Gen II Prius Individual Battery Module Replacement

Discussion in 'Gen 2 Prius Technical Discussion' started by ryousideways, Apr 24, 2013.

  1. ericbecky

    ericbecky Hybrid Battery Hero

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    You still may be able to go to an independent shop and have them install it for less.
     
  2. kiwi

    kiwi Member

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    Did they mentioned how that capacity was measured? From what voltage down to what voltage and at what current? Just capacity numbers are not good enough and could be misleading. e.g. some "professor" here was even testign over 7Ah capacity on dergaded modules and was very frustrated when I suggest them using "abacus" for their "calculus".

    With your inquisitive mind - if you wish - you can start battery rebuild business in Illinois. I still have some cool domains to accompany my tools:
    Prius Lexus Camry Honda Hybrid Battery Repair Rebuild Testing Equipment and Training

    Eric, my father used to say, quote: "we are not that rich to buy cheap stuff".
    Have Dorman's started providing Quality Test Results displaying Usable Remaining Capacity available to the end user on the batteries which you are installing?
    If still not, then it is like selling a drink in a dark glass bottle without labelling how much exactly it contains.

    I would imagine what folks would say if the bar tender will start pouring beer under the table (so that you can't see how much is in there) - just a little bit of beer with a lot of froth on top.
    With numerous so called hybrid battery rebuilders around doing exactly that without providing test data (but they may do unnecessary nickel-plating of the bus bars or promising reconditioning of nearly dead modules to 95% of original capacity etc ) - it still surprises me why people are so tolerant to accept a lot of marketing froth from those and not just looking for that tiny little sticker with the test results?

    When their car will stop during interstate trip because of the poorly rebuilt battery - I suggest they hop in the nearest bar, ask for a beer - look at the froth and remember this post.
     
  3. gdanner

    gdanner Member

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    I totally agree with Kiwi about the difficulty of getting a reliable answer to this question:

    "How does one determine how much life is left inside a used Prius module?"

    Right now I'm extremely happy that my HV battery is behaving perfectly after replacing 2 modules in it. I'll keep the forum updated as to how many miles I get from my "fixed" HV battery.

    My experience with small NiMH batteries is that there's no such thing as a "reconditioning" process. Any given individual single NiMH cell is either good, weak, or totally bad. There are 6 individual NiMH cells inside one Prius module. The entire module is ONLY as good as the weakest single cell in it.

    Every "used" Prius module is likely to be somewhat weaker than a brand new module

    This just about guarantees that no "rebuilt" Prius HV battery is as good as a brand new genuine Toyota HV battery. That's one reason why I decided to rebuild my own HV battery. I couldn't justify paying $ 1,000 or more for something that might not be much better than what I already have. I didn't bother visiting the local Toyota dealer because I already knew that every salesperson in the entire place would be jockeying to sell me a 2015 Prius. Actually I could be happy buying a new car! That said, my wife and I have to finish paying off her car (2013 Nissan Juke) before I can think about trading in my 2005 Prius for a new one. So I need to get another year or 2 out of my 2005 Pri.


    Best regards, EB
     
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  4. kiwi

    kiwi Member

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    I run tests on my Analysers - Li-Ion and NiMH of all form factors including Power Tools, RC car batteries, Radios, Remote Control - AA and AAA type etc. Even tried so called "burp" or "negative pulse" NiMH programmable charger to see if any improvements could be done. None.

    Common mistake by DIY enthusiast here is using RC cycle charger and not being able to see that one cell inside 6-cell module is dead.

    I saw that scenario of one dead 1.2 cell inside different packs: in back up security NiMH pack, in RC car NiMH pack, in Ryobi Drill 12v NiMH pack. And many times in Prius packs.

    http://imgur.com/MT9g7yi
    E.g. In that 40 module pack (e.g. 40 modules in Lexus GS450 or Prius 1998) with DIY approach you can only spot on #26 but miss on another 6 failed modules.
    Common scenario when they approach me for a "one good module" but proper test reveals the hidden problems...

    P.S. Last night was running test on another pack when suddenly lights went off. It was dark and the only lights were coming from my Analyser. UPS took care of the test to be completed and results to be recorded. Happened for the first time when UPS was very useful.
    In that pack Technician equipped with his Techstream has identified 1 bad module. But that Auto Tech based in Auckland has now a lot of experience, so instead of calling for a 1 good module - they asked the owner whether they would mind running the test as there might be more than one bad module.

