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3.3. Power Consumption Measurement Devices
Table of Contents
Kill-a-watt and Harbor Freight, and others make devices in to $20 to $40 range for reading power from a single plugged-in device. These are useful for devices that are always on or easy to predict how long and how often they are used. Just type these values into a database. Most devices have intermittent or variable power consumption; you'll want a computer interface to track them.
Devices currently supported include the Energy Detective 5000 (TED5000) and the SMA Sunny Boy solar energy inverter.
The Energy Detective 5000 is a device for measuring energy consumption on an entire house via clamps over the power lines in your electrical circuit breaker panel and a networked web server interface. The measurements are fairly noisy in some installations (including mine) and can quit functioning for long periods of time. However it is relatively inexpensive and with improved software could become an affordable tool for answering questions like, why is my electric bill so large and what is on and when?
The most annoying anomaly of the TED5000 is its freezing updates. The Home Energy Explorer software detects this when none of the following six values changes: Total and MTU1 values for Voltage, power, and KVA. While unchanging values can be expected to occur normally on a simple house with very little noise, long stretches should not occur. The longest stretch of no updates I observed was about ten hours. The first thing I noticed about the freezes was they seem to be be time dependent occurring in the early morning and late afternoon. Then when I began to implement net metering calculation for my solar panels, I noticed the TED5000 froze up minutes after my solar inverter started up in the morning. By flipping breakers on and off, I further determined that the freezing only seemed to occurred when one particular breaker was on. This breaker goes to an older part of the house with old ungrounded outlets. I speculate that the solar inverter and the old wiring interact in some form of resonance that keeps the MTU and the gateway components of the TED5000 from communicating over the power line. I liked leaving that breaker off, but my wife complained that the front porch light and garage door opener quit working, so I need a new solution.
Another annoying TED5000 anomaly is occasional unbelievably large values. This is apparently a software bug where twelve bit values are interpreted as 32 bit values. Home Energy Explorer attempts to fix-up these values by discarding the extra noise bits and sometimes switching sign.
The SMA Sunny Boy solar energy inverter is one of the most commonly used solar energy inverters, but its computer interface was one of the most expensive when I bought mine. Later (and on-US) models have the RS-422 and Bluetooth interfaces built in. Other companies are providing the Sunny Boy with a built in blue-tooth adapter. The Web Box has been a reliable and flexible interface, showing a direction the TED5000 could grow.
Common installations of the TED5000 with solar energy production have the TED5000 reading not your houses electrical consumption, but the difference between electrical consumption and solar production. I would expect that a positive value would indicate net energy consumption while a negative value would indicate that more electrity is being produced than is being consumed. Unfortunately the current version of the TED500 does not have a sign, so its net metering value is ambiguous. Since what you generally want to know is how much electrity you consume, Home Energy Explorer tries to guess the correct sign. Sign values that would result in negative consumption or unreasonably large consumption are rejected. Since the sign would be expected to change once in the morning and once in the afternoon,Home Energy Explorer assumes electrical consumption is close to the previous value.
Watts up has several models for reading a plugged in device. Have Windows software for old Serial program it came with.
Smart Circuit 20 Ethernet network interface is wired into a breaker circuit. One of mine failed shortly after installation, the other has not been addressed yet due to its peculiar server (push) interface and that data captured over the USB interface is implausible.
$30 at swap meet, hundreds new.Per measurement point cost can be just over $1. Non-standard RS-232 interface (8 pin Ethernet type receptacle) (2.3.4.-Please-insert-brain-power-here) Reads current of each outlet. Can turn each outlet on and off.
$10 at swap meet, hundreds new. Non-standard RS-232 interface (8 pin Ethernet type receptacle) Reads current of entire plug bar. No outlet control. Undocumented temperature interface. (2.3.4.-Please-insert-brain-power-here)
Inexpensive about $10 (more for split core, less for solid) per circuit measured. Probably requires a custom circuit to read scaled AC current with a standard ADC (analog to digital converter) and 3.5.-micro-controllers. The interface circuit would likely include a diode to make the signal uni-polar, a capacitor to smooth the reading, and a resistor to measure the current across. See example device.