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Prius II HIV battery module change

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by flyingstoo, Oct 29, 2012.

  1. flyingstoo

    flyingstoo Junior Member

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    I have a 2006 prius Ii with 118000 miles. I live in the uk in a relatively cool climate. Recently had a p3016 (weak module) failure code and Toyota wanted £1450 ( $2100) to replace Hv battery. So decided to do research into DIY investigation and repair. Removed the battery and discovered module 6 open voltage at 7.65v all the others at 8.15v. This tied in nicely with the fault codes. I found 2 replacement modules from eBay . They arrived and appeared in good order. Bothe around 7.5 v open voltage. I used a hitech model battery charging system that I had to charge up the modules individually, monitoring the in going charge to arrange for a matched open voltage reading with the rest of the pack. I got this voltage within about .1 v of the others. Put the battery back into the car and switched on. All fault codes had cleared. Drove the car for about 40 miles with everything looking normal but then a fault came up and investigation showed an P0AFA ( low voltage) . This was cleared but returned again after several miles.

    My questions are,
    1. When individual modules are replaced, to get a good balance, is there a good method that should be used, eg: fully charge the module then bring it down the to other pack open voltage level or is there a known other method of doing this
    2. When a module is replaced will it in time balance into the rest of the pack and is it often the case that a P0AFA fault may re occurr sometimes?

    I am awaiting a Bluetooth obdii device and have loaded TorquePro onto my smart phone so that I can monitor the battery in more depth , having set up the prius codes as by spreadsheet else where.

    Any further advice or observations on my methods would be most appreciated
    Thank you
    Stu
     
  2. Britprius

    Britprius Senior Member

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    Hi Stu, welcome to PC.

    The normal method when replacing a battery module is to fully charge and discharge each module 3 times and on the last discharge check the time and current to give the amp/hr capacity of each module. This allows you to build a battery with modules of as near as possible the same capacity "balanced".

    If there is a modules that is low in capacity in the battery when the battery is discharged the low capacity module will become discharged first and then be reverse charged by the rest of the modules "destroying that module".

    There are chargers on the market made for battery packs used in model aircraft, cars, ect that are designed to do just this and these work fine on the Prius modules. The problem is the time taken to do each module charge/discharge 3 times then multiply this by 28 the number of modules.

    The problem also arises that when a module goes bad it overheats causing the modules next to it to dry out damaging those or reducing there capacity. It is also a good idea to swap the modules from the center of the battery to the outside to help balance the effect of the heat in the center of the battery drying out cells to help longevity.

    Do not let this put you off the DIY route but changing one module in isolation rarely works as also you do not know the capacity of the modules you have purchased.

    The other way round the problem is to purchase a complete battery from a wreck (I have seen them on Ebay for as little as £250) and then sell your modules to offset the cost.

    Hope this helps. John. (Britprius)
     
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  3. Britprius

    Britprius Senior Member

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    Forgot to add the Imax B6 or similar charger is what you are looking for.
     
  4. flyingstoo

    flyingstoo Junior Member

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    Thanks John that is some excellent information. On inspection of the battery modules I could not see any outward signs of over temp or leakage. I am hoping to get my Bluetooth obdii device tomorrow and will investigate the SOC,and other parameters.

    At the moment the fault code has cleared and not returned, I believe though that the battery ecu will probably return the code after a few trips but we will see.
     
  5. Britprius

    Britprius Senior Member

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    Something to try is to force charge the battery by putting the car into drive holding it on the brakes rev the engine until you have 8 green bars this will help to balance the modules.
     
  6. 2009Prius

    2009Prius A Wimpy DIYer

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    If there is a weak module in the HV battery pack then it would almost certainly be further damaged by force charging to full 8 green bars.
     
  7. Britprius

    Britprius Senior Member

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    Not really, do not forget that 8 green bars is still only 80% of full charge and going to this level of charge "that could happen anyway in normal use" helps bring cells within a module into a better state of charge.

    Bad cells are quickly going to be reverse charged anyway if they are not bought into line of better charged cells. It is almost certain that it is only one cell in a module that goes bad but means the whole module has to be discarded.

    Going too 80% of full charge is much better than being completely discharged and then being reverse charged.
     
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  8. Britprius

    Britprius Senior Member

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    There is not usually any sign of leakage on gen2 modules. The cells are vented and over time the water content evaporates off more so when the cells in each module get hot, "not so hot that there is any outward sign".

