# Energy Meter energy calculation from power

I have interfaced a smart energy meter IC (ADE7878) to a microcontroller. The datasheet of the IC can be found here,

As per the datasheet, on page 50 total active power of each phase can be read from the registers AWATTHR, BWATTHR, and CWATTHR. What parameters I should consider and formula I should use to calculate the kwh value ?

• As I read it, those are already in Watthours - so to get kWh, just divide by 1000. The chip itself is calculating the energy. You just have to add the three for the sum of all phases, or use all three separately if you need to track energy use by phase.
– JRE
Mar 11, 2017 at 19:34

If each register is numerically in kW then add all three and integrate over one hour to get kilo watt hours.

You might find that the register is updated on a cycle of AC. If so, then average the power for each second and that figure can be used to integrate over 3600 seconds.

If the registers are in watt hours as the name implies then just add all three.

Somewhere in the data sheet it will give you a value for each bit in watts or watt hours. You need to make conversions using this figure into proper units.

• Thanks for your reply. But the values given out of these registers are 32 bit. I was thinking how do I convert it to the actual value. I think there is some conversion factor. Mar 12, 2017 at 7:24
• As per the datasheet(page 58), PMAX = 33,516,139 = 0x1FF6A6B, the instantaneous power computed when the ADC inputs are at full scale. So will dividing the value obtained from the register by Pmax give me the actual wh value ? Mar 12, 2017 at 11:50
• What units are the WATTHR registers representing? PMAX is nothing to do with accumulated energy (watt hours). Mar 12, 2017 at 12:40