This week we try to catch up a bit on the eCobra project, which I would like to finish sometime in THIS life. This car has been a struggle.
The bad news is it has just featured some really difficult geometry to fit in a 41 kWh battery pack in a small two-seat sports car. I’m very pleased with the power plant. The Netgain Warp 11HV and the Netgain Controls Industrial controller are very strong in this 3000 lb monster. We haven’t done any performance testing yet, but I can already tell you the performance will be very strong.
This week we tie up some cooling system issues and some instrumentation. And most of all wire in our Elcon 5000w charger.
[jwplayer file=”news100711 – iPhone.mov” hd.file=”news100711-1280.mov” image=”http://media3.ev-tv.me/news100711.jpg” streamer=”rtmp://s3einxnpkaij93.cloudfront.net/cfx/st/” provider=”rtmp” html5_file=”http://media3.ev-tv.me/news100711 – iPhone.mov” download_file=”http://media3.ev-tv.me/news100711-1280.mov”]
The Elcon has emerged as the default charger by virtue of its power and price. It is NOT fully configurable and that poses some problems and the guys selling them have just enough information to be dangerous about the charger and are actually doing some damage out there to cars. Their cocommittant desire to sell battery management systems with them being part of the problem.
We need the Elcon’s 5000 watts because we have a 41 kWh battery pack. At full power from 240 vac, this would still take about 8 1/2 hours for a full charge. So we can’t really use a smaller charger. And this unit is physically BIG. By lifting the body almost off the car, we managed to squeeze it into the rear trunk area right behind the roll bar.
We also wired it into our J1772 connector and the little AC31 board David Kerzel of ModularEVPower provided. Given the mirroring of the proximity switch pin and the copilot signal pin between the plug and the socket, I can NEVER get them right. Sure enough, I had them swapped in our install and it would not charge. Swapping the wires on the little circuit board solved the problem. The car now charges quite well on the Clipper Creek EVSE we had installed for such testing. Our eCobra should charge smartly from any available SAEJ1772-2010 EVSE.
I prefer fully configurable chargers such as the Brusa, which you can easily change everything about the charge process including the stages, currents, voltages, rest times, etc. But a Brusa is close to $4000 now and this project would have required TWO of them. Eight grand for a charging system seems a little bit much since my first car I drove at age 16 cost me $60 cash money hard come by.
The Elcon at $1695 from Evolve Electrics just seems a better buy. But you have to specify voltage and charge curve algorithm. We’ve had a lot of questions about these charge curves. In this episode, I talk a bit about why we use curve 502 and how you can add a little bit of “configurability” by having 10 charge curve voltages stored in memory.
Here’s an image of the 500 series algorithms they ask you to choose from. We picked 502.
The document basically describes a very simple charge curve, which works well for these cells. Basically, you pump all the current you can into the pack, until it reaches a certain voltage. You then HOLD that voltage by ADJUSTING the current, until the amount of current needed to maintain that voltage diminishes to some set value.
The spec on most of the Thundersky and CALB and Sinopoly cells actually does call out this value – 0.05C. This is 5% of the rated capacity in amps. So a 180 AH pack would cutoff at 9 amperes.
This is not one of the choices. But AH/30 seems to be. Since we are at 180 AH, that would be 180/30 or 6 amperes.
With 69 two-cell pairs, we are looking at a charge VOLTAGE of 251.85 volts. AGAIN and I repeat for the 40th time, this charge voltage has almost nothing to do with the fully charged voltage of the cell, which in all cases will be something less than 3.4 volts if you are indeed using LiFePo4 cells. It is part of a PROCEDURE to get you to that fully charged state. We use 3.65v rather arbitrarily. The original spec on these cells was 4.2v. Then it was lowered to 4.0v. I think it is now 3.8v. It doesn’t matter, we developed our OWN procedure that seems to work better. I feel ever more validated as the MANUFACTURERs’ procedure is clearly dropping a couple of tenths of volts per quarter as we go along.
In any event, the terminating CURRENT is an important part of this procedure. You do not WANT to keep putting energy into the cell past this point. With 502, we actually ARE overcharging the cell. But since we used 3.65v to UNDERCHARGE the cell, it all works out.
The proof is of course in the pudding. Twelve hours after charging, we are seeing a pack voltage of 230.4v. This works out to a cell average of 3.34 volts – exactly where I like to see it. 3.35 would be good too. But with this many cells, I actually feel better at 3.34.
One thing stressed in the video is to actually observe and measure the end of charge activity before entrusting your pack to ANY charger. This is kind of important – under the rubric that in any product shit happens. You don’t want it to happen TO your expensive batteries. So its worth the time to go through the process with the charger a couple of times to make sure it is doing as you THOUGHT you had it configured to do.
In this case, instead of charging to 251.85 volts we actually hit a peak briefly at 253.4 volts. But it settled down quickly to right at 253 volts and maintained that very nicely. The current tapered quickly since we are charging at a low percentage of capacity. We were seeing about 22 amps IN to the pack from this charger and it appeared to be a very nice 95% efficient comparing the current into the cells with the current from the wall AC. I was quite surprised by that.
The current tapered nicely and the voltage was pretty steady, minor wandering in the 0.2-0.4 v range. As the current decreased from 22 amps down to six amps, the charger terminated abruptly at an indicated 6.2 amps. This is actually very good.
Bottom line is that bang for buck, this is an excellent charger operationally. It is a bit of a pain to order and configure. But once installed it works well and is quite powerful for the price.
We also discuss in this week’s video the announcement pending from EVnetics of a monster controller they are calling SHIVA. This controller will crank 3000 amps peak and 2500 amps continuous using EIGHT 600 ampere IGBTS. It is pricey at $7500 and they are only going to make 25 of them initially. But it promises to become the immediate darling of the drag race community. It probably has little application in a general electric vehicle UNLESS you happen to be doing a Cadillac Elescalade with twin 11 inch motors. In that event, if you paralleled the connection to the motors and backed it up with some 400 Ah cells, you could probably do 1500 amps into each motor briefly and tear up transmissions all the way between here and Florida.
I think this going to be huge for EVnetics. That the vast majority of their sales will be Soliton Jrs is not the point. Everyone will know the upgrade path to the BIGGEST dc PWM chopper on the block. And I actually think they’ll sell out of the 25 run quicker than they think. The Tim Allen/Tooltime riff on MORE POWER worked for that show and that comedian because he hit the nail on the head. Just because I don’t USE all the power under the hood, doesn’t mean I don’t want it there. At $7500 it’s just beyond the reach of most builds. But I would goess the drag racing community will waste no time neatening up their wiring with this little controller. As always, the package SEB does is just gorgeous.
