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building a battery pack from 12 v lifepo4 batteries

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    building a battery pack from 12 v lifepo4 batteries

    hi all

    I'm building a 48v 32 ah pack from 8 12v 16 ah in either a 2p4s or a 1p4s configuration. I'm wondering if I should treat these as 2 separate packs or wire them as one pack, so in the end I'd either have 2 48 volt packs wired in parallel or 1 pack for each 12 v battery I wire 2 in parallel and then 4 of them in series.

    the batteries I'll be using are sold on amazon 12V 16Ah Deep Cycle LiFePO4 Battery, 2000 Cycles Miady LFP16AH Rechargeable Battery,…


    here is a what I'm thinking of


    2 packs at 48v 16 ah ea

    + 48v -- [ + - ] --- [ + - ] --- [ + - ] --- [ + - ]


    + 48v -- [+ - ] --- [ + - ] --- [ + - ] --- [ + - ]

    in this example 4 batteries are wired in series with 1 parallel connection to the second pack


    OR

    1 pack @ 48v 32 ah

    [+ - ] --- [ + - ] --- [ + - ] --- [ + - ]
    | | | | | | | |
    | | | | | | | |
    [+ - ] --- [ + - ] --- [ + - ] --- [ + - ]


    in this example 2 batteries are wired in parallel then in series





    Any thoughts?


    #2
    What kind of amperage, and capacity/range do you need for your type of riding? That would drive my decision.
    If 1P handles 40A, and the controller needs 40A, then I would go 2P. no matter what.
    If 1P handles 80A, and the controller needs 40A, I might go 1P for reduced size/weight. That depends on range needs. If using the bike daily means a 16AH pack will run out in a couple of days, , maybe I would be OK carrying the second pack around occasionally. If a 16AH pack might realistically run out before the end of even a day of use, then I would build 2P.

    When building my battery, other members who use their ebikes alot all gave me the same advice. Build in as much capacity as I could fit in my given space. I did that, and my battery is pretty huge, but I know for riding around town it will be all I would ever need to get me everywhere in might go, and not require daily charging. I am sort of thinking I might build a second, smaller pack for when I go to just ride around trails with friends though. I'll have to see what it's like to ride my bike in the rough first.

    Good luck with your build.

    Jose

    Comment


      #3
      The kit states it draws a max of 30 amps and a single 4s set has a rating not a lot higher. Common sense dictates going with a 2P4S at a minimum to reduce stress on a single pack. as far as ah sizing goes, I can't answer that question do to the fact this is my first ebike. also we are off topic my original question was what is the best way to wire up 8 12v batteries, either 2 sets of 48 in parallel or parallel each battery pair 12v at 32 amp hr then in series to get 48 at 32 ah

      Comment


        #4
        Those have a discharge current of 42A - plenty more than the 30A you need

        A 4s (actually 16s as these are 4s by themselves) would suffice and they are heavy and large compared to most the batteries in electric bike applications - do you really need 32Ah?

        If you really need 32Ah and want to go with eight batteries in your battery it's going to be very large and heavy (8 x 1.8Kg = 14.4Kg = ~32lb!!) and in any case but particularly if you are going for a parallel setup I would want to make sure the batteries are all from the same lot... the preferred connection would be to put four sets of two in parallel in series so that each two batteries in the series string are paralleled if that makes sense

        It'll be very interesting to see how you charge these - you'll want something setup for LiFePO4 - it's a lot different than most Li-ion chemistries

        Any reason to go LiFePO4 instead of the far more common electric bike chemistry of LiNiMnCoO4? They are a lot smaller and lighter... e.g. a 16Ah 48V would only weigh 8-9lb instead of 16lb

        Generally the two main reasons to go LiFePO4 is to maintain reasonable comparability with 12V/24V vehicle systems (not likely here) and for safety - they are one of the most tolerant to abuse and don't go up in flames




        Click image for larger version  Name:	81nl2GA8txL._AC_SL1500_.jpg Views:	0 Size:	318.7 KB ID:	109357

        Comment


          #5
          I run dual 52v 12.5ah packs in parallel(18650's). Each pack rated for 50amp continuous, 80amp bursts. Being I have a Ludicrous controller on my BBSHD, I did not want to draw the full 50a from one pack. Makes the cells get too hot. Each of my packs weigh 7lbs. That is a TON of riding. Unless you are building an electric motorcycle, I think you may be over building. Not something I say often. But only you, the user can make the right call on what your needs are. Good luck

          Comment


          • toddbailey
            toddbailey commented
            Editing a comment
            I'll have to wait and see what what range i get with a single battery pack. as far as max discharge current goes I don't see pulling 42 amps through a flimsy F1 connector, at least not safely, for a prolonged period. about 15 minutes I live in a very hilly area so i suspect that a single 16 ah pack might not have the capacity. The motor is also rated as not very efficient but it was cheap, comparatively. I found a 10 amp compatible charger so I'm good, my first charger was a 12v 2a unit and it took all day to charge just 1 of these new batteries at a time. I can only imagine what empty batteries will take. I'm new at this so don't know what to expect or for how long. sadly, 32 pounds for the battery pack is a bit much, but what can you do. it is what it is. I didn't want to drop the coin for a spot welder to make a more traditional 18650 pack. maybe after these expire.
            Last edited by toddbailey; 07-09-2020, 09:45 PM.