    I have actually spotted 4 bad ones in that pack. One was spotted straight away during the charge mode - as Analyser shows dead modules Live in Red.
     
    #924 kiwi, Jul 13, 2015
    Last edited: Jul 13, 2015
  5. Texas Hybrid Batteries

    Texas Hybrid Batteries Active Member

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    Kiwi,
    After reviewing your graphs it looks to me like all your doing is discharging 20 modules simultaneously down to some stopping point (6 Volts I assume) and then comparing the capacities to find the ones that are out of balance with the rest. I would agree with you 100% that this should be the first step in identifying the bad or weak modules in a pack, but I'd like to know why anybody with enough "Toy RC Charger/Dischargers" couldn't do the exact same thing? I realize those machines may not have the pinpoint accuracy of some lab grade equipment but in this application +- 5% will certainly tell you what you need to know. Right? Thanks, Matt
     
    #925 Texas Hybrid Batteries, Jul 13, 2015
    Last edited: Jul 14, 2015
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  6. gdanner

    gdanner Member

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    Kiwi's point is that it's all too easy to ignore the module voltage when testing with RC charger/discharger units. A failed Toyota module with one shorted cell may still have 5 working cells in it, and therefore test with mAh capacity near normal on the RC charger/discharger. But of course it won't work in a Prius!

    To declare a used Toyota NiMH module "good" it must pass 3 tests:
    • Adequate mAh capacity
    • Sufficient output voltage
    • Low enough ESR (equivalent series resistance). This confirms it can deliver plenty of current without a voltage drop. Peak currents in gen2 Prius can reach +/- 100 amps. This is 15C for these 6500 mAh modules. That's a lot of current!

    My 2005 Prius was producing frequent POA80 DTC codes. It had one module with one shorted cell. The output voltage on that one bad module was 6.62 V compared to an average of 7.7 V for the other 27 modules. I also ended up changing out a 2nd module that kept testing about 10 mV lower than it's block partner. I plan to run bench tests on that module to confirm that it's truly getting weak. I'll also be using Torque/Android and a mini VCI in my car to watch what the HV battery is doing while it's in the car.

    As soon as my Prius logs about 1,000 miles without any performance issues or codes from my "fixed" HV battery then 'll be starting a new thread on priuschat to discuss my testing method, which is a bit different than any I've read about so far.

    Cheers, EB
     
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  7. strawbrad

    strawbrad http://minnesotahybridbatteries.com

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    I have to disagree. Modules with one bad cell are easy to catch with an RC charger/ discharger. Most RC dischargers will terminate at 5.4 to 6 volts. With a dead cell dropping to zero this threshold is reached while the good cells have lots of capacity left. I tested this and shared the results in the battery re-hydrating thread. I cut the top off a module with a bad cell to expose the cell interconnects. This allowed me to bypass the bad cell and measure over 6 Ah capacity on the good cells. Capacity of the whole module through the bad cell measured under 1 Ah.

    I would change "Sufficient output voltage" to "Low self discharge" . Or holding at over 7 volts in long term storage. I will not attempt to reuse any module that self discharges below 7 volts. I have tested another module that had fallen to 6.8 volts. Sheet metal screws were inserted through the top to contact the cell interconnections. Five of cells read about 1.2 volts and one had dropped much lower. These are the modules that some try to fix with grid or cycle charging. I just send them to the recycle bin.

    Brad
     
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  8. gdanner

    gdanner Member

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    That's interesting. The bad module I removed from my Prius appears to have ONE cell which is a dead short. The module seems to have normal mAh capacity, and low ESR, but with 1.2 V less output voltage than a good module. In contrast it appears that the "bad" cell didn't short out in the module you dissected.

    Oops, I forgot to mention "Low self discharge" in my list! You are 100% correct. NiMH cells always have some self-discharge, but if a module drops from a normal value to less than 7 volts during a couple of weeks of "resting" time (neither charged nor discharged for 2 weeks) then it is certainly faulty.

    -EB
     
  9. kiwi

    kiwi Member

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    . ....

    The word "easy" is something I would like to chat about here. Also while typing that - safety reminder in the bottom of my blurp...

