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Re-hydrating the battery modules.

Discussion in 'Gen 2 Prius Technical Discussion' started by Britprius, May 6, 2015.

  1. tracy ing

    tracy ing Active Member

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    They were suspected of being bad only due to their lack of response when compared to the others.
    Two of them came around, one ended up being bad, number two.
    I made them red just as a note to me as I worked the cells, I work one side, odds, then the other, evens, this allows me to keep all the test leads on one side, then reverse them to the other, prevents reverse polarity errors, the charger can accept it, the battery tester blows an internal fuse and it is a pain to replace it. Not moving the leads back and forth also reduces labor.
     
  2. dolj

    dolj Senior Member

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    Sure, no problem. It is refreshing to come across someone so confident and enlightened to extend such an invitation.

    It is interesting how a thread about rehydrating batteries has been hijacked to yet another charging thread.
     
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  3. alftoy

    alftoy Senior Member

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  4. tracy ing

    tracy ing Active Member

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    yes
     
  5. TMR-JWAP

    TMR-JWAP Senior Member

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    I'm curious about your thoughts of how to do this?
    I've always thought that internal resistance of a battery is a calculated value.

    Measure the battery voltage with zero load.
    Measure battery voltage with a controlled load. (an exact known or measured current)
    The difference between the zero load battery voltage and the 'loaded' battery voltage, divided by the measured current gives you the exact value of the batteries internal resistance.

    Is there another way to do it?


    Another small point, there are no 19 or 30 ohm modules. Techstream displays in ohms, but a prius ecu uses 0.019 as a starting default value and is also typically in that range for new modules. Values usually increase over a modules life into the low to mid 0.03's, but will always show as 0.019 if power has been lost and restored to the car, until the ecu has time to recalculate.
     
  6. tracy ing

    tracy ing Active Member

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    In every forum I have ever participated in, there is always THAT GUY.

    The last time I met YOU it was after I had posted about 30 hours of video and complex detailed plans instructions testing and summaries on the conversion of the honda insight to prius modules, the end goal to provide a plug and play alternative to that community for those wonderfully inadequate honda cells.

    This included all the info needed to create the tempanerd monitoring and control system, which also scaled to the prius auto and took advantage of the temperature welll in every module, which has since been made wireless using 30 esp32 internet enabled microcontrollers internetworked to each other and your smart phone showing temps voltages and loads on each module with alarms.

    In the end, I deleted every bit of it, due to the constant harassment and critical commentary of THAT GUY.

    I can see where I am headed here, as well.
     
  7. alftoy

    alftoy Senior Member

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    Can you enlighten us on the discharger?
     
  8. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    As it happens I am also looking at designing a less costly set of gear to mimic the Prolong type of gear. While the grid charger and discharger are 2 devices, they will have a communication port. This will allow the user to exercise the battery automatically.

    I employ Nichrome heater wires as discharge elements driven by PWM FETs with Allegro systems Hall effect (isolated) current sensors.
    The process of discharging allows for 20 to 30A pulsed loads at millisecond periods which permits fairly precise sampling of the battery's internal resistance.
     
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  9. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    Anyway..back on topic of Rehydration of the cells. I assessed the void above the plates in a 7.2V NiMH blade. It is about 15 mm depth between the bottom of the plastic cap and the cell plates. The plastic PP welded cap is 2.5mm thick at minimum. 5.25 mm thick by the pressure vent and the temperature well. The centre temperature sensor 'well' is 18.4mm deep from the top of the cell cap. So the bottom of the temperature well extrusion works out to(15+5.25)-18.4 = 1.85mm thick.
    I drilled and tapped 6-32 holes on a trial basis. No probs once u don't let the tap go too far. Drilled on a precision Proxxon PCB drill press. Not the big Delta tabletop press. Doing it on the big press is ok, but harder to see close up. Also, the holes in the cell tops can't be done centred in all the cells due to the pressure valve and the temperature sensor well locations. But there is adequate space around those items to drill.

    I used plastic 3mm 6-32 screws as well as nylon ones. But I am evaluating zinc plated steel 4-40 screws as the thread is finer for a better seal. A dab of liquid electrical tape on top of the metal screw heads should provide a good seam seal and electrical isolation for long term service with corrosion proofing.

    I have an assortment of PCB carbide drill tips down to .05mm stepping so I'll look at self tapping the smaller 4-40 machine screws for a real tight fit. I am doing some corrosion testing of these galvanized screws in concentrated electrolyte. From the chemistry it seems corrosion can happen but at temperatures well in excess of those found in the battery.

