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Thread: BMS replacement help

  1. #1
    Junior Member
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    Apr 2021
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    BMS replacement help

    Seeking advice and help about BMS replacement.

    I have an electric scooter, an e-Max 120s, 48v, 4000w.
    Originally it had lead batteries but was converted to LiFePo4 it has a 16x, 60A cells.

    The BMS board is a (see photo):
    HCX-PCB-D131A 120*80 24S 60A
    HCX-PCB-D131C 120*80 24S 60A

    I believe this a Bestech Power model.

    The BMS board is dead but the scooter works and charges if I disconnect the BMS board.

    Im unable to locate the guy who has done the conversion several years ago and Im still trying to find expert help here in Portugal but until now no luck. So Im stuck!

    Meanwhile, Ive contacted Bestech to buy a new board. Their boards are custom made so, among other questions, theyve request the following information about my scooter:
    The max continuous charge current and max continuous discharge current.

    Ive ask them to clarify and theyve replied:
    According to the following photo, I know the charge and discharge from the different terminal, but we don't know the exact current, so we can't provide another board to you, thank you.

    Can anyone please clarify what they are referring to?
    Is there a way I can determine this values?

    Any help on this or advice on any other solution will be appreciated.


  2. #2
    Senior Member
    Join Date
    May 2013
    Kildare, Ireland
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    The board you have is very clearly marked for 60A, however given it has failed, I suppose the question is warranted.


    Based on the spec above, the following.

    Relating to the max discharge current.
    - The power rating for the bike is 4kW and the pack nominal voltage is 48V suggesting max sustained discharge of 4000/48 = 85A
    - However, you're not going to hold max power for more than about 10 seconds tops at any given time so you can derate this figure somewhat.
    - So personally, I'd be inclined to tell them that the max sustained discharge current will be in the 70-80A range.

    Relating to the max charging current.
    - The spec above indicates 3-5 hour charge time for a 60Ah pack.
    - Taking the faster end of this, 3h, this means an average of 20A over the full period for a 100% charge
    - However, the last 30% of the charge is at lower current so we should conservatively say 30A for the first 70% of the charge.

    Based on those numbers, and the data in the photo you provided, I reckon this is what you have in there: http://www.bestechpower.com/512v16sp.../PCB-D131.html
    What's more I'd be willing to bet it's the thermal fuse that's gone.


    They have plenty of other good options beyond that one in the lineup at that link, but if they won't play ball then I'd be looking towards this as a first alternate.
    Note that they've got the balance voltage wrong in that spec sheet however - most likely just a copy-paste error from the LiPo version, but worth checking before you buy if you do go that way.
    Last edited by Spoonman; 15 April 2021 at 1101.

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  4. #3
    Junior Member
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    Apr 2021
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    Thank you for your detailed reply.

    I’ll will try the litechpower link you’ve posted.

    Thank you,


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