barnard's Toyota MR2 - now Mr240

[barney]

So much to say, so little time before family arrive for roast dinner - the veges are burning so I cant stop!

I'll get back to this later tonight (Perth time) but I took some photos of the main battery gauge towards the end. I need to build a timeline with pics Amps In, pack V, as well as the logger screen. It seems that the A in dropped at ~1h37 from 19.4A to about 12A. And it gradually dropped all the way to 0.7A near the end. I'll find some way to build the timeline to show the data (maybe without the neat pics, just the data) and this will explain how the Zivan is performing. No temp sensing going on, and I dont know exactly who turns things off, but I think the Zivan does most of it. It knows all about LIFe cells and has a curve built in, I think.

I did notice that B45 was the highest of the 8 at the start, all the rest level and B44 (the second graph's datapoint is for B44, sorry its not clear, Excel does the popup miles away from the data point you are hovering over) became the overloaded one (logger kept beeping saying OVER, at something like 3.69 or 3.701V, iirc. By this stage they were all at about 3.65, VERY close to B44, and only B45 was much lower (3.55V, maybe?) and waiting to 'go bypass' (!)

Back later... Barney

[barney]

Apologies to anyone waiting for more info on the traction pack of ZEV240... wont be until tonight, Perth time.
Barney

[Johny]

PERTH time! First I have to wait while you do your day job just so you can eat and not get wet when it rains, then I have to wait for the other-dimensional time frame (WA) to catch up - which it never does. It just isn't good enough!
The EV comes first - always - nothing else matters.....
(dragged off kicking and screaming...)

[roddilkes]

Hi Barney,

If I am reading the data correctly B45 seems to be swinging alot higher than the other cells when on charge.

Is B45 one of the weak cells?

[Johny]

..takes medication.
If B45 was the only cell being monitored it's not that bad. The comparison with the other cells is what makes it stand out. It seems to charge OK.
Near the end of the first graph the charger appears to have dropped the current - the cell bypass is swamped by the charger current prior to that (there is a discernable kink in the first graph at 3.65V for B45).
Then in the second graph at lower current, it appears that B45 went into bypass causing the odd curve on B44.

[coulomb]

Then in the second graph at lower current,

Ah! Something I missed. Two runs, one at lower current, so the bypass current is massively more significant in the second graph.

it appears that B45 went into bypass causing the odd curve on B44.

Huh? How does B45 going into bypass affect B44? That's sounding a little like a bad connection between B44 and B45. If the connections are sound, I can't see why one cell bypassing could possibly affect another, except as a second order effect by changing the overall string voltage (diluted by the number of cells), which could affect the charger current, which will affect all cells.

I'm guessing that there is only one connection between the pack and the logger between cell B44 and B45. So a significant voltage drop across the B44-B45 link could cause a change in one cell to appear to affect its neighbour on the other side of the link. But it would have to be pretty high resistance to have an observable effect at 180 mA.

[barney]

Here we go. First some explanation, the next post will have all the graphs. As weber suggested, researching the performance of one set of 8 was a possible way to analyse the batteries' overall performance. So I have the charging data logged as rows in a spreadsheet for a charge from 70% to 100%. As weber also pointed out, the first lot is grass-growing stuff, but I thought you'd like to see Excel's pretty colours so left it in. Well, some of it, anyway.

Also on the vertical timeline, as well as photos and observations of the MAIN traction pack gauge (An Expert-Pro), are photos of the CellLog 8S's screen. The pics are all pretty grubby quality, Im afraid... just whipped the phone out whenever it looked interesting (one of the gauges, not the phone), or I was walking by, or I heard an alarm. The performance of battery 45 in Pack B aka B45 is particularly riveting - well, perhaps just interesting - as many of you have noticed... it starts higher, and suddenly drops as the charger slowly scales back, and suddenly B45 is the lowest scorer on the block.

Three things I should explain:
1 the previous excel graphs are of this same datalog covering the whole 2-odd hours. Johny referred to them as two graphs, and I think coulomb decided this corresponded to two 'runs', ie two separate charging cycles? Just to clear this up: They combine into the one graph but I couldnt see how to connect them as one, when I first captured it. My apologies if this caused confusion.

2 the CellLog calls the cells 1,2,3...8, and the column graph represents each cell's V as a vertical bar. They are in fact B38, B39....to B45. Here is an example screen shot from the CellLog. The 8S means 8 cells are connected, and their total V is 26.53 atm. 8H means the highest cell is currently #8 (in this case B45) in the graph; and L3 means the lowest is #3.