The IGBT’s have an interesting feature. They have internal temperature sensing. What this means is that the coder guy, Martin, can actually throttle this thing back very quickly and very accurately based on temperature. ANd what THAT means is the better you are at getting cooling glycol to this beast, the more power you can get out of it. The spec limitations are 4800 amps actually but they’ve got it cut back to 3000 amps. I don’t know the voltage drop, but if it’s a volt at 3000 amps you also have a 3000 watt heater. NoGiven the forward voltage drop on six IGBTs, that’s still a lot of heat. But there’s room there if you beg…. and don’t mind blowing a $7500 controller every other race. it’s all software…
We did talk a little bit about the Tesla party. What I didn’t mention, but am looking into is the Tesla/Panasonic battery. March 2012 will be the first run of a new 18650 cell by Panasonic that is really quite a thing. It uses a couple of innovations. They call it their Nickel New Platform or NNP cell. It is actually a Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) cathode with a 3.6v voltage and 3.4Ah in a single 18650 cell. This works out to 46 grams and 12.2 watt hours or 265 wH per kilogram. By contrast, our cells are about 106-109 wH per kilogram. That’s how you get a 300 mile range.
Interestingly, they have even bigger plans for March 2013. At that point they will do a production run of the same cell, but they intend to replace the carbon anode with a silicon alloy anode. This will boost the Ah rating to a full 4.0 Ah in this cell.
As to cycle life, there’s some bad news but then some good news. To the standard quoted 80% of the initial capacity, this little cell will only do 500-600 cycles. But if you can deal with 70% capacity, it will go to 2000 cycles. And so given the 265 wH per kilogram, build in a little extra capacity. It will be a MUCH improved package over the Tesla Roadster battery module. And it explains the Tesla 300 mile range claim.
I found it interesting to note that since acquiring Sanyo, Panasonic may be the world’s largest Lithium battery supplier. But it is also interesting to note that they are building factories to produce all this in CHINA. In fact, due to the strength of the Yen, they’ve dramatically cut back plans on a new factory in Japan.
Bottom line, the cell march goes on. Our 80 mile cars will soon be in the 250 mile range (really). But it will cost you. And of course, all roads lead to China.
63 thoughts on “Follow the Yellow Brick Road”
it seems to me that you don’t ever want to exceed 3.6V on any cell if you want them to last long.
top balancing is clearly superior for this, you just have to make sure you stay away from full discharge.
I would top balance and charge to an average of 3.45 or even lower. the last part is not worth it.
How many of them have you charged Dan? And how many have you lost….
We don’t have a theory any longer Dan. Top balance is dead here. Nothing more to investigate. Didn’t work out. Sorry. You can’t THINK you’re way to new information in the face of our doing this for three years with a half dozen vehicles.
Second, there’s really no problem exceeding ANY voltage. The cells are not harmed whatsoever by a voltage spike. This is a conceptual problem across the board. If you are MAINTAINING a voltage using a CURRENT to do so in a continous fashion, you will OVERCHARGE the cell. I can make the cell voltage 10v for 10 seconds and it does nothing to the cell. But if I hold it at 4.3v until the current decreases to about 0,05C I’ve put 11 lbs of potatoes into a 10 lb bag. Mashed potatoes.
I can have cells at 3.45, 3.65, 3.85, and 4.15 volts all in the same string at the end of the charge process. Not to worry.
Again, the time zone at top and bottom are in different continents. We’re charging at 20 amps and discharging, often in the driveway, at 200 amps. A minute of charging is the equivalent of six seconds of discharging at those two current levels. I’m all about preventing damage at 200 amps, and a couple of minutes at 20 amps and 4.00 volts is totally irrelevant to the cells and I.
Dr. Doerffler noted at the conference that you failed to attend that bottom balancing was not very convenient. As I mentioned there, in all the times I’ve worked with these cells and all the testing I’ve performed, I’ve never once had a cell express any sympathy whatsoever for my convenience. They are really quite cavalier about it.
At this point, thats our process. That’s how it seems to me.
Nice video, Jack. I’d be tempted to check what’s the configuration element of Elcon charger. EEPROM? Jumpers? Some hacking SHOULD be possible…
Btw, I made EVTV as a podcast subscription process even simpler. No need for copy and paste URL. Just enter http://www.projectooc.com/evtv/podcast/ and click a link titled “click here”.
Jack, I’m proposing not overshooting at either end. you are overshooting at the top every single time you charge.
it’s true I don’t have statistical data with which to be certain that such overshoot shortens life significantly but it’s certainly consistent with everything I know about the cells and what you have said yourself many times.
and yes convenience can’t be a argument for doing it wrong but in this case doing it right is also a lot more convenient.
I know you often pick a stand point and stick with it, facts be damned. but it can’t be helped Jack. it’s just wrong.
if I were to suggest one thing you could change to improve you effective intelligence it would be to be open to reconsideration.
an error doesn’t become a problem until you refuse to correct it.
I’ll gladly stipulate that it’s dangerous to run the pack down during driving and more so if top balanced. but you simply don’t run it down. it has no business there. that may be inconvenient, you may have to add instrumentation to ensure it doesn’t happen but the truth is quite cavalier about such inconvenience.
for long life you stay away from the extremes. both of them. there is no 10 second exception.
a short burst midway wouldn’t be a problem. but you are cruising to 4.1V at 6amps for much longer than 10 seconds. it is a clear cut violation of your own principle of staying away from the extremes.
Wow this stuff is moving fast. 200+ watt hours per kg next year is a big jump. Pity about the zillion little connections making a pack with 18650s.
But as you say the wretched things are pretty uncaring about what’s easy for us.
Very glad the event went well the other weekend
After hearing the Cobra is over 400W/mile on town runs. Will you be including our much loved soap box derby using the cobra in this Fridays show?
What if the new owner drives his EV too far out and takes a risk coming home? Does he…
A: Go home. If it runs out, it runs out. It’s bottom balanced so it will not reverse charge any cells. No harm done either way.
B: Go home with an unbalanced pack at the bottom. If it runs out, he ruins the weaker cells. (Expensive and fiddly).
C: Phone you. Then you can imagine his route home cam be halved because you thought it so.
Read about the scientific method. You say you don’t have any statistical data to say “overshooting” (overshooting, by what definition?) shortens life significantly. So you have no evidence essentially, which needn’t be the case this is something that you could actually test for with time, money, equipment and a published, by video if you like (has this been done IIII WONDER??), for everyone to see methodology.
So, if you want to know the best way to fry a burger, or lots of burgers without burning or undercooking a few…….ya got a actually fry a few burgers.
And before you tell me I don’t know what testing you have done, you already told me you’ve done jack shit except ponder. Now don’t take that as an ad hominem, this is a critique of what’s missing in your argument, not a critique of you personally.
D: After giving your ample warning on the SOC meter or “gas” gauge that your are running out of charge the amp hour counter shuts down the controller, opening the main contactor. You have just “run out of electrons.” Gas cars have been abruptly running out of gasoline for 100 years. It’s familiar behavior, no more unsafe than when it happens in an ICE vehicle.
