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pwm errors

Discussion in 'Vape Modding and Technical' started by lru00, Nov 13, 2015.

  1. lru00

    lru00 New Member

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    i just stuck this up on UKV .. proud if it, kets see if a copy works with tapatalk..

    sigh .. a normal voltmeter does NOT give an rms, or correct answer unless its a DC only device or an exxy true rms meter.
    thats it, no ifs or buts .. wrong.
    at high dutys, single batterys, the error is not huge though and simply makes NO difference in vaping terms.

    heres a couple of graphs .. I can show the error between rms and average volts is 1/root(duty)

    so this graph is a plot of duty cycle (bottom axis) vs error to rms volts (left axis)
    [​IMG]

    highlighted point is vmax on minimum duty roughly 36% .. rms is 1.6 times higher, 3v is really 4.8v
    an ego is waaay over on the right, 0.9 duty .. 1.05 rms, 5% error

    but .. you square it to find power ..
    this is duty cycle .. bottom axis, vs error in power if you measure the voltage with a meter and use that to calculate your power.

    [​IMG]

    again, highlighted spot ... vmax on min, the power is 2.7 times what you calculate..
    again.. ego .. waaaay over on the right at 0.9 .. error about 10% now. big deal.

    so I state again .. it makes bugger all difference on single battery mods, HUGE difference on dual batt mods particularly at low voltages.
     
  2. caaaribou

    caaaribou New Member

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    Very handy graph mate.
    Great Stuff!
     

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