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  1. #1
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    Charging LifePo4

    I'd like a little advice, im gathering the bits for a build but im having some trouble with the batteries.

    The build im doing it the 7 up XP-g, and planning on using a MaxFlex 5A to power it, i dont wanna go for the full on 1500Ma i think maxing out at 800 will prob be my lot, if t doesnt melt at 18W! I ordered a chinese special lot of LifePo4 cells from the Flea, and thats where im stuck. Originally i was gonna build a 8s pack and run a Bflex driver, but i cant find any way of charging/balancing for the 8cell pack, where as the RC people use lots of 6 cell pack, so i figured go with the MaxFlex and a 6cell pack, but that would only be 6600Ma and as i bought 20 cells i figured, i could just make a 6s3p pack instead. My question is can i charge a 6s3p pack as a 6 cell pack, and hope the 3 cells in parralel stay ballanced or is there some trick to balancing them? And on the other hand if i build a simple 6cell pack and use a smart charger with a programable limits can i get away without a pcb on the pack? Or having read everywhere how resilient the LifePo4 cells are and dont explode(useful) can i get away with being a bit lazy with the care of them and build a 6s3p pack and just stick anything on it to charge ignoring any balance and not using a pcb on the pack, and just build another when it knackers? the cells cost less than a pcb and being in th eUK i have to order everything form the US so is annoying getting a pcb anyway.

    cheers in advance.

  2. #2
    Drinkin' the 29er KoolAid
    Reputation: kwarwick's Avatar
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    Quote Originally Posted by jimbojones1000
    I'd like a little advice, im gathering the bits for a build but im having some trouble with the batteries.

    The build im doing it the 7 up XP-g, and planning on using a MaxFlex 5A to power it, i dont wanna go for the full on 1500Ma i think maxing out at 800 will prob be my lot, if t doesnt melt at 18W! I ordered a chinese special lot of LifePo4 cells from the Flea, and thats where im stuck. Originally i was gonna build a 8s pack and run a Bflex driver, but i cant find any way of charging/balancing for the 8cell pack, where as the RC people use lots of 6 cell pack, so i figured go with the MaxFlex and a 6cell pack, but that would only be 6600Ma and as i bought 20 cells i figured, i could just make a 6s3p pack instead. My question is can i charge a 6s3p pack as a 6 cell pack, and hope the 3 cells in parralel stay ballanced or is there some trick to balancing them? And on the other hand if i build a simple 6cell pack and use a smart charger with a programable limits can i get away without a pcb on the pack? Or having read everywhere how resilient the LifePo4 cells are and dont explode(useful) can i get away with being a bit lazy with the care of them and build a 6s3p pack and just stick anything on it to charge ignoring any balance and not using a pcb on the pack, and just build another when it knackers? the cells cost less than a pcb and being in th eUK i have to order everything form the US so is annoying getting a pcb anyway.

    cheers in advance.
    My understanding is that any cells connected in parallel like that automatically stay balanced just by the nature of being connected in parallel. So treat each 3 cells in parallel as just one big cell with 3 times the capacity of a single cell. You still need (or should) balance charge the 6 big cells with a proper balance charger if you want to get the most life out of those batteries. What is the maximum voltage of a fully charged LifePo4? I think I read 3.6v, and if so and driving a maxflex you'd be above the maximum input voltage (20v) so best to go with 5 in series instead.

    Karl

  3. #3
    mtbr member
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    building packs is not that easy, if done right.
    cells should be mached, befor pack assembly,
    I'd recommend to add a balance plug, so you can monitor/ balance

    6s os odd,... recommend 4s
    if you need 8s, you can do 2x 4s packs, and use 2 chargers, or charge one after the other, still need to monitor it, measure, before connecting them,
    maxflex does boost, so 4s be fine too. 8s+ chargers are few, and expensive.
    lifepo4 are good. still need a pcb

    other option, cut the 7up, into 2x 3, yeah loose one, for now,
    but now you can use some buck drivers, they are cheaper,
    and later you can still put the 7th on later,
    full blast, 7x xpg ~25W, need some heatsink,....
    maxflex should be able to set a temperature throttle.


    Quote Originally Posted by jimbojones1000
    I'd like a little advice, im gathering the bits for a build but im having some trouble with the batteries.

    The build im doing it the 7 up XP-g, and planning on using a MaxFlex 5A to power it, i dont wanna go for the full on 1500Ma i think maxing out at 800 will prob be my lot, if t doesnt melt at 18W! I ordered a chinese special lot of LifePo4 cells from the Flea, and thats where im stuck. Originally i was gonna build a 8s pack and run a Bflex driver, but i cant find any way of charging/balancing for the 8cell pack, where as the RC people use lots of 6 cell pack, so i figured go with the MaxFlex and a 6cell pack, but that would only be 6600Ma and as i bought 20 cells i figured, i could just make a 6s3p pack instead. My question is can i charge a 6s3p pack as a 6 cell pack, and hope the 3 cells in parralel stay ballanced or is there some trick to balancing them? And on the other hand if i build a simple 6cell pack and use a smart charger with a programable limits can i get away without a pcb on the pack? Or having read everywhere how resilient the LifePo4 cells are and dont explode(useful) can i get away with being a bit lazy with the care of them and build a 6s3p pack and just stick anything on it to charge ignoring any balance and not using a pcb on the pack, and just build another when it knackers? the cells cost less than a pcb and being in th eUK i have to order everything form the US so is annoying getting a pcb anyway.

    cheers in advance.
    ----
    DIY battery + light working on it

  4. #4
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    Hello,
    cells aren't the same, and they change a lot with time running. So you should place them in a holder, to be able to discharge each one totaly some times to times. Then you should blend them when they go back in the holder. The parallel mode is that worth that the ohmic value of each string is never really balanced with others. Discharging each cell some times to times will place them starting from the same line for about 5 or 10 cycles, without boring mesurements. This could avoid overheating of a cell with a higher capacity in a low resistance string...
    P.S. : LiPoFe4 need a specific charging device. They accept a big incoming current, and a bit of overcharge without popin...

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