This week, we take on a couple of oddities. The first is the Leaf range loss issue. This has been widely reported elsewhere with an inordinate amount of information I’ve found implausible. So this week we went to Tony Williams, organizer of the group in Phoenix purporting to refute a Nissan claim that there was nothing wrong with the batteries.
This call cuts so many ways I’m loathe to try to make sense of it. One thing is certain, a number of Leaf owners, otherwise delighted with the car, are very unhappy over the range issue and Nissan’s response to it.
This is enough to represent a setback to the entire movement to electric cars, and tends to confirm the fears of those who hesitate to purchase electric vehicles because of “range anxiety.”. A most unfortunate turn of events.
Nissan has been stoically obtuse in dealing with it. Part of this is the very nature of being a large corporation. In building large numbers of anything, correcting errors must needs be involves large numbers. 20,000 is not a huge number in terms of automobille manufacture, but it is still a pretty expensive number if replacing the batteries in each of them is the fix. And once they agree to replace a few battery packs, ALL Leaf owners everywhere will want theirs replaced as well on any event where they don’t get 100 miles on a charge – Nissan hoisted on the petard of their own inflated range claims.
So it is difficult to work out the real from the perceptual, and at some point perception BECOMES reality in these matters.
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For us, and our viewers, we actually need to know what is happening in reality, not perceptually. There is little we can do about Nissan and the broad damage caused to the mission by their cars and their reaction. But is there anything in here we can learn from the issuance of a large number of cars and a large number of batteries into real world applications? Anything we could learn and use for examples?
So far not much. The obvious opportunity to me would be actual evidence of decreased battery capacity in hot climates. Even the Chinese engineers tell me that the cycle life would be diminished at 45C compared to 25C. But when I press for some test data on that, they first refuse, and then finally admit they haven’t actually tested it with cycle tests.
I kind of implied in the video that there is no theory or mechanism for cycle life deterioration in heat. That is not PRECISELY so. There IS a bit of a theory. It COULD be true. I can find no one who has tested it and the tests of Professor Jay Whitacre on A123 cells seems to imply MUCH longer cycle lives for these LiFePo4 cells than previously predicted. But there IS a theory.
When the battery is first manufactured, lithium exists in two places and two forms. LIthium Iron Phosphate in the cathode LiFePo4 and Lithium Carbonate in the electrolyte LiPf6. And the battery has no charge at all.
The battery is initially charged very carefully and HOW it is initially charged is in all cases secret sauce because it has a great deal to do with battery performance later. Electrons are of course pumped OFF the cathode and ON to the anode externally by a power supply. This separates an electron from the outer valence band of the Lithium in the cathode, which then loses its place in the crystal structure and deintercalates or oxidizes. As a cation (Lithium ion positive) It then migrates to the Anode side where it picks UP an electron from the anode current collector to again become lithium metal. That electron is what allows it to hold hands with the carbon crystal lattice and INTERCALATE into that structure. In doing so, the addition of the electron to the anode and removal of one from the cathode makes the anode two electrons more negative than the cathode.
As this process continues, the anode becomes increasingly negative with respect to the cathode, until all the lithium is extracted from the cathode and appears as lithium metal in the anode. At that point the battery is fully charged.
During this first formative charge, there are some consequences in the breakdown of the organic solvents used as the electrolyte. This chemical breakdown causes the deposition of a flexible layer of by product on the SURFACE of the lithium/carbon anode. This is called the Solid Electrolyte Interphase layer or SEI. This sounds bad, but it is not really all bad. The addition of lithium metal to the carbon crystal matrix causes signficant changes in volume to the structure. It is somewhat brittle and this volumetric change causes it to fracture. The SEI layer acts as kind of an epoxy cement, that holds the carbon particles in place on the copper current collector. That’a GOOD thing. But it does slow the migration of lithium ions INTO the carbon structure and OUT of the carbon structure and so presents a portion of the diffusion delay limiting the amount of power we can produce.
Though most of this happens on the FIRST charge, there continues to be a MUCH lesser decay of solvents on subsequent charges. And so this SEI layer thickens very slowly – further limiting power. Somehow, it is felt this also translates to CAPACITY though I’ve always been a little unclear how. I understand the diffusion delay increasess, and I understand total instantaneous power might decrease, but it is felt that this also plays a role in capacity reduction.
And the theory is that this breakdown of electrolytic solvents is accelerated with heat.
Can’t find ANY test data to indicate that. I understand that this MAKES SENSE to a lot of people. To me, that implies it MIGHT be true, despite so many instances of things making sense and not being true that I have a personal bias that if it DOES make sense it probably is a great sign that it ISN’T true.
So the Leaf / Phoenix association takes on a bit of interest to me personally. Might be some data there.
Arizona and Florida have long been obvious havens for electric venicles, and it has never worked out very well. That is because Pb cells – lead acid, absorbed glass mat, whatever, have DRAMATICALLY shortened life cycles at elevated temperatures. If you get 3 years from a lead pack in Oregon, you MIGHT get a full year in Florida. But you won’t in Arizona. This is widely known and thoroughly proven. But I fear that knowledge has leaked into THIS situation, and thus making sense of the resulting conversation is problematical. How many ways to say it. Li batteries are NOT an improved form of Pb battery. They are entirely different devices, with entirely different chemistries, sharing nothing but an affiliation for electrons at one end and an abhorrence of them at the other.
The controversy took on a point when Andrw Palmer, Nissan Executive Vice President who has been involved with Nissans electric vehicle projects for many years, made a public statement that they did not have a battery problem, but most likely had an instrumentation problem.
