Gen II Prius Individual Battery Module Replacement

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

  1. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    Your geo said CA, so I assumed California... Where in Texas? I've got an installer outside of Houston too.
     
  2. MichaelN77

    MichaelN77 Junior Member

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    I never said I was in California, Neptune is sadly a fictional place. I am on the complete and other side of Texas. The closest cities in order are Phoenix, San Antonio and Denver. All of them are about a ten hour drive at 70+ MPH.
     
  3. George W

    George W Active Member

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    What side of Houston? I'm in San Antonio. city-limit to city-limit is 190 miles.
     
  4. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    NE around Shepherd. But has an install shop closer to HOU itself.
     
  5. MichaelN77

    MichaelN77 Junior Member

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    I am on the complete other side of Texas in El Paso. I was thinking the local community college here on the other side of town has a student repair shop. I can see how much they charge and take the battery there and have them install it hopefully without screwing up the interior. Maybe they can fix the bumpers too. I can very confident I can install it myself and take it apart to and replace the modules if I have to. It is putting back the interior and having look, feel and perform the same way it was prior I can never seem to get right.
     
    #2305 MichaelN77, Feb 9, 2019
    Last edited: Feb 9, 2019
  6. MichaelN77

    MichaelN77 Junior Member

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    Do not worry, I am not driving it. I am waiting for the replacement harness to arrive.
     
  7. dolj

    dolj Senior Member

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    Michael your battery experience has been moved to here: My Prius Battery rebuild experience | Post #52. Please continue to post about your rebuild experience over there and do not use this thread anymore for that purpose. Thanks.
     
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  8. Phildo

    Phildo Member

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    Cables:

    I couldn’t find anything mainstream off-the-shelf so I found these on AliExpress.com (ie the Amazon of China).

    Mayitr 2pcs Copper 4mm Banana Plug to Shrouded Alligator 15A Banana Plug to Alligator Clip Cable Leads 1M For Testing Probe

    Link: Mayitr 2pcs Copper 4mm Banana Plug to Shrouded Alligator 15A Banana Plug to Alligator Clip Cable Leads 1M For Testing Probe-in Alligator Clips from Home Improvement on Aliexpress.com | Alibaba Group

    Store link: Son Day Day Up Store - Small Orders Online Store, Hot Selling and more on Aliexpress.com

    The description says that these are rated to withstand 15A. I didn’t want to mess around with making cables (ie I couldn’t find suitable alligator clips and bullets locally), so bought four sets of these.

    I know nothing about cables, but the alligator clips have a strong spring in them, and the cables are much thicker than the cheap test leads that I had been trying to use.

    [​IMG]

    I’m assuming that this is the specification for the cable - does anyone know how to decipher it?

    [​IMG]

    Another option is these ones, which are rated at 32A (but obviously a lot more expensive). These would be useful for discharging at 20A with a Turnigy Reaktor and regenerative discharging:

    2pcs 1M length 13 awg32a TL332 2.5 square power supplier super soft silicone manostat alligator clip output line

    Link: 2pcs 1M length 13 awg32a TL332 2.5 square power supplier super soft silicone manostat alligator clip output line-in Alligator Clips from Home Improvement on Aliexpress.com | Alibaba Group

    Store: KSST Store - Small Orders Online Store, Hot Selling and more on Aliexpress.com | Alibaba Group
     
    #2308 Phildo, Mar 14, 2019
    Last edited: Mar 14, 2019
  9. Phildo

    Phildo Member

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    Car: 2007 Prius
    Battery removed from car: 18 months ago
    Odometer: 148,000km (ie around 92,000 miles)

    This car gave error codes a year and a half ago. I replaced the battery with a secondhand one from a wreck and this battery has been sitting around since.

    Techstream was showing low voltages in block 5 and block 7 (although only gave an error code for block 7, not 5).

    [​IMG]

    For the first run I connected a Reaktor QuadKore to modules 1, 3, 5 and 7:

    [​IMG]

    Things went ok on these four modules.

    Any ideas on why the mAh tended to drop on the third cycle from the second cycle?

    [​IMG]

    [​IMG]

    [​IMG]

    The end result:

    [​IMG]

    --------------------------------------------------------------------------------------------------------
    Previous load testing confirmed that modules 10 and 13 have failed, but the others were fairly good. Modules 24 and 26 had 0.45 and 0.43 voltage drops, so they might need replacing as well.