That said, I don’t think Dan has the hands-on experience to tell anybody how to set up a pack. Please prove me wrong Dan.
I am running a top balanced pack. It hasn’t been a problem. Perhaps 5% of the cycles have even been in the bottom 20% of capacity. It is nice to see things are fine by finding the cells within a few hundredths of a volt of each other near the end of charge, when I care to check.
At what point does “been there, done that” kick in? After you have.
Do you want to hear a dirty little Tesla battery secret? I got a rumor from someone that attended the Tesla party. Tesla is randomly replacing battery modules in the Roadsters due to cell failures. The new battery cells are tested before they leave the factory and then again when they make it to the US. In the weeks it takes to get here there is a 10% failure rate for cells that weren’t even used. Tesla has high standards for the cells which explains why they even bother checking them a second time. As Jack has predicted the batteries aren’t lasting as long you’d expect.
About the “extra” voltage points in the Elcon charging profiles: I remember looking at the charging profile for my Zivan chargers (I got the same profiles to choose from) when they were programmed for lead acid batteries. Each of the voltage points were for the different parts of the lead acid profile: bulk charge, absorption phase, equalization phase. IIRC, V4 was the absolute maximum voltage during the equalization phase though my 48V pack never saw the 66V limit I did note that the voltage would slowly climb and peak about midway during this phase and then drop as the batteries heated up. A timer would shut off the charger.
It appears that for the lithium algorithms it was a simple matter of “faking” out the lead acid charging profiles. If the pack was at V1, a very discharged pack, then charging could happen at a very slow rate until V2 where normal full current charging could take place. V3 wasn’t needed for the lithium profiles so it is just some value close to the saturation voltage, possibly chosen close to some 90-95% SOC voltage estimate. On my charger this is where the red light starts blinking. When V4, the saturation voltage, is reached the light turns yellow and charges until the current drops sufficiently low or the timer runs out. I charge to 3.465vpc so the ending current I had programmed in is quite low.
This seems like a rather simple way to adapt these chargers for a battery that wasn’t commonly available when the original design was done.
You don’t have to do the testing yourself if you watch some of the past Friday Shows; Jack has done it for you and that is why he has such a strong opinion on how to manage the batteries. If you go to the November 13, 2009 show, Jack will explain in detail why he favors bottom balancing over top balancing and why he is against using a BMS. Since then he has proven that bottom balancing works through actual application in working vehicles.
Andyj, I’d just like to extend your argument back to the abstract a hair to simplify our discussion.
To me, when designing anything and everything, it is all and ONLY about controlling failure conditions. To simply insist that one should practice moderation at all times to prevent disaster is horrifically naive and foolish. That’s like condoning cigarette smoking in a fireworks stand and simply saying “watch your cherry”. Consider the above mentioned Shiva controller. Theoretically, it will handle 4800 amps. Yet, EVnetics is insisting to derate it by nearly 40%. Why? To control failure conditions. If you truly believe that self-moderation of human behavior is sufficient safety, then you must also believe that fuses are utterly irrelevant as well, no?
We could argue endlessly about different situations where one may be tempted to violate the rules, or where another operator than yourself may be ignorant of them. But that’s all skirting the issue. You MUST DESIGN FOR GRACEFUL FAILURE MODES. And top balancing violates this imperative so fundamentally that the only way to band-aid over it is with additional complication and with it more potential failures.
And in the case of these cells, what we are really worried about is significan deviation from the average capacity. Why not over-purchase and test the capacity of every cell, then throw away the out-liers? After all, the argument against bottom balancing was that there might be a solitary cell that is much higher voltage than the rest. The good news is that larger production runs will automatically iron out the inconsistency; and as Dr. Dohrfler’s presentation indicated, it is possible for good consistency to be produced. One of his slides showed in the Y axis of a graph a summarized consistency metric and in the X was each individual cell received and tested across 270+ cells. There was a region on the right side – indicating more recent acquisition – that showed a much better consistency than the left where instead of being randomly scattered across the entire spectrum, this grouping was all in the lower quadrant or less (lower was better btw). My point is that as time marches on we will quickly have nearly identically performing cells that will not need any apreciable balancing techniques – top, bottom, middle, or dynamic. At which point we will all remember these good old days of arguing endlessly about butter side up or butter side down.
Until that day, and thereafter, we must diligently design for the most robust and graceful failure mode in all conditions for all our components.
You are right Nabil.
Bottom balancing it is!
Quite so Nabil. We’ve learned to survive by bottom balancing. But in truth, the cells we are getting now are SO much better than three years ago with regards to uniformity and consistency. You’re not really going to see any 4.0 or 4.1 cells. What I clearly said in this week’s episode is that in actual practice, I might see a cell at 3.8v, but I wouldn’t be ALARMED at all in seeing 4.0 and 4.1v.
Again and I’ve never adequately conveyed this, though I have SAID it and it makes no sense to armchair theorists such as Dan. The charge voltage isn’t anything. It isn’t even “real” in a strange sense. It is an EXHIBITED voltage that shows up on our meter, when we apply an almost unknowable voltage against a cell voltage. Like any series or parallel circuit, we measure the result. If you apply a 12v source against a 7 volt source of opposite polarity, your meeting indicates the result 5v. But there is no 5v source in reality. It’s a result.
A charger works a little bit this way. You’re really pumping current into the cell, and observing a resulting voltage. It’s enough current that actually WHERE you measure along a large diameter cable has a large effect on what shows up on the meter.
Now it is of course nonsense for me to say that that voltage, which IS measurable, doesn’t matter. But it doesn’t matter. The “voltage” doesn’t do cell damage. The only thing that does is forcing more power into the cell than there are ions to work with. But we can’t SEE that and it is difficult to measure. ONE way is to count AH, but if each cell has an unknown and varying capacity this is heroically difficult to manage (although the cells still don’t care). And you have to know your EXACT state of charge when you begin to charge anyway, which you are NOT going to know.
So we are left with voltage indications. And so that’s what we use. And we can PROCEDURALLY approximate a full charge. But it is one level of abstraction away from what Dan and many think it is. We are NOT measuring state of charge by voltage. Repeat, we are NOT measuring where we are in the charge process by voltage. ANd it is NOT the voltage of the cell at all.
By PROCEDURE, and it’s really quite a flexible and good procedure, we can pump ANY level of current into the cell. If we do so at ANY RATE until the MEASURED or APPARENT exhibited voltage is such and such, and THEN we HOLD that exhibited voltage until the current tapers off, indicating the cell filling up with energy, then at some specified CURRENT level we terminate the charge.
If you follow this procedure, you will approximate full state of charge.
The other area NOT understood apparently is that ALL the cells are at the SAME state of charge at the end. They each have EXACTLY the same amount of energy in them. The apparent voltage variation is due to their different CAPACITIES. With top charging, you are actually manipulating DIFFERENT energies into each of them, so they APPEAR to have the same capacity. They never will.
