ebike Li-ion battery pack

Fabian
Fabian Registered Users Posts: 131 ✭✭
edited January 2020 in New Battery Technologies #1
I have a huge lot of modem battery pack consisting of (3) 18650 Li-ion cells in each of the pack. Each modem battery pack is rated at 10.8v @ 2600mAh as each of the cells inside is rated at 3.6v, 2600mAh and they are connected in series, hence you get the 10.8v rating. The packs comes with built in BMS (battery management system) in each of them.

I am wondering if it is possible to wires these packs in series/parallel connections to be able to increase the voltage and the current rating to bring the battery to 54v for a 48v ebike with a much higher amps than what one pack would offer?
I have a total of 84 packs so after the series/parallel connections i would end up with a total pack of 54v with an estimated 43amps overall.

My question is, with this proposal each pack would already contain their own built in BMS, so therefore would it be possible to charge the overall pack with a 48v ebike Li-ion charger rated at 54.6v without causing any issues to each of built in BMS bearing in mind that the entire pack is made up of several smaller packs of 10.8v that are connected in series/parallel connections to get an increase in voltage and current.

Would there be any balancing issues or any other issue(s) that may or may not arise from this method?

Next question is if the charging is possible would each of the packs auto regulate the cells inside of them so they don't overdischarge during charging stage of the overall pack and they don't underdischarge during discharging stage when using the ebike?

Would i be able to can pull large amount of current from the overall pack for example 30-35amps without any adverse effect on the cells or each of the built in BMS?

Thanks in advance for the support.
Why i want this to work would be because it would be much easier and less time consuming to built a big battery pack with this method instead of having to scrapping out the cells out of each pack which would be a total of 84 modem packs then have to rewire them in series/parallel connections and then to add a 48v BMS to the overall pack. It would be a very time consuming task.

so what do you think guys would my method work perfectly without causing any issues?
what are your recommendations and suggestions or input on this regards?
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Comments

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    The way to assemble a bank of the required voltage/capacity would be to disassemble the packs and assemble the cells first in parallel for capisity then in series for voltage. Then use a BMS designed for the nominal voltage  to monitor each cell block,  sounds simple but there are other considerations, each cell would need to be ballanced then assembled into cell blocks, then each cell block would need to be ballanced, either top or bottom depending on application.

    This is a tedious process which may be possible with matched new cells, however with unknown cells  perhaps of different age  it would be a gamble at best. Using the individual BMS theroy wouldn't work because as soon as the first "individual battery " reaches full charge the voltage on the ballance of batteries would likely exceed the requirements causing them to shut down...... or worse 

    Be very careful with lithium cells some can react violently outside their required voltage parameters, be aware I'm not being negative but rather realistic. Know the exact chemistry, study their requirements before proceeding, this is something I personally wouldn't recommend but do understand the curiously, behind the question.


     
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  • Fabian
    Fabian Registered Users Posts: 131 ✭✭
    #3
    the cells are LG brand LGabb41865 these are made for storage and not for high drain.

    However suppose i build a large battery pack with a lot of these in parallel would i be able to pull at least 25amps constantly from them without causing any issues????
    I am planning to use 130 of them to build a 48v ebike battery packs. with (13) strings of (10) cells group together in parallel with a total amounting to 48v @ 26amp.
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  • Fabian
    Fabian Registered Users Posts: 131 ✭✭
    #4
    my ebike is limited to 30amp draw.

    SO if i use 12 of these in parallel with 13 strings in total for a 48v ebike would it be able to power the ebike with no adverse effect on the cells seeing that these are non high amp discharge cells?
    I am just thinking that if i can pull 2.6amp from one of the cells constantly. then 12 of them in parallel mode i would surpass the 30amp limit of my ebike.
    what do you think or suggest?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Remember the "Hoverboard" from 1/2 a decade ago... And the fires:

    https://www.cnet.com/news/why-are-hoverboards-exploding-and-catching-fire/

    And the Escooter fires now:

    https://duckduckgo.com/?q=escooter+fire&atb=v122-1__&ia=news

    In general, the major cell manufactures do not sell single "bare cells" to civilians. A major factor being that placing these batteries into banks and commercial products can be dangerous if not done correctly/safely.

    Not a comment against you or your skills... But this is a very complex engineering project with lots of issues.

    This forum has a lot of information about Li Ion batteries:

    https://www.candlepowerforums.com/vb/forumdisplay.php?9-Flashlight-Electronics-Batteries-Included

    Just want you to be safe.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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