    [​IMG]

    On the next round I did modules 9, 11, 13 and 15 (module 13 is already known to be failed).

    However, on the three good modules the Reaktor terminated.

    I’ve seen people use settings of 7250 and 7500mAh, and sometimes people use 9000mAh.

    I even tried 8000mAh on two of the channels (but I’m going to set them back to 7500).

    What went wrong here? What are the circumstances that result in termination? Charging was set at 2A.

    I can’t see how I can see the last discharge figure so how can I find out he mAh on terminated modules?

    [​IMG]

    [​IMG]
     
    #2309 Phildo, Mar 14, 2019
    Last edited: Mar 14, 2019
  10. SuirpEvets

    SuirpEvets New Member

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    Hi all, I just joined PC and have read all 116 pages of this fantastic thread, plus many others and would like to contribute, and also ask some questions.

    I have a 2005 Prius with 285,000 miles on it. I got it from a friend after the engine spun a bearing, otherwise everything was working just fine. The car sat for a while before I decided to buy it after doing the research to find replacing the engine isn't that bad. I found a cheap engine and trans with about 130k on it and swapped it all (easier than pulling the engine only IMO). With the new engine in, I fired it up and got the red triangle with a P0A80 code, and thus began my research into the traction battery rebuilding. I have the Torque Pro App and used the custom PIDs to find the low voltage block #5 (15.6V vs 16.9V all others).
    Prius_Block5_Faulty.png

    So next I pulled the pack and did voltage measurements and load testing, but only with a single element headlight bulb (~45-55W), which I know now after reading this whole thread that it's better to do this with a higher wattage, but it's a start. Here are my results.

    #, resting voltage, voltage after 120sec load test
    1 8.15 7.98
    2 8.13 7.96
    3 8.14 7.93
    4 8.14 7.95
    5 8.14 7.96
    6 8.08 7.95
    7 8.14 7.94
    8 8.14 7.94
    9 6.77 6.54
    10 8.14 7.97
    11 8.14 7.95
    12 8.13 7.94
    13 8.14 7.96
    14 8.14 7.95
    15 8.14 7.96
    16 8.14 7.96
    17 8.13 7.95
    18 8.14 7.96
    19 8.13 7.96
    20 8.13 7.95
    21 8.14 7.96
    22 8.14 7.95
    23 8.15 7.96
    24 8.13 7.96
    25 8.15 7.97
    26 8.14 7.97
    27 8.14 7.96
    28 8.18 8.02

    Clearly module #9 was the source of the fault given the classic ~6V dead cell symptom. Otherwise the rest looked pretty consistent to me. So I sourced a pair of Gen3 modules from a local battery rebuilder and replaced #9 & #10 (block #5). I used a regular 12V charger on low for a very short time to bump the voltage up slightly to match the others. I also bought completely new Toyota bus bars and nuts since there was the typical corrosion. I've read many accounts of others having successfully cleaned their bus bars, but I've also read many accounts of the sensing wires getting badly corroded back to the computer or having wires break off, so I figured I would spend the $200 as a relatively cheap insurance and also save me the labor of the cleaning.

    With the block #5 modules replaced and brand new conductors installed I put the pack back in. Fingers crossed I fired it up and had the red triangle but noticed no clicking of the contactors. Fortunately I figured out I didn't have the service plug latch down all the way, which seems to be the #1 rookie mistake. Once I properly engaged the service plug latch I fired it up and I was in business, all good!!!
    I went for a test drive and checked my block voltages and everything was looking good. SOC was previously ~55% and is up to ~65% after. Not sure this is relevant, but thought it was interesting to note.
    Prius_Block5_ Replaced.png

    Since then I've been driving the car about a month now with to faults, but I'm still a little hesitant to trust this battery pack, especially given all the information most of the veterans have shared regarding balancing and such. Plus I've been getting low 30's MPG which seems to be a sign of pending battery failure. However, it's also been really cold here and most Prius owners claim much lower MPG in cold climates. So maybe this is normal. It's warmed up a bit recently and it's getting around 37 MPG, which makes me feel a little better, but still not great given the nearly 50 MPG others claim.

