14.8v li-ion pack w/ cells out of balance- Mtbr.com
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  1. #1
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    14.8v li-ion pack w/ cells out of balance

    The pack is a couple of years old and has only had a dozen or so rides on it. It has 8-cells, 4400 mAH, w/ PCB, similar to this one at all-battery.com:
    http://www.all-battery.com/li-ion186...connector.aspx

    The cells measure 3.69, 3.69, 4.07, 4.07, 4.21, 4.21, 3.96 and 3.96. I use the pack on a homemade triple-cree led light. It runs about 25 minutes and then the power-out drops to zero. I'll put it on the charger, it charges w/ the red light on and after a few minutes the green light comes on and the output reads 15+ volts.

    Can this imbalance be corrected with a balancing charger? Will this one work?
    http://hobbycity.com/hobbyking/store...idProduct=5606

    Just need to get back on the night rides! Thanks for any help you can provide!

  2. #2
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    Sloshred, that pack is horribly imbalanced. The 4.21V cells are at 100% state of charge and the 3.69V cells are about 50% state of charge. By charging it up, you probably hit the high voltage cutoff on your PCB and by discharging it, you probably hit the low voltage limit of the PCB. I suspect the pack has taken some damage with both an overcharge on some cells and an overdischarge on others.
    But yes, that charger can do a balance charge if you make your own charge cable. Your cells are way out of balance so you need to do a very low amperage balance charge with that charger. Balancers work by clicking on a relay to the highest voltage cell to bleed off a little current - 300 mA in this charger. You don't want to set your charger current much higher than the bleed current.

  3. #3
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    ..JST-XH 4s balance leads off Ebay



    ..........wire one in like this.......



    https://scriptasylum.com/rc_speed/_lipo.html
    ...Scun.thorpe, UK

  4. #4
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    Perfect, thank you so much for the replies. That's exactly what I need is the wiring diagram. Not having alot of electronics experience I was thinking I needed a charger for 8 cells, but they are paired up. It looks like a balance charger for 4 cells will work. I've also seen "Turnigy" brand recommended on this forum; this one doesn't list the "Current drain for balancing.." like the Imax @ 300mAh/cell.
    http://www.unitedhobbies.com/hobbyci...lancer/Charger
    Any recommendations on the best balance charger for 4-8 cell Li-ion packs? thanks!

  5. #5
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    i`m running that turnigy accucel 6 charger
    its a bargain at that price too
    .......... will you ever need an 8s charger?
    ...Scun.thorpe, UK

  6. #6
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    I didn't start out with balance chargers. I have a couple of lab quality power supplies and charged with them. Lately, I have started putting balancer harnesses on all my batterys. I started last year, and am still collecting data. Seems like batteries charged on the balance charger do run longer. I can't prove that they will last longer, more data needed. I have decided that the li-polymer cells SUCK. Even with balance charge, they are short lived. I like the 620b Chargery charger. It comes with a JST-XH adapter board. It runs on 12-18 volts, so I can use my truck to charge. It also comes with a "city power" power supply for home use. I got it from AC-RC Hobbies.

  7. #7
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    Is there any benefit to using a balance charger to charge battery packs w/PCB circuit that do not have a balance wire harness? Do PCB circuits keep individual cells in a battery pack in balance when using a regular type smart charger? Just wondering if it would be beneficial to purchase a balance charger to charge my battery packs with PCB circuits that do not have a balance wire harness.

  8. #8
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    I have been using my home made 5 cell 18650 pack with balance leads fitted for the last 4 years and it is still going strong, also a 3 cell 18550 pack that is starting to die that's in it's 5th year.

    So there must be something good about balancing. I use a GT Power A6 charger that I think is the same as the Turnigy accucel 6.

  9. #9
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    Quote Originally Posted by Brooks04
    Is there any benefit to using a balance charger to charge battery packs w/PCB circuit that do not have a balance wire harness?
    Measure the voltage of each cell. If they are not close to equal, then you will definitely benefit from a balance charger. An imbalanced pack will not achieve its full rated capacity. The charger will cut off when the strongest cell reaches 4.2V, regardless of what the weaker cells are at. And at discharge, the PCB will cut off when the weakest cell hits ~3.0V, even if the stronger cells can still be discharged more.

  10. #10
    A waste of time it is is
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    sloshred, that charger you linked doesn't include the power supply. Just wanted to make sure you had picked that up.

  11. #11
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    I am clueless so please someone elaborate.

    How does the balancer accomplish anything? Looks like in the wiring diagram that it just 'monitors' the voltage between each cell or paralleled cell to me. I don't have much electrical experience but want to add a balancer if this would be easy enough to my 3s2p 11.1v battery....
    "mountain biking and flyfishing, what more do you want?" - Yeah, I said it

  12. #12
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    Quote Originally Posted by jbflyfshr
    How does the balancer accomplish anything? Looks like in the wiring diagram that it just 'monitors' the voltage between each cell or paralleled cell to me.
    The balance cable is not just monitoring voltage. Depending on the design, there should also be current going in and out of each wire in the balance cable. Effectively this will stop net current flow into the fully charged cells, but keep current flowing into the non-fully charged cells.

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