3 So you know where B45 actually is: The photo below of the pack when some bypass LEDs are on, shows B22 (red LED y) and B45 (n), each of which has orange-covered power coming into the pack. B45 is connected to the right orange cable; B22 to the left.


Finally, if any of you is silly enough to want more data, the complete spreadsheet is available as a zipped XLXS file... the conditional colouring etc apparently makes it less workable as an xls file; but if your rather, I can easily save it as one if you'd rather.

Thanks again for your help, your good humour, and keep taking the tablets, Johny.

Barney
PS The aluminium jointing compound arrived this afternoon, so Im ready to blow my fingers off trying to scrape and re-attach some connectors. Is there a reason they are called terminal connectors? )

Edit: Simplified (1); typos; and added explanatory pics in prep for viewing the spreadsheet/timeline.

[barney]

A long spreadsheet, snapped as half a doz pics. I have left out rows and rows of data where not much is happening (in my opinion - I could be wrong!) just using it as a timeline to add comments, pics etc on the right.










And the full spreadsheet should be here, standard (xls) and newer (xlsx) format:
LoggingZEV240-PackB38-45.xls (size: 410k)
or the xlsx version:
LoggingZEV240-PackB38-45.xlsx (size: 537k)

Cheers, Barney

[Johny]

.... But it would have to be pretty high resistance to have an observable effect at 180 mA.

I think you've cross-threaded with my battery pack. The Zivian charge rates appear to change. I wasn't stating fact BTW - just my theory on what was happening. B45 connections are bad or the cell is bad. The good news is that the other 7 are nice and close to each other = curve wise.

I'm about to try to digest barney's new data....

[T1 Terry]

My theory:
B45 is not fully charged, there is a high resistance joint somewhere, either at the terminal or internal. At around row 734 something happens, either the BMS starts to load the cell or the high resistance joint is over come by enough voltage differential, if I've got this part right it indicates an internal problem but once a connection is made the problem seems to go away in my experience with my cells.
which ever it was it continues to drain the cell and is still draining when the logging finished. If it's the BMS unit then it needs to be swapped out but if it wasn't the BMS unit burning off current then cell 45 needs a charge all by itself.
A quick and dirty charger can be made from a wall wart, if it's output isn't DC a diode bridge will need to be added. As long as the voltage output is 5v or better it will charge the cell, slow as watching the friends holiday movies but it will get there. If the BMS does it's thing at the required voltage it will protect the cell from over charging.

T1 Terry

[roddilkes]

It does indeed show the symptoms of a high resistance joint on B45.
This could be confirmed by taking the car for a short drive right after charging and logging the same cells.

A few times my own BMS has alerted me to loose terminal connections left from when I was fiddling with the battery pack. Under load the voltage drops radically on loose or oxidized joints.

The data can also suggest that BMS cell module on B45 is staying on bypass after it drops back below 3.6V. However this would not explain why B45 is reaching full charge first.

Barney if you are going to remove cell terminals please MAKE SURE THE BATTERY PACK IS COMPLETELY ISOLATED FIRST.

This includes from chargers and TBS meters etc. Disconnect at a point away from the battery pack. Apart from the obvious safety hazard, BMS cell modules can be damaged by the high voltage that occurs as the busbar or lug disconnects from the terminal.

Usually it just blows the internal fuse but sometimes a fast spike can make it behave erratically afterwards. This is the single biggest cause of BMS and subsequent battery problems.

[weber]

Wow Barney! That's quite an epic you produced there. Well done!

Now that I have some idea what the current was doing, I agree it looks more like high resistance than low state-of-charge or low capacity. But taking it for a drive straight after charging won't tell us whether the high resistance is inside or outside the cell. Only cleaning cell 45's connections and then repeating some already-logged activity will tell us that. Don't forget to also clean cell 44's terminal and strap that connects to cell 45.

[barney]

Hmmm, thanks weber - it might be an epic, but its no work of art @@!! Sorry its so long, but it DOES provide an understandable timeline, I think.
For example there is a lot happens as the Zivan charger drops the first time from 19.4A to c.2.5A, and not enough photos fit in the limited region... this is around the 734-738 area T1 Terry mentions, just as B45 drops away. Is this the cause or the consequence of the drop in charge rate to 23.5A? Presumably its the CAUSE, but the change is almost instantaneous... isnt that unexpected? Its not intuitive, for me, I have to say.