Enraged that Nissan was apparently dissing their concerns, the Nissonoids of Arizona, led by Tony Williams of San Diego, decided to do a SCIENTIFIC TEST to PROVE that the Nissan did in fact have a BATTERY PROBLME. Then they embarked on a test of RANGE. This kind of muddled thinking drives me crazy. A battery is a battery and range is range. If you think they are the SAME thing, you should try to design SCIENTIFIC TESTS. They tried to control a ridiculous number of variables like tire pressure, wind direction, elevation, temperature, the weight of the car, even ballasting the weight of the driver. But they THEN used Nissan’s instrumentation to determine range.
By ALSO using the GIDMETER, they think they have elminated that as well. Not really. The Nissan BMS monitors voltage, energy usage, and battery SOC with a Battery Management System. This system reports results on the bars displays and of course using the graphic TURTLE. More accurately, it reports it as data on a CANbus and of course the display translates that data to graphics. The GIDmeter takes the SAME CANbus data and displays it in cruder, but more complete form, as numbers. In both cases, you are using the data from the BMS.
But pack voltage, indeed individual cell voltages I think, are available on the CANbus.
And so they did a RANGE test, terminated by a TURTLE, to determine the range of the cars. All ended with a turtle, but the pack voltages at the end of the test varied WILDLY, from a low of 295 volts to a high of 352 volts. I would posit that the batteries at 352 were not at the end of charge at all, and the cells at 295 very well may have been beyond it. In other words, they have a very fickle TURTLE on the display.
And it papears that Mr. Palmer was likely correct that they have an instrumentation problem, not a battery problem. And the Phoenix group is most likelyreading messages from God in cloud formations, leaving my hopes for some actual data deriving from a number of vehicles operating in the Phoenix heat rather lying in a heap – dashed in disappointment. We don’t know. And Nissan doesn’t know. And nothing in any of this will likely tell us. A number of Nissan Leaf’s HAVE been operating in Phoenix for over a year, and we have NO results to report. Gads.
Of course, long time viewers know MY biased conclusion. The BMS – AGAIN. You most likely have some perfectly operation automobiles with perfectly capable battery packs crippled and disabled by Yet Another Bad BMS Design. YABBD. Should something be done about it? Obviously. Now what would Jack do?????
Should Nissan be the one to take the financial hit? Or should the buyers of Nissans’ cars take the hit. I vote Nissan. But they can do whatever they think is in their own best interest.
My hope is that the more savvy viewers of EVTV now have some information. I’m sorry to report you still have no data. But you now know WHY you don’t have any data and how NOT to do a battery test. It has hard to do conclusive battery testing with turtles. Bars are not much better. And representing the SAME faulty data numerically offers only slight improvement, in that we were able to get FOUR terminating voltages anyway. Enough to ascertain that the testing methodology was comically wretched.
We struggle with such testing ourselves and with instrumentation ourselves. You will note a couple of failures here at EVTV. First, I apparently pulled the mic cord on the 70 mph range test of the Cadillac Escalade. Too bad. I spumed forth many precious Rickardisms on that drive lost to us all forever. As we are still two hours and forty two minutes long, I suspect you’ll forgive me when I summarize them thusly – 834 wH per mile.
WATT HOURS? Now where did THAT come from? Don’t we usually measure amp hours? Yes we do. Why do we do that? Because that’s the only instruments we have and can afford in an EV. Watt Hours have always been preferable in that they represent in a better way the total energy use accounting for both voltage and current, while the voltage varies widely during the drive. But we haven’t had a good wattmeter to use. BEFORE you crawl up my skirt on Cycle Analyst, I HAVE one, I HAVE tested it, and it cannot even measure current accurately, so any wH it would derive would also be inaccurate.
I have worked for several months with an instrumentation company in CHina to modify one of their current meters to use a 12v supply for example, and to display WATT HOURS, VOLTAGE< and CURRENT simultaneously on the same screen. It winds up being a LARGISH meter to display all that in large numbers I can read. It is a little complicated. And it was a little difficult to exlpain to them the DC nature of our world and our ongoing disinterest in power factor and RMS values. But we got er done and I got my prototype. They are anxiously awaiting a quantity order. one wee problem. I never really specified that it measure current in BOTH directions. As we are using a shunt, it never occured to me that their meter would measure in ONE direction only. But in going from AC to DC that's what they did, and they do not think it's economically viable to correct this little feature. I think it makes the meter nearly worthless. Oh, not entirely. I just have to zero it out after every drive. And it doesn't count back down while charging. Since the JLD404 does, by using BOTH it works reasonably well. But not well enough to be a product I'm afraid. And at the price, really a disappointment. I feel foolish to have never brought it up. Both sides are worn out from trying to communicate a feature set for a meter in Chinglish. So it has kind of died as a product. So when beating up Nissan, we have our own little design setbacks. Unlike Nissan, we are afforded the LUXURY of being able to offer a FULL REFUND to everyone that bought this killowatt meter. Of course, Im the only one who has and unfortunately the Chinese vendor is not as generous as I am so I eat the cost of the one meter delivered I'm afraid. So I commiserate with Nissan at the cruelties of the market place. But would encourage them to address the problem with some much simpler but more accurate instrumentation. I would also note that they TOP balance and the 352 volt car might INDEED be dead, with one short cell that the BMS has noted and shut down the car. BOTTOM BALANCE INSTEAD if you must. But in all things, I think Nissan should strive for a collegial and consensual relationship with their early customers, and avoid allowing this to become an adversarial relationship over ducats. With 20,000 cars down, and a new car plant AND a new battery plant coming online in Tennessee, the stakes are actually quite high and the lessons learned bill really pretty low by comparison. I like Teslas approach of gathering battery performance data by cell phone from their cars. Less guess work. More knowledge. Maybe we'll fund John Hardy to do some cycle life testing using a styrofoam cooler and a light bulb. Or maybe I'll do it. Jack Rickard
Jack,
From Ingineer, on September 19th:
“The biggest problem with the Leaf’s BMS (in my opinion) is the use of the Hall-effect current sensor.”
http://www.mynissanleaf.com/viewtopic.php?f=30&t=9981&p=228473#p228573
Warren
I agree. And I don’t know that it does. It just sounds like it does. Temperature moves the zero point on hall effect current sensors.
