
content: 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...

author: Unknown
author_rank: Unknown
timestamp: September 05, 2013, 09:32:33 am
content: 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.

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 05, 2013, 10:46:27 am
content: I think, the voltage change by 'loading' the cell with 0.9µA (10MOhm) or +/- 25pA (hi ohm mode) has something to do with theionic polarizationeffect.That's a quasi static displacement of ionic charges to or apart from the electrodes by(small)electrical fields. This will change theEMKEMF, 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 revealsThere'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

author: PA4TIM
author_rank: Super Contributor
timestamp: September 05, 2013, 12:12:02 pm
content: 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 againThere 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.

author: saturation
author_rank: Super Contributor
timestamp: September 05, 2013, 03:32:54 pm
content: ... 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 plotI 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 quicklybut it was cheaper to get multiple 3456a and plot with a PC than a single new DMM.Quote from: EEVblog on September 05, 2013, 01:10:28 am

author: 99tito99
author_rank: Regular Contributor
timestamp: September 05, 2013, 09:45:53 pm
content: It's Time For A Battery TeardownCheers, Mark***************

author: PA4TIM
author_rank: Super Contributor
timestamp: September 05, 2013, 10:09:08 pm
content: http://www.wisebread.com/the-40-hidden-inside-a-12v-batteryFunny, 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/AAANot 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.

author: Dread
author_rank: Regular Contributor
timestamp: September 06, 2013, 06:34:25 am
content: 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.

author: Harvs
author_rank: Super Contributor
timestamp: September 06, 2013, 09:29:13 am
content: Quote from: redben on September 05, 2013, 08:14:45 amIf 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 testingherewhich you may want to look at.

author: PA4TIM
author_rank: Super Contributor
timestamp: September 06, 2013, 10:51:23 am
content: 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,)

author: saturation
author_rank: Super Contributor
timestamp: September 06, 2013, 04:56:32 pm
content: 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.Quote from: PA4TIM on September 06, 2013, 10:51:23 am

author: Unknown
author_rank: Unknown
timestamp: September 06, 2013, 05:34:13 pm
content: Several cheap handheld DMMs have >> 10 MOhm input impedance for the mV ranges. I believe the Uni-T UT-61E is one such meter.

author: IanB
author_rank: Super Contributor
timestamp: September 06, 2013, 05:40:32 pm
content: I imagine it would be possible to design some small device like the µCurrent to be used as a high impedance front end buffer for a regular DMM? It would echo the input voltage to the output terminals, but it would provide something like a 10G input impedance instead of the regular 10M from a DMM.

author: PA4TIM
author_rank: Super Contributor
timestamp: September 06, 2013, 06:16:59 pm
content: Bob Pease has a design for a meter in his book trouble shooting analog circuits , page 52 It is logarithmic and the scale with a goes from zero in the middle via +/-1pA to +/-1 mAAnd to my big shame, I read this book several times, that he also describes the multimeter way from Harvs,but to my defence, he used it as part of an other schematic and I did not study itr because I have an electro meter for current.

author: saturation
author_rank: Super Contributor
timestamp: September 06, 2013, 08:18:12 pm
content: You could make a poor man's differential voltmeter with just a good low noise and stable PSU, like the Power Designs precision supplies or the HP 6114/5a.http://www.fluke.com/fluke/usen/community/fluke-news-plus/ArticleCategories/DMMs/Take-the-Lead.htmA problem with a snap on differential or high impedance front end for any DMM is even if made well, it won't change the inherent accuracy of the DMM. So if one is measuring uV variations on a 10V scale, it takes at least a 6.5 digit DMM or better to make sensible readings off it.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: September 07, 2013, 10:41:22 am
content: I also played around with a 1.5V battery and my DM3068 and it's clearly the heat transfer that made it change in my case. I couldn't make it move when pressing hard with isolation between it but could easily make it drop with a slight touch and paper between it.Even breathing above it made it drop. (that's what made me test it, since it changed when I got close to it)But like in de video the AA battery doesn't recover easily. see picture below:(if you wonder what caused the 'big' up spike, that's a frozen fry getting friendly with the battery)