    Battery rebuilder from Moldova - they hired a low pay "pair of eyes" with the task to stare at 28 RC Toy dischargers with the goal to "easy catch" the bad ones. Doable? Of course. Easy? Who would have doubt that. Make sense? … You answer that…. I have my own opinion…

    But is that so easy as you may think? Did you look at the graphs I've uploaded for you?
    Toyota / Lexus hybrid battery tested on 20-channel HV Battery Analyser - Imgur

    RC discharger you are talking about will allow you to catch #40 (right bottom - the one which has dropped first). No doubt.

    You will (100%) miss on failed #26 (3.8AH) It does not have dead cell. It has one cell which is near dead. My standards disallow to reuse those. But some people would perhaps sell those on eBay without any remorse..

    I am making point here not for the DIY person who have all time in their life and can test back on their car and redo in case things did not work for them. This info could be useful for a person who is choosing where to put their trust and money when they buy second hand (claimed as "tested") modules or choose who would "test", "fix" and test again after it has been “fixed”.

    P.S. As for me what I call “easy” is being able to spot bad modules with no efforts even if I am not near the Complex. Drinking coffee in a kitchen and have a Remote Control Station which is monitoring what is happening in the garage on the Analyser(s) and what the UPS status is. That allows remotely stopping or intervening if there are any alarms and/or voice prompts.

    Two days ago I had to stop only twice – first during initial charge of the unknown pack when one dead module went into red in few sec and another 2 jumped up in voltage (that is what I call easy – to spot 3 dead in few sec) and second time after there was a power loss in the area and I had to save records (took couple of seconds) before terminating the program and doing controlled power-off of all the devices. UPS would allow to run Battery Analyser for another few hours but the test was actually finished anyway.

    Power cut reminded me to put another safety feature in the LAB to add to my multiple safety alarms – e.g. to plug an emergency light into UPS in the High Voltage area and to set up independent secondary Emergency Light powered by the batteries. In case of power loss you do not want to be in a dark and touch something lethal.
    I actually made emergency light ages ago from the PIR sensor and bright white LED, powered from 12VDC. It is easy.

    Doing "exact same" - mission impossible.

    Note: Capacity measurements vary - the higher the current the lower the tested capacity. That is the rule. Nominal in batteries is rated at C normally (in datasheets could be rated at different levels - e.g. you can see different capacities for one battery) but we do not know for sure whether EV Energy has rated theirs being 6.5AH at 6.5Amps load. Let's assume at 6.5Amps.

    a) You can not have current high enough with RCT (going forward I would use that abbreviation for RC Toy Charger) They only draw 1A and dropping in uncontrolled manner.

    b) You can't have the same current appllied simultaneously as you have to disconnect all you modules while testing with RCT. That takes time.
    I save time by not dismantling the pack at all even if there are bad modules.

    c) Capacities/voltages captured by multiple RCTs although you may capture them as a snapshot (e.g. HD Cam shooting all of 28 RCTs) will be captured in different "points" of their real life performance. Hence you would not have a bigger picture - i.e. what would be voltage/capacity and DeltaV on assembled pack. And that is "a key" - the missing part in what you are doing with the pile of RCTs .. Do I need to explain that? Or is it logically straight forward from a) and b) above?

    d) You would miss the "knee" shape of discharge curve (unbalanced module with near dead cell)

    e) Accuracy of 4 (RCTs of different brands and models, one was 4 channel) RC device I have tested and posted on Priuschat is > 10%

    f) If it would be that "easy", efficient, productive and reliable with RCTs - I would've done it myself as I am frugal too. Although I am not limited in resources when it comes to quality.

    "We are not that rich to buy cheap stuff" - was the second phrase in English I've learned as a kid.
    "Don't trouble trouble untill trouble troubles you" was the first one.

    RC Toy Cycle chargers? To much trouble to be troubled with....when it comes to Prius.
     
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  10. gdanner

    gdanner Member

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    It seems to me that the key items to look for when testing modules are:
    • A sudden voltage increase while charging a module (for example, from 7.0 to 7.6 volts)
    • A sudden voltage drop during a discharge test (for example, from 7.8 to 7.2 volts)
    I suggest that any change >500 mV which occurs in <1 second will qualify as a "sudden change in voltage."

    Either of the above "sudden voltage changes" makes me suspect that one of the 6 cells inside the module is much weaker than the other 5.

    I also think that a discharge test should automatically stop immediately if there is a sudden voltage drop >500 mV. By immediately I mean within 1 second. Do any of the RC testers have a voltage detector which could be programmed to do this?