Looks like its time to stop measuring and start doing; and Rod's warning is duly noted and taken to heart.... Ive just been learning about Arc Flashes, which need reasonable voltages to sustain them. Apparently anything over 80V or 100V is enough! Roddikes mentions:
    "if you are going to remove cell terminals
     please MAKE SURE THE BATTERY PACK IS COMPLETELY ISOLATED FIRST...."

Im hoping that pushing the big red isolator button in is a great start, but I realise that is NOT separating the pack of 150 volts from itself. There is still a string of cells connected together, and even these should probably isolatable into 4 lots of 40V or 3 x 50V, to simplify working on individual cells, for example. Since I cant do that atm, I'll have to take some care as I undo individual connectors, scratch/sand and then add jointing compound to at least both of 44 and 45's connectors and BMUs at the same time.

Any more specific advice about steps involved in charging idiv. batteries in this system? From a small voltage on a single cell sounds easy; But to the traction pack voltage of ~150V there is quite a difference, of course.

Cheers, Barney

[edit-changed 150 to V... thanks T1]

[coulomb]

Barney if you are going to remove cell terminals please MAKE SURE THE BATTERY PACK IS COMPLETELY ISOLATED FIRST.

My apologies is this is too childish, but I'm sure it will help some readers, if not you, Barney.

How you blow your BMS when you don't first disconnect all the loads.

It has this nifty video:

[T1 Terry]

"Any more specific advice about steps involved in charging idiv. batteries in this system? From a small voltage on a single cell sounds easy; But to the traction pack voltage of ~150W there is quite a difference, of course."
I'm guessing you mean 150v, individual cells are still only 3v nom. each so simply connecting the charger between the neg and positive of an individual cell allows that cell only to be charged at 3v plus.
If i've got the bull by the tail and that's not what you meant then maybe worded differently might help or my third coffee will kick a few more braincells into life.

T1 Terry

[Johny]

I'm really hoping for Barney's sake that the obvious high resistance of cell B45 is something to do with it being the end cell - a mechanical connection issue or some such. Either way, can I thank Barney for posting this data and allowing us to comment and colaborate. Even though I realise the intention here is to help Barney, this thread has been/is very informative - I think for everyone. Geez I hope his name really is Barney...

[barney]

Hey Johny
(Is that really your name? he-he )

Glad its been useful for you as well. I have learned volumes about volts, amplitudes about amps and a bit about bypass... It's when stuff matters that your brain pays the most attention (aided by coffee, like you say, T1!). So I now understand lots more about this charging stuff. Ive made some mistakes explaining stuff and you have all been generous with your explanations and very circumspect (I think that's the right word!) in your criticism - thank you!

I may not have responded directly to every single question, but I now understand how the Zivan charger works, I think I understand how Rod's clever little EV-Power battery cell bypass works even tho each BMU, or cell module, is only able to handle small loads; and that video was a winner, coulomb, thanks. Schoolboy physics taught me electrons flow when a switch is closed, no electrons when its open, but the idea of 'potential' charge waiting to cross a gap. Wow! The 'principle' was there in my head, but I hadn't actually thought thru what it meant with a multimeter. In fact potential is the right word for it, right? I knew the word but didn't imagine putting a multimeter at different points in a circuit would show anything - and of course it must!

I see this as more evidence that you are all masters of your craft - masters are those who not only understand but can teach others too. Feeding ideas just as they are needed to explain important ideas.

But Im still a bit confused - may I be honest? - about battery B45.
First, how do you decide that there is resistance BETWEEN the cells (ie B44 and B45) not INSIDE a cell that fits the data better? That was getting towards magic for my little brain.

Second: Why is it that B45 looked to me like it was going into bypass, but its red led never came on?

For example B45 (masquerading as cell 8) gets to a ceiling of 3666 (line 734) in the ridiculously long Excel table above, about the same time as the CellLog alarm came on. This makes sense, as 3650minivolts* is an Important Number for lithium batteries, I have learned! For the second time, of course - the alarm had already complained back at row 569 when there was 19.4A, swamping any bypass ability, presumably. But back to row 734. At this point B45 suddenly starts dropping, while all the other cells continue to rise. It falls to 3638 by line 737. At this point exactly, B44 (aka cell 7) jumps up to be the highest cell in the room. Doesn't some of this data suggest that bypass is going on? I know its not though, as the photo of B22 and B45 (around row 770) shows B22's red led on, indicating bypass, and B45's led is nowhere to be seen.