Note that they don’t all get very focused on the current, which is the actual charge delivery of energy. It’s an important part. This is the Elcon disconnect. They THINK that 1 amp is SAFER than 6 amps because it is less amps. It is ACTUALLY the point where you QUIT putting in energy and an important part of the PROCEDURE. So we QUIT at 6 amps. They wanted us to CONTINUE PUTTING ENERGY INTO THE CELL until it tapered down to 1 AMP, to be safer? HOw is putting MORE energy into an already by formula fully charged cell MORE safe?
nd again, the proof is in the pudding. After going through the PROCEDURE, if you wait an hour or so, or 12 hours to be absolutely accurate, you can measure the REAL open circuit voltage of the cell. For these LiFePo4 chemistry cells, that is 3.40000 volts fully charged. You will observe some difference from that I DO hope. 3.35 we love. 3.33 we like. 3.37 we start to worry. And 3.396 is cutting it TOO close for the accuracy of this equipment to be depended upon to NOT overcharge our cells.
And at that point, you will actually observe remarkably small variations from cell to cell.
So both the “top balancing” and the “bottom balancing” are neither what Dan “thought experiments” himself into believing. In reality top balancing is UNBALANCING energy levels to accommodate different container sizes.
Bottom balancing is a kind of alignment to ensure that whatever their capacities, if you put the SAME amount of energy in them, and then discharge the car, they will wind up back at the SAME place simultaneously in time at the END of the discharge. This keeps them from kiling each other.
This is NOT the way this stuff is taught or described. It is very difficult to actually get a visceral grasp of this, so they don’t bother. Memorize the equation/formula and do as the preceding guy did.
I don’t mean to make this sound mystical. It isn’t. It’s a very ordered process in a very ordered universe. But it is not a child mind “read this voltage” kind of thing that it is constantly portrayed to be by Davide Andrea, the BMS crowd, and Dan, who only recently got his first RIDE in an electric car, doesn’t own one and has never built one, but has fantasies of being master of the universe.
Finally, let’s talk about over discharging your car. It is a car. It is used as a car. And 10,000 American drivers run out of gas each DAY if AAA is to be believed.
I built the car. I know the car. I drive the car. AND I have it set so it disables as soon as it reaches say 90% discharge. Won’t move. All good.
Now, I’m going down the freeway and hit 90% and the controller clicks off. I pull to the side of the road. But I can SEE the exit in front of me a quarter of a mile. And down that exit ramp is a gasoline station, restaurant, bar, grill, and casino with lap dancers, hot coffee, and the best cinnamon rolls made in the universe.
I can whip out the cell phone and call the flatbed to come get me and sit in the cold on the side of the road dutifully fulfilling my vows and obligations to my cells.
Of course, it’s all based on this Xantrex state of charge indication. I can reach down and press both arrows simultaneously, resetting the Xantrex to full. And drive the 1/4 mile, then down the ramp, and pull into lap dancing coffee drinking cinnamon roll heaven where I’ll await the flatbed.
I’m hitting the button.
Turns out they had a plug in down there, I kind of got caught up with the lap dance thing, and next thing I know I’m fully charged anyway.
Go drive all over creation. Again I’m getting low, but I’m almost home anyway. Stop by my mothers apartment to see what she’s doing. She’s just cut her hand about half off slicing an onion and is bleeding all over the place. She’s 76. Should go to emergency with this one.
Put her in the car and drive to the hospital. Whoops – hitting 90%. Two little buttons will let me reach the hospital. Or I can call the flatbed and we both sit there….
I’m not trying to cause range anxiety here. BUt I actually DRIVE these cars. In reality, they rarely actually reach 50% discharge in daily driving. And sometimes I go over. And I HAVE driven them experimentally until they use won’t roll any more. WITHOUT KILLING CELLS.
But in the end, it’s just a car. And these are just batteries.
You are right Jack.
Bottom balancing it is.
Is there a good way to remove onion smells and blood stains off leather?
Club soda is the universally recommended happy housewife claim for all things stain related. I don’t know why and I’ve never used it.
Why? Were you attacked by a road rage crazed onion farmer?
Guess we have come full cycle. Back to the BMS BS.
A year ago I jumped off the cliff and said f*ck it. If this BMS manufacture will not help me install their BMS I paid $2700 for even after offering to pay the $80 bucks per 30 mins for tech support. Maybe I should do what this old guy on youtube is doing. So I did and its been a year and I’ve put over 6000 miles on the car. Again I would like to thank you Jack for your advice. Bet Jack can guess the BMS system too.
I’ve always said with all these B*S “manufacturers”. Unless they actually guarantee their work from any cell death, EV fires and so on for the fair life of the product, whatever the installation. It’s not even going to be considered.
Blood ‘n onions. No, I don’t have a clumsy French wife. I’ve got much worse but it’s good to know she can make the distance by pressing two buttons on the Xantrax and not having to worry about losing any cells where I can have my stomach pumped and knife wounds stitched. Luckily, according to the openrechargemap There is an EV point near Leeds hospital.
Top balancing is inverse to the way one thinks with wet fuel cars. You go on a trip noting how much you have to empty. Yet many in the EV community insist on top balancing every cell and charging to the nth degree what they cannot empty out anyway.
People are fascinating.
I think I got it:
The lowest capacity cell in a pack will have the highest internal voltage.
First, thanks for the additional information on charging LiFePO4. If I might add, I just learned, through a little charging experiment of 16x100Ah Thundersky cell, the importance of that “0.05 C limit”.
I have a Delta-Q charger and it can output 18Amps. The algorithm I have charges the cell up to 3.675 Volts and then ramp down the current to about 1.8 Amps before it shuts down. As you said in the last show, I was watching my battery charge as I charged for the first time my batteries with this algorithm. (By the way, I bottom balance).
In my charge cycle, everything seemed to work great until the current started dropping. At one point, the current was around 2.5Amps, I had a few cells going from 3.7 Volts down to 3.55 Volts. The problem that creates is that I had two cell around 3.85-3.9 Volts. Well, these two cells “took” the available voltage and now I got two cell charging at 4.1 and 4.15 Volts.
My conclusion in this is:
1. Try to charge to a maximum of 3.65
2. It is VERY important to stop charging at 0.05.
Out of these two points, if my charger only followed the “stop charging at 0.05C” rule, my cells would have all stayed at a voltage under 3.90 Volts.
I am still learning by playing with these cells, but I would like to take the opportunity to thank you for all the information you have given us. From what I have learned so far, you nailed it.
I guess that one difference between you and I, Jack. I will actually call for the flatbed tow truck. Back in the day when my EV was lead powered because Lithium wasn’t available, I did exactly that to save less than $2000 worth of Optimas. I haven’t come close yet with the Lithium pack except for the range test. I had a tow bar in my pickup ready to go, but I didn’t need it.