Jack Rickard
If there is a chance that the instrumentation is at fault. How are you going to test whether it is a battery problem versus an instrumentation problem if you are using the instrumentation, which may be faulty, to measure “battery degradation”?
Anyways, back to reality.
Jack did you mention a charger option for your superlight speedster?
Padraic McDonnell
Not yet.
Jack
I thought you didn’t mention one. I am looking forward to that build.
Padraic
This is in all ways a A++ show..!
Which Wh do you use? I tried to get this one:
http://www.etradeasia.com/products_detail/433186/433186/5561/D_Solar_Multifunction_power_meter.html
but was not very successful…
Why don’t you use the JLD7100 to check your temperatures? They are pretty simple like the 404 when you once got that kind of thinking.
Pin 1 and 2 for the 12V, a cable bridge between 6 and 7 and a PT100 thermo resistor bewteen 6 and 8.
Or a K-type thermocouple beween 6 and 7 with no cable bridge.
They have both types thermo sensors at :
http://www.lightobject.com/Search.aspx?k=temperature%20sensor
I really wanted to come to your convention but I have to work….that’s too bad.
The meter you provided a link to has a little problem and I’ve run into this a LOT with Chinese meters. It does NOT display kWh. It will display kW in real time, but no cummulative. You can get kWh either by a pulse output or a serial port RS-485. But not on the display. You would think this would be programmable. But it is not.
Yes, I should probably have digital temperature meters for both motors at this point. I like the JLD612 better.
Jack Rickard
Jack great show NICE ride! I was wondering when you were going to test the auto pilot. I kept watching and waiting and just when I thought it wasn’t hooked up, the dim light bulb went off over a brilliant mind.
See You at EVCCON! (but not EVIE, maybe next year)
But the JLD7100 is half the height (48mmX24mmX75mm) of the 612 and so it fits easier in every dashboard. even in a big car. I really like that it is so small.
Hi Jack,
I’ve been watching your show since the beginning and love it.
Good to finally see the results of the Escalade conversion. I have a Mercedes Gelandewagen that I’d like to convert. The Escalade project is a good reference to see it that would be viable as the weight is similar and it’s also an automatic. I guess the Mercedes should be simpler as it’s from 1985 and has little to no computers onboard. I’m searching the web for an pre made adapter plate because I see this as the biggest challenge. However haven’t found anything that will work with Mercedes transmissions yet.
You mention the inversion point of 3500 pounds where the weight starts to be a more important factor than wind resistance up to a point. Do you think it would be worth while to look at regenerative braking again? Perhaps with higher weight the benefits increase?
Interested to learn your thoughts.
KR,
Alex
Kind of hard to do regenerative braking with an automatic transmission. They are essentially incompatible. I do like the fact that the Escalade free wheels really quite well though. I can coast for a mile or more sometimes using about 11 amps to idle while rolling merrily along downhill.
Jack
Jack, I have a Escape Hybrid with regenerative braking and my drivetrain has a cvt. How do they do it.
I have to say I like the ride along test drive. Boring? Sure, but it really helps give a feel for exactly what you’re doing, and why, with your builds. For example. I hadn’t heard much about the DC motors overheating on long drives being as big of an issue as it apparently is. I mean I’d heard about it and seen all sorts of supplemental cooling solutions used in different builds, but never had much of a sense that it was as common of an issue as it apparently is. In hindsight it’s perfectly obvious why it could be an issue, especially at lower rpm’s and relatively high continuous draw you see on a long interstate drive; especially in a larger vehicle. Great show as usual. Seeing some bench tests of DC motors with different cooling methods and seeing how they perform will be a real treat.
A brilliant show!
.
Hall sensors and Leafs.
Here’s food for thought on equalising electronic circuits. A trick with less stable sensors, Is to have a matched equivalent sensor away from the magnetic source but running in the same temperature regime to balance. It works. A simple potential divider circuit feeding an ADC. Much easier and more reliable than pulling the sensor away occasionally for a zero reading.
.
I’m almost certain UK Leafs were called back early on due to the instrumentation reading short. Many have noted the consumption meter dropping fast when least expected. Maybe when the weather cools down the available mileage will go up? I would hate to guess what scheme they use to calculate this. At least the calculation I gave is self correcting but as we always say, GIGO.
Jack, three runs of approx 72 miles, assuming 15 mpg (UK) would cost over £30 ($40) in fuel over here. I think you pimped your ride very nicely!
An interesting solution. And yes, that would probably work. Just use two identical sensors and take the one with no conductor as the zero point. I should have thought of that.
Finding two that are identical would be nearly impossible. That’s why you calibrate them in the first place. Again, chasing hall effect sensors for accuracy is a frustrating exercise.
Jack
I just wanted to point out that with the Leaf we are discussing a Lithium battery with a completely different cathode chemistry. The behavior of LiMn2O4 cells may be different than for LiFePO4. We should avoid leaking “obvious” knowledge gained from working with Lithium Iron Phosphate cells to Lithium Spinel cells.
It is not a completely different cathode chemistry. It is a somewhat different cathode chemistry. The behaviour of the two cells is going to be different. But the charge and discharge curve shape is not substantially different at all. And in fact they share more in common than apart. So what is your point?
We should avoid “leaking” obvious knowledge? We should instead focus on leaking non-obvious knowledge? We should not leak obvious knowledge? We should retain obvious knowledge in secrecy?