I suspect that Qs 1 and 2 may even be related, but can't yet see how. Any takers?

really-barney(!)

*not their real name, but since there are no decimal points anywhere, whatever! Actually they are probably millivolts, as I muse about it, but then musing doesn't always work this time of day...

[Johny]

....First, how do you decide that there is resistance BETWEEN the cells (ie B44 and B45) not INSIDE a cell that fits the data better?

I'll answer that one. We can't - not without some better physical measurement. That's why we are waiting with bated breath to see if disassembling the connections and improving them helps.

The better physical measurement I allude to is to get multimeter probes onto the actual cell terminal - not bolts or lug - the aluminium bit - during that part of the charge cycle where the B45 voltage excursion is obvious. Compare that voltage to the measurement on the lugs or that reported by the logger.

[T1 Terry]

My theory, (a bit of a laugh for Monty Python fans)
The 3.650v was enough to create sufficient voltage differential between the other cell pouches in cell 45 and the one with the oxidised contact to create a breakthrough path (no idea what the technical term would be). once the path was made the other pouches discharged into that pouch trying to create an equilibrium in the voltage by charging the wayward pouch. Now this bridge has been formed that pouch will continue to charge so a single cell recharge will bring this complete cell back up to the same capacity as the other 7 cells.
This was the reason for my suggestion before to charge that cell to 4v, to create a large enough voltage differential to break through the oxidised joint internally in the cell.
No way of knowing if this right or wrong so it's just my take on what's going on but I have seen it before and the results have been similar.

If you decide to go venturing into the other cell packs to fit the 8S JST-XH 9 pin plugs these can be used with the hobby charger I posted the link to for cell balancing and charging with 2 adaptor cables and plugs so the pack can be charged/balanced 4 cells at a time or even a series of adaptors for single cell charging, worth thinking about.

T1 Terry

EDIT: Just thinking, another logged recharge without doing any terminal cleaning would show if the same thing happens again or if the problem has self rectified, internal or external.

[coulomb]

First, how do you decide that there is resistance BETWEEN the cells (ie B44 and B45) not INSIDE a cell that fits the data better?

Well, initially I thought that B44's voltage rise happened at the exact same time as B45's voltage fall. But now that I look at the data, I see B45's voltage starting to separate from the rest before the sharp change in B45's voltage. So maybe it's not so clear.

Second: Why is it that B45 looked to me like it was going into bypass, but its red led never came on?

Well, I have to say I've been assuming that the only thing that could cause the sharp voltage change in B45 is bypass coming on. If the LED didn't light, maybe the LED is faulty? Have you seen B45's LED come on at other times?

If the LED is working, then I suppose I have to consider T1 Terry's idea that one or more internal pouches inside the prismatic cell suddenly started connecting when initially they were not. Somehow, that seemed way less likely than the bypass coming on, but now I'm not so sure.

[ Edit: fixed singular and plural mismatch ]

[weber]

Hi Barney,

Any DC voltage above 120 V (and AC above 50 V) is considered capable of delivering a lethal shock via uninsulated body parts. And any battery over about 24 V and 10 Ah is capable of sustaining an arc once started (say from a dropped uninsulated tool), over a distance in millimetres about equal to the number of volts in excess of 24. So if you don't feel 100% competent, don't risk it. Find someone who is competent.

You don't need to disconnect different parts of the pack from each other for this. But it would certainly make it safer to work on if you could break it up. particularly near the middle. However, that would be likely to require undoing connections where BMUs are. And that is exactly what you can't do (without risking damage to BMUs) until you've isolated the battery from everything else. (BMU = Battery Monitoring Unit = BMS cell module = Battery Monitoring System cell module).

Coulomb and I have designed a BMU that doesn't have this limitation, it can withstand the full battery voltage in reverse. But that's another story.

As Rod said, you must isolate the battery by disconnecting battery cables at their end which is away from the battery. The big red button certainly would be a good start. And it might be the only disconnection you have to make to the heavy-duty cables that leave the battery, provided there are no other wires connected to the battery-side of the big red switch. I assume the big red switch is in the positive lead.

If the big red switch disconnects the positive side of the battery from everything else, this is good, because then you won't have to use a spanner to undo any cables.

