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Author Topic: With 108 cells in a ZF9, whats the chance a few aren't as strong as the others?  (Read 2344 times)

Electric Terry

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Ok, so I have a little over 10,000 miles on the 2012 ZF9.  Had it for almost exactly 5 months now, although it was out of commission for almost a month while I waited for a belt and then a new BMS board, so a good 4 months of riding it every day.  1/2 the time I charge off solar at 1 kw, and another 1/2 the time I charge at 4 kw at charging stations.  With 120AH pack at 48A that's .4C or less than EiG's recommended charge rate of .5C and 60% less than their 1000 cycle test at 1C to 100% DOD.  Or similar to the XU 3kwh pack charging with just one charger.  Yet the XU (40AH) can charge with up to 2, for 2 kw or .7C, and the ZF6 (80AH) is also supported to charge with up to 4kw for .7C as well.  So charging between .1C and .4C should be pretty easy on the batteries.

Discharge should be even better.  i ride fairly agressively, but looking at my logs, most of the time it rarely pulls 100A and usually a lot less.  With a ZF6 or XU the C rate of discharge would be a lot higher.

So I was confused the past few weeks when I seem to be losing range.  A lot.  Tonight from a full charge, the bike quit with only 26 miles on the odometer with city riding (no highway or speeds over 55).  A ZF9 remember.

It appears I might have a bad cell in banks 14 and 15 and is decreasing the capacity of the 6 cells in those banks.  Over the past week or two, after a full charge and balance to within 10mv, and usually within 2mv (4.15-4.17 for the entire 18 banks), by the time it reaches 75%-50% on the fuel guage, the bike without warning cuts off.  I push it home, or stop at a strangers house to plug in for a bit, and get home to find that the pack is at 3.4v for all cells, but bank 14 and 15 have reached 2.7v-2.8v and caused the BMS to shut the bike down to prevent over discharging the cells.

This was tonight with only 3 bars disappeared.  8 bars remaining!

09886     09/27/2012 20:10:42   Discharge level            035 AH, SOC: 71%, I: 77A, L:2782, l:2925, H:3323, B:541, PT:036C, BT:034C, PV:57634, M:Bike On
 09887     09/27/2012 20:10:53   Bike Turned Off

Yet the bike had a full charge and balanced completely before the ride.

Because the cells take a dive and have little energy left after reaching 3.2 volts the inbalance of .54 volts is a lot more than once I start to charge as the low cells quickly reach 3.2 as there isn't much capacity between 2.7 and 3.2.

Here's a few examples from a few different days this week:

ZERO BMS> balance
  -   Bank  Voltage(mV)  Diff(mV)   Graph
    -   01        3442       249    -------------------------|
    -   02        3436       243    ------------------------|
    -   03        3388       195    -------------------|
    -   04        3384       191    -------------------|
    -   05        3365       172    -----------------|
    -   06        3393       200    --------------------|
    -   07        3426       233    -----------------------|
    -   08        3457       264    --------------------------|
    -   09        3402       209    ---------------------|
    -   10        3401       208    ---------------------|
    -   11        3375       182    ------------------|
    -   12        3357       164    -----------------|
    -   13        3313       120    ------------|
    -   14        3193         0    -|
    -   15        3195         2    -|
    -   16        3255        62    -------|
    -   17        3327       134    --------------|
    -   18        3373       180    ------------------|

  - Highest Bank :  08 (3457 mV)
  - Lowest Bank  :  14 (3193 mV)
  - Imbalance    : 264 mV

ZERO BMS> balance
  -   Bank  Voltage(mV)  Diff(mV)   Graph
    -   01        3450       226    --------------------------|
    -   02        3447       223    -------------------------|
    -   03        3411       187    ---------------------|
    -   04        3420       196    ----------------------|
    -   05        3392       168    -------------------|
    -   06        3421       197    -----------------------|
    -   07        3443       219    -------------------------|
    -   08        3453       229    --------------------------|
    -   09        3414       190    ----------------------|
    -   10        3422       198    -----------------------|
    -   11        3414       190    ----------------------|
    -   12        3409       185    ---------------------|
    -   13        3375       151    ------------------|
    -   14        3240        16    ---|
    -   15        3224         0    -|
    -   16        3321        97    ------------|
    -   17        3376       152    ------------------|
    -   18        3423       199    -----------------------|

  - Highest Bank :  08 (3453 mV)
  - Lowest Bank  :  15 (3224 mV)
  - Imbalance    : 229 mV


ZERO BMS> balance
  -   Bank  Voltage(mV)  Diff(mV)   Graph
    -   01        3437       411    --------------------------|
    -   02        3425       399    -------------------------|
    -   03        3354       328    ---------------------|
    -   04        3356       330    ---------------------|
    -   05        3314       288    -------------------|
    -   06        3359       333    ---------------------|
    -   07        3407       381    ------------------------|
    -   08        3417       391    -------------------------|
    -   09        3387       361    -----------------------|
    -   10        3388       362    -----------------------|
    -   11        3360       334    ---------------------|
    -   12        3337       311    --------------------|
    -   13        3273       247    ----------------|
    -   14        3088        62    -----|
    -   15        3026         0    -|
    -   16        3203       177    ------------|
    -   17        3314       288    -------------------|
    -   18        3384       358    -----------------------|