          #6
          as far as max discharge current goes I don't see pulling 42 amps through a flimsy F1 connector
          I thought the same thing when I saw the specifications

          I'd just solder to them - I wouldn't even want to pull much current through the mating connectors but the tabs themselves seem ok

          Comment


          • toddbailey
            toddbailey commented
            Editing a comment
            I tried soldering li ion batteries before, the batteries got to hot and died a few months later. now if the 18650 cells had F1 or F2 connectors I could build a bunch of pig tails using 10 or 12 gauge wire and i'd be ok with that.. any way hope to test ride the bike with the 16 ah pack later today.
            fyi the "lightweight mtn bike" is now a tank weighs in at 57 pounds w/o battery pack

          • AZguy
            AZguy commented
            Editing a comment
            I meant soldering to the F1 connector

            Soldering to a 18650 cell is a fool's errand IMO


            There's good reasons these large LiFePO4's aren't being used in electric bikes and LiNiMnCoO4 is the preferred chemistry

          #7
          Learning from every thread and discussion. This is great!

          Jose

          Comment


            #8
            Originally posted by Defjr333 View Post
            I run dual 52v 12.5ah packs in parallel(18650's). Each pack rated for 50amp continuous, 80amp bursts. Being I have a Ludicrous controller on my BBSHD, I did not want to draw the full 50a from one pack. Makes the cells get too hot. Each of my packs weigh 7lbs. That is a TON of riding. Unless you are building an electric motorcycle, I think you may be over building. Not something I say often. But only you, the user can make the right call on what your needs are. Good luck
            yeah, i hope 32 amp hr is too much, weigh issues are becoming an issue, once i get out on the trails I'll have a better idea if I need the added capacity or not, the bike with 1 battery pack is goint to be close to 70 pounds, and close to 85 fully loaded, plus what ever supplies I buy in town.

            Comment


              #9
              Being mine is a "street only" cruiser, I was not very concerned with weight. Mine is around 85-90lbs fully loaded, but not an issue with the extra current going to the BBSHD.

              Comment


                #10
                well It appears I won't need the added capacity (32 ah) after all. Yesterday I put 20 miles on the bike of mostly level but also stretches of very steep roads/trail. I'm happy to share the battery pack shows as full on the lcd panel. I hope Amazon won't hit me to hard with a return.

                Comment


                  #11
                  Originally posted by toddbailey View Post
                  well It appears I won't need the added capacity (32 ah) after all. Yesterday I put 20 miles on the bike of mostly level but also stretches of very steep roads/trail. I'm happy to share the battery pack shows as full on the lcd panel. I hope Amazon won't hit me to hard with a return.
                  I would think 16Ah should be plenty. However, I wouldn't count on what the LCD panel shows. You are running LiFePO4 which fully charged is at about 58.4V. You're LCD is likely calibrated for lithium ion which charges to 54.6V. If so it will show 100% until you drop the voltage below 54.6, which would be really somewhere around 35% discharged.

                  Comment


                    #12
                    Yes, please double check batt pack with a multimeter to verify those numbers. 16ah should be enough for most uses, unless u are a throttle junkie like me. 60-70% of my riding is at full or near full throttle. Takes a lot of juice to propel me and a 90lb bike to 45/50mph.

                    Comment


                      #13
                      There's zero possibility that a "battery gauge" for typical Li-ion has any meaning with Li-iron... for the most part the "gauges" don't even mean much with the batteries they're meant to work with

                      And don't trust voltmeters either! They are not terribly accurate but at least they have some repeatablity so you can get used to them over time

                      Comment


                        #14
                        Originally posted by AZguy View Post
                        There's zero possibility that a "battery gauge" for typical Li-ion has any meaning with Li-iron... for the most part the "gauges" don't even mean much with the batteries they're meant to work with

                        And don't trust voltmeters either! They are not terribly accurate but at least they have some repeatablity so you can get used to them over time
                        Precisely! The only way to get a reasonable approximation is to use a Cycle Analyst or other Watt meter inline to tell how many Wh have actually been consumed...and even that needs to be tempered with common sense and experience.

                        Comment


                        • toddbailey
                          toddbailey commented
                          Editing a comment
                          "...a Cycle Analyst or other Watt meter..." possibly, but I'm thinking a just digital voltmeter will adequate for my needs, after all I just want to avoid a unexpected shut down in the middle to no where.

                        #15
                        I think I will trust my fluke multimeter that has been in my tool kit since my AT days in the navy. Good enough for multi million dollar jets, should be adequate for ebikes electronics. May be millivolts off at the worse case due to cell chemistry.

                        Comment

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