16F877 ADC using the Allegro ACS754 Current Sensor

[dhouston]

With a purely resistive load, you should be able to establish the peak through timing. At 60Hz it will occur 4.17mS after ZC while at 50Hz it will occur 5mS after ZC.

However, this will change with reactive loads because of the voltage/current phase difference. It will also change with non-linear loads which most electronic gear presents. The only way to do this accurately is with many nearly simultaneous samples of current and averaging over time. Digital power meters sample voltage and current several thousand times per second. Your PAUSE 100 means you are only sampling a few times per second and so are unlikely to get the peak.