Since my range test ended with 0.102 volt difference between the highest and lowest cell I don’t think it actually makes much difference which end my pack is balanced too. My controller won’t let the pack voltage below 2.4 vpc to save the DC to DC and that was enough to limit the practical discharge to where the cell voltages are just over 3 volts at the end.
We all pay our money and take our chances. Hopefully we can all share our experiences without these issues always turning into flame wars.
I’ve been wondering the inner resistance of the cell. The inner resistance of the cell is said to increase in cold temperature. If I have a large pack of cells, all neatly bundled together, and no insulation around it, and the temperature outside on the driveway where I left the car drops below 0 degrees (Celsius). Now I’ll start charging the pack, where the cells on the outer edge of the pack are the same temperature as the air outside, but the cells in the centre of the pack are still cozy 15C because of the mass around them. The warmer cells start taking charge right away, but the outside cells are slower, turning the initial current into heat because of the increased resistance, before warming up and catching up with inner cells. Will I end up with massively “unbalanced” pack, because some cells turned the current into heat receiving less charge than other cells? Will this cause the warmer cells to overcharge? Is this just stuff for MythBusters? Anybody tested this yet on record?
You’ve got a thought experiment going there. And a whole new term to hang it on. The “inner resistance” of the cell. You got this from some bullshit forum. Cells do not have any such characteristic as “inner resistance”.
This is a one off copy/reproduction of the oft alluded to with no understanding whatsoever term used in the EndlessFear and DIYElectricjunk forums “internal resistance” which they also don’t have any of.
This all derives from a concept properly termed “equivalent series resistance” which is a modeling technique to account for the fact that cells under load decrease in voltage.
Now you’ve got that all wrapped around a concept of the “resistors” resisting charge current and giving off heat. If they’re giving off heat, then they aren’t cold are they?
You’ve wandered off down a dark road with Dan where you try to conceptualize this to death. GO MEASURE IT. They are part of an ordered universe. You don’t have to DEVINE IT.
Bottom balance the pack.
Put them in the cold.
Measure the voltages at the bottom.
Yah, i know that’s a lot of work. It’s inconvenient. And it’s easier to type. But the cells do NOT care about our “convenience.”
Jack I don’t understand where you are coming from on the inner resistance thing. Modeling a system as a black box with an internal resistance is not a new concept in electrical engineering — the “system” just happens to be a cell in this case. Anyway, I’m not clear what point you are trying to make. When I run high currents through my lithium cells they get hot. When I run current through them the voltage goes up (charging) or down (discharging), just as if there is an “equivalent series resistance.” I feel like I’m missing something here, thanks for any enlightenment.
Just to clear my point; I do not read bullshit forums. I might have sometimes misinformed by people who themselves have been misinformed. I even know people who like BMS’s, and I don’t think they are bad persons, just misinformed in some cases. I also have been directly hands on involved in building several conversions, but unfortunately I don’t own one myself, so I can’t test things myself whenever I want to test something. I sincerely hope I’ll have a chance to test it myself some day soon, no matter how inconvenient it is, because I’m not stranger to hard work. I might be wondering on a dark road of misinformation, but certainly not doing it with Dan, because I’m not claiming any superior knowledge over anybody else here, quite the opposite.
I’m here acquiring knowledge hard to come by, that is why I ask questions from you, Jack, or anybody following this blog. If just asking questions about things confusing me (because all the misinformation surrounding the subject) makes me obnoxious pest, who doesn’t deserve straight answer without subtle hints of being stupid and lazy, I have to take my questions somewhere else, where I might be misinformed further. This is not good thing to conversion movement in general. The “whole new term”, inner resistance, is not my theory, but something I have read from seemingly respectable sites (not forums), but I have no way of knowing if it is true or not, because I have no way of testing it myself at the moment no matter how hard I wish I could. It would be nice to get more information about the subject without being stamped as imbecile, even if most people here think the question is stupid. Isn’t this all for sharing information, enlightening the people wondering about on the dark roads? Thank you James for at least taking me seriously, although not being able to give any further information.
Thanks again for all the hard work and deep thought which goes into producing EVTV. For the Cobra build, were the batteries paired randomly? Is the “Aux”(?) battery in the Cobra a 12v lithium? If not, would a lithium motorcycle battery offer a solution to the discharge/’phantom’ load problem? I’m glad the convention and the news coverage spurred new interest in EVs: have any sense what might be broadly driving the new arrivals, e.g., green/ecology, energy independence, etc.? Rolling resistance in a second SPORTS car? What was the lowest speed at which you tested the Cobra? Did you downhill derby test the Cobra?
My apologies if my tone offends you. There’s nothing to “not understand”. I gave you a step by step procedure to answer your question.
There was a rather circular knot in your entirely hypothetical that lower temperature causes higher “internal resistance’ and so more heat, in cells that were colder. That’s kind of a self healing problem. BUt if a matter for curiosity, here is the step by step to learn the answer.
What’s not to understand?
ESR does not accurately equivalent a “resistor” inside the box. I know they teach this. I would offer it is not that simple and doesn’t work that way.
A battery is not an electrical device of any kind. It is a chemical device. The drop in voltage under load is an indication of diffusion delay, not a resistance in the usual meaning of the term. Similiarly heat generated on output current or charging will not calculate out to this ESR. That is because it is a chemical process and not an electrical one. It CAN at times be useful to black box an equivalent circuit to try to model a battery. And I have dozens of conversations with people who try to do this all the time. I usually try to get out of them. I do not share the view that they are at all useful.
Sorry if I sound like an asshole. Some days are better than others.
CosMiik: No need to get expensive about it, you don’t need an EV to learn about internal resistance. Buy a single lithium cell (one designed to be recharged), or use one from an old battery drill, or get an RC battery, or something like that. Get a voltmeter that can also measure amps. Get some light bulbs or a heater or something you can use as a load. Check the voltage of the cell. Put it on the charger, measure the current and voltage again. The voltage will jump up. Once charged up, put various loads on the cell, and measure that the voltage goes down.
The basic formula is V = IR. Usually an internal resistance is measured using two points, two different discharge levels:
R = (V2-V1) / (I2-I1)
Once you have that number, you can predict how low a cell will sag for various voltages:
V = Vresting – IR
So if you have 0.01 Ohms of internal resistance, you would get a chart something like this:
Current (A) Voltage (V)
One caution is the battery might have an artificially high voltage due to surface charge, so 0 Amps (no current) is often avoided for internal resistance measurements.
If you have a gasoline car, you could measure this on the main battery. With the car off, turn on more and more loads, measure the current and voltage, and do the simple calculation.
Jack is generally good at explaining things and I’m sure has a valid point that we are missing. I think maybe he was trying to say the inner resistance doesn’t vary much for Lithiums and to not worry about batteries at the edges of the pack? Maybe it’s that battery boxes help keep the battery temperatures even?
