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    Converting/ upgrading power packs

    hello everyone, I recently acquired an E scooter and the SLA batteries were knackered ( and extremely heavy) so I have decided to try and convert it to Lithium power packs, the SLA batteries were 4 x 12 volt in series at 12 ah (knowing not to multiply the amp-hour when batteries are in series), the motor they were running is as follows: 48 volts 26.7 amps, 1000 watt and does 3000rpm chain drive motor, I would like to max out the batteries amp-hour and staying with 48 volts but I am not sure how high I can go with the amp-hour, any help/advice/ ideas would be greatly appreciated

    #2
    Think of the amp hours as the size of the tank. 2 amp hours is 2 liters of fuel. 20 amp hours would be 20 liters. If your motor only uses 1 liter per hour it will work fine with either tank its just you can run a lot longer with the bigger one.

    The amp rating of the pack and BMS is what has to match that motor draw. If you have a 500w motor at 48v thats 11 amps so your cells and BMS need to be rated for at least 11 amps, I would go for something rated at at least 20 amps. This could be a 6amp hour pack or a 20. BMS can go either way its just about the cost. For the cells the bigger packs tend to get a higher rating just because there are more cells to share the load so even if they are cheap cells they still end up with a decent draw capacity.

    You will also need a new charger for the new pack since SLA and pretty much every other style of battery use a different style of charger.

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      #3
      Originally posted by Razr1969 View Post
      ...SLA batteries were 4 x 12 volt in series at 12 ah (knowing not to multiply the amp-hour when batteries are in series)...
      No multiplying with Ah for series - series just adds voltage. Conversely parallel just adds Ah (and A) and doesn't affect voltage for the most part.

      A 48v/12Ah Li-ion in the typical chemistries used for electric vehicles purpose built for Li-ion will weigh ~3-3.5kg so huge improvement over lead acid however fully charged they will be at a considerably higher voltage than lead-acid and the voltage will change more from "full" to "empty" so you need to make sure your vehicle controller is up to the task (many are, but no guarantees)

      For direct lead-acid replacement there's a different chemistry that's commonly used (lithium iron phosphate) but those weigh a lot more than the previous EV typical chemistries mentioned although they tend to be "safer" (electrolyte isn't flammable) and many can even be charged by conventional lead-acid charging systems although they won't get 100% charge so even heavier for similar capacity

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        #4
        Thanks for your replies, Am I correct in believing I can put 3x 48 volt 20 ah lithium power packs in, this will provide 48v - 60ah as they will be parallel? there is plenty of room, the lead batteries were massive and extremely heavy, I can even leave a small gap between them so air can circulate,

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          #5
          Originally posted by Razr1969 View Post
          Thanks for your replies, Am I correct in believing I can put 3x 48 volt 20 ah lithium power packs in, this will provide 48v - 60ah as they will be parallel? there is plenty of room, the lead batteries were massive and extremely heavy, I can even leave a small gap between them so air can circulate,
          Paralleling lithium batteries is fraught with perils but there are folks that do it without issues and yes, Ah capacity is additive that way

          I run multiple batteries for capacity sake but just switch from one to the other - much safer and simpler IMO. If you parallel them for higher current handling that's another animal and has additional perils/concerns

          Li-ion batteries that are typically used in electric bikes hold a lot of energy and they can catastrophically release it... search internet for "electric bike fires" or "lithium battery fires"... literally h ours of entertainment if you are into those kinds of thing

          For discussion on paralleling see: https://electricbike.com/forum/forum...d-li-ion-packs

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            #6
            Thanks again, yeah I think I will go with what you suggested, defiantly safer, takes 1 min to change the connection to another battery and I'm getting on a bit now, not into blowing myself up anymore. you have saved me a massive headache and a lot of money, much appreciated

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