Lithium Spinel is not a term. They are sometimes refered to as LIthium Manganese Spinel. LiMn206 in a spinel structure.
From this thoroughly confused message I have to assume you are one of the “fallen Leafs.”
Jack
I was trying to borrow your language to make myself more clear. “But I fear that knowledge has leaked into THIS situation, and thus making sense of the resulting conversation is problematical.”
I’m sorry it didn’t come across clearly. Please accept my apology for accidentally leaving Manganese out of the description of the cathode in one instance.
If you have assumed I am a Leaf owner you have demonstrated the problem with making assumptions. I own an EV, but not a Leaf.
The Leaf problem looks like, based on voltage, a problem with the coulomb counter (state of charge calculation.) I’m don’t know how closely the cell level BMS is tied to SOC calculation.
I see the LEAF problem in a slightly different view. The owners are seeing the bars which indicate capacity loss disappear. At the same time they are seeing the range that they can drive the car before it reaches “turtle” diminish. This is a real problem for drivers in Phoenix right now. When they bought the car it would do 70+ miles on a daily basis and now 18 months later it is in the 40’s. These are reported numbers from the owners who are using them with climate control on (as required in Arizona). The owners are taking the cars back to Nissan and the dealers and even the Nissan corporate technicians are reporting back to the owners that this is normal capacity loss and it is not covered under warranty. As an owner you’d be pretty upset if your car is not getting you to work and back any longer and Nissan is not doing anything about it. BMS problem or not, the cars don’t go as far as they once did, and Nissan’s response for months was that it was normal. This is why they ran the test. Not to check the battery, but to show that the car does not go as far as it once did. Really all the owners want is to get their range back. Most owners don’t know or car what a BMS is or does, they just want to drive the car. It used to go 70 miles and now it only goes 45. Nissan please fix it. If it is a BMS issue, it should be an easy fix for Nissan. As an owner of a Nissan Leaf (an a home conversion), I can say that the instrumentation regarding the power consumption in the LEAF is wildly erratic. It is hard to make it give me the same numbers twice on a repeated drive. It would not surprise me to find out that all the problems are related to the instrumentation in the car, but I’m not discounting a possible battery capacity issue either. I’m looking forward to Nissan’s response. They have already made some very promising changes. They put a Nissan employee into the Forum, http://www.mynissanleaf.com/viewtopic.php?p=229585#p229585 and have asked Chelsea Sexton to head a focus group on the issues.
Even if it’s the BMS, which it probably is, it’s definitely not easy to fix. If they’re using a Hall effect sensor they might have to switch to a shunt to get a more reliable reading regardless of temperature. Adding a shunt and adapting the instrumentation for it might sound simple, but it isn’t when you need to do it to a thousands of cars and keeping in line with whatever standards exist in every corner of the planet.
Oh well, if “Chelsea” is on the case I’m sure it will be fine. Sorry guy, I can’t go there. This is a classic effort at shrill “activism” gone awry. The point is NOT that they are losing range at all. I agree that should be a Nissan problem and not a Nissan owners problem. The editorial was unequivocal on that.
The issue is that Andrew Palmer was quoted as saying he thought they had an instrumentation issue, not a battery issue. And a small group in Phoenix held a “scientific test” complete with “wind direction accounted for” that was curiously unscientific and used Nissan instrumentation to prove that the problem was the batteries themselves. They actively sought national press attention and dutifully got it from Green Car Reports, Autoblog Green, and Electric Car who all uncritically reported the testing and the results as PROVING Nissan was wrong and there WAS a battery problem and that the batteries fade in capacity in the heat of
the Arizona climate.
There’s so much wrong going on there I don’t know if it can be unravelled. But I gave it a go. Since it didn’t prove ANYTHING it set out to prove, I would have to assume it was a useless exercise in further confusing the public on the issues of electric car ownership. In other words, it muddied the waters and to little other effect. It remains that hot climate MAY reduce battery capacity, or it may not. I suspect not. But have no real good data set. And still don’t.
Further, I think it is also damaging that owners do have concerns but are prone to jumping to conclusions and making hasty claims of corporate malfeasance – leading to a defense of the corporate posture. You don’t fight corporate lies with activist lies. You fight them with the truth. And it can be hard work to get to that. Jumping to the conclusion that a guy who has been invovled with the EV project at Nissan since its inception doesn’t know what he’s talking about is probably counterproductive. It sets up an adversarial relationship based on misinformation and confusion.
It remains Nissan’s job to manage all that and deal with it and at this point I would rate their performance poor and so to no surprise the results poor. That does a disservice to those working to further the cause of electric vehicles.
Adding a “yes but what we REALLY meant” at this point is scurrilous.
Jack Rickard
Jack,
EVTV’s assessment of the Leaf test is published in an Autobloggreen article:
http://green.autoblog.com/2012/09/25/nissan-addresses-leaf-battery-woes-customer-communication-short/
Leaving from Ohio in a couple hours to attend EVVCON, see everyone this evening.
Randy
Jack,
First congrats on the escalade. Getting that bad boy rolling is no small feat of engineering and i know that dealing with the ECU software is a monumental task of endless possible combinations…
I know that my little PLC system can very accurately measure KiloWatt hours in and out of the pack. It can measure time accurated down to the ms. It can measure current accurately Dow to 100ma. It can measure pack voltage down to 0.01 volts. Doing a simple integration routine will yield amp and KiloWatt hours in and out of the pack.
