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I have an ac to dc power supply and it measures at 244.0Vac on the primary side and the secondary side it is reading 21.34Vdc. I attached a load to the secondary side that is drawing 0.390amps and when I measure the current drawing on the primary side it reads at 0.090amps. Can somebody explain to me the calculation behind this. Thanks

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    \$\begingroup\$ What exactly are you measuring on the AC side? The amplitude? The RMS? \$\endgroup\$–Eugene Sh. Jul 23 at 15:12
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    \$\begingroup\$ If you're asking about efficiency, you can't actually know that without knowing power factor, too. \$\endgroup\$–Hearth Jul 23 at 15:25
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    \$\begingroup\$ There's nothing to calculate, if is what you measured then that is what it measures. We don't know what kind of power supply it is (linear, switch mode, regulated, unregulated. etc). \$\endgroup\$–Justme Jul 23 at 15:26
  • \$\begingroup\$ RodgerKL - Hi, To avoid readers having to guess, pleaseEdityour question and add context & more details e.g. Why are you asking - what will you do with any answer? What type of power supply do you have in your test? Please link to its datasheet (if it's COTS), or add its schematic (if it's your design), or supply the full question and any relevant preceding parts (if it's homework). What analysis have you already done of those results? || When there are sufficient details added into the question, we can consider re-opening it. Thanks. \$\endgroup\$–SamGibson♦ Jul 23 at 15:52
  • \$\begingroup\$ Hi, Thanks for your reply. The power supply that I am using is a Puls PIC 120.241D power supply. Efficiency up to 92.3%. Measureing the rms on the AC side. This is just a table top test to see if I could work out the results measured against a calculated test. \$\endgroup\$–RodgerKL Jul 26 at 9:29

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The only calculation you can reliably make is to calculate the input power and the output power. The output power can never be greater than the input power, and it might be much less. Doing a little algebra, this would allow you to calculate theminimumpossible input current for a given output current and voltage.

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  • \$\begingroup\$ Hi Thanks for your reply. I have caluclated the output power at 8.322watts with the load thats connected and the input power at 21.83watts. Do you think these seem correct values I should be seen? \$\endgroup\$–RodgerKL Jul 26 at 9:31

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