If you do need to use a spanner on this, and when you use one on the battery terminals, make sure the handle is insulated (and as much of its other parts as possible), say with a few layers of electrical tape wound around it.

If you do have to unbolt the positive battery lead (at its end away from the battery) then make sure to insulate its bare end, say with a few layers of electrical tape.

You also have a bunch of ribbon cables that leave the battery. These must be disconnected too. Again, this must be done at their ends away from the battery. Presumably by unplugging some plugs that connect the ribbon cables to some circuit boards.

Strictly-speaking you don't have to disconnnect every cable that leaves the battery. You can leave one if you're really sure it is the only one. Say the heavy-duty negative lead. But you may want to unbolt it (again at its end away from the battery), just to be sure. If the negative battery lead connects to the car chassis (it's not supposed to) then you should disconnect it for safety from shock while working on or near the positive end of the battery.

If you do unbolt the negative lead, then make sure to insulate its bare end, say with a few layers of electrical tape.

Then when you open up the battery box containing cell 44 and 45, use some old towels (or good ones, I don't care ) draped around to cover everything except the cells you are working on. Like a surgeon doing an operation. Cover all the surrounding bare metal such as the box itself and the hold-down bar.

[Edit: Spelling]

[weber]

First, how do you decide that there is resistance BETWEEN the cells (ie B44 and B45) not INSIDE a cell that fits the data better?

Like Johny said, We can't decide that yet, although your observation below is certainly suggestive that it's between cells.

Second: Why is it that B45 looked to me like it was going into bypass, but its red led never came on?

One possibility is that the datalogger is looking at the voltage across the combination of cell 45 and its link to cell 44 (I can't tell from your photos, but you would know), while the BMU is only looking across the cell, and the link has a high resistance.
[Edit: In fact the datalogger was looking at exactly the same voltage as the BMU was, in the case of cell 45, as shown in the last photo of this later post viewtopic.php?title=barnards-toyota-mr2 ... 920#p38709.]

My theory (of the brontosaurus) is that cell 44 took off because it happened to be the first to become really full at 3.65 V and the charger was still putting in more than its BMU could bypass. And the peak in cell 45's curve corresponds to when the charger went from current limit to voltage limit. The charger's voltage limit is slightly too low to let all cells get to bypass, so the current started to drop and in effect cell 44 "stole" the voltage from cell 45.

I have to admit I'm a bit hazy on the details there. But I think it's better than the pouch theory.

As far as I know there are no pouches inside these cells, just stacks of graphite coated copper foil, permeable plastic separator, LiFePO4 coated aluminium foil, permeable plastic separator (repeat many times) all soaked in electrolyte. All copper foils are joined at the top at one end and joined to the copper terminal, while all aluminium foils are joined at the top at the other end and joined to the aluminium terminal. Jack Rickard did a video of a dissection.

[T1 Terry]

Here is a Hi power cell with the side and top cut out showing the pouches. 2 in the case of this Hi power 100Ah cell but as the cell capacity grows so do the number and size of the pouches. The connections are clearly seen so the theory that one of these connections is a bit oxidised is viable in my opinion.
I'm interested in Webers theory but maybe a sketch with a few voltages and arrows and resistors or something symbolising the resistance joint would make it easier to follow.

T1 Terry
EDIT: Maybe don't worry too much about the audio part, in a post on the DIY forum he admits he got it wrong regarding the swelling, the gas leaks out around the terminal blocks, they weren't a gas tight seal in that particular cell, the fact the pressure release valve is a simple plug in the cell is interesting, seems not all the manufacturers follow the same path. If the cases are warmed to around 45 deg to 50 degC they push back flat quite easily, just a property of the plastic used and the fact that when the cells overheat they gas so the plastic is already soft, the reason for compressing the cells in a pack, for some reason this is another idea Jack Rickard doesn't go along with, to each their own.

Not sure what happened there, I'll try putting the link up again http://www.youtube.com/watch?v=mpzjkF5X ... r_embedded

[coulomb]

Here is a Hi power cell with the side and top cut out showing the pouches.

I see no picture. I assume you meant one something like this:



Here there are effectively two "pouches" in parallel. It would be conceivable for the connection to one of them to be insulated by some oxide layer or similar that was somehow voltage sensitive.

[evric]

Great photo... It appears as if there maybe at least 12 pouches in parallel.