If I can only get my car finished, I know that I can prove this to a reasonable degree of accuracy. I really hope to share this real world data with the community in the near future. I am quite disappointed at my slow progress on the car, but it is what it is……
Anyway, thanks for another interesting show……
Don’t beat yourself up about how long it’s taking. Did you not watch the Mini build…or for that matter the Escalade build? Lots of the builds I watch from afar take ages. Yours actually seems to be racing along. 🙂
We take too long on a build. There are two factors. First, we are filming it as well. Second, we have several going on at once. We did an eCobra and a Swallow interrupting the Escalade both times.
But yes, these things take time. After doing several, my advice is relax and enjoy the process. Once they are done, you will actually have a little depression from “your car doesn’t need you anymore.” Kind of like the kids going off to college.
Jack Rickard
Hi Jack, I am just about finished my trip in China, but have been reading your blog. I have been giving our previous discussion a lot of thought and now am certain that the small balance problem is due to my cell boards being unbalanced. I have had plenty of time to redesign them so that they will be balanced at all times, and will try this design when I get back. Once this has been proven, I will bottom balance to try see how it performs.
I can only see one disadvantage at this stage to bottom balancing, and that is that the car will have a slight reduction in range. Will keep you posted all my test results once I start.
With the hall effect current feedback, this is what I have implemented and find it accurate and I keep it accurate by resetting the zero point every time I turn off the ignition. My biggest design problem with my hall effect design was the hysterisis for power/regen ie current going constantly forward or backward, rather than temperature. I have not implemented the kwhr part of my meter, but may do this to check the reduction of the kwhr due to bottom balancing. I have never had any anxiety with my gauge and my accuracy check was simply to predict the time it should take to fully charge, based on the amphr used, and always seems to be correct. Of cause I never allow my car to go further than 90%DOD as shown on my amphr meter.
Walter
Afaik it doesn’t matter whether you are using top or bottom balancing – you will always be limited to the exact capacity of your weakest cell (unless you actually do active on-the-fly charge transfer between cells which gets very complicated very fast – not to mention probably using as much power in the process as you could gain). In top balancing the weakest cell will reach lower voltage limit first and can break if you’re not quick enough to stop driving whereas in bottom balancing all cells arrive at low voltage limit together and it is very difficult to kill any cells. The weakest cell will demonstrate it’s weakness by reaching the highest voltage while charging.
I just gave this “bottom balancing cell protection” a test with my motorcycle. I have a 25 cell CALB pack which I charge to 87.6 volts. I had set the low pack voltage limit to 50 volts on my AXE7245 controller. I drove the pack empty and kept pushing against that 50 volt limit over and over again by letting the pack go up to 60 draining to 50. In the end after doing this a couple of times the bike wouldn’t go anywhere anymore. Basically slow walking speed at most and then stop. I then pushed the bike back home and the cells, after a bit of rest, were at 2.5V or so. I couldn’t kill them even though I pushed them to 2 volts. Recharge and good to go again.
And that IS the advantage of bottom balancing. You cannot kill a cell by reversing it when overdischarging the cells. Try this with top balanced cells but be prepared to purchase a few.
Jack Rickard
Hi Guys, absolutely correct that the advantage of bottom balancing is that they all discharge together. The slight change in range has nothing to do with the amphr of the weakest battery. It is because the total average voltage of the pack is slighly higher on top balancing, so the amps required to get the power needed, is lower, giving a slightly higher kwhr. Having said that you probably call this your God sprickling fairy dust from the sky, or what ever you say, but keep this in mind,what I was trying to say is, if that is the only difference, then bottom balancing has a lot going for it.
Walter
I re read my statement about “nothing to do with”. I of course mean that the weakest battery hangs on longer because less amps are needed when the average pack volts is higher.
Walter
You assume the cells would stay at the voltage they are charged to? They will not. Whatever voltage you charge them to they will come back down to around the same, lower voltage anyway after you disconnect the charge and let the cells rest a while (for CALBs 3.33V IIRC). So I don’t think your pack voltage will be any higher after top balancing. Also if you compare charging to 3.5 or a couple of tenths more you can see that the amount of energy going in is quite insignificant. The voltage rises very fast at the end. Just as it does when going down. When I noticed the bike was running out of juice the pack voltage was around 60V loaded, IIRC, and that’s where “the turtle came out” in Leaf speak. Got very slow very fast. That last 0.5V per cell had nothing in it. Just as 3.5 to 4.0 has nothing either.
Great demo Jarkko
BTW I know zilch about Leafs. Can you get individual cell volts out?
BTBTW – Arrived in Cape last night (Monday) – hoping to pop down to Morgan Oak today (Tues)
I had a change in how my Leaf registered the miles remaining after my last checkup but that was because of the software upgrade if you want to call it that. I drove nearly 15,000 miles the first year which is over the national average. I have a varying reading but use the bars mostly to figure the range and if all is fine. I get about 4 1/2 to 5 miles per bar and I have specific spots on my route that I use to check to see if things are fine. Same boring route every day. When I get to my halfway point I should have dropped 2 bars from full for a total of 9 to 10 miles used depending upon the outside temps. When cool in the AM I usually find I get about 4 1/2 miles per bar so when the second bar drops I should be at 10 miles but only really have gone 9. When the morning temps are warm like in the 72 degrees I can get to 11 or 12 miles sometimes before my second bar drops. This has been pretty much like this since I have gotten the vehicle. Some days it seems like the charger did not fully charge the vehicle and those days I don’t get but like 4 miles per bar or maybe a touch less. I still get to work and back and have never been stranded.
Some days it seems like the charger is not fully charging and somedays it seems like it charges more. I always wondered if the charge algorithm was wonky too. Or if the homes output of power had anything to do with charging less or more. Some days our power output is higher than other days and the input coming in from the grid is not a nice clean stable voltage. So maybe the charger is averaging it out and charging to what it thinks is the right voltage and amps. It seems like the charger is more on a timer than actually charging and holding until the amperage is x amount. If on a charger and my input from the home is unstable the charge one day may actually be less than another day.