    Batteries in hot climates show this effect more than cooler climes. This is why it is recommended to change the center modules to the outside when rebuilding a battery, because the middle of the battery is always hotter than the ends causing those to dry out slightly faster.

    There are experiments in re hydrating cells in modules to bring them back to life.
     
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  9. flyingstoo

    flyingstoo Junior Member

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    I have now been fortunate enough today to find a breakers yard nearby in Aylesbury that has a prius with a traction battery. I went along and dismantled the battery covers to gain access to the modules. All the modules showed a very balanced open circuit voltage of 7.53v giving a total of 211v off load. This seemed to be a good sign so I paid the guy £150 and took a chance. I have put the battery into the car this afternoon and so far it looks good, no faults and an mpg of 51.3 miles over about the 20 or so miles covered so far. It is still early days but if I get past 40 miles without a fault reoccurrence then I may be ok.

    With regard to the removed battery that had 2 modules replaced. This kept giving a P0AFA error code which suggests a low voltage output. Examining the off load voltages showed that all cells were 8.1v but the 2 replacement cells were 8.2v. I didn't expect them to be higher. If this breakers yard battery continues ok I shall dismantle the extracted battery and see if I can do a balance and refurbishment when I get the IMAX b6 and obd2 reader.

    Will keep you posted..... Thanks again for the info
    Stu
     
  10. Britprius

    Britprius Senior Member

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    It is quite likely the cells you bought have been balanced "the reason they now appear to be more healthy than your own".

    That was a very good price for a HV battery do you know the year of the car it came from if it is later than 2005 have they got a drivers side rear light as I need one desperately. Let me know if you can find out.

    As you can work out if you sold your cells at say £25 each you would only need to sell 6 to break even.

    Make sure you buy the power supply with the charger, still good value for under £30. There is another charger I think it's called the Super mate DC6 and that connects to a laptop to keep all the data (but more pounds).
     
  11. Britprius

    Britprius Senior Member

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    One other point I should have mentioned. Do not charge the modules unless they are either still in the complete pack or if not clamp them with timber either side in a vice or with G clamps as they will swell if you do not do this.

    It is also a good idea to have a fan blowing on the modules to keep them cool while charging.
     
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  12. flyingstoo

    flyingstoo Junior Member

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    The car I worked on had no rear lights. There was another but the lens was broken on the drivers side. The breakers yard is on 07864001121 if you want to ring them.

    With regard to the IMAX d6 , I noticed that there are a lot of comments about fake products on eBay and some people are saying that the cheaper ones are fake. Have you had any trouble with yours at all? Can you recommend a good source?

    Cheers
     
  13. Britprius

    Britprius Senior Member

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    Thanks for the info on the lights.

    The charger of choice is the Suppermate dc6, I did have ten of these but sold them at the beginning of the year. They are available on Ebay at around £50.

    The Imax D6 should do the job just as well model shops are perhaps the best source but not the cheapest.

    Scan Ebay or Amazon you may pic up a second hand unit at a good price.
     
  14. bwilson4web

    bwilson4web BMW i3 and Model 3

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    There are two characteristics that need to match:
    • open circuit voltage - you' all mastered that one.
    • Ahr capacity - a module with a lower Ahr capacity will have a greater voltage swing going up and down in the state of charge.
    When I got my ReInVolt pack, I fully charged the pack by descending a 160 m, 8% grade hill and parking. Using a data recording scanner, I monitored all 19 pairs (the NHW11 has 38 modules) while I had the car in "R" against the curb, fans and lights on maximum. This gave me 19 lines in a plot that spanned 80% down to about 45% when I stopped the experiment. This allowed me to see that all 19 pairs were well matched and I would have no problems.

    I suspect the two replacement modules had a different Ahr capacity than the other modules. But since the code is more warning, by the time you got back to check, the replacements had achieved close to the same open voltage as the other modules.

    If you still have the old modules, one of them has a short, 1.2V/cell for six cells, 7.2V nominal although they can range up to 8V safely. Over 8V is . . . not such a good idea as this can lead to oxygen generation.

    Look closely at the rim of the terminals for evidence of the "O" ring having failed. Alternatively, a pH solution can detect evidence of the KOH electrolyte leak.

