Power Meter for Variac

[ledtester]

The Peacefair units use the V98XX series of energy metering SoC chips:

https://youtu.be/G0AlH3vtT0k?t=9m12s

http://www.vangotech.com/int/uploadpic/157234475389.pdf

Update: In section 18.3 (physical page 275) of the V98XX datasheet there are some tables showing the update and settle times of the metering registers along with this note:

... In 60Hz power grid, the time for updating and settling is 1.2 times of that for 50Hz power grid. ...

[coppice]

I also find the chinese power meters have very long averaging time in firmware, it takes a few seconds to get a settled reading with a constant load. They aren't useful for fast response unless you communicate directly with the IC.

I wonder if that's because they use cheap/slow parts and a low sample rate?

Its because they use the cheap, but quite accurate, devices made for the utility energy meter market. That market cares about accuracy over a wide dynamic range, but not about the update rate.