At this point I can’t tell if I am getting less than when I first got the car. Maybe a touch.
Pete 🙂
Have you tried charging, unplugging, perhaps waiting a few hours and replugging again? Does it start charging again or not? If it doesn’t do a full charge every time you could try this to see if the previous charge was cut too early.
I think it has multiple cells in parallel so down to single cell is not possible anyway and I guess you can only get pack voltage from OBDII. At least only pack voltage was mentioned. I have no personal experience with Leaf.
How are you doing with the Civic? Is the legislation in your part of the world (UK?) better than here in Finland? It seems any car that has been EC type-approved as a whole is quite impossible and the approval became mandatory here in 1998. I was thinking of a 1997 A140 Merc, but seems it’s also type-approved too and quite complicated with ABS, BAS, ESP, etc. I may have to go as far back as 1995 or even 1993 before I can be sure the car will pass our MOT after conversion due to the EC business. Sure makes DIY conversions less appealing.
I do a full charge every time, or at least the last charge of the day is a full charge which happens to be most of the time. On some days I do partial charges while out and about doing errands. What I need is a meter on the EVSE going into the car and a meter after the cars charger going into the batteries to see. I do not have a 240 volt meter for the EVSE or I’d already have one connected.
The charge just seems like it floats about a bit from one charge to the other. I have charged and let set a bit and replugged in but the charger will not put much back in if the level is above 80% so I can’t really tell if it was fully charged to begin with.
If anyone has an idea I am game to give it a spin.
Pete 🙂
Hey Jack,
It might be a little off subject, but guess what, You nailed it with the Tesla charging station… except that you didn’t say charging would be free 😉
http://www.engadget.com/2012/09/24/tesla-supercharger/
http://finance.yahoo.com/news/tesla-motors-launches-revolutionary-supercharger-032000226.html
I must say, this is fantastic news… but I don’t get why the stock took such a hit?
Again, I heard it first on EVTV 🙂
Hey Jack,
It might be a little off subject, but guess what, You nailed it with the Tesla charging station… except that you didn’t say charging would be free 😉
http://www.engadget.com/2012/09/24/tesla-supercharger/
http://finance.yahoo.com/news/tesla-motors-launches-revolutionary-supercharger-032000226.html
I must say, this is fantastic news… but I don’t get why the stock took such a hit?
Again, I heard it first on EVTV 🙂
Hi Jack,
Is there any indication that Tesla is going to share it’s specs, provide hardware/software for other cars(namely us) so that we or anything that is not a Tesla can plug into their charging stations and recharge our cars?
Hi Jarkko, When you have 20 or even 40 batteries, you may be lucky and have batteries that are very close in amphr, but when you have 114 batteries, the difference in amphr can be as high as 15%. The voltages are indeed very similar at rest but when you start taking 3C from a battery the voltages are very different as the battery changes its state of charge. I watch the voltages as I drive.
I will be checking all these things out as I convert to bottom balancing, but I estimate my range will reduce by as much as 5Km with my setup. Not much I guess considering my range is about 160Km, but its not so friendly if you have to walk it.
Jack is right that it is safer to drive to a point of having a flat battery, which is one of 2 reasons why I am interested in changing to bottom balancing, but because I monitor all my cells, I know when the weakest cell is empty and so I stop.
Walter
I don’t see how the pack size matters, especially it they’re all in series. How can you get more Ah in to your weakest cell now compared to bottom balancing? The weakest will still go from lowest to highest voltage in either scenario.
Walter, I was assuming you were explaining things oddly. What do you use to “monitor” your cells while you drive?
Walter:
In a word: Total Bullshit.
Actually that’s two words.
Where do you get this stuff?
Jack Rickard
I wasn’t going to “go there”.
Walter,.
If your weakest cell is 15% down, say 110AH instead of 130AH then that’s your lot. Your pack is 110AH.
If you are using them paralleled, I suggest you mix a strong cell with a weak one.
[b]The strength of the chain is only as good as the weakest link.[/b]
You wrote earlier:
“..so the amps required to get the power needed, is lower, giving a slightly higher kwhr.”
In reference to a top balanced pack holding more energy. That, seriously, is garbage. If you wire a string of resistors, all the same value, the voltage drop and the current along each and every one will be the same. If you can find a mechanism to change this fact then you have found a gaping hole in the fabric of reality.
What Walter is saying is entirely correct, but likely insignificant.
If you top balance you can have the entire pack resting at the max voltage, let’s say 3.4 vpc. With a bottom balanced back you will have whatever voltage your average is when your top cell is at 3.4 v. Depending on how closely matched your pack is, the average might be 3.3, or it might be 3.39.
Assuming it’s 3.39, then at 100A you get 339 watts per cell (minus sag). If your average was 3.4 you’d be getting 340. Obviously there’s a difference, and how much that difference is depends on how close your cells match. Likely it won’t be much, but it’s not 0.
Thanks Jack. I was only trying to explain that there are two things that determine range. One is the amphr of the weakest battery and the other is the pack voltage.Thats not bull shit.
I have a pack of 114 * 60amphr batteries and at least one is 72amphr which I happen to measure while comparing it to a different type of battery so I could have an amphr range of up to 20% . Thats not bull shit.
The battery voltage reduces as the battery is depleted. Thats not bull shit.
It is likely to be insignificant, that is true so the 5km reduction may be bull shit, however thats not the point, I said right from the start that it was “slight” .
I’m a electronic control engineer, not a battery expert, so constructive critisim would be more helpful.
Why are you all so touchy anyway, it is what it is. Personally I had to eat enough humble pie to agree that bottom balancing has it all over top balancing and I respect you for your contrarian attitude, but
if all you want on your blog is yes people then its not for me.