I have personally measured the batteries at both ends of a series string tend to be slightly lower in voltage for both Lithium and lead acid. It was a very slight effect (1/100ths of a Volt), but it might have been due to the end batteries being slightly cooler.
Editing the show tomorrow morning – much about your questions.
The cells were paired randomly – mostly. Each pair was actually discharged , USUALLY as a pair, and set to a static voltage of 2.75v.
The aux battery, originally a 7Ah cell, then a 35Ah cell, and now no cell at all.
The problem was that we were using the aux cell to allow the ignition switch to “turn on” the DC to DC converter and it was just a hopelessly bad concept from the beginning. The problem is numerous parasitic loads that I’ve been driven to by equipment that all wants 12v to come from somewhere.
David Kerzel’s J1772 board is a case in point. We started with a diode, a switch, and two resistors. It works fine. But I kind of bought into the additional functionality brought by this small, inexpensive board. Actually mostly we got the proximity switch to actually do something. Not much beyond that. But there IS a little relay in there that I use to turn on an LED which lights up the cool billet aluminum connector.
Anyway, it HAS to have 12v all the time or you can’t charge the car.
The Xantrex uses the 12 v and needs to be on to count AH when charging.
Same with the Zeva II that runs the gas gage.
Same with the GPS speedometer so it doesn’t have to reacquire.
Etc. etc. So the aux battery was draining down in just a few hours.
So we started piling up devices so you could short circuit our OTHER devices to jump start the system and charge the dead battery. It was a MESS and the more I worked with it the worse it got.
So we stripped it all out and went back to the beginning. The original problem was that the WarpDrive Industrial was throwing faults when we shui it OFF. Something to do with the 12v. The battery fixed it because we separated the ignition switch side (using battery) from the DC-DC converter side (turned on by relay.)
The real culprit turned out to be the fanes. The Derale heat exchanger fan and the XSTurbos fan we use to cool the motor. When you cut them off, they turn into generators and maintain 3-5v on the line for a couple of seconds.
The WarpDrive sees this on a DIGITAL input (the ON signal) and assumes it is on. But the voltage is below the 9v needed for its 5 and 15vdc DC0DC converters. So the pedal input looks wrong, and the contactor opens and so the pack voltage looks wrong. So it throws these faults.
The solution is to fix the controller. It shouldn’t do that. But in the interim, we’d like the car to work. We put the fans on a relay connected directly to the DC0DC converter. The ON signal of course comes from the DC-DC but through the ignition switch.
Now when turning off, the ON signal goes completely to zero, and the 3-5 volts only appears on the line to the relay, which opens.
We did the Soapbax Derby this afternoon. Longer than SPyder. Shorter thanks Speedster Duh.
We had the rear end aligned, but need a part before we can complete fromt end alightment. Currently using 2 AH per mile which is much higher than hoped for and puts us at 90 mile absolute max instead of 120 safe.
But it kind of takes off really nicely. And I’m getting into driving this car.
No, the ESR does vary both by temperature and by SOC.
I guess I thought I was being gigged here. IF you have a problem with cold cells not charging as efficiently and this causes heat, then they rapidly become “not cold” don’t they?
So it’s kind of a self healing problem or “canceling of errors” type situation. We just don’t’ see much activity from end to end.
Speaking of ends, I’ve observed the greater sag at the ends. I think it is just diffusion – the circuit naturally deals in current into each end. Those ends will sag sooner than the next one in the line largely because that’s the exit point.
Let’s say you had glasses of water with each siphoning to the next until they were all at the same level. Now go draw water from the one on the end. If you do it hard enough, the level on the end one goes down first, they don’t’ all go down simultaneously. But they quickly all come to the same level when you stop taking water out of the end glass. It’s a delay of mass.
Similarly, we are accustomed to thinking of electronics as very fast. Even the nature of current. How fast do electrons move through the wire. Answer, at nearly the speed of light. Actually that’s the WRONG answer.
The force of one electron acts on the force of the next and the next and the next in a chain. Like a row of BBs in a soda straw. Once the straw is full, when you put one in one end, one pops out the other instantly. But the actually BB didn’t move far, nor fast.
Electrons actually flow through copper at inches per minute. And believe it or not, it is this SLOW flow that causes the heat. WE FORGET ALL ABOUT THIS IN THE MODELS.
Dealing with it formulaically is much simpler and much more understandable, but it’s not what HAPPENS. The movement of actual electrons through the wire, kind of bumping and grinding into whatever trash is in the hallway, is where the heat is. The EFFECT, and just as accurately the CURRENT, is much faster – a combination of actual electrons moving and more importantly charges reflecting down the line.
In chemical batteries, charges work the same way, but ions must also actually MOVE and they must pass through the Solid Electrolyte Interpahse layer and actually intercalate INOT the crystalline structure of anode or cathode. These ions are actual atoms and they must physically move.
Hope this helps.
Apologies accepted, it must be hard sometimes dealing with people of such varying backgrounds and knowledge level, let alone personalities. And some days are harder than others, I hear you. I guess I got most heated up with the comparison to Mr Know It All, which is so far from the truth. Thank you for explaining things further, and still leaving some things to test and verify myself, which I will do given the next chance. When I do, you all will be informed about the results. Thanks James for suggestions on test methods. Actually my inability to test things at the moment has more to do with my living conditions and situation rather than not having access to cells… unfortunately.
I was aware of the resistance not being electric in nature, but chemical diffusion delay, which, I’ve been told, increases in cold temperature, and have even tested that in one occasion with a single cell by similar method to James’ suggestions. I also know it’s a “self healing” condition, as the cell heats itself up in time. My confusion, which I haven’t yet been able to clarify by testing, is that the heating up means energy from charging going somewhere else than chemical storage in the cell. So putting the same amount of energy in two cells with very different temperatures causes the warmer cell to receive more charge than the cold cell, in which some of the energy goes in heating the cell. To make sure, I do not claim to know this happens, but if someone has hands on information on the reality of what happens, or even good theories, I would welcome this information most warmly. I will still test this myself some day when I can, but if someone has already existing data about the subject, it would be nice to know.
If there’s any reality in this, it is relatively easy to prevent by insulating the pack and having some kind of circulating system (air or liquid) to even out the temperature differences, especially in colder climates, but is this necessary evil or just a problem for us living in the Arctic?
We are going to experiment with cell heating in Elescalade, buy circulating heated glycol in a false floor of the battery box. I have always been uneasy about the constantly moving spec on the lower end of temperature for charging – like 0C which is 32F. I’ve asked a number of times what happens if you charge below that and get a garden variety of answers, all vague from the Chinese.
Could capacitors or parallel cells at the ends of the pack act as a reservoir to help prevent sag during acceleration until the rest of the pack catches up?
I don’t know. Sounds plausible.
