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Measuring Current & Voltage in a Pure Sine Wave Inverter System

June 19, 2014

Home Depot Smart Home

Building a “Green” house these days may actually include something other than providing a humid glass room with rows of vegetables and flowers. The “Home Depot Smart Home” in Durham, NC is an example of how technology can be refined with the goal of saving energy and working towards advancing sustainable living.

The DC to AC inverter in this home and other designs similar to it, utilize the effects of the sun’s energy to power household loads which cuts down on the ever-increasing demand from the grid source.

Inverter drawing and reference

(Note: Drawing of system is for reference only, and does not include outage safety detection/disconnect switching or represent any actual system).


The incoming DC current side of these types of inverters can be monitored with several types of sensors from Ohio Semitronics, Inc. In Durham the CTLP-025 is recommended due to its small size and low current range. Running 2 amp-turns through the sensor window provides a scaling of 0-12.5Adc to equal 4-20mAdc output.

Using panel meter model OFM811-221 and precision 500 ohm resistor, we are able to convert 4-20mAdc to 2-10Vdc and scale the OFM meter for 0-12.5Adc displayed using it’s zero and span adjustments. The OFM also provides the loop power 24Vdc needed to power the CTLP-025.

The DC voltage developed from the incoming panel array is wired directly to the LED display meter part number FC101-650 and scaled for 0-600Vdc.


Measuring the AC side of the inverter uses watt-hour meter model ESP3-354EDM-N. Wiring in single phase mode, the ESP required 1 current transformer SCCT-013-200. This ESP3 is primarily used for totalizing and displaying kilowatt-hour usage. It also loops through and displays AC volts, amps, watts and power factor. It has an auxiliary solid state relay output running at 1 kWh per pulse and additional RS485 connection for running into a PC/software.



FC101-650 reading 286.3Vdc from the array input.

OFM811-221 at bottom left reading 1.51Adc from array input.

CTLP-025 (hidden).

ESP3-354EDM-N for AC side shown at bottom right.

Photos reproduced with permission of Duke University.