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Forum DIY AC power measure (240 V, 50 Hz, < 10 W)
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Related

DIY AC power measure (240 V, 50 Hz, < 10 W)

Jan Cumps
Jan Cumps over 1 year ago

Looking for your advice to make an AC power meter.

requirements:

  • can handle 240 V
  • 50 Hz sinus
  • from low power (50 mW) to up to (say) 10 W
  • 1% accuracy would be great

bonus:

  • power factor

If you know a makeable circuit, or a device that works in that low range, chime in please

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  • Jan Cumps
    Jan Cumps over 1 year ago in reply to Jan Cumps +4
    The efficiencies make sense now. I've not taken in account the rectifier and input protection loss, but extremely close to the data sheet: PI data sheet: My measurements: 30 mW standby power…
  • Jan Cumps
    Jan Cumps over 1 year ago in reply to Jan Cumps +3
    fully executed :
  • Gough Lui
    Gough Lui over 1 year ago in reply to Jan Cumps +2
    It's not unusual for switchers to have poor power factor at low loads that improves at higher loads. This is especially true for passive PFC designs or those with no PFC considerations at all. The power…
  • Jan Cumps
    0 Jan Cumps over 1 year ago

    I may do a little cop-out, a use Power Integraton's wattless meter approach:

    Break DC path just after the rectifier, and before the bulk capacitor. Amp meter over the cut, volt meter over the bulk cap.

    Then improve accuracy by assessing the loss in input protection and rectifier.

    It's documented here: https://www.powerint.cn/sites/default/files/forum/files/PIU-102_MeasuringEfficiency.pdf

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  • Jan Cumps
    0 Jan Cumps over 1 year ago in reply to Jan Cumps

    This is the plan, halfway executed:

    image

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  • Jan Cumps
    0 Jan Cumps over 1 year ago in reply to Jan Cumps

    fully executed Slight smile :

    image

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  • Jan Cumps
    0 Jan Cumps over 1 year ago in reply to Jan Cumps

    The efficiencies make sense now. I've not taken in account the rectifier and input protection loss, but extremely close to the data sheet:

    PI data sheet:

    image

    My measurements:

    30 mW standby power

    efficiency at load:

    • 51% at 1% 
    • 77% at 10%
    • 81% at 100%

    image

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