    But as a safety/reliability protocol, I suspect the best approach is to dip the screw in the liquid tape 1st, then install for a strong corrosion proof seal without the possibility of galvanic corrosion or electrical conduction.

    Injection of the electrolyte blend additive (20% NaOH) takes place via a 20ml syringe equipped with a slim red spray straw as found on any WD 40 or compressed air spray cans. I heated the tip of the syringe nozzle with my PCB hot air soldering tool set at 100C for a few secs. Blowing hot air into the syringe nozzle with the syringe plunger removed. Then force fit the red straw into the nozzle and trim to length. All went well, tight fit and zero electrical risk to inject the electrolyte.

    Next post is about electrolyte volume observations and why OH ions are lost causing electrolyte loss.
     
  10. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    Both venting gases/ water vapour and electrode corrosion consumes electrolyte which shortens cell life:
    https://www.researchgate.net/publication/324096418_Increasing_NiMH_battery_cycle_life_with_oxygen

    This implies that enriching the void above the cell plates with oxygen could be useful for performance. Now oxygen is about 10% more dense than air. So it's going to stay in the cell void if we squirt some in b4 sealing up. Easy to make...electrolyse 5ml of salt water inside a 20ml tipcapped syringe using a wireless charger & nichrome coil....for simple storage & injectable delivery, the hydrogen will float out of the cell but the oxygen will stay after being injected, no dehumidifier needed. The benefits are harder to quantify as it will take monitoring the cells overall life expectancy. So that's more of a thesis grade project.

    To assess electrolyte volumes I used food colouring in water to inject in the cells of the blade. The cells will accept 10ml and absorb it down to a 1mm level above the plates within 5 mins. Maximum b4 overfilling is 15ml, but 1cm remains above the plates after 15 mins.

    Based on this , I would go with 8ml per cell for weak cells (<2.5AH) so no electrolyte will slosh around and make for a 'wet' cell situation, also we want the void above the cells to be free for the venting process to be good.
    For mediocre cells (<4.5 AH) I would suggest 5ml hydration per cell.

    I would suggest 10% NaOH to ensure the electrolyte has decent conductivity as some of the KOH crystals will take time to go back into solution and we need some homogeneous electrochemical performance from the get go.

    To make 10% NaOH, just get the lye crystals at a pharmacy or grocery household cleaners aisle. Using a jewelry digital scale (Amazon.com @ $17) weigh out , say, 10g of lye, add 90g of deionised or distilled water and dissolve. Use a glass container as it gets hot, it's exothermic.

    So 10g/90g = 10% by weight. This heat is useful as u can inject the hot electrolyte for a bit better dissolution of the KOH crystals in the dried out cell. But this is not critical, as the battery will heat when charged anyway.
    The electrical conductivity is around 13 EC or 9000ppm using hydroponic EC meters.

    For those wondering about using the more common NaOH vs KOH in the electrolyte, please note that NaOH as an additive actually reduces cell corrosion. I have a paper linked somewhere on that if u need it.
     
    #410 Ancel Bhagwandeen, Jun 25, 2022
    Last edited: Jun 25, 2022
  11. TMR-JWAP

    TMR-JWAP Senior Member

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    Everyone has a different way of doing things. Your way is different from mine. Mine is different from others.
    We all have different levels of knowledge about electrical stuff. Some peoples only knowledge is that it hurts when you get shocked and others may have decades of training and experience in several fields. Those things show themselves in posts.

    Maybe it has something to do with Qtips and saran wrap and a can of baked beans, on a kitchen table.
    Right or wrong, that may be having some effect on how serious you're taken by complete strangers.
     
  12. Daniel CW

    Daniel CW Junior Member

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    Good day, @TMR-JWAP i’m trying to get in touch with you, the number posted on your profile doesn’t seem to be working.
     
  13. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    The readouts are in mΩ. the blades are sub 10mΩ usually. So the blocks are double that.
    Ohm's law (V=I*R) determines the max. currents the cell can deliver vs the voltage drop.It is this voltage drop that triggers blade imbalance error codes.
    Current * current * resistance*time = the joules of energy going into heat. Joules per second = Watts. A calorie of heat is 4.2J of energy, which is the energy to raise 1 gramme of water by 1°C.

    As a reference. a 12V starter battery is usually under 10mΩ when healthy. Typically a 4 cylinder car starter turns over at 150A or so. Then .010 * 150 = 1.5V drop...so the battery will be at about 12.8 -1.5= 11.3V when tumbling the engine.
     
