Add A Balance Lead to my Li-Ion????- Mtbr.com
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  1. #1
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    Add A Balance Lead to my Li-Ion????

    Ok Gents, (and ladies just not sure any troll here)

    With all the talk about the issues with Li-Ions floating around, I was wondering if there is any benefit to adding a balance lead to my 3s2p pack?

    I have not run it to date since my build is taking an inordinate length of time to complete. But before I get too far I wanted some opinions and as the saying goes...

    Thanks,

    JB
    "mountain biking and flyfishing, what more do you want?" - Yeah, I said it

  2. #2
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    the general consensus is that it allows for full capacity for longer and most people that I've heard on here recommend it. You'll need a new charger and some other bits and pieces, see [URL="http://forums.mtbr.com/showthread.php?t=664708] here, near the bottom [?URL] - it's what I'll be doing as soon as my charger arrives

  3. #3
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    ...Scun.thorpe, UK

  4. #4
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    thanks Hendo, brain fart there

    although it reminded me to get some 2s leads for a commuter light I'll be building, so that's a good thing..

  5. #5
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    Quote Originally Posted by jbflyfshr
    Ok Gents, (and ladies just not sure any troll here)

    With all the talk about the issues with Li-Ions floating around, I was wondering if there is any benefit to adding a balance lead to my 3s2p pack?

    I have not run it to date since my build is taking an inordinate length of time to complete. But before I get too far I wanted some opinions and as the saying goes...

    Thanks,

    JB
    Like everything there are tradeoffs. If your pack is built from high quality cells and includes a good protection PCB, then that is the better option in my opinion.

    Sometimes I will put a balance connector on a pack just so I can monitor the voltage of the individual cells without having to take the covering off the pack and it gives me the ability to balance charge it if necessary. But, I've never had to balance charge any packs built with high quality cells of the same age and history. And I don't balance charge them as a precaution.

    The main tradeoff against using a balance charger is the charger itself becomes a single point of failure since the balance connector bypasses the protection PCB in the pack. If the charger were to fail and put more than 4.2v into the cell during the charge, bad things can happen. Yes, I know this is rare, but having a fire is a big deal so you should try to make the chances of that happening extremely rare. The way you make this kind of thing extremely rare is make sure it takes two things failing to have a serious problem. That's why Li-ion packs always have protection PCBs that are completely independent of the charger. That means both the protection PCB and the charger have to fail to have something really bad happen.

    Have you measured the voltages of the cells in your pack. Does it need to be better balanced?

  6. #6
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    MtbMac,

    I haven't checked lately. I take so long to decide on the smallest stupid things that I haven't bought a charger yet. I was going to do one like E34 sells but with 6cells total I was apprehensive to say the least.

    I am ready to pull the trigger on a charger but thought I should get some advice from the experts before I do.

    BTW, I think it would be hysterical to change your handle to MtbMcGrubber and see how many people notice.

    JB
    "mountain biking and flyfishing, what more do you want?" - Yeah, I said it

  7. #7
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    Quote Originally Posted by MtbMacgyver
    Like everything there are tradeoffs. If your pack is built from high quality cells and includes a good protection PCB, then that is the better option in my opinion.
    Thanks MTBM. I'm probably being a bit thick here but... isn't it possible to use a balance connector with a good quality cells?

    Quote Originally Posted by MtbMacgyver
    ...And I don't balance charge them as a precaution.
    As a precaution against what exactly? The key charging issue (safety and cell life) is cell voltage on the terminals & not charge retention.

    Quote Originally Posted by MtbMacgyver
    The main tradeoff against using a balance charger is the charger itself becomes a single point of failure since the balance connector bypasses the protection PCB in the pack. If the charger were to fail and put more than 4.2v into the cell during the charge, bad things can happen.
    Geez, that answer was fast!

    For most balance chargers the charge current still enters and exits the pack via the protection PCB. The balance plug is only used for cell voltage monitoring and balance discharge, the the benefit here is slight (only protection against shorts on the balance wires which should act somewhat like a fuse anyway).

  8. #8
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    Quote Originally Posted by Mark2c
    Thanks MTBM. I'm probably being a bit thick here but... isn't it possible to use a balance connector with a good quality cells?
    Yes, and as I said, I do put a balance connector on some of my packs just so I can monitor the individual cell voltages. I just don't typically use it for balance charging. I would if a pack really needed it, but when built right they rarely need it. If they do need it, I think it's important to understand why they need it. As it can be a sign of a more serious problem with the battery pack.