    To test things out a little more I messed around with the logging available in the Torque Pro App and took a few samples of block voltage to see what kind of spread I have to use as a gauge of "balance". Here is one example and in general the lines maintain a fairly constant spread as shown, i.e. the top Red and Grey lines are always well above the rest. This seems to indicate that there are a few fairly strong blocks, and the rest are all a bit weaker, but relatively evenly matched. Unfortunately there are only 7 colors of line, so I can't tell exactly which is which from this, but I can run the same test 7 at a time to pick them apart. Regardless I think this is still useful information overall.
    Prius_Block_Voltage_ Sample.png

    The next thing I plan to do is the force charge and discharge in reverse test procedure to use as a benchmark, since that seems to at least give some sort of reasonable gauge on overall battery health. I'll post those results when I get there.

    Regardless, I am planning to get a Synchronous Balance Charger/Discharger (SBCD) to do charge-discharge cycling as is the intent of this thread. However, I'm thinking of taking a slightly different approach, which is where I'm hoping to get feedback to see if this makes sense or not. I've looked over lots of different SBCD's, such as the DC6, the Hitec X4 AC plus, you name it. But one I've found that looks really good is the iCharger 106, 206, 306, etc. What I like about these is that they have a 20W, 30W, or 80W internal discharge capability. When you have 10W or less, the discharge process is just sooo slow, and these batteries can handle much higher rates of discharge, although I know it's better to do it slower to avoid killing particularly weak batteries and reversing cells.

    That all said there's one particularly neat feature of the iCharger SBCD's that I think will make the discharge much faster with less risk of damage which is called Discharge Reduce. As the manual states, it will discharge at a constant current until it reaches the set voltage, and then change to constant voltage and continue discharging in a high precision discharge mode until the current reaches a set xx% of the initial discharge current. My thinking here is that this will also give you more accurate and consistent capacity results.
    What do you think?
    Anyone have experience with this?

    The other neat feature that seems really useful is the Forming Charge feature. This simply charges at a 1C until it reaches 1.48V/cell, then charges at constant voltage until the current reaches C/4, then charges another 25% at C/10. This is intended specifically for balancing up low cells according to the manual. From what others have posted, 350mA seems to be the "safe" indefinite charge or trickle charge rate, and assuming 6.5A would be the 1C rate, the C/10 rate would be 650mA. However, given it's only for another 25%, this may be fine.
    What do you think?
    Anyone have experience with this?

    The last part of all this is that I'd like to progressively recondition my battery one block at a time rather than pulling the whole pack and reconditioning every module individually all in one long go. The idea here is that I can use the Torque Pro App to identify the "weak" blocks using a histogram of the HVB Min #(Num) as shown below. From this you can see that block 2, 3, and 8 are coming up at high counts, meaning they are registering as the Low Voltage Blocks more frequently than the others (I cut the scale to 11 because 12, 13, and 14 had few to no hits and it's easier to read like this). I would also use the logging as shown above to confirm what the histogram is indicating.
    Low_Block#_Histogram.png


    So this is my overall concept given all of this information so far:
    1. Collect data on current performance using the force charge and discharge in reverse to benchmark overall battery capacity and state of health.
    2. Use logging and histogram in Torque Pro App to identify the "weakest" block(s) and select 1 for reconditioning.
    3. Remove service plug for safety.
    4. Remove battery cover in vehicle and front bus bars to maintain blocks (side with sensing wires).
    5. Install service plug to reconnect block #10 only if this is the selected block.
    6. Record block voltage of each block.
    7. Use Forming Charge to top balance block (apply forced cooling to battery).
    8. Discharge at max (~2A @ 30W) to 12V using Discharge Reduce to bottom balance and record initial capacity.
    9. Use Forming Charge function to top balance.
    10. Discharge back to starting block voltage using Discharge Reduce function to achieve steady voltage.
    11. Reverse disassembly
    12. Return to service and collect new data.
    13. Repeat periodically as time permits.
    Total time ~6-8 hours

    The idea with all this is to basically prevent weak modules from getting so weak that they die and to recondition the pack a bit at a time. I'm curious to see what kind of gains there may be with this approach since so much of this thread has been focused on complete rebuild working thru every module. I'm also curious to see how much gain there may be from doing a single block each time, since again most of the data is shown for a completely reconditioned pack. I understand that complete reconditioning is ideal short of a new pack, but as is the issue with many others, it's a LOT of time or money or both to do it that way, and I thought this might be worth trying. I know this may turn into a lot of time as well, but at least it's spread out, which should be easier to manage. I know not to expect major gains in MPG or overall performance with a single block reconditioning, but that I may over time as I work thru the whole pack. However, having a block with increased capacity should only be a good thing, and should also prevent weak modules from dying. I guess you can consider this my thesis.