    GOOD LUCK!
    Bob Wilson
     
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  15. flyingstoo

    flyingstoo Junior Member

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    Thanks for that Bob.

    The seals you mentioned all look okay. There was some white powder deposits on some of the module terminals. This just brushes off with an old toothbrush. I assume though that this is probably just copper oxidation as there is no sign of blue acid coating on any of them.

    When you carried out your kerbside experiment was there much of a rise in battery temperatures as I assume there was a large current flow?

    I have now received my bluetooth OBDII scanner and have setup TorquePro on my HTC phone. I must say it is a very impressive app ( less than £15 for the App and device) and with the installed extra PID's for the prius it can really show the battery details very well. My breakers yard battery looks like a good one with a well balanced pack, High to Low block voltage variation over a 5 mile trip was only about .1v

    There are PID's for the HV block 'Internal resistance'. They seem not to be working though as they all show zero. Maybe they need scaling does anyone know?

    I shall now consider whether to re install my bad battery to do some more testing or whether to just go through a rebalance and refurbishment.
     
  16. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    If you choose to rebalance, make sure you heed what Brit said about keeping the modules under compression. If you don't, you WILL ruin them. They will blow up like balloons.

    Here's a pack that was charged without being placed under compression. Its a sad sight to see.
    [​IMG]
     
  17. flyingstoo

    flyingstoo Junior Member

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    That is an impressive photo

    I have been using a vice for individual charging and intend to rebalance individual modules in the pack whilst clamped in the frame but obviously being cautious about heat dissipation.

    I have seen some opinions on charge rates and would be interested in what is a safe charge and discharge rate. I believe the modules are 6AH which would give a 0.1C rate of 600ma. Is it safe to go to 1 A or maybe higher without causing damage?

    Also what cutoff voltages should be used?... particularly the lower one on discharge
     
  18. Britprius

    Britprius Senior Member

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    Stu, just to clarify the purpose of balancing the the modules and the method.

    The idea behind balancing is that each module is made up of 6 cells. Over time these cells are likely to become out of balance, that is some cells will have a greater charge than others.

    The principle of balancing is that you over charge the module by a small amount, and those cells that are fully charged will not accept any more charge and will give off the excess charge as heat. This is normally done three times. This helps condition the cells. The cells that are not fully charge will continue to charge until they too become fully charged.

    The chargers mentioned in previous post will do this automatically once programmed. Modules should be clamped if not in the complete battery to stop them swelling and should also be cooled with at minimum a fan.

    Once all the cells have reached the fully charged state the module can be discharged at a known rate discharged the process being timed. This will give the amp/hr capacity of the module. The ideal amp/hr capacity is 6.5 but even down to 4 seems to be ok as long as they are all the same (as close as possible).

    The amp/hr capacity of the weakest or lowest charged cell will always be the same as that of the complete module, and the complete battery. Hence the reason for balancing the modules.

    When all the modules in the battery have bean balanced and checked for amp/hr capacity plus some spares a choice can be made on those that have the nearest characteristics to build your battery.

    The modules themselves need to be all charged to the same level before assembling the battery. The way I do this is to charge each module to the same voltage (7.2 to 7.6 not critical but all must be the same) then connect in parallel and let stand for 24 hours.

    The battery can then be assembled.

    This all takes patience and being methodical. With just one charger expect about 30 days.
     
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  19. Britprius

    Britprius Senior Member

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    Gen1 modules were prone to leaking at the post gen2 are not so problematic. The battery in use will accept 100 amps for short periods but limit your charging to about 1amp with continuous cooling. Discharge to .85v do not go below this .9v or .95v if you wish to be on the safe side.
     
  20. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Interesting about the modules. I have not had occasion to work with failed NHW20 or later modules. I'm pretty busy right now but it sure would be great if we could get an analysis of failed, NHW20 modules.

    Charging NiMH batteries is exothermic so only the hill descent warms them up. Once up against the curb and in "R", the temperatures don't really go up. MG2 gets a little warmer but it easily handles the load.

    The internal module resistance is very low but I don't have my metrics handy.

    Thanks for the heads up on the app. I'll take a peek.

    Please take these as my ad hoc metrics on charging:
    up to 8V - little or no risk of heat and gas generation
    up to 8.5V - must be clamped and starts to get gassy and warm, I don't like it
    over 8.5V - were you trying to destroy it?

    GOOD LUCK!

    Bob Wilson