“So putting the same amount of energy in two cells with very different temperatures causes the warmer cell to receive more charge than the cold cell, in which some of the energy goes in heating the cell. To make sure, I do not claim to know this happens, but if someone has hands on information on the reality of what happens, or even good theories, I would welcome this information most warmly.”
That bit right there contains the key issue you missed. The cold and warm cells that are in series do not receive the same amount of energy. Because they are in series they receive the same amount of current, but that current will cause the colder cell to have a higher charging voltage. That extra measure of voltage, times the current, is the extra watts of heat that warm the cell and make the problem go away. Since the cells receive the same amount of current (same number of electrons) they move the same number of Lithium ions back to the other side and so the same amount of charge is returned (unless you go so far off in the extremes that side reactions start happening.)
Your explanations above about balancing and charging PROCEDURES has to be the clearest I’ve seen put into one place. Hopefully more people get it now.
@EVfun: I hadn’t thought of the voltage difference due to higher IR as the compensating factor with cells of different temperatures. Thanks for pointing that out.
David D. Nelson
You mention that higher voltages when charging do no damage if the cell is not full:
“I can make the cell voltage 10v for 10 seconds and it does nothing to the cell.”
but if you are above 4.5V aren’t you above the breakdown voltage of the electrolyte, and therefore potentially damaging the cell?
No. The electrolyte has NO “breakdown voltage” This is a preposterous notion. Electrolyte deterioration is solely a function of heat – and perhaps something we do not have diagrammed well at the intercalation point as this is where breakdown components seem to migrate. The electrolyte has no cognizance of “voltage” and it has no effect on electrolyte whatsoever.
Thanks for the good theory EVfun. Now just have to confirm that with testing, find out the extremes, and we’ll have a fact:)
All electrolytes have a breakdown voltage.. Thats when it goes “BBBZZTT” inside. No doubt this is far outside standard charging ranges. In fact right into the BMS range of EV mounted Lithium balloons. haha (Just kidding).
The apparent speed of light through various materials have always fascinated me. A radio signal through a cable is maybe around 96%. Through co-axial cable it appears to be around 60% but between the driven element of an aerial and its reflector it appears to be 105%. A tuned reflector is also around 105%.
Any nuclear physicists want to type me smart?
“The electrolyte has NO “breakdown voltage” This is a preposterous notion.”
Then what are they refering to here when they talk about the breakdown voltage?
“Silatronix organosilicon compounds can be advantageously used as replacement for conventional electrolytes such as acetonitrile and alkyl carbonates. Organosilicon compounds have lower conductivity than these competing electrolytes, but have the important advantages of lower flammability, lower vapor pressure, and higher electrochemical breakdown voltage. These features combined make Silatronix organosilicon electrolytes a disruptive technology in the energy storage field. “
“A third parameter for the practical electrolytes is its
kinetic electrochemical stability window. This was determined
by linear sweep voltammetry on a cell containing
polymer electrolytes sandwiched between stainless steel
working- and a lithium counter-electrode, with a lithium
reference-electrode. The potential of current onset may be
regarded as the breakdown voltage of the electrolyte.”
I didn’t just make up the term “breakdown voltage”.
More directly related:
“Regenerative braking can cause problems
for Lithium Ion batteries because the instantaneous regenerative braking current inrush can cause battery voltage to increase suddenly, possibly over the electrolyte breakdown threshold voltage.”
When I heard the term breakdown voltage, I also wondered if they were referring to voltage breaking down the electrolyte or if they were referring to the voltage that produced enough heat to cause the electrolyte to change from a liquid to a gas. It doesn’t make since to me that the voltage by it’s self would cause the electrolyte breakdown but rather the heat generated from that voltage. In the presentation by Jay Whitacre, he spoke of the voltage that the electrolyte broke down but did not mention if this was from the actual voltage or the resulting heat.
I’ll leave further testing to you CosMiik. I’ve done enough field testing to be confident in the results. I mount my cells between aluminum end plates and then bolt the end plates down instead of boxing the cells. This leaves the end cells in a block considerably more exposed to Seattle weather. I’m finding no drift between the center and outsides of the pack.
In looking at the links you privided, I am questioning now if the electrolyte break down could be electrolytic instead of thermal. Not trying to type myself smart, just confused.
My interpretation has been that voltage break down is independent of heat break down. I’ve heard reference to different cell component pairings that would have higher voltage than current lithium chemistries but would need development of an electrolyte that is stable at higher voltages than most existing products. That suggests to me that it is indeed the voltage that is the issue.
If you want to drag forum nonsense into this blog (EVDL) and quote it as authoritative, I not only cannot help you, but there is a REASON I’m not reading that nonsense on EVDL anymore.
And if you want to debate it, take it to EVDL.
We’re just not going to do that here.
You’re trying to have a discussion of the breakdown voltage of antifreeze. I’ve answered the question.
“Regenerative braking can cause problems
for Lithium Ion batteries because the instantaneous regenerative braking current inrush can cause battery voltage to increase suddenly, possibly over the electrolyte breakdown threshold voltage.”
Two “can”‘s, a “possibly” and adding in words like “instantaneous” and “battery voltage to increase suddenly”.. Sorry young fella, this is a non-fiction area.
That was a quote from a paper done by Delphi Automotive Systems, if you bothered to read the link. It was not an opinion piece from myself or anyone on the EVDL, though the link was hosted there. So I’ve quoted three separate industry sources discussing electrolyte breakdown voltage, and I’m the one indulging in fiction?
You know JP. I did NOT bother to read the link. Now I have. And now I remember why I didn’t bother.
HAD YOU read the link, the reference to an voltage breakdown in electrolytes was in 2001, and it is an entire paper on an overview of cell balancing techniques and BMS design parameters.
Three years ago, I myself was trying to design a BMS. I’m not now. We’ve moved on. And we’ve learned a lot.
The link you provided is NOT about breakdown voltage in electrolytes, it’s a passing reference to something the guy clearly knows nothing about, but doesn’t matter because we don’t use those electrolytes now anyway.
Theres a big long roundabout story I can go into about how some electrolytes in some devices are also the current barrier. Our electrolytes are ion charge carriers and we use perforated propylene ad a current barrier. But it just IS NOT WORTH IT. This is in relation to WHAT in this video and WHAT on this blog. It’s so far off topic it doesn’t matter and it cites random garbage from space that doesn’t’ matter. Why would I want to spend ANY time chasing your links and refuting this BS one by one to what point at all?
IF you believe that exceeding 4 v will harm your cells then don’t’ DO that. I have already DEMONSTRATED ON CAMERA CHARGING A CELL AT 8V with NO DAMAGE AT ALL nearly two years ago. And I’ve assured you that allowing an individual cell to go to 4.0, 4.1, or 4.2v does NOTHING in and of itself. That the VOLTAGE doesn’t matter out of context, and ONLY matters in the context of how much energy is in the cell.