  - Highest Bank :  01 (3437 mV)
  - Lowest Bank  :  15 (3026 mV)
  - Imbalance    : 411 mV

And one when close to a full charge:

  - Load Resistor States
  - Cell: 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18
  - Res :  0  0  0  1  1  0  0  0  0  0  0  0  1  0  1  0  0  0

  -   Bank  Voltage(mV)  Diff(mV)   Graph
    -   01        4152         2    --------------|
    -   02        4151         1    ------------|
    -   03        4152         2    --------------|
    -   04        4156         6    --------------------|
    -   05        4156         6    --------------------|
    -   06        4151         1    ------------|
    -   07        4152         2    --------------|
    -   08        4153         3    ---------------|
    -   09        4152         2    --------------|
    -   10        4152         2    --------------|
    -   11        4152         2    --------------|
    -   12        4151         1    ------------|
    -   13        4155         5    ------------------|
    -   14        4150         0    -----------|
    -   15        4161        11    ---------------------------|
    -   16        4152         2    --------------|
    -   17        4153         3    ---------------|
    -   18        4152         2    --------------|

  - Highest Bank :  15 (4161 mV)
  - Lowest Bank  :  14 (4150 mV)
  - Imbalance    :  11 mV

Notice 15 is the highest by a lot, telling me it has reduced capacity since it is also the lowest when the pack is low.

Is it time to disassemble the pack and test all the cells to see if there is a bad cell in bank 14 and 15?
I know with headways the chance of getting 108 cells and not having 4 or 5 go bad in the first month was almost a given.  EIG makes a good pouch cell, but I'm sure they're not perfect either.

Any suggestions?

Should i wire a 12V DC to 4.15VDC charger to bank 14 and 15 to let the on board 400w DC/DC converter bleed the highest cells to charge the weakest?  Surely with all the electric motorcycles over the past years, this situation has been encountered and resolved before.  Thanks in advance for the suggestions.  Going from a pretty average 70-80 mile range a few months ago to 20-30 miles makes it a little rough to use as a primary form of transportation, lol.

If I had to guess, I'd say 106 of the 108 cells are at 95-98% of the original capacity or more, and 2 of the cells (one each in bank 14 and 15) have decided to quit. 




« Last Edit: September 29, 2012, 09:47:10 AM by offthegrid »
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Richard230

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Offthegrid, I am sorry that I can't help you because I just don't have the technological knowledge to do so. But I am surprised that you commented that your bike rarely required more than 100 amps while under way.  The 36V/48V D&D sepex motor that was used on my GPR-S, with its bank of 24 50 Ah Hi Power LiFePo4 batteries, would typically pull 180 amps when going up any hill or under any acceleration, or while running above 50 mph.  That is likely what cooked my batteries after riding only 1000 miles on that bike.
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Electric Terry

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True Richard, the logs only do a reading once every 60 seconds, and i rarely go full throttle more than 6-7 seconds in a burst every so often, so the readings probably just don't catch it.  The controller can put out 440 amps so I'm sure its a lot higher somewhere I just don't see it in the logs.
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BSDThw

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The diagram displays the RMP in red at the right y-axis and the battery current in yellow at the left y-axis.

It is a snip of a test drive I did to see how data of the SevCon look like.
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Lipo423

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Offthegrid,

If you have lost the ZERO warranty, I would strong suggest you to check the cells you mentioned. 2 "malfunctioning" banks out of 18 is a lot and will drive the bike BMS/control system crazy.
I'm not surprised a lot by this potential problem. Malfunctioning cells in such a large number is a "high risk" that we all have  :( I have seen it happening in much smaller configurations very easily

From another post I seem to remember you do not leave the pack for balancing a lot. Is that right?
Try to leave the bike with the onboard charger for 2-3 days and check again the banks voltage, if the voltage in bank 14 & 15 is still that low you definitely have a cell/few cells to replace.
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lolachampcar

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Please shoot some pictures of the battery pack construction if you end up getting into it.  Also, if you do not mind me asking, would this not normally be a Zero Warranty Issue?  I ask as I am interested in how Zero does with the bigger ticket issues like battery problems.  I was told there is a three year, unlimited mileage non-prorated warranty on the battery.  The value of that warranty is directly tied to Zero's willingness to address problems and the time it takes them to correct issues.  They seem like they are doing a good job so far given the posts I have read.
Anything you can share would be appreciated.
Thanks!
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dahlheim

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the manual does mention a couple of times to please leave the bike plugged in whenever possible during non-use.  it might be hard to redeem a warranty claim if that hasn't been the case.  i'd imagine that's to give it plenty of opportunity to balance the battery cells?
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ColoPaul

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I'm not surprised a lot by this potential problem. Malfunctioning cells in such a large number is a "high risk" that we all have  :( I have seen it happening in much smaller configurations very easily

From another post I seem to remember you do not leave the pack for balancing a lot. Is that right?