Andyj, I have a display that shows me my maximum, average and minimum voltages twice a second and the system was designed by me. I also display a number of other parameters like torque and errors and if I notice any problems I have a laptop that can display all the battery voltages and temperatures at once.
The problem with it though is that the cell boards that monitor each battery have different current requirements depending on the battery’s number so they are not balanced and can’t be used in a bottom balancing system. I have redesigned them to use the same current under all circumstances, so once that is perfected I will bottom balance and add an auto turn off when the ignition is turned off.
I was planning to write some articles on how my car is put together, particularly on my bottom balancing progress but I dont believe Jack is too interested.
Walter
Hall effects on Leafs part two.
Jack, do you remember asking “Where’s my 1000 amps?” The smallest of things can be the most embarrassing.
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To further on my last post which was barely thought out properly. It’s possible to use both hall sensors together reading the field current and increase the sensitivity if one is placed the other way up with the other. As goes perfect linearity, I’d not really care. It’s the repeatability that matters.
So, 4 sensors. One pair reading one way and another pair sat the opposite way to balance current reversal. This ensures a more perfect count on regen/recharge.
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Devices like the SS49E (<$3 ea.) are sort of stable to <0.2%/C. Not silly expensive. If the device gets anywhere near to saturation then you need another set of sensors calibrated at a set distance….. How awkward. hahaha.
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Mores the pity an EV that has longer power leads, (or stator windings) are not also used as the shunt. The resistivity, (voltage drop) being measurable and copper having a known resistivity/density product of 150 nΩ·m·g/cm³. Need temperature compensation for saving money.
Good readings above noise?.. I don't know..
Absolutely wonderful show. Absolutely wonderful results with the Escalade.
Just a Leaf note: My battery pack temp gauge rarely ever goes much above the middle line in the blaring heat of the parking lot at the Hospital where I work. I frequently come out to a car that has been baking in 112 degree temps and inside the car must be higher, yet the pack temp gauge is well within the safe range. Even when cold it rarely goes very low either. But when the morning ambient temps are like in the 50’s the car will drop about 10 miles range. I have always thought that the car depends upon the ambient temps quite a bit but little on the actual battery pack temp. Seems like the pack temps are pretty stable. Wish I could get an aux temp gauge stuffed in the pack to check. Over all I have lost no bars and fully charge daily and drive it at 55 to 60 mph daily on the same route. Main thing that varies the most is ambient temps and the varying voltages coming into the house. Yes even with solar it is not very smooth and stable.
Hope to hear some excellent news coming out of EVCCON on a daily basis so we can post and please include photos.
Pete 🙂
WalterK,
The thing is you can’t get that extra 12 Ah out of that best cell no matter what. Even now your car is drivable only as long as the 60 Ah cells have energy left. If you swapped all but one 60 Ah cell to 180 Ah cells you could still only drive for 60 Ah or that 60 Ah cell would die and go into reversal.
Voltage is insignificant because it doesn’t change much until at the very ends of the curve. Here’s a typical Lithium cell voltage curve:
http://www.efirstpower.com/images/li_clip_image002_0005.gif
In other words voltage is good for two things and two things only. Charging up to and not discharging below certain limit. Do not read anything else into voltage. It does not represent charge level in any measurable way. And it changes under load. A lot.
Jarkko you are seconded here. Liked the bit where you ran out of juice on your blog.. No cells killed!
The max attained voltage will always be reached on the weakest cell and be the first to show the voltage dropping when approaching discharge. You understand this? Your weakest cell determines the full packs AH. You understand this too?
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At the end of the day, if it is 1 or 2 errant cells holding you back, you might gain a better range by removing the things!
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Therefore at no point will the KWH capacity be reduced on demand due to top balancing.
Another soo odd thing you said,
“The problem with it though is that the cell boards that monitor each battery have different current requirements depending on the battery’s number so they are not balanced”..
If your boards steal a different current from each cell you are heading for a bad day, no matter how minuscule the differences are. If your boards show different currents then throw them away.
If you are stating your cells have differing current loads. Then I suggest you clean your contacts. Beware of your terminals heating up! Heat is possibly more important in the use of these cells than mere Voltages which ought to be automatic between the controller and the charger.
oopths!
Second line onwards was meant for Walter.
From Mr. Reuter, the Nissan communications executive:
“What we have to do is improve communication to help them understand how cars are engineered and supposed to operate. We’re looking at where Nissan needs to do a better job in terms of educating customers about expectations and performance.”
From the road gang captain, in Cool Hank Luke:
“What we have here is a failure to communicate.”
Leaving to spend more time with the family, no doubt.
http://www.plugincars.com/leaf-point-man-mark-perry-retiring-124634.html
Hi Jarkko and Andyj,
Thankyou for the discharge graph, it looks just like mine. Now have a look at the average voltage from FULL to 15% FULL(85% discharged). The voltage is allways above 3.05V, so lets say the average voltage is about 3.2V. Now look at the volts from 85% full to empty, it ranges from 3.25 to say 2.5V and we will call that about 3.1V average.
So if I had 1 battery at 60Amphr and the rest (113) at 69Amphr (not likely but the worst possible case for 15% difference in a batch of batteries) Then the watthr for a top balanced pack would be
192 + 113 * 60 * 3.2 = 21888
The watthr for the bottom balance case would be
192 + 113 * 60 * 3.1 = 21210
Thats 678 watthr less. In my car I can drive 1km for every 137watthrs so my range in this unlikely case would be reduced by 5km. I have the complete discharge curve data for my nominal 60Amphr battery that is actually 72amphr, so I will set up a spreadsheet and determine the exact average voltage for the top 60amphr and the bottom 60amphr of that battery and let you know. (remember I can only use 60amphr out of this 72amphr battery because the weakest battery is 60amphr.)
