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  1. #1
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    Power consumption calculations including efficiency

    Hi All,

    I did the below calculations but i`m not sure if i figure them correctly especially when i need to add the DCDC converters efficiency and the external ACDC PSU.

    So my example:

    Board 1: 12v x 2A = 24w
    Board 2: 28v x 1A = 28w
    Board 3: 5v x 2A = 10w

    Each board is power by a different DCDC converter (12v, 28v, 5v) and each converter has 90% efficiency.

    The whole system is powered by an external ACDC PSU with output 30v.

    My calculations:

    Total system power consumption: 24w + 28w + 10w = 62w
    DCDC converter efficiency 90%, 62/0.9= 6.8w
    3x DCDC converters 6.8wx3=20.6w (due to efficiency)

    New total system power consumption=62w+20.6=82.6w

    For the external ACDC PSU which runs on 30v:

    I=82.6w/30v =2.75A is required

    Questions 1: Is the efficiency calculation correct?
    Question 2: I found somewhere that for the efficiency calculation i need to use this approach "multiply the input current by 1 + (100/efficiency)" but the values i get are not logical (*4.34A vs 2.75A)

    *1+(100/90)=2.1
    Input current = 62w / 30v = 2.06A
    2.06A * 2.1 = 4.43A

    Thanks,
    Christos D

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  2. #2
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    Re: Power consumption calculations including efficiency

    DCDC converter efficiency 90%, 62/0.9= 6.8w
    Perhaps just a typo of yours, but the corretc value is without the decimal dot:

    • DCDC converter efficiency 90%, 62/0.9 Input Power = 68w


    I did not check anything else after this point, the error should be propagated from then on.
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  3. #3
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    Re: Power consumption calculations including efficiency

    Quote Originally Posted by stoui333 View Post
    ...
    DCDC converter efficiency 90%, 62/0.9= 6.8w
    No, Pin_tot_converters = Pout_tot_converters/efficiency = 62W/0.9 = 68.89W
    3x DCDC converters 6.8wx3=20.6w (due to efficiency)
    No, you've calculated the total input power to the three converters as Pin_tot_converters already.

    New total system power consumption=62w+20.6=82.6w
    No way. This part is not supposed to be there.
    The calculated Pin_tot_converters = 68.89W is Pout_tot_converters + Plosses_tot_converters already.

    For the external ACDC PSU which runs on 30v:

    I=82.6w/30v =2.75A is required
    No, Iout_acdc = Pout_acdc/Vout_acdc = 68.89W/30V = 2.296A
    N/B: Pout_acdc = Pin_tot_converters.
    Last edited by Akanimo; 13th June 2019 at 16:24.
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  4. #4
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    Re: Power consumption calculations including efficiency

    Hi Akanimo,

    Thanks for your reply, i did understood the logic.



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