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Thread: Cant figure out how to weight up range/power

              
   
   
  1. #1
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    Cant figure out how to weight up range/power

    Hi, I am considering upgrading an ICE vespa to an EVespa! I would only consider this project worth the effort if I can get at least 100km range, (the vespa's original range being about 120km) I'd like some help figuring this part out (motor + batteries requirements)

    I have done some limited research into parts and batteries. Looking at other builds and converts to see what I can do. And the numbers don't seem to add up. I don't know if it's my lack of understanding but between what I calculate to be possible, and what others have done, there is a big difference!

    In the commercial market - there are many electric bikes with a top speed of 150kmh and at least 200km (or 300) range! These seem to be powered by 4-6 Kwh capacity of batteries. OK, so this is possible now.

    I looked at the range of completed projects, not many have used Lithium batteries, which I will use because of the larger capacity to weight ratio. These homemade projects that use kelly hubs I found are :

    A 2009 Roketa Jamaica MC-46 “Escape Velocity”, a overclocked kelly motor (15kw?) batteries at 76v 40Ah winstons for 3 KWh, weight of 180kg and a top speed of 120kmh, but it's range is only 70km

    And a 2010 e-Fun D-5000 “Morcega”, which has the kelly 6kw hub motor, and a bigger battery pack at 76v at 60Ah for 4.6Kwh, weight of 168 Kg and a top speed of 96 KPH. So lower power to the motor, more battery capacity, yet it's range is 64 Kilometers.

    (Apparently he limits his pack to 3.7 Kwh, if used at full it would still only go up to 80 km range. Barely exceeding the range of the above more power intensive and heavier bike.

    Why are these homemade bikes with higher battery capacities so pitifully short ranged?

    I calculate my possible vespa to weigh around 220kg with me loaded on it, and the kelly hub specs page seems to state that that weight would require 1.2kwh or 14 amps (of 76v - those 2 numbers dont match either! weird chart) to motor along at 120kmh.

    This would theoretically give me a range of 300km on the 76v 40ah pack, or 450km on the 60ah pack. The real life numbers seem way off. Am I missing something?

    Thank you in advance for any advice!
    Josh

  2. #2
    Senior Member Hugues's Avatar
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    Hi,

    300 km range with a 40 ah pack you won't get, clearly your calculation is wrong somewhere,

    there is a nice spreadsheet to help with range and performance calculation, look a this thread:
    http://www.diyelectriccar.com/forums...or-172002.html

    i've used it and gives realistic figures,

    there is another one that was discussed on our forum here, but i forgot it's name,
    Regards from Switzerland
    My 2.5 Upgrade Thread

  3. #3
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    Quote Originally Posted by Hugues View Post
    Hi,

    300 km range with a 40 ah pack you won't get, clearly your calculation is wrong somewhere,

    there is a nice spreadsheet to help with range and performance calculation, look a this thread:

    Yeah, I calculated it due to the kelly motor spec saying it only needed 1.2 Kwh (I think, per hour, at 120kph?) and the 76v 40Ah being a 3.0 kWh capacity pack.

    Also the kelly spec sheet isn't even labeled properly. All the headers are single letters and I have to guess what they mean!


    EDIT :

    I got access to that EV design spreadsheet you linked, and I don't like it... The numbers seem odd.

    I set the weight to 220kg, tweaked all the other numbers as best as I could. Put in the battery stats too. 76v 40-60ah. I can't make the thing go further than about 20km range. Set it to 1kg weight, still 20km. 1000 kg weight. Increase / decrease the motor kw and torque, it does not affect the range / speed stats. I don't know how to use that sheet properly, I guess.
    Last edited by Stubkan; 20 January 2017 at 0816.

  4. #4
    Senior Member Hugues's Avatar
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    not necessarily wrong,
    i've got 13 kwh on my 300 kg build and at 80 km/h i can reach 150 km,

    you've got 3 kwh only, 3/13 * 150 = 34 km

    check the attached exel file, you need to set your cruise speed to 80, and you get about 40 km range, that seems not far off

    if you increase your cruise speed to 120 km/h, your range falls quickly due to aero drag forces....



    Copy of EVdesigner.xlsx.zip
    Regards from Switzerland
    My 2.5 Upgrade Thread

  5. #5
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    Here are 3 small bikes from the DIY Electric Car Garage:

    http://www.diyelectriccar.com/garage/cars/390
    Range at 30mph: 20 miles with 1.3Kwh of lead acid
    http://www.diyelectriccar.com/garage/cars/328
    Range at 30mph: 42 miles with 2.8Kwh of LifePO4
    http://www.diyelectriccar.com/garage/cars/40
    Range at 30mph: 61 miles or Range at 55mph: 37 miles with 4.3Kwh of LifePO4
    "obstacles suck but challenges are fun"

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