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3s Lipo Charging trouble

Discussion in 'Electronics' started by vman38, Mar 13, 2018.

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  1. vman38

    vman38 Well-Known Member

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    Hi
    Had a rather big crash at the weekend and one of my 3s hard case lipos cracked open the case - no visible damage inside. Just taped up with T-rex tape and all working fine.

    But now when balance charging at 5A it takes about 3 hours to finish. Usually takes around 50 mins. Cell 1 gets to 4.2 V in about 50 mins but cells 2 and 3 only at 4.18 V after 50mins.

    All works fine after charging but would it be ok to stop the charge after 50 mins and use the battery with the cells at 4.2, 4.18 + 4.18V?

    I run 2 identical 3s batterys to achieve 6s - 5500 MAH 65c hard case.

    Any help or advise much appreciated!

    Thanks.
     
  2. olds97_lss

    olds97_lss Premium Member!
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    It will throw off your LVC circuit if all the cells aren't the same voltage as it only does simple math to divide the remaining V by the number of cells. So, by the time it thinks your at 3.2V per cell, you will probably have dipped those two cells below that and we all know what overdischarging lipo's does... fire bad.
     
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  3. vman38

    vman38 Well-Known Member

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    Thanks for your reply. I run a HW Max8 and have it set up so that LVC is around 3.7V. Maybe this would possibly let me away with it?
     
  4. olds97_lss

    olds97_lss Premium Member!
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    It's your rig, but if you have cells that are becoming iffy, your best bet is to balance and wait it out.

    I have a couple old packs that take a long time to balance as well. Seems a year of abuse is about how long they last, at least that's seems to be the case with the SMC 9000mah 2S packs I run in my savage flux and revo.
     
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  5. vman38

    vman38 Well-Known Member

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    Ok man thanks - seems like sound advice! Thanks again!
     
  6. vman38

    vman38 Well-Known Member

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    Just found the problem! The black wire in my balance connector had pulled out into the plastic cover - don't know how clearly you can see from the photo I have attached. I only noticed today as this is the first time I got a chance to work on the problem in day light! D'oh! Anyways all is good again! DSC_1668.JPG
     
  7. jrwalte

    jrwalte Well-Known Member

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    Over discharging a battery wouldn't cause it to start a fire. The battery will just run out of power and be harmless. The risk comes when you try to charge it again. If you don't have a good charger that watches individual cells and diverts power to the low cells during the balance phase, then you run a risk of fire as the cell(s) not over discharged now get over charged.

    As OP found out, no battery should be taking hours to balance. If it all of a sudden is taking longer, something is wrong and it should be looked at closely.
     
  8. olds97_lss

    olds97_lss Premium Member!
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    I see. Was under the impression that overdischarging causes them to be unstable like overcharging. I didn't realize it was when you charge them back up is when they are potentially unstable.
     
  9. jrwalte

    jrwalte Well-Known Member

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    You can have a potential discharge fire caused due to a cell overheating to the point of burning through the insulator and causing a short. This would happen because the cell has a very high resistance compared to the others. I'd think this would be less likely to happen in RC cars that take 15+ mins to discharge a battery compared to RC heli that can discharge same battery in less than 5 min. IE, cars aren't pulling so many continuous amps to probably cause enough heat from resistance.
     
  10. vman38

    vman38 Well-Known Member

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    Thanks for your reply. After further investigation it turns out the black wire in my balance connector had pulled out into the plastic cover and I didn't notice till I looked at the issue under daylight. I posted a picture in a previous reply in this thread. It seems to be working fine now. Thanks again. Strange thing happend last night - I put a 2s lipo onto storage charge. Both cells were 3.71v before the charge started. I kept an eye on it up to 60 mins but the voltage went over the 3.8 end voltage and both cells crept up to 3.84v! Just switched off as I had to go to bed. No idea what was going on there!
     
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