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Thread: Using a balance charger on a big pack?

              
   
   
  1. #1
    Senior Member __Tango's Avatar
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    Using a balance charger on a big pack?

    Hey folks,

    Short story and question:

    Can you use a Balance charger (like one of these: http://www.hobbyking.com/hobbyking/s...r_Charger.html) to charge a subset (6 cells in series) of a large pack (e.g. a 36s1p) without dismantling the pack first?

    Longer explanation below:

    So, i've been running fairly well with my thundersky (thundersag?) batteries for about a year. My pack is a 36s1p Thundersky 60Ah LiFePO4.

    In my haste to finally get rolling, i never did a full balance of my pack before i started. Now i think i need to do that since my pack voltage is fine (the canbus on my controller spits out that my pack voltage is fine), but my MiniBMS is tripping even when the pack voltage is fine. Note: The MiniBMS has all cells wired in series, so if any cell goes under the LVC, the BMS trips. However, it's an analog system, so you can't do per-cell monitoring with the MiniBMS, so i didn't know which cell is low.

    I was able to figure out that there is some large variation in my pack voltage.

    I have a couple of CellLog 8s cell monitors (http://www.hobbyking.com/hobbyking/s...2_8S_Lipo.html), however, i only have wires to test 2 of my 6 "banks" of 6 cells at a time. While the bike was at rest, I tested each 6 cell "bank" in my pack individually and found that there was one bank that had a couple of cells that were lower then the others (most of the cells were at 3.32-3.38V, the low ones were at 3.29 or so). I kept that pack wired to the celllog (and one other for reference) and went for a ride.

    I graphed the cell data after the ride, which can be seen here:



    One of the cells ("G1", the orange line) is sagging and is in general lower than the rest. The cells in the "G" pack all seem to be a bit lower than the "H/I" pack.

    In any case, i while back, i bought one of these: http://www.hobbyking.com/hobbyking/s...r_Charger.html, it's an 8 cell balance charger. it'll do LiFePO4. What i want to know is if you can take 6 cells in a 36s1p pack and do a balance charge. I'm guessing it'll work, but i wanted to make sure before I go light my garage on fire.

    I was basically do a full charge of my pack using my normal series charger, then balance all 6 banks one at a time using the balance charger. I'd like to do that without having to take my entire pack apart.

    Thanks!
    EVs: 2007 Zapino Scooter, Honda VF500 Conversion (electriceptor.wordpress.com), Red Nissan LEAF SL (Arrived!)

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  3. #2
    Senior Member larryrose11's Avatar
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    In my expirence with the B6 charger, this ones brother, you will need to hook up both the balance lead and the +/- over the 6 cells to charge.
    it should work fine, asuming it is all wired up correctly.
    I have never taken a 6s lipo apart to see how the balance plugs are connected to the cells. If you replicate that setup, then it should work without fire.
    Ted might have some expirence with this. I know he has used the hobbyking balance chargers.

    Paging Ted....

  4. #3
    Senior Member Hugues's Avatar
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    for what it's worth: i charge one cell of my 7s lipo+bms with my lipo charger/balancer, without disconnecting any cells,
    i was told i could charge any number of cells that way, though i never tried more than one at a time.
    WHen experimenting with this, always triple check the polarity first with a voltmeter before connecting,
    then after connecting, stay there and check if the pack is not becoming hot or something, probably a good thing to stay nearby until the charge is finished.
    Never too cautious with this stuff.
    Regards from Switzerland
    My 2.5 Upgrade Thread

  5. #4
    Old EV Racer EVcycle's Avatar
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    Yes.....

    Do it all the time....

    EV Ed
    Never let being a responsible adult get in the way of passion and curiosity.
    Motenergy.com
    Ev album 2456, 2458, 2457, 2681, 3456, 3630, 5511, 5512

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    Senior Member __Tango's Avatar
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    Nice Ed. I want to see what the other end of that (the part that's hooked up to the batteries) looks like.

    Thanks folks.
    EVs: 2007 Zapino Scooter, Honda VF500 Conversion (electriceptor.wordpress.com), Red Nissan LEAF SL (Arrived!)

  7. #6
    Old EV Racer EVcycle's Avatar
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    It is a standard Molex connector. 3 on the main pack and 1 on the second pack.

    Last edited by EVcycle; 30 April 2012 at 1519.
    EV Ed
    Never let being a responsible adult get in the way of passion and curiosity.
    Motenergy.com
    Ev album 2456, 2458, 2457, 2681, 3456, 3630, 5511, 5512

  8. #7
    Senior Member soyachips's Avatar
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    Hi Tango,

    Did you ever find out if you can use RC chargers to charge large Ah batteries? I'm thinking about getting something similar to balance the cells after getting them most of the way there with another charger.

    Thanks,
    Andrew

  9. #8
    Senior Member SplinterOz's Avatar
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    One nice way to do it is with one of these....
    http://dx.com/p/bc168-1-6s-8000ma-20...charger-124483
    This is Ed's solution in a box.

    This is basically individual lipo chargers in one box low and high voltages can be set so all chemistries (lipo ones) are supported. Requires external DC supply.
    Don't connect them in series as the first charger and the negative input are connected. I have one of these and it is MUCH faster than the imax and others as it "bulk charges" the series and shunts the high cells.
    SplinterOz
    From Australia'a Capital
    http://rgelectric.wordpress.com/

  10. #9
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    Mind if I slide in here with a similar question? I am about to start wiring up my scratch built moto-bicycle. (We have different rules down here in CR). I have bought 500-26650 A123 cells, new old stock, unused, at a great price. I am planning up to 6 packs of 23S3P, for 74V nominal.

    I have charged and balanced the first 140 cells, and soldered them as 3P. Then, I plan to solder them into 23S packs. Each pack will be connected to a + and - busbar, with bullet connectors, with, up to 3 packs on each side of a center support in the frame, all strapped to "trays" running the length of the frame.

    I would like to be able to balance charge them, even if it means unplugging each pack from the bus bars, first. Hopefully, after a few runs, the cells would all stay pretty close, and, I WILL keep an eye on them.

    How can I connect a charger to be able to balance and bulk charge. Do it separately? Can I even do this ??

    I also got 2 of the DeWalt 36V tool pack chargers, so, if I can use them, in series, that would be perfect. I don't NEED to ride every day, being retired and forgetting more than I can learn, so, I'm really not sure of what I can or can't do, without burning things up or down. Somewhat slow charging won't bother me, until I get my Solar panels built and working, along with my Micro-hydro system. I can charge with those with a higher charge rate, and, monitor them, also.

    I could rig up 3 connections on each side of the bike for plugging in 3 non logging cellogs, if that would help. Don't necessarily need to log this stuff right away, as long as I can read and write the info in a book, for now.

    I did receive several of the laptop chargers from Ted, quite a while back, and wired up 4 in series to charge NiCd packs of 36V in series for my Super Weed Whacker. That works fine, so, I'm thinking what's the difference if I wire up a 72-74V series, with 23 parallel groups of 3 cells. Should just bleed off to balance each P group ??

    Now you might see how I'm confusing myself. Thanks for any helpful input. Harold

  11. #10
    Senior Member soyachips's Avatar
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    Quote Originally Posted by SplinterOz View Post
    One nice way to do it is with one of these....
    http://dx.com/p/bc168-1-6s-8000ma-20...charger-124483
    I've been thinking about getting one of those. If they had an 8S version I'd buy one as I've already got balance wires setup for CellLog. Do you just use it for balancing or to do full charge? I read somewhere the small balance wires might get hot!

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