    The problem with continuing a discharge test AFTER a sudden voltage drop is that the weak cell will get "reverse polarized" which will permanently destroy it.

    I'm planning some bench tests for my spare and/or defective Prius gen2 modules. I have a total of 4 modules to test at this time: 2 "used tested" modules that I bought on eBay, 1 module removed from my Prius that measures 100 mV lower than the other 27, and 1 module removed from my Prius that's 1.2 V low (to be precise it is 6.62 V). I think the 6.62 V module has 1 cell which is permanently shorted. I believe the 6.62V module is the main reason why my Prius had POA80 codes.

    I've put about 100 miles on the car after changing the 2 modules. No DTC codes. Performance and gas mileage have been excellent. The SOC on my Prius MFD id usually staying at the 6 bar (highest blue) level. I occasionally see bar 7 (green) when I'm going down a hill. The only time I saw the SOC drop to 4 or 5 bars was while the engine was warming up after the car had been parked 14 hours.

    -EB
     
  11. kiwi

    kiwi Member

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    Here you go:
    Spotting bad modules in Charge Mode - Imgur
    Note that sudden increase (my Analyser highlights it in Red) is one of many indications the module is dead.
    In that particular pack there are two other dead modules on channels #13 and #14. Those did not increase at all - they were not taking charge at all and after I stopped charge - the voltage on those dropped.
    Note that this is what I see in live view on the assembled pack with Analyser's 20 probes attached.

    Inquisitive mind would notice that I've ticked off the channel #8 - that was to disallow automatically shut the charge but rather see what will happen next. After a while that module's voltage dropped a bit still over 10V but below threshold I have set up in that test.
     
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  12. strawbrad

    strawbrad http://minnesotahybridbatteries.com

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    Ok, our disagreement is just a matter of wording. My dischargers stop at .9 V per cell. So set at a 6 cell module they easily catch a dead cell. I will try discharging a bad module with the charger set to 5 cells- 4.5 V and compare that to a 5.4 volt cutoff.

    From the re-hydrating thread.

    I cut just the very top of the module off. I had to clean up and finish the cut with a file to reveal the inside of the module. I could not find the vent holes between the cells. I might have cut through them if they are at the very top of the cells. I can fill one cell full and it does not drain to the others. The module I opened had one bad cell that measured .06 volts. On a 6.5 amp charge it took just 27 seconds for that cell to reach 1.5 volts. So I learned something today. Watch for a rapid voltage rise in the first half minute of charging. That would be an indication of a dead cell with little capacity. I charged the module at 6.5 amps with just the 9 ml of water the plates held on to. The dead cell started to gas right away so added enough water to cover its plates. The bad cell bubbled away like a slow boil. The other cells started to gas at about 1.45 volts. It is cool to see inside a module charging. I stopped the charge at 3000 mAh. On discharge the bad cell had just 85 mAh before going in to reversal. I continued the discharge on the other 5 cells for about 2500 mAh. The 5 cells are now on a cycle charge and discharge for the night.

    So I managed to NOT burn my garage down overnight. I always worry about leaving chargers unattended. I set the charger for nine cycles with a 6.5 amp charge, 1 mv delta peak per cell, 20 amp discharge to .9v per cell :eek:. This was done to just the 5 good cells. The dead cell I bypassed. The five good cells had just the tap water that the plates could absorb, 1.5 ml each. The dead cell was filled with tap water to the top and did not drain into the other cells(n). The last discharge shows 6091 mAh at a 20 amp discharge rate. Not too bad for a junk module.
     
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  13. gdanner

    gdanner Member

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    I really like the idea of cutting the top off a bad module and that way being able to access each individual cell. I've skimmed through the "re-hydrating" thread but now I will re-read it much more carefully.

    I can't properly explain the chemistry/physics that cause cell failure except to say the following:
    1. I've seen many NimH (and NiCd) cells where the failure mode is a permanent short circuit.
    2. In some cases it was possible to temporarily "burn out" the short circuit by pulsing a very high current through the shorted cell.
    3. But this was never more than a very temporary repair.
    4. I believe the internal short circuit is caused by a "dendrite" (metallic whisker) which penetrates the insulator that separates the anode and cathode.
    5. When there is a physical hole in the insulator then these metallic whiskers will always tend to regrow, causing the cell to short out again and again.
    6. The "dendrite" itself may vary in its resistance: A very thick metallic dendrite will act like a dead short. A very thin dendrite (or perhaps just some semiconducting salt crystals forming in and around the hole in the separator) will act as a continuous load resistor on the cell, causing it to self-discharge quite rapidly.
    -EB
     
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  14. gdanner

    gdanner Member

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    That confirms what I was thinking: Bad modules may have a very rapid voltage rise when they are charged. The most likely cause of this is that their electrolyte dried out or leaked out. In the worst case a bad module might test as a completely open circuit.

