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First build - Can someone help me confirm my calculation ?

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    First build - Can someone help me confirm my calculation ?


    HI there,


    I hope you are all doing well. Thanks for the great forum and all the information provided.

    It would be my first build. I have been reading a few documents and I believe I made some progress in understanding a few aspects on how to think my battery pack. But the further I read more question are arising (it is definitely a very interesting topic). I feel I am almost there ready to buy and build. Nevertheless, I still have few questions that I did not manage to answer myself. So if someone would be kind enough to help me, I would be very grateful



    Project: Build a battery pack for a golf trolley.

    A) Specs of the golf trolley:
    • The trolley comes with two engines of 120w each running on 24v.
    • They is a module linking the two engines, the control panel and a remote control (picture attached). On this module, one can read the following:
    • G7R – 24v – D 60S
    • Vol: 21-29,4V / CUR 15A
    • STM5K Rev_1.2 8BC2
    B) Specs of the original battery pack:
    I have attached a picture of the battery that comes originally with the trolley. On the sticker one can read the following: 24v – 13 AH – 327,6WH

    C) Autonomy of the trolley:
    The autonomy given by the original battery is satisfactory but why not building slightly more powerful to facto in the inevitable loss of capacity of the battery through the time and use.

    D) Why build the battery pack myself?
    As you know, they are a lot of restriction for plane travel when it comes to lithium battery pack. I work oversees and change residency every year or so. I wish to build this pack using the Vruz. battery kit which would allow me to disassemble the pack when traveling. I figured out it would an option for me since where I generally work and leave, lithium battery are not always available and surely it would help saving some buck not buying a new one every time I move.



    As far as my understanding goes I calculate the following:
    • I should build a 7s5p battery pack with (of course) a BMS
    • I could use the LG MJ1 3500 mAh 18650 battery cells are they are well renown
    • I would get a 24v / 17.5 ah battery.

    E) Questions:
    1. 240w / 24v = 10ah so why on the module linking the two engine it is written 15ah ? Which one should I consider to calculate the power needs?
    2. As you might know Vruz. offers two kits the 1.6 and the 2.1. I understand that the main difference is the current discharge one can take from one cell: 3.5A from the cheapest kit and 20a on the most expensive. Which one would be more suited for my use ?
    3. What other cheaper cell could I use staying with well know brands?
    4. How many kilometer could the trolley run on one charge ? I calculate the following but I am not sure: Using the 17.5ah battery pack mentioned above plus knowing that the maximum speed of the trolley is 8km. Theoretical autonomy would be: (17.5ah / 10ah) x 8km = 14km – Is that correct ?

    Thank you very much for any help given
    Last edited by andyB; 07-18-2021, 02:13 PM.

    #2
    My 2 cents worth:
    1. 240w / 24v = 10ah so why on the module linking the two engine it is written 15ah ? Which one should I consider to calculate the power needs?
    The 15A (amps not Ah) written on the controller likely means that is maximum current the controller can support. In your calcs you come up with 10 amps needed so you would be within the capabilities of the controller.
    2. As you might know Vruz. offers two kits the 1.6 and the 2.1. I understand that the main difference is the current discharge one can take from one cell: 3.5A from the cheapest kit and 20a on the most expensive. Which one would be more suited for my use ?
    I don't know much about Vruz. However, you have 5 cells in parallel and are projecting a max draw of 10-15 amps. That means 2-3 amps per cell. The 1.6 kit should work.
    3. What other cheaper cell could I use staying with well know brands?
    No comment. Just get good quality cells.
    4. How many kilometer could the trolley run on one charge ? I calculate the following but I am not sure: Using the 17.5ah battery pack mentioned above plus knowing that the maximum speed of the trolley is 8km. Theoretical autonomy would be: (17.5ah / 10ah) x 8km = 14km – Is that correct ?
    Lots of variables here. You are assuming you draw 10 amps flat out all the time. Probably won't happen. Your battery has about 420Wh fully charged. Not knowing the weight of your cart, load, etc., a rough guess of consumption would be 20-30 Wh/Km. this would give a range of 14-21 Km.
    ¡Buena suerte!

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      #3
      Thanks for you time and answer!

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