    Sorry this turned into such a long post, but I guess I just got it all out at once rather than over a dozen separate posts. I hope some of the information I've shared is helpful for others, and that there are still some veterans out there who can provide a sanity check for me.
    I look forward to hearing any feedback, criticism, or comments.

    Thanks
    Steve
     
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  11. SuirpEvets

    SuirpEvets New Member

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    Phildo,
    What settings are you using?
    I believe that the deltaV setting can cause early termination, otherwise I think it should go to the set capacity.
    Full disclosure, I've not run these yet, but I've read this entire thread thoroughly, so I hope I know what I'm talking about.
    Either way I know others will ask for your settings, so you might as well post that now.
     
  12. ericbecky

    ericbecky Hybrid Battery Hero

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    Steve,
    That was a great write up.
    Also a great use of the the inexpensive tools available to folks.

    Smart move about the buss bars. $200 is money well spent for peace of mind against corrosion. Too bad more people don't do it. They brag about what a great deal they got on the car, or money they are saving, and often not willing to spend that savings on the buss bars.

    I appreciate the honesty about the service plug. We've all done it at some point. Classic way to make you question yourself, and then slap your forehead.

    Enjoyed the graph. A great way to visualize the spread. The more modules that get swapped in the more interesting that graph becomes. You can see the differences of the newly inserted modules. They never quite match the ones from the original pack.
     
  13. strawbrad

    strawbrad http://minnesotahybridbatteries.com

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    Awesome write up Steve!

    You are off to a great start. Here are some suggestions.

    Try the app Hybrid Assistant - Hybrid Reporter. They do the same stuff that you'r using Torque Pro for but they are more refined.

    I think you'r going to really miss up your pack by reconditioning one block at a time. The reconditioned blocks will no longer match the rest of the pack. Before you do that try discharging 200 mAh from each module in the yellow, red, and grey blocks. That will bring them closer to the average.

    The Ichargers and their clones, Reaktor and Charsoon Antimater are awesome chargers. The formation charge is a great tool to help speed things up but it's still a 3 1/2 hour charge. The new version of the Reaktor 300W has dropped the formation charge feature. You did not mention that they are also capable of a regenerative discharge at a 20 amp rate.
     
  14. Phildo

    Phildo Member

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    Charger: Turnigy Reaktor QuadKore, currently powered by a Turnigy 23A power supply but it sounds like i need to get into regenerative discharging ASAP.
    Charge: 2.0A
    Discharge: the full 30w per channel, which works out to around 2.7A per module when cycling four modules
    Wait between cycles: 5 minutes
    Discharge and then recharge for 3 cycles
    Cut-off: I kept getting termination errors at 7500mAh and even 8000mAh. I saw a comment previously by S Keith that he either turned the cut-off off, or set it to 9000mAh. So, I’ve set it to 9000mAh.
    Timer limit: turned off
    DeltaV: Default

    I’ve also got an iCharger 106B+ with pretty much the same settings so I’ve been using that sometimes to do an extra module at a time.

    My data so far (the last three modules are still cycling):

    [​IMG]

    Modules 10 and 13 are clearly finished (ie dropped a cell in each module).

    For the load testing, I don’t know how much of a difference is too much. I used a Hybrid Automotive Load Tester (Prolong® Battery Module Load Tester - Hybrid Automotive) and ran a car headlight globe for exactly two minutes on each module.

    I read on this thread that modules should be kept within a 500mAh range, so after looking at the list of capacities so far it seems that a 4,700 to 5,200mAh range would cover most modules.

    Below that range: module 5 (4,537mAh), module 8 (4,311mAh), module 11 (4,492mAh), module 12 (4,281mAh) and module 14 (4,369mAh).
    Above that range: module 22 (5,398mAh) and module 25 (5,468mAh).

    As we can see, the lower capacity modules are in the centre area of the pack.

    How important is the 500mAh range for module capacities?