    Quote Originally Posted by Mark2c
    As a precaution against what exactly? The key charging issue (safety and cell life) is cell voltage on the terminals & not charge retention.
    Some people think they should always balance charge the pack as a precaution against it going out of balance.


    Quote Originally Posted by Mark2c
    For most balance chargers the charge current still enters and exits the pack via the protection PCB. The balance plug is only used for cell voltage monitoring and balance discharge, the the benefit here is slight (only protection against shorts on the balance wires which should act somewhat like a fuse anyway).
    To a certain extent you're right. If you use the type of charger that puts the primary charge current through the main pack connector, and only shunts current around cells to correct the balance then some of the safety issues are reduced. But, this assumes folks have a detailed understanding of exactly how a particular balance charger works. Some charge completely through the balance connect and others inject additional current through the balance connector.

    My overall point is that I don't think one approach or the other is clearly always better and there are trade-offs. If you really know what you're doing with batteries then you can decide for yourself. If you're not as sure about what you're doing then I don't think it's necessarily the right advice to tell people to throw a balance connnector on every pack.

  9. #9
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    Quote Originally Posted by MtbMacgyver
    Yes, and as I said, I do put a balance connector on some of my packs just so I can monitor the individual cell voltages. I just don't typically use it for balance charging. I would if a pack really needed it, but when built right they rarely need it. If they do need it, I think it's important to understand why they need it. As it can be a sign of a more serious problem with the battery pack.



    Some people think they should always balance charge the pack as a precaution against it going out of balance.
    So how much trouble is it to retro fit a Li-Ion pack with a balance lead? I have seen some on eBay but most say 3s1p...not sure where to find the right one.

    JB
    "mountain biking and flyfishing, what more do you want?" - Yeah, I said it

  10. #10
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    Quote Originally Posted by jbflyfshr
    So how much trouble is it to retro fit a Li-Ion pack with a balance lead? I have seen some on eBay but most say 3s1p...not sure where to find the right one.

    JB
    It's not much work at all if you do it while you're building the pack. If you're adding it to an existing pack, you have to rip off the shrink wrap, solder 5 wires (assuming 4s pack) to the protection PCB terminals that go to each cell, and re-shrink wrap the pack. The wiring diagram for various pack configurations is shown on this site.

    http://scriptasylum.com/rc_speed/lipo.html

  11. #11
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    ..if you think about it your 3S2P pack is in effect 2 x 3s1p packs
    so a 3s1p balance lead would be correct and wired as so


    ...Scun.thorpe, UK

  12. #12
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    Balancing chargers and protection boards are really totally different topics.

    A balancing charger is better for the cells because it is kind of like charging them individually. Each cell should get charged to a nice and ever 4.2 volts.

    Protection boards are a safety device. Some of the higher end versions will do the balancing function. However, the main purpose of a protection board is to prevent batteries from blowing up or catching fire. They are always a good thing to have. They are not a guarantee. There have been many stories recalls of laptop and other lithium batteries.

    I think of balancing chargers as coming from the model airplane application. You see they might need 20 or even 100 amps to fly. The protection boards just can't deal with those current levels so that application generally uses LiPoly cells and no protection. The currents for LEDs are low so we can use the protection boards. I think that they are a good idea to use.

    One thing is for sure though. Lithium Cobalt oxide based cells are inherently dangerous to some degree. Sure fires are rare, but they do happen. Be safe and be careful while charging them. Why do we use them? Becauswe they store the most power. There are other Lithium chemistries that are safer, but do you want to carry a heavier battery?

  13. #13
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    Quote Originally Posted by HEY HEY ITS HENDO
    ..if you think about it your 3S2P pack is in effect 2 x 3s1p packs
    so a 3s1p balance lead would be correct and wired as so


    SWEET...thanks Hendo that is exactly what I needed to hear. I could only find 3s1p leads but wanted to be safe than sorry.

    BTW, your crazy cat always creeps me out a bit. Bit it's cool

    JB
    "mountain biking and flyfishing, what more do you want?" - Yeah, I said it

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