    -EB
     
  15. kiwi

    kiwi Member

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    Re-conditioning by experts vs other methods (a) Re-hydrating vs b) Re-conditioning by Pulse Treatment):

    a) Toyota has a patent about refilling the original electrolyte. That requires vacuum and precise measurements of the lost amount. Not possible DIY.
    I did not come across any patent from Toyota /Denso / EV Energy suggesting “Pulse Treatment” as a “Reconditioning” method for NiMH traction batteries. If that was efficient and reliable – there would have been already a Patent from those reputable manufacturers covering that. There is none.

    Re, quoting gdanner: “Pulsing a very high current through the shorted cell”.”never more than a very temporary repair” unquote.

    Spot on!
    That pulse treatment is what we believe “The Hybrid Shop” does (Mark Quarto and tyre mogul Matt Curry) and claim it to be their “scientific method” of reconditioning batteries. They actually have never scientifically proved that being a sustainable solution.
    Matt Curry claims World Domination of their technology. - Imgur
    Quoting Mr. Quarto: “…we can get them back to usually between 88% to 95% of new capacity” end of quote (he closes his eyes - perhaps dreaming about the numbers he is about to say...):
    Mark Quarto closes eyes when talking numbers - Imgur

    Baloney! How long will that pulse treated battery last? How about you recondition it, leave it idle for a month, 6 month, 12 months (just top up charge monthly) and I will arrange it to be tested in USA on my Analyser by independent Garage?
    They have been promoting their franchise for over 3 years now but I have not seen results from independent Lab.

    Failures of batteries “reconditioned” by that method are now anecdotal.

    Other “magical” but very similar in principal method” allegedly aimed at fighting crystallisation on plates inside the NiMH battery is called “burp” or negative pulse charging. I’ve spend time and money, bought diagrams, components and have built one of those with the source code for the chip given to me by inventor of that “burp charger”. No prejudice I said to myself at that time – people believe in magic, let me test and see by myself if that works or not.
    By analysing the source code and observing pulses on the scope and battery behaviour on my Analyser I confirmed that device was charging as designed. I saw initial improvement and even recorded the raise of the battery capacity in Prius modules (NHW-11, GEN-I), in my cordless drill (12V, NiMH) and in the Race Car 8 cell NiMH batteries.

    But, those improvements did not last for long. Initial excitement faded away. All those pulse treated Prius batteries and Drill battery have already been dumped as they have deteriorated rapidly. RC battery was dismantled and 2 dead cells removed. Pulse treatment did not kill the good cells, but have not improved their capacity long term.

    Pulse treatment as a “reconditioning” method is waste of time and money IMHO.

    All you need is to have right tools to test modules following right procedure (e.g. periods of idling) to compile the pack from good tested modules which are in conformance with each other and aim at getting maximum Usable Remaining Capacity (my metrics) to produce long lasting results.

    With no alternative to re-hydrating – the only reliable and sustainable option is to compile working pack from good tested modules which are “in conformance with each other”. I’ve designed my tools keeping Toyota way in mind – to support that way of battery rebuild.

    Think about what you buy on eBay from clueless sellers who display voltmeter readings alongside Prius/Camry NiMH battery modules trying to convince you that the module is good.

    They claim voltage readings in the 7 volt range and think it means the module is good. Baloney.

    I have just finish couple of tests on two NHW20 packs and tests on another 120 modules.

    Sharing here for you to avoid costly mistakes when buying so called "tested modules" on eBay.

    In brief:

    Tested 2 x NHW20 packs for one local friendly garage. They have got from wrecks and were told "the cars were running before the crash". Surely they did. That what every wrecker tells you...And it is true. To crash the car you have to run it, right? ;)

    One pack appeared to be good - URC (Usable Remaining Capacity) showed 3.7AH - that will work for a long time and they will get decent price for that one or may use it in their own Prius with confidence.

    Charged second pack (3AH pumped in) and left that pack idling for 3 days. Temperature was about 10C (50F).