    Can I get away with just replacing the two dead ones (ie modules 10 and 13) or it is worth finding suitable replacements for modules outside of the 500mAh range?
     
  15. ericbecky

    ericbecky Hybrid Battery Hero

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    You can do as little much as you want.
    You may end up going back in there regardless.

    Sometimes by blind luck you slap a completely random module in there and the pack lasts as long as the on you soebt 20hrs meticulously going through.

    There are no hard and fast rules to this. Consistency is always better than inconsistency. Both in the process and the results.

    You are going to always have done factor that limits you. For example, sometimes that is simply because of your supply of modules. The likelihood of getting an exact match is low. So you just deal with what you've got.

    Do the best you can, and realize you may be back in there in the future.
     
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  16. SuirpEvets

    SuirpEvets New Member

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    Thanks strawbrad!

    I'll look into the Hybrid Assistant - Hybrid Reporter, sounds like another good tool.

    I understand your concern for the pack imbalance, as that's been a constant theme of this thread - the importance of matching capacity and such. Just to elaborate a bit further on my thinking, my process as I outlined is: forming charge (top balance) - measured discharge (to get capacity, and bottom balance) - another forming charge - then discharge to original voltage. The idea is that I'm only doing 1 full cycle each time, which from all the collective reading typically results in a minor gain, with further increase in capacity with additional cycling (typically 3 cycles or more). Therefore, I might only slightly improve overall capacity without causing an extreme imbalance between the others, but also hopefully improve the overall health significantly by catching the weakest blocks before they get too far gone. The other idea here is that I'm focusing only on the lowest block each time, which should theoretically bring the modules closer together and not farther apart, but I guess that all depends how low they are, and how much they improve in a single cycle. Another thought may be to even eliminate the last discharge and try charging up to the desired voltage, but I have a feeling that might be bad as the capacity can be hugely different over a small range of voltage. Then again maybe the same is just as true by discharging down to a certain voltage.
    What do you think would be the consequence of doing one block only for example?
    Any thoughts on discharging or charging back to the original voltage?

    I'll try the 200mAh discharge idea before I do anything else just to see what happens. If this idea works, I wonder if I might be able to use this to better tune the pack after doing the block cycling.
    Is that something you've done before, or is that just an idea you have?
    Where did you come up with 200mAh? Is that just a guess, or is that based on the ~0.1V differential?

    I didn't mention the regenerative discharge capability to shorten the post as much as I could because I'm planning to use a dedicated power supply, so it wasn't relevant, but it is good information for others who might like that approach. I just don't want to mess around with an additional battery and charger for that battery working right. I feel safer with less discharge and a dedicated power supply. I've not lost power at my house in years, so i'm not concerned about the battery backup.

    Thanks again for your feedback. Much appreciated.
    Steve
     
  17. SuirpEvets

    SuirpEvets New Member

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    Hi ericbecky,
    Thanks for the affirmation!
    Glad to know I'm on the right track.

    Strawbrad had an interesting idea to selectively discharge the higher blocks by say 200mAh to get them more tightly grouped to the others. The interesting thing I don't know yet, is if those lines even correspond to the swapped modules. But I'll look into that next.
    You think something like this might work for achieving better balance with swapped modules?
    Maybe this could be another way to fine tune a mismatched pack..

    Thanks,
    Steve
     
  18. strawbrad

    strawbrad http://minnesotahybridbatteries.com

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    Yes,

    I have done this. The 200 mAh is based on experience. You could try 100mAh on the yellow block since it's a bit closer to the average.


    The cycled blocks will have improved performance. They will then not match the charge and discharge rates of the rest. Their voltage will be the lowest on charge on the highest on discharge. That's the opposite of how a weak module behaves.


    That discharge graph could just mean the Red, Grey, and Yellow blocks are at a slightly higher SOC than the rest. Combining a charge graph will show a more complete picture.


    Voltage is a very squishy target. Lets say all of your modules are resting are 8.00 volts so you cycle one blocks modules to 8.00 volts. Come back the next day and the pack will still be at 8.00 volts but the newly charged modules will have settled in around 7.9 volts. This is part of the need for consistency that Eric mentioned. Doing anything different to just a pair of modules is going to make them behave differently from the rest.
     
