4S Li-On Balance Charging- Mtbr.com
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  1. #1
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    4S Li-On Balance Charging

    Happy New Year all.
    Iíve spent the afternoon/Evening freezing my nuts off in the shed, milling a 4S 18650 holder as my battery pack doesnít fit in my Orange 5 Frame!
    So I came up with this, which will simply strap to the shock mount..







    Question is do I need to balance charge a 4S li-on, If so how do I connect a 4S balance lead to the battery pack?
    Cheers

  2. #2
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    If you charge the cells separately you are OK. If you want to balance 'em here is the scheme and needs 5 wires:

    LipoWiring-1.jpg Photo by mahgninnuc1 | Photobucket Credits go to the author of the image and that is not me

    Oh heck a nice pack and holder anyway!

  3. #3
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    Are you going to weld those cells together or you are going to make contacts on the housing? If they are going to be welded and not intended to take out frequently I would make balance connections. You would need something like this 4S JST XH to connect the pack to the balancing charger. Unfortunately I don't see how much room do you have in the housing.
    Anyway in general you need to wire up + and - side and every connection between cells. So for 4S you need 5 wires.
    Balancing is mandatory at least from time to time so your cells won't have different voltages which can lead into overcharge and dangerous things like venting, blowing up, etc... Panasonics are the best and this very likely won't happen soon. Still you need to take all safety measures you can.
    The other option would be to open the pack from time to time, take the cells out, measure the voltages of each cell so you can see the differences and somehow charge them indvidualy.
    Also you gave to few information about your charging setup, what is the light you are going to power up, why do you have 3 strand cable, ....

    PS. On the pictures you have put the cells in a 4P not 4S setup. It is intentionaly just to take the pictures or you are going to connect them that way?

  4. #4
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    Cheers MK96..

    ledoman
    Cells are staying in the pack, hence why I got NCR's with solder tabs.
    Cells are in parellel just for the picture..
    there's 5mm off head room in the pack, so should hopefully be enough room for a JST, if not I'll take some more material out of the lid.
    charger is a Accucel 6.. that I use for all my lipos/li-ons/NiMh.
    Cable has 3 wires as its a 3 pin plug..
    The lights I will be using with this are:
    https://forums.mtbr.com/lights-diy-d...-l-820142.html
    https://forums.mtbr.com/lights-diy-d...ml-727664.html


    Hope that answers all your questions :-)

  5. #5
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    OK. This is much better. So you are powering 3 leds lights with 4S Li-Ions and some buck driver (which one?). Still don't know why you use 3 strands. Never mind, but they looks pretty thin to me. You are probably getting some additional looses on them.

    Since you are using Accucel you should already know how to charge li-Ions (Li-Pos) in series. Wireing is done as MK pointed out. The picture is more for Li-Po cells not for the 18650 where negative is on the other side, but I hope you got the point. Try to get JST connector under the cover somehow. Then you should use some 5 wire extension along with main cables.

    Since Panasonic are high quality balancing would not be needed every time. I would say once out of 5-10 charges. On the first few charges I would check the voltages of the cells and see if the balancing is needed. The difference can be up to 0.05V before balancing is needed. This is just my unproffesional opinion.

    BTW, very nice lights. I have still some work to do on my Ledil Cute 3up sitting in the drawer for quite long time....

  6. #6
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    Yep the pic is for LiPo, sorry for that. I assumed we are quite skilled Just get a 5 wire JST-XH and the extension. If you want to have a water/mudproof connector you may need a dummy JST-XH connector to cover the output wire connector from the pack while riding.

  7. #7
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    Very neat as always Goldigger.

    Holy wars have been fought over whether balance charging is necessary or desirable, hopefully w can avoid that here. My opinion is that going "out of balance" is a bad sign for the cells - either they are poor quality cells, not well matched or at the end of their life. I have noted that cells that need to be balanced at the top of the charge, are out of balance at the bottom.

    For a 4s1p battery I would strongly recommend using a protection circuit, eg 4A or 8A depending on which will fit in your case.