This makes me nervous.  It's bad enough all the recalls so far - but if at 10,000 miles we all start needing major battery work done.....  :(
I am just hoping that it's OffTheGrid's solar-charging-without-balancing and frequent-4kWH-charging that brought this situation on.

Did they use the pouch cells in the 2011 models?  Or are they new to 2012?
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protomech

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New to the 2012 bikes.
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Electric Terry

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I've kept it balanced to within 2mv on every charge recently, and I would always leave it plugged in when possible before, it's just it was not possible very often.  And I don't think the .4C charging with 4kw is much different than 1kw charging.  Remember this is about the same charging rate as the XU charging at 1kw.

If it does turn out to be a few cells that went bad I am sure ero or EIG will replace them, I just don't want to do without my bike at the dealer for a few weeks.  I'd rather, take the pack apart, find how many cells have severely reduced capacity, put the pack back together so I can continue to ride, but get some sent out right away, then once they get here, disassemble the pack again, and install the new cells, so I don't have any downtime.

I just need a good set of instructions so I don't have to figure out all the tricks myself the first time if someone can tell me what to look for.

But for now I'm gonna keep riding it as is, and see if the daily balancing helps the cells or not.  

I think there is an error that may cause part of it.  i noticed reviewing the logs that the day before the cut out it read 100% SOC with the batteries at 3.7 volts each.  They should have been at 4.15.  So when i ran out at 8 bars left, it actually should have been empty.  the "fuel gauge" just had a glitch that day I guess.

Didn't really happen till over 10,000 miles so even for a few bad cells to show up this late is a good thing.
« Last Edit: October 02, 2012, 09:15:41 AM by offthegrid »
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Lipo423

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My 5 cents is to suggest you not to "play" with the pack (not meaning you are not skill enough to do so), but it is better to let ZERO take care of it.
ZERO claims very proudly that "the battery pack has a very special & patented technology they own", fine, let them fix it for you...
Lithium chemistries behave differently, but there is a common way of extending their life:

- Charging a warm pack(after the pack has been subjected to a high drain application). Let the pack cool down ALWAYS.
- The higher, the charging current, the lower the number of discharging cycles (charge at 1KW whenever possible)
- Balancing is a must do
- Never leave your bike/battery pack exposed to heat/sun, or high temperatures when fully charged
- Never leave an empty pack for a long period without charging
- When not in use (long period of time) leave the pack at 30-40% charging capacity
- Avoid using full battery capacity -full discharge- whenever possible, partial discharge is better (I know this sounds a bit fool, but that's the way to extend their life)

Last, but not least, any committed "above 1000 life cycles" is always measured taking into account perfect-ideal use or laboratory testing which is totally impractical in real life..and yes, there is a risk of having a defective cell  :( in a high capacity battery pack
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Electric Terry

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Those are good suggestions Lipo423.  The only thing is I am in Orlando, FL.  How am I supposed to get Zero to replace the cells for me.  I'm 3,000 miles away.  This is why I worked closely with their tech team on trying to diagnose the glitch, since I was one of the first it appeared repeatedly on.  I've fixed it 3 times now, just don't have the new firmware yet, so I keep having to recalibrate every 1500 miles or so.  I mean I could drop the battery box and send them just that, but still, I feel it could be done faster and with equal precision if I just do it myself.   I just don't see a better way unless I had a backup bike to ride while it was being fixed.  I vowed not to use another drop of gasoline ever and plan to stick to that.  How soon till there's a beta test 2013 bike ready?
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Lipo423

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I see...so, I guess it is obvious they have no dealer in your area :(
One of the tricky thing also, is that if you replace a few cells, the rest of the pack will not have "same age cells" which is also a bit tricky...I gave you such suggestion because the potential replaced cells + soldering might be a bit tricky/risky for you to perform (unless you have proper tools/equipment + ZERO's advice)

With all the help you have provided to ZERO in fixing "the glitch" they should definitely send you a replacement pack while yours is being repaired, no question...
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ColoPaul

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Why in the world would "same age cells" matter?
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Electric Terry

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I'm thinking now its more of a problem with the fuel gauge and less with a cell having severely less capacity.  I'm basing this on the following graph of the EIG 20 AH pouch cells.  And at 3.7 volts per cell average, my pack should not be at an SOC of 100%, and at an average cell voltage of 3.4 volts it should be close to empty, not reading 50-75%.  I'll update more soon as I run more tests.
« Last Edit: October 03, 2012, 09:33:33 AM by offthegrid »
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