You disagree with that I gather. Noted. Now, if you want to offer an easy to put together test that YOU YOURSELF have performed and gotten a different result, and want me to verify it, we’ll talk. If you want to randomly collect GARBAGE from EVDL and every other written source you can find because they are INDUSTRY SOURCES and because it is in WRITING I have zero interest in the topic. Appeals to authority don’t work here because we’ve busted them too many times over too too many years in too too many fields WAY beyond EVland.
Show me something odd you’ve found with voltage and cells on your test bench and I might become interested in it. Defending my statements against your disbelief based on BS you’ve dredged up from forums and Google has zero interest level FOR ME. As I’ve said, there is no shortage of people to debate that with you, there is just a shortage HERE.
“Typing oneself smart”. Not you my good man, the text quoted.
The copy/pasted piece is a complete admission to no facts, just conjecture.
Don’t be taken in by simple words or you will be forever the slave to the minds of others. When they have your mind, they have your money.
Delphi once an engineering giant for the automotive sector is now defunct. Hmmmmm.
I never said anything about charging to 4.2V damaging cells, I was talking about the claim that higher voltages had no effect on the cells. The fact that you held a cell at 8V or so for a few minutes proves nothing, you have no idea what long term damage you may have done. You could have shortened it’s cycle life from 2000 cycles to 1800 cycles and never know the difference. In practical use it won’t matter and you’ll never see such voltages anyway, but that’s quite different than saying an electrolyte held at a higher voltage doesn’t degrade. I’m not saying it does but I’ve seen enough references to it from enough people, including battery researchers, that I’d like a bit more proof than Jack typing in capital letters that it doesn’t exist. If you can’t provide such proof that’s fine, but the concept of electrolyte stability in relation to voltage seems quite common in battery literature. Indeed, in the lithium battery video by Jay Whitacre he says the following about the voltage of LiFePO4 vs LiCo:
“By virtue of it’s lower potential the electrolyte is more stable and there is much less chance of it evolving gases that can lead to venting and combustion”
You can find that at the 11:50 mark. So we have a direct reference to voltage affecting the stability of electrolyte from someone who actually makes batteries.
You have out of context excerpted comments with no apparentl understanding of them at all. Venting and gases come from heat, and voltage is very indirect. It is very different from a “breakdown voltage”. Your ability to comprehend this in context is apparently pretty limited. A very good reason for me to avoid getting drawn into it.
You are striving to have an Endless Debate that belongs, as I’venoted several times, on EndlessFear or EVDL NOT HERE (in ALL CAPS). You’re on my blog and I will certainly type into it in any style that pleases me and I take grave offense that you would offer to correct me on style issues. I’ve been writing in printed publications, for a living, and on blogs and forums for 32 years now and with no small success.
I don’t know what you’r on about, but I AM going to ask you one final time to take it somewhere else.
Fine, I’ll simply end with this, go to the 50 minute mark in Jay’s video and listen as he talks about electrolyte solvent breakdown above 4.3 volts, equivalent to water electrolysis at 1.3 volts, and then continue to pretend voltage doesn’t cause electrolyte to break down independent of heat. Feel free to assume Jay has no idea what he’s talking about.
JP, Jays video depends on current at that voltage. Current is the killer when charged. Who needs to go much over 3.55V anyway?
In all of Jay Whitacre’s charges, he demonstrates a fully timed current feed then knocks it off. That means no voltage limiting or the charge current would be tapered down with cell voltage rise. I=V/R
Don’t forget, for sapping transients these cells will with no issues. After all, they are basically capacitors. If you want these regenerative braking transients to place a charge into the cell it will have to be maintained for over for a good few (to very many) seconds. Meaningless and pointless.
You can charge them over 3.4V then let go. Give it a few hours, that extra voltage has gone!!! It’s just like a surface charge. Waste of time.
This hectic discussion is barely in the same ball park as overcharging all night because of a faulty B*S.
Andy, there is no way to spin this into Jack being correct. Since Jack does not want to discuss the topic further I created a post on my blog for more discussion if anyone wishes.
YOUR NOT GOING TO LET IT GO.
One hundred monkeys, trolling through Google seeking scraps of information to support their already docked up world view CAN FIND THEM. If you have NO basis for understanding, NO training, and NO experience, just randomly read shit until you HEAR or SEE what you WANT to see to support your view. This is EXACTLY the driver to NOT spend my valuable time on YOUR BLOG or YOUR FORUMS. It just devolves to nonsense.
IF you really want a definitive discussion of electrolytes, THE MAN in Kang Xu. http://www.tinhoahoc.com/Battery/cr030203g.pdf is the document. And it does cover the electrolytes we use. THE LIMITATIONS ultimately described in summary are low temperature (-20C) and high temperature (+50C). The dielectric electrochemical window, of no particular importance and alluded to, involves oxidative components on the anode and cathode and have nothing really to do with a “break down voltage”.
For those TRULY interested in the role of electrolytes and their history, this is a REASONABLY readable and reasonably exhaustive treatment of the topic by someone who both knows and understands what he’s talking about.
In any event, I assure you it’s more than you want to know at that. But it does explain our low temperature charging restrictions.
I’m considering upgrading my 2002 GEM Car to (25) CALB 130Ah LifePo4 cells and trying to understand how to select the best Charging Algorithm to reprogram my Zivan NG1 charger to.
From among the various profile options I received from Electric Conversions in Sacrament, (who will do the reprogramming), I’ve narrowed it down to two candidates that seem feasible: Charging algorithms 524b & 617M.
Both algorithms provide I3 at 20/Ah, which is, if I understand correctly what Jack has said above, what I want/need with these cells.
The key distinctions between these two algorithms appears to be charging current, with I2 max at Ah/2=130/2=65A (534b) vs Ah/1=130/1=130A (617M), as well as charging voltages, with V2 at 2.8v (524b) vs at 3.2v (617M) and V4 voltage holding level at 3.65v (524b) vs at 4.13 (627M).
If I’ve understood Jack above, he essentially says that charging voltage doesn’t matter & won’t hurt the batteries because it’s actually current that’s doing the charging, so I conclude that either of these charging voltage profiles is ok…but I’m wondering about charging current max I2.
In particular, on the 617M algorithm, can the Zivan NG1 actually deliver I2 at 130 Amps, or not? If so, would my expensive new CALB batteries handle that level of current just fine …or not? Would algorithm 617M it make my charging time shorter or could it hurt the batteries in any way?
Which algorithm should I choose and why? Or, are there other charging algorithms I should consider?
Though I am an electrician, I’m a novice on what’s best for these cells, so if anyone on this blog can help me make a smart choice, I’d really appreciate it,
I am unfamiliar with the particular charge curves presented. Your charging current will never be any more than your charger can deliver. The “holding” voltage should be 3.65, NOT 4.13, and yes C/20 would be the correct termination.
For what its worth, we charge to 3.55v not 3.65. The spec is 3.65.