Now Andyj, the cell boards were designed by me and the difference in current draw is because of the communications with the BMS which changes the length of time the optos are on and off differently for each battery. The optos are the highest current draw in the system. Even a couple of milli amps upsets the balance of the batteries. If this wasn’t so, then top balancing would not need shunts. I spoke with Jack about this problem a few blogs ago.
Ok guys, this is technical stuff, and my original comments were only made to suggest bottom balancing is so good that it only has one disadvantage, and bang, I get blasted.
Jack, you asked where I get this stuff from. I get it from the same place I got my fully isolated amphr/kwhr display, my BMS, my auto isolation tester and my meters, and they all have been working without problems for over 4 years and 50000Km.
Now my interest is in making it all work under a bottom balancing scenerio.
Walter
Ok Everybody, its happened again. Seems like when your a long way away from your car (China) the imagination runs away.
Well its my data and my calculations for the 72amphr battery (60amphr nominal) and the watthrs for the top 60amphr is 1 watthr greater than for the bottom 60amphr. That could be measurement error I suppose, but in any case its insignificant.
I will double check it with new data one day but it seems that I’m getting well fead with bottom balancing pie.
Walter
Walter,
The long complex answer is usually the wrong one. The FULL KWH of your pack is irrelevant.
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Your presumptions are totally incorrect but you are entitled to them.
‘
The ONLY WAY to increase your useful capacity to the full pack KWH is to use the whole pack to actively charge the weak cell(s) when a set low voltage is reached…. AND To actively limit its overcharge condition upon charging. A silly expense no mfr’r is willing to make a loss over.
I’d simply dump or add in parallel to your weakest cell of 114 cells to gain an overall increase of USEFUL capacity. 113/114 is a smaller loss than 85% (Worst cell).
Thanks for your persistance Andyj, but I never said the FULL KWH. What my thinking was , is that the PARTIAL WATTHRS of the top 60amphr range of the 72amphr battery is higher than the bottom 60amphr.
What has absolutely stumped me is that from the data of my experiment I have determined that the top watthr reading was so close to the bottom watthr measurement, that it makes this assertion irrelevant. Try the experiment youself, its a real eye opener.
Walter
HI Jack, if your still reading anything I write, I have a query about a few of my batteries. If you don’t know, I have a display that shows me the voltage of the maximum and minimum batteries. The point is that at 3C the maximum battery reads about 2.9V and the minimum (always battery number 6 of 114) is 2.5V. Is this normal?
When I take 54amp hrs out of the pack, battery number 6 is fully charged at the same rate as the others.
Why would one battery be so low at 3C compared to the best?
Walter
Jack probably busy at EVCCON. Maybe it’s a bad cell that you could replace?
We have no idea what your cells are. Whether you have swapped the units that do the reading to see if the numbers alter. Whether you have over extended that cell on charge or over discharged. We don’t know if that cell has sufficient AH or your connections are clean. We know nothing. You are an adult and its your car. All of Jacks video’s can be perused as you need in the archives. Look around 2010 and earlier.
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Walter, please, if not me. Listen to Jarkko. Never over (dis)charge. That is your only Voltage scenario that matters. Where your pack voltage is highest has nothing to do with power. The available power on these is constant. It’s your cell capacity that is the cell capacity. The voltage as the size of a number means next to nothing.
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EVCCON2 is now. This means anyone else who can answer you is not here.
Walter… As regular viewers of EVTV, we have all watched countless hours of Jack selflessly destroying thousands of dollars worth of cells, all in an effort to prevent us from doing the same. When we tell you that the only safe way to handle these cells is to bottom balance and undercharge them, you’d do well to listen. Top balancing a pack results in dead cells. Period. Kill enough cells and you’ll end up overcharging the remainder of the pack, burning up your car, house and anything else nearby (including yourself). That extra 5km of range you think you’re getting is not worth the risk. Please please please heed the advice you’ve been given.
Regarding your most recent post… From the sounds of it, you may have already damaged a few cells in your pack. You might want to do some capacity testing on those cells, and replace them if necessary. Consider that a lesson learned.
Thanks guys, None of my 114 batteries have ever been over 3.8V nore under 3.0V except when taking 3C out of them, when a few hit as low as 2.5V. The pack volts is 315V at 3C so the average is 2.76V. The batteries are 60amphr type B sinopolys’ and are the only batteries that are light and small enough to give me the range I want.
I have never lost a battery in 4 years. I only mentioned the battery number 6 to show that it is always the same one that is the lowest at 3C, but there are others. It is never the lowest volts at rest. I cleaned the terminals of number 6 untill they gleemed so there are no terminal issues. All the batteries still have over 60amphr capacity. I know this because I restrict myself to 54amphr at which time all the voltages at rest are still over 3.2V. (I will double check this). When I subsequently charge them, all batteries including number 6 arrive at full together.
The only things that haven’t been mentioned are that I may occasionally take 3.3C from the pack for up to 20sec going up my hill and it has been like this since I installed them in April.
Walter
Walter;
I HAVE replied on several occasions, apparently to no good effect. ALL of this has been covered in past videos. At length. In gory detail. Yes, I suppose I could stop and write a book, but then we can’t do weekly videos.
It sounds like you are making progress.
Jack Rickard
Hello :). We did miss you, just as I suspected we would. It was a bit of a letdown for us, but very pleased we put all the eggs in the TVR basket because Bob was thrilled to be there. If you don’t speak to Royce this week, I wanted you to see this in case you haven’t already, Jack: http://www.smithsonianmag.com/science-nature/Forget-the-Volt-Make-Way-for-Electric-Trucks-169807746.html
Hope you are recovering from your big week and that it was a shining, fulfilling success. K