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Thread: Charge time on a LiFePO4 battey pack

  1. #1
    Ocracoke's Avatar
    Team Kaizen

    Hey everyone,

    Following on from my last thread on LiFePO4 batteries, I've bought a pair of 2S1P batteries and now they need charging. However, the first set I've got on charge is approaching 70 minutes and still hasn't finished. They are charging I think, I am using a Turnigy Accucell 6 on the LiFe program with 1.2A amperage.

    How long are they supposed to take to charge? I know it reads like a "how long is a piece of string" question but I am sure it isn't meant to take this long.
    Team Kaizen - Build Diary for all the robots

    AW: Amai, Ikari, Lafiel, Osu, Ramu
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  2. #2
    Depends on the amperage, and the capacity of the battery (and starting voltage of course).

    If your putting 1.2 Amps in for an hour, your adding 1.2 Amp hours worth of life.

    Dystopias will usually take 90 minutes to fully charge after 2 fights on a 2A input.

  3. #3
    Ocracoke's Avatar
    Team Kaizen

    Thanks, first battery pack is nearly there now (I had to stop and upped the amperage a little to 1.4). I'll see how long it will take for a ~30% battery to get there but I am likely going to need a extra charger, power source and set of batteries for this as well.
    Team Kaizen - Build Diary for all the robots

    AW: Amai, Ikari, Lafiel, Osu, Ramu
    BW: Shu!, The Honey Badger
    FW: Azriel
    MW: Jibril, Kaizen

  4. #4
    Let us think a bit theoretical.

    The Zippy LiFePo4's are 4200mAh capacity. 2S means 2 cells in series =6.6V and because there is is only 1P, it's 4200mAh

    6.6V x4.200A=27.72W fully charged. Adapting to the charge losses and inffeciencies, add 10-15%=30W
    So, charging @ 4200mAh means you'll be charging a completely exhausted battery in 1 hour and 10 minutes.

    Cheap chargers like the imax B6 are rated at 50W peak. So you can charge the cells with 50/6.6= 7,5ah , in about 40 minutes.
    Balancing can add a lot of time if the cells are out of tune with each other.

    Some batteries can accept higher charge rates, meaning they can be charged in 10-15 minutes, but then we're talking high end cells. Also, getting chargers to do that higher charge speed is not cheap.

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