author: PA4TIM
author_rank: Super Contributor
timestamp: September 07, 2013, 12:01:58 pm
content: Nice, test. Only strange thing is your voltage dropped ? Temp should make it go up. Or do i read it wrong, Seebeck effect can go up or down depending on the metals (if I remember well) So maybe it is thermal EMF of the connection to the battery.This picture is a result from sunlight. around 8:00 pm (20:00 hour). The sun was going down a a faint light beam was shining through the window at the other side of the room and tought the table my battery was on. I saw it creeping over the battery. It was spring and around 15 degrees outside. So not something like the aussi sun power. But this little bit of light managed to make a significant voltage jump.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: September 07, 2013, 02:31:36 pm
content: Yes it seem to be a thermoelectric effect (but not necessary only from the battery), we are in this 10µV range, I removed the battery and replaced it with a wire (on crocodile clips)And I could reproduce the effect, by cooling one end it went up, by cooling the other end it went down, although one end was more sensitive than the other.

author: thesgoat
author_rank: Contributor
timestamp: September 09, 2013, 03:43:24 am
content: These guys has managed to simulate a battery at the atomic level, interesting it seems to mimic very closely much what happens in a real battery.http://arxiv.org/abs/1308.3424

author: robrenz
author_rank: Super Contributor
timestamp: September 15, 2013, 04:07:30 pm
content: Finally found this pic I had of a 9V cell on high impedance mode on my 8846A. The meter is zeroed out on the 9V to get the high resolution variation over the 7hrs and 37mins. Total vertical scale is the 277.52µV. What's up with the squiggles?(No, its not the meter)Edit: It helps to actually attach the picture

author: IanB
author_rank: Super Contributor
timestamp: September 15, 2013, 06:59:37 pm
content: Quote from: robrenz on September 15, 2013, 04:07:30 pmDid you have any kind of heating or cooling system running at the time? You could be looking at the effect of ambient temperature cycles on the battery.

author: robrenz
author_rank: Super Contributor
timestamp: September 15, 2013, 07:57:48 pm
content: My shop is fairly temperature stable. A shorted input test for drift over 6 days on the 8846A in the same location is a min max span of 1.08µV. I can see daily cyclic external temperature influences as you can see the 2 humps in this 2 day (1 day 23-1/2 hr) trend plot but the total vertical scale here is only 716nV so the actual "centerline of the noise" hump height may be about 50nV.

author: Unknown
author_rank: Unknown
timestamp: September 15, 2013, 11:53:37 pm
content: That's the tempco of the meter. The tempco of the battery will probably be much higher. Tracking the temperature in parallel to the output voltage would be useful. That's why you need a meter with a scanner option, or multiple multimeters. I think you need at least an many bench meters as precision power supplies.

author: robrenz
author_rank: Super Contributor
timestamp: September 16, 2013, 12:23:21 am
content: I think you are right, thanks for that excellent advice as always alm

author: jh15
author_rank: Frequent Contributor
timestamp: September 21, 2013, 05:06:03 am
content: What advice, this?: "I think you need at least an many bench meters as precision power supplies ".That's what you tell the wife when she says "don't you already have one of those?"

author: robrenz
author_rank: Super Contributor
timestamp: September 21, 2013, 02:37:02 pm
content: Quote from: jh15 on September 21, 2013, 05:06:03 amI use "You have way more purses and shoes than I have bench meters and power supplies, and most of my power supplies are cheaper than your purses or shoes"

author: PA4TIM
author_rank: Super Contributor
timestamp: September 21, 2013, 03:14:05 pm
content: And if she does not approve you sneaky pull a fuse from the TV an hour before the bold and the beautifull begins. Then make sure you are not finnished "repairing" it before the end of the program. And while struggeling to "repair" it, you complain a lot about your multimeter and that you had been ready on time if you had that multimeter.