I have been wondering about that. Are these meters built on the assumption of a purely resistive load, or will they give accurate readings even with a switch mode power supply? My very limited understanding says these draw current in a very different pattern than a resistive load. The meter would actually have to integrate voltage×current to be accurate, I think.
Thanks, that is helpful to know. However, a switch-mode power supply is quite different from a reactive load. Cheap ones tend to draw power only near the voltage peaks, whereas better ones improve on that. See [1] and [2]. So the question remains how well these cheap power meters cope with such a nonlinear load.
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I have been wondering about that. Are these meters built on the assumption of a purely resistive load, or will they give accurate readings even with a switch mode power supply? My very limited understanding says these draw current in a very different pattern than a resistive load. The meter would actually have to integrate voltage×current to be accurate, I think.
Most of them report power factor, which requires measurement of reactive loads.
Thanks, that is helpful to know. However, a switch-mode power supply is quite different from a reactive load. Cheap ones tend to draw power only near the voltage peaks, whereas better ones improve on that. See [1] and [2]. So the question remains how well these cheap power meters cope with such a nonlinear load.
[1] https://en.wikipedia.org/wiki/Switched-mode_power_supply#Pow...
[2] https://en.wikipedia.org/wiki/Power_factor#Power_factor_corr...