    After 3 days modules were still showing around 8V. Your best guess? good or no good?

    The point I am making is about voltage. That is where clueless eBay seller measure module with voltmeter, notice something like 7.4 or 7.8 or whatever, thinks it is good and will sell you complete rubbish!

    I have load tested those modules on my HV Battery Analyser down to 6V @ 6A load. Test revealed those had only about 0.6 - 0.7AH remaining capacity. Those will not work in the car! Charged again in controlled manner – pumped in 3.6AH but modules only took about 0.7AH charge.Temperature on those did not even rise above 19C (66F). Ambient was 14C (57F).

    Alongside those 2 NHW20 I just have finished tests on other 120 modules from wrecks. Failure rate is 36 modules out of 120 = 30%!!!.
    By failed I mean – either dead or showing very low capacity. Those will not be reused. As for the voltage readings – they show above 7.4V after 6 days so far. Pretty sure will show above 7.2 weeks later.

    Good luck with eBay purchase. Baloneys
     
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  16. gdanner

    gdanner Member

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    I fully agree with Kiwi on this point:

    Voltage alone isn't enough to prove that a module is good.

    Yes, the voltage must stay >7.5V for several days of resting. I have a module that charges OK but after 24 hours of resting (no load) it always drops from 8V down to 6.6V. This indicates it contains 1 cell with excessive "self discharge." Therefore this module is confirmed bad. There's no reliable way to "fix" or "recondition" it. In fact, I'm sure this module is what caused my Prius to have POA80 codes.

    But it is also possible for a module with very low mAh capacity ( < 1 Ah) to measure >7.5V when tested only with a voltmeter (no load on the module).

    I'm observing and logging discharge/charge currents during normal driving. There is brief high current (+100A) charging during braking and brief high current (-100A) discharging when ICE starts up and when driving in EV mode. These pulses of high current are usually <5 seconds in duration. Continuous HV battery current is <20A. While cruising on expressway battery current is often <2A. I'd guess the average HV battery current is about 5-10A. ​

    Therefore I suggest testing mAh capacity with load currents of 1C (6.5A) up to 2C (13A). This is close to actual load conditions "in the car. Unfortunately most RC chargers have a maximum of 1A discharge current for measuring mAh capacity.

    Because Prius battery ECU is programmed to keep HV battery between 40% and 80% SOC, I'm thinking that the "discharge test" should be programmed to stop when the module falls to 40% SOC. i'm studying all the literature I can find in order to coordinate 40% SOC with the "end voltage" of a discharge test.

    I have 6 spare modules on hand: 4 were ebay purchases. 2 were removed from the HV battery in my Prius. I'm starting a series of bench tests on these 6 modules and will post my results. I'll be comparing mAh measured with a RC charger to mAh measured with a 1C and a 2C load.

    -EB
     
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  17. kiwi

    kiwi Member

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    This weekend tests - forgot to mention: In some tests I've discharged every module down to 6V under 6Amp electronic load without dismantling the pack. That is to charge the whole assembled pack as a next step in controlled manner (e.g. charge 4.5AH in).
    2 important things:

    1) as soon as Analyser swithed the 6Aload off from the individual module at 6V level - the module's voltage springs back to > 7.2V and stays like that even after 24 hours. That is deemed to be completely discharged module! You can do the same. If it does not spring up and the next day shows <7.2V - it is most likely dead.

    2) 20 modules in NHW20 pack showed <1AH under 6 Amp load (tested assembled pack 1/2 at a time). I tried to charge that pack back again "pumping in" 3.6 AH with 2A constant current charger -> but modules took only about 0.7 - 0.9 AH each. (I can see it straight away on the charge graph/bar in a charge mode). The result is in line with that common scenario which you have faced and reported on this forum many times before - when you use RC charger - you pump in say 6.5 AH, do load test at 1 A just to find out that full chanrge capacity in that module is very low whatever number is - 0.X - 2.X AH.

    When you are doing that 28 times at 1A - it takes forever and you have to do charge first and then discharge to find that out.

    I designed my HV Analyser(s) to conduct tests hundred times faster - do not need to do load test sometimes - as even in charge mode failed modules can easily be spotted and discarded. I do load test on 14, 19, 20 or 28 modules simultaneously (i.e. 28 times faster) and with newly built 6A 2.4KW portable load it is 6 times faster and that is 1C test.