  19. SuirpEvets

    SuirpEvets New Member

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    Phildo,

    You may be in a range of charging current (2A) where the -dV function may be hit or miss, which could be causing early termination on some but not others. I believe when you are using -deltaV it will stop charging when it detects the voltage sag that occurs when the battery reaches full charge. However, at lower currents this sag is more difficult to detect. From other reports it seem that -dV works reliably over 3A, and many charge at up to 5A.
    I think what you want to do is set your mAh cutoff to something like 7250mAh or so, and increase the -dV setting to max or turn it off if you can. Some chargers won't let you turn it off, so setting it to max is the next best thing. This way you are more certain to reach your mAh cutoff, otherwise I think you may get little to no "top balancing" if it cuts off early by -dV.

    Looking at your earlier post data more, what it's looking like is that the ones that reach termination are getting to the mAh setting of either 7500mAh or 8000mAh and stopping, which I believe is what you want. When it shows Done, I think that's ending due to the -dV setting, which is why on one module (I'm assuming a bad one) it's ending at 6.89V and 1971mAh, because it can only take so much charge and is exhibiting enough charge characteristic to trigger the -dV, otherwise I would expect it to go to termination.
    Yeah I think this is all making sense looking at it more, all your other successful D>C cycles show Done with something over 8V and some variation in the mAh less than 7500 or 8000, which tells me it's ending by -dV, rather than hitting the mAh cutoff.
    The idea of using the mAh cutoff is to help top balance by gently overcharging. The thing to be careful with these batteries is not to overcharge at too high a rate or you end up too hot, which isn't good for them and can be dangerous. However, 2A is probably okay if you have some sort of forced cooling or very low ambient temp or both. It seems that 3A or more is where most people get nervous.
    That said, it looks like for the most part you're safe as it's not overcharging, and it's still taking on a fairly high charge, but you may still be missing the opportunity here to combat the voltage depression by overcharging. Since charging is not 100% efficient (most say 60-70% for Ni batteries) then putting in 6500mAh is only storing 3900-4550mAh and the rest is lost as heat. This is part of the reason some set their charge as high as 9000mAh because (6500/0.7 = 9285) which means you would have to pump in 9285mAh @ 70% eff. to get in 6500mAh.

    So I hope this makes sense, and I hope I'm right with all this. I think it makes pretty good sense, but again I'm still pretty new here. Just my hopefully well informed opinion. Sorry if this is a bit all over the place, was kind of on the fly, no time to edit much.

    Lemme know how you make out.

    Regards,
    Steve
     
  20. SuirpEvets

    SuirpEvets New Member

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    strawbrad,

    Thanks again for the feedback.

    Experience says a lot. I'll try it out and let you know. Will be a bit yet before I get to that tho. But I'll definitely start there.

    I think I follow you. But just to elaborate, what I think you're saying here is that weak modules charge and discharge faster, and therefore their voltage will fluctuate more and to a greater extent, whereas better performing modules hold more charge and therefore will maintain a more constant voltage thru charge and discharge since the system basically reacts to the weak modules, not the strong ones.
    So on charging, the stronger modules will hold relatively steady voltage and the weak modules will run higher voltage as they charge up faster than the strong ones, and basically the opposite on discharge, the strong will again maintain relatively steady voltage while the weak will exhibit greater sag and drop to a lower voltage as they discharge faster than the strong ones. My feeling is that there's probably a much stronger effect of this on discharge rather than charge, but I would trust your experience to say if this is the case or not. This all makes perfect sense tho. Case and point it seems is the method for picking out weak blocks using the HVB Low Block# on an active battery, or the basic load test to identify weak modules.
    Is this correct?

    What do you mean by a charge graph?
    I assume you must mean the watt-hours or Ah's in and out of each block, but I'm not sure I have that ability with Torque.
    I'd be very interested in that if you feel it would be a better indicator.

    Your comments about voltage gave me another idea. It would be interesting to discharge all modules to the typical 6V and then pump in a fixed charge, say 3500mAh or so and see what voltage they each land on. Maybe this could be another way to sort of gauge balance. Going off the theory above, the weak modules would basically fill to 100% SOC and reach a higher voltage, and the stronger modules would only reach say 60% SOC leaving them at a lower voltage. I think the flaw here may be the voltage sag after charging as the weak modules may drop to a lower voltage after resting. Again, just kinda thinking out loud. Just curious to hear your thoughts.
    What do you think?

    Thanks,
    Steve
     
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