    #413 Ancel Bhagwandeen, Jun 26, 2022
    Last edited: Jun 26, 2022
  14. TMR-JWAP

    TMR-JWAP Senior Member

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    Sorry, my Techstream version displays values in ohms. Thanks for explaining that a display of 0.019 ohms is equiv to 19 milliohms. I thought that would be pretty clear. I appreciate you educating me, spending half my life as an electronics tech apparently isn't enough.
     
  15. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    It's for everyone reading the thread. I train technicians and being clear is often of benefit.
     
  16. TMR-JWAP

    TMR-JWAP Senior Member

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    I guess I'm not being clear......
     
  17. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    Update:
    The two spent blades I cycled through 3 charge/discharge exercises yesterday are ID#'s
    184p3h03127p & 184p3h03126p.
    They're both about 2.0AH capacity. (from same battery pack) This battery pack has been sitting w/o charge for about 2 years after being removed from an Prius C.Their internal resistance is just under 8mΩ each.

    I gave the blades a full days rest for their 'charge V' & psi pressure to settle before hydrating them.

    Today I 'hydrated them' with 7 ml of 10% NaOH in each of the 6 cells per blade. This was done via a 2.5mm drill hole at the top of the cells which was then tapped with a 4-40 thread pitch tap, dosed with clear liquid electrical tape and resealed with 4-40 steel cap head screws, 3/8" long.
    Hand torqued to prevent thread stripping.

    7ml NaOH is based on my prior posts on electrolyte volumes and the fact that my 20mL syringe can hold 21ml just fine so it does 3 cells at a time.
    Charge/discharge efficiency is about 70%+, and sonication pulse charging to encourage cavitation and electrode cleaning is being used. The blades whine audibly as they are being charged.

    Charge/discharge cycling has just begun.....
     
    #417 Ancel Bhagwandeen, Jun 26, 2022
    Last edited: Jun 26, 2022
  18. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    Update:
    I processed 4 blades on my prototype 'sonication/cavitation' charging /discharging gear. Pulse frequency of 1300Hz with battery reactive resonances reaching in the MHz. These old cells were processed using the Prolong gear: 3 charge /dcharge cycles 2 years ago and have been sitting at about 7.1V for 2 years as rejects.

    Results: NaOH effort produce no improvement. Water/hydration of 3 cells seems to work.

    Summary: i am seeing approx. 50% improvement in AH capacity with some impedance improvements as well. My discharge is down to 4.8V per cell with ramped down current to 0.3A at 4.8V and 6A above 6V. Further, with this process ONLY 1 Charge/discharge/Charge cycle is required. Further cycles ( i did 3 ea, make no change).

    Conditions: 30C ambient. Cells pulse charged before sealing hydration ports. Cells over driven to create 80C temperature in the cell (FLIR sampled) . Overdriven to ensure reconstitution of the crystallized KOH into the electrolyte and very active cavitation as evidence by much sputtering and spitting of electrolyte which is absorbed by paper towels over the cells during processing..
     
    #418 Ancel Bhagwandeen, Jul 3, 2022
    Last edited: Jul 3, 2022
  19. dolj

    dolj Senior Member

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    Do you mean 4.8V per module (0.8 V per cell)?
    This is not quite clear what you mean exactly. You ramp down the current to 0.3 A at 4.8 V (per module) but then stop at 4.8 V? What happens between 6 V and 4.8 V?

    Personally, if I could program my discharges as you can, I would ramp down to 300 mA at ~ 7 V - 6.8 V (per module) which is the approximate tipping point where the voltage 'falls off the cliff'. I'd also discharge down to 0.5 V per cell or 3 V per module for the third discharge. On the other hand maybe with the 'sonication/cavitation' feature you have built this is unnecessary?
     
    #419 dolj, Jul 3, 2022
    Last edited: Jul 3, 2022
  20. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    Yes 0.8V per 1.2V cell....my bad.
    The max current load at 4.8V is 300mA.
    I use a stepped algorithm down from the full 1C draw to 300mA at different voltage points. I'll have to check my firmware code for the exact stepping points.
    What I notice as well....is that we can expect about a typical 0.3V drop from constant charge current when the battery is about fully charged. Now I charge at 3A until 8V then 1.5A until finished. I have seen peak V at about 8.8V and then a decline back to as low as 8.37V.

    I may change ,my charge profile to just look for the 0.3Vdrop and then supply another 0.5AH 'topping off' before ending.