Building A Motor Spreadsheet

Discussion in 'General Bike Discussion' started by safe, Feb 9, 2011.

  1. safe

    safe New Member

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    Building A Motor Spreadsheet

    Data starts on row 8:

    Column A : Rpm : From 0 to 3700 I spaced 100 per row
    Column B : Voltage : MIN(((C8)+(SQRT(C8^2+4*($Voltage)*($Current*$Resistance))))/(2*$Voltage),1)*$Voltage-C8
    Column C : BackEMF : A8/$Kv
    Column D : Current : B8/$Resistance
    Column E : Heat : (D8*D8)*$Resistance
    Column F : Power(In) : (B8+C8)*D8
    Column G : Power(Out) : ((B8+C8)-(D8*$Resistance))*(D8-$NoLoad)
    Column H : Efficiency : G8/F8

    Constants are:

    $NoLoad : 2.25
    $Resistance : 0.337
    $Voltage : 48
    $Kv : 78
    $Current : 40

    ...if you create a spreadsheet with these formulas you can then plot the graph yourself:

    [​IMG]
    [​IMG]
     
  2. scootergal

    scootergal New Member

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    @[email protected] too many numbers!

    So this is interesting, but what is it supposed to be used for?

    or am I being dumb?
     

  3. safe

    safe New Member

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    Some people like to experiment with different electric motors, current limits and battery voltages and they often are unable to figure out what results they will get. These (relatively) simple formulas give very accurate data about how a motor will behave.

    These days spreadsheets are a "common language".

    For someone interested in "enhacing" their machines this is valuable.

    I've known people who struggle for months trying to figure this stuff out, so this is a HUGE help for people who want to know.

    Just try it. Create a spreadsheet with these formulas and use the default values. (create some "range names") Then plot the results in a chart and you will see the powerband of an electric motor. Alter the parameters and watch the change in shape.
     
    Last edited: Mar 24, 2011