    Wiring it up is exactly the same as for balance charging - ie the point of the circuit is to continually check the voltage of individual cells, eg from the 4A PCB linked above
    4S Li-On Balance Charging-%24_57.jpg


    I would add a jst connector in there anyway, so if you end up needing to balance them it is easy enough to do. You can check the voltage at the start and end of a charge using a simple voltmeter like this, or if you can't fit a PCB in your battery case, use a low voltage alarm like this.

  8. #8
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    I'd prefer PCB w/o balance charging due to current limitation. But everyone to his own taste. Solely a protection PCB is a good idea here.

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    I haven't seen any PCB with balance capabilities yet. I don't know about the one on the picture, though. I think bruce meant to add JST connector to the batteries in parallel to the PCB so the balancing can be done independently.

  10. #10
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    The JST will be stuffed inside the canister, so no worries there..The lid sits on an oring along with the bolt that holds it on..
    Lipo/Li-on what's the difference there still batteries just different chemistry..

  11. #11
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    Thanks Bruce..
    Never thought of using a PCB...
    Surely the Maxflex is amply as I have it set to shut down when the voltage gets to 12v for a 4S pack?

  12. #12
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    Quote Originally Posted by ledoman View Post
    I haven't seen any PCB with balance capabilities yet. I don't know about the one on the picture, though. I think bruce meant to add JST connector to the batteries in parallel to the PCB so the balancing can be done independently.
    There are some PCBs with balancing caps, but the drain current is PITA making the charging endless story

  13. #13
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    4S Li-On Balance Charging

    Quote Originally Posted by Goldigger View Post
    Thanks Bruce..
    Never thought of using a PCB...
    Surely the Maxflex is amply as I have it set to shut down when the voltage gets to 12v for a 4S pack?
    Maxflex only detects total pack voltage so using a pcb is best practice. In your case however you will probably get away without one as the Panasonics, unlike most li-ion cells, are safe down to 2.5v so you would either have to have a serious fault for one cell to be less than 2.5v with the pack above 12v or a fault with the Maxflex - rare but not impossible.

    Of course it also means if you use Panasonics you should get a pcb designed for the lower cutoffs.

    I wouldn't recommend a balancing pcb for reasons touched on above.

    You are giving up a bit of capacity by cutting off at 3v, but giving the cells an easier life - iirc its less than 400 mah.

    2nd best practice would be to check voltage of every cell before charging - the volt meter I linked to connects to the jst plug & scrolls through the voltage of each cell so it only takes 20 seconds.

  14. #14
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    That battery holder looks great! Really puts my old inner tubes to shame. Raising the bar once again.

    I have used pcb equipped and balance tap equipped 4s li-ion and lipo over the years. My preference is already in favor balance taps and seems to only be going more that way over time.

    I had a pack from all battery with pcb that went bad pretty quick and when I disassembled and checked sure enough cells were way out of balance.

    Also charge and discharge for lipo / lion are slightly different and the accucell 6 does this, not sure about pcbs.

    The accucell 6 is a good charger and the same model I have been using for some time.

    I have a 2 year old turnigy nano lipoly pack that has a lot of cycles on it and i just did a discharge test on it. Its labeled as a 2.65Ah and I got a respectable 2.4. Quite impressive given the age of the cells.

    Another cool thing about balance taps is you can plug in voltage alarms and now turnigy/hobbyking does a clever little usb charging accessory that connects to the balance tap. It lets you use the pack a portable usb power source.

    Something to consider adding to the pack in addition to balance tap is a polyswitch. It basically a self resetting fuse and protects pack from over current and probably short circuit. I can't think of any downside for using a poly switch. The voltage drop really is minimal.

    Also having checked voltage reading of my accucell 6 charger against a calibrated lab grade bench top meter , I trust it way more than any cheap pcb or little device than plugs into jst balance tap. Yes you have to charge or discharge to see individual cell voltages but at .1amp the voltage difference is minimal. Its nice being able to see the reading of each cell as its balance charging.

    Since max flex lets you set the cut out point I just set mine a little bit high - light turns off at 3.2V x4 =12.8V Sure I loose some run time but in exchange for more cycles and less riskk of over discharging.

    An other thing to consider for those not using taskled flex stuff is you can get a lipo alarm that plugs into the balance tap and color changing leds and a really loud buzzer to warn you of capacity / over discharge. Its actually kind of nice if using a helmet light to have the audible beep.

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