Multi-channel AC Power monitoring

Link to PDF of Schematic of Power Monitoring Circuit (16KB) 

Warning Potentially Dangerous. Don’t try this yourselves unless competent and careful.

Prototype of circuitry using SAMES SA2002E  IC  (see  Download sa2002e.pdf )  to measure power (instantaneous V-I) at each SSR . This is NOT an suggestion for anyone to build the circuit. It  could be dangerous. Values of some components have been omitted to help discourage folks that are not qualified from trying this themselves.

I've put shunt and dividers on a small PC board directly connected to the 25amp SSR terminals (shown as :”High Voltage Board”). The “Low Voltage” board” has the SA2002E but has potentially dangerous voltages and should also be in a UL-listed  line-level AC enclosure.  Run the optically isolated output to a third board (that can be in an enclosure with other low-voltage devices)  to a pair  of  divide-by 12 or 14  LSTTL's, followed by a pulse shaper, followed by another 4Nxx optoisolator. Pick the frequency output from the taps of the second divide-by-n that suits your needs. This circuits will provide a well isolated, low-frequency pulse with output frequency proportional to instantaneous power that you can route elsewhere over twisted pair and remotely convert to a DC signal with a LM2907 frequency-to-voltage converter, count directly with a PIC/PC, or both.

A single monitoring channel can be put together for less than ~$15  You will need to recalculate all the resistor values for the current range and voltage range you want and the specifics of the shunt you use. Some of the capacitor and resistor values are what I happen to have on hand. Calculate the dissipation of the front-end resistors twice -- and then check your results and size accordingly.

For instantaneous measurement, the SA2002E will work fine as just described with most any HA controller with 8-bit resolution and 5-volt input range or DMX512 input. For totalized (accumulated) measurements you will also need a high up-time data logger which generally means a dedicated device rather than a HA controller or build a hardware-based accumulator with CMOS memory.

Don't expect your measurements to exactly match the usage metered by your power utility. The number of KWH you consume is what the power company tells you that you use. Be careful..