Back to the drawing board.

Discussion in 'Gen 2 Prius Main Forum' started by Prius92, Jul 13, 2022.

  1. dolj

    dolj Senior Member

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    Pretty much as Mr Mann said.
     
  2. Prius92

    Prius92 Member

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    I might have asked this before but wanted some clarification.
    Even when using a .5A charge, I still get some swelling towards the end.
    The charger often misses the delta peak.
    So what is a "safe" voltage I can charge these modules up to? I can't sit there and monitor the modules for when they start to show signs of expansion.
     
  3. jdenenberg

    jdenenberg EE Professor

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    The low cost hobby chargers that I have (IMAX B6AC and Supermate DC6) both automatically reduce the charging current as the module approaches a full charge if you tell the charger what battery chemistry it is charging (Lead Acid, NiMh or Lithium).

    JeffD

    ps: you do clamp and provide cooling air while charging the modules to avoid swelling.
     
  4. Prius92

    Prius92 Member

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    Is that a separate program? Mine has both charge and "auto charge" but doesn't really clarify what auto charge does.
     
  5. jdenenberg

    jdenenberg EE Professor

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    There is a menu which allows you to set parameters and say which battery chemistry is attached to the charger. It then figures out how many cells in the module itself.

    JeffD

    DoctorD.webhop.net/Prius/iMAXB6ACmanual.pdf
     
    #45 jdenenberg, Jul 20, 2022
    Last edited: Jul 20, 2022
  6. Prius92

    Prius92 Member

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    I've asked before but didn't get an answer yet.
    What is generally considered "good" for capacity? Let's say you've done 3 charge/discharge cycles on a module and it won't get above a certain amount of MAh, what number would that be to decide it needs replaced?
    I've read 2500MAh on YouTube but wanted to make sure.
     
  7. jdenenberg

    jdenenberg EE Professor

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    The important thing is to have 28 modules with the same capacity. When I rebalanced the modules from my 2004 Prius (195k miles at that time) all of them had over 5000 mAh but that was at a low discharge rate (they should be measures at a 6.5 amp discharge rate) so the capacities were overstated. If the modules had measures less than 4000 mAh i would not have sold then to others as useful.

    JeffD
     
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  8. alftoy

    alftoy Active Member

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    5000 mAh at low discharge is overstated in what way? What would you expect at 6.5 amp discharge for a normal or good module. Measure mAh after 1, 2, or 3 discharges? Discharging 6.5 amp to 6V or less per module?

    As opposed to grid charging and discharging pack at .325 amp? Seems to be different suggestions on the best charge and discharge rates for grid vs module.
     
  9. Prius92

    Prius92 Member

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    Not an expert but for the purpose of capacity testing I'd imagine you'd want at least a 5A load.
    Some batteries like car batteries might test OK on a very small load, like leaving the lights on overnight, but wont test well if put on a 100A load bank tester.
    Likewise I'd imagine the same for the prius modules to mimic the high amperage load the hybrid system puts on these modules.
     
  10. alftoy

    alftoy Active Member

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    I'll have to wait until I pick up my BD250 discharger at the border. I send any USA shipments to ND, try to group a number of shipments to make it worth my while. My 4 channel charger fans really ramp up if I discharge at 1 amp per channel, gets fairly hot.
     
  11. Prius92

    Prius92 Member

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    The fan on my particular charger quit working after a week, I need to email the company and see if they can send me a new one.
     
  12. jdenenberg

    jdenenberg EE Professor

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    The discharge rate does affect the performance of a battery. Measuring the capacity at a low rate will result in a higher capacity reading than at the "1C" rate (6,5 for our NiMh modules) that is used for the new module specification of capacity. A low discharge rate can overstate the capacity by 5 to 10%.

    JeffD
     
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  13. Prius92

    Prius92 Member

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    Well, this is interesting...

    Last night I fell asleep while the charger was still going. I had it set to 0.5A on two modules.
    When I woke up, the "capacity limit reached" was showing for both modules, which I had set at 7500MAh.

    Neither module was warm or showed signs of swelling. So I'm curious at a very low charge rate of 0.5A, does the extra charge "bleed off" or is the battery discharging faster than 0.5A?
     
  14. SFO

    SFO Senior Member

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    The extra charge is turned into heat.
     
  15. Prius92

    Prius92 Member

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    So this is why swelling occurs when going over about half an amp?
     
  16. alftoy

    alftoy Active Member

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    You're charging at 0.5A but then you ask if the battery is discharging at 0.5A?
     
  17. Prius92

    Prius92 Member

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    I know batteries discharge naturally over time, I'm just not sure at what rate.
    But I was also reading about form charging which overcharges the battery a few hours after making a completed charge.
    If I have the capacity for the charger set at 7500 MAh and charging from around 5-6 volts, at 0.5A, should I be safe?
    I don't want to blow the modules up.
     
  18. Prius92

    Prius92 Member

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    Freaking wonderful, I'm going to have to repeat some tests.
    I noticed a few modules were completing discharges awfully early. When one I fully charged completed in 10 minutes with only 800MAh capacity, it really raised my eyebrow.
    These El-cheapo alligator clip leads I got..the wire is crimped with the insulation still on, and the connection is made by what looks like about 1/2mm stripped off the ends, just folded underneath the insulation. I swapped them out with a better pair and the results are much more realistic.
     
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  19. Prius92

    Prius92 Member

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    Well the 1st module I drained down to 3 volts is done.
    On the first discharge cycle down to 6 volts it came back at 2580MAh, now after two more cycles, including taking it down to 3V and letting it charge at 0.5A all night, it discharged to 6V with 6.5A current to 4174MAh, a 61.8% increase.
     
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  20. alftoy

    alftoy Active Member

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