    During last week I was able to test 296 modules, rebuild 3 x 40-module packs and 1 x 28 module pack. And that is all in my free from main duties time, after hours, observing tests running remotely from the comfort of my kitchen!

    With first ever Prius and Honda which have cylinder type 6 cell modules ("bamboo sticks") I can run tests on individual cells - those then can be cut and spot welded back if anyone is interested. I am personally not interested but my technology allows to test those in piles as well.
     
    #937 kiwi, Aug 2, 2015
    Last edited: Aug 2, 2015
  18. Josh B.

    Josh B. Junior Member

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    Hi everyone,

    I am doing my own rebalance project with Hitec X4 chargers based on all the info in this thread. I just replaced my one obviously bad module and two weaker capacity ones after doing all my reconditioning cycles and load testing. I just rebuilt my pack trying to as closely match module pairs by capacity. All my modules tested very consistently with load.

    The replacement modules ended up being very close in capacity to the others. In fact, the majority of my modules (24 total) showed between low 5400 to high 5500 mAh capacity, with two over 5600 mAh and one just over 5700 mAh. I have one outlier at 5380 mAh (40 mAh lower than its pair), which was also one of the three replacements I got. An extra cycle yielded no improvement.

    This same replacement module, I noticed during its discharge cycles, ended up stopping at 5.8 V instead of the 6 V cutoff I set on the charger, which makes me think it's dropping more rapidly at the end of its discharge than others. I never noticed that on any of the others I caught in their dry period. 5.98 V was the lowest.

    I load tested all three replacement modules, which had supposedly not been charged in over three weeks or longer, with my 100 W bulb (measured at a 4.92 A draw) before doing any cycling/charging and they performed consistently to the other modules, so it seems to just be at that low voltage.

    I know voltage drops off rapidly based on the graphs I've seen, but that one module is just enough different that I need to ask the experts before equalizing voltages and putting it back in the car. Is that something I should be concerned about or will it always be at a SOC level that it won't matter?

    Thanks,

    Josh
     
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  19. gdanner

    gdanner Member

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    There's one more important test that you should do: "Self discharge."

    This is done after charging. Disconnect the charger. Then let the charged modules sit with no load on them for 24 hours. Measure the voltage of each module with a voltmeter (the voltmeter has a very high resistance. Measuring the voltage with a voltmeter puts no load on the modules. Technically this is called "open circuit" voltage test).

    Then repeat the open-circuit voltage test after 24 additional hours of "resting" time. There should be little or no difference in the voltages.

    I have 8 spare modules on my workbench. Some of them haven't been charged for >10 weeks. All of my good modules are holding their open-circuit voltages above 7.50 volts. The best of them are between 7.70 and 7.80.

    I haven't finalized my bench testing analysis yet, but it does appear that a useful criteria for "used" modules might be open circuit voltage >7.50V.

    I have one bad module that drops to less than 7.0 volts within 1 hour of removing it from the charger. After a 24 hour rest it always measures about 6.60V. This corresponds to this module having 1 cell inside it that self-discharges very quickly. The other 5 cells are likely OK, because this module will then hold the 6.60V open circuit voltage for several weeks. However, this module could NEVER be used in a Prius due the one bad cell in it. I am certain that this module was the cause of my Prius having POA80 DTC codes.

    -EB
     
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  20. kiwi

    kiwi Member

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    To add couple of notes to what gdanner absolutely rightfully mentioned about self-discharge:

    - one particular country's standard (I have the copy, will not mention which one not to feed trolls) stipulates in black and white that NIMH batteries have to be load tested to check for self-discharge ONE month after charge ;

    - Toyota's patent for recycling does not specifically stipulate the period but mentions importance of idle before load test;

    - As I've mentioned earlier - i see it all the time: good modules discharged under electronic load of 6A down to 6V "spring" back to above 7.2V in few seconds after removal of the load vs bad ones may not (not always, depends on how bad they are).

    Important to note that even modules with low capacity - e.g. 1Ah or 2 Ah would behave like "good" - i.e. spring back to above 7.2 after discharge to 6V and stay like that for a long time even 24 hours later. Hence beware of what you buy on eBay if you only rely on voltage measurements.

    Sometimes I keep HV Battery Analyser running after the Load or Charge was cut off - to see what's happening with temperatures and/or voltages. That give another colourful view of modules performance after load/charge removal.

    Play safe.
     
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