Author: scruss

NB: this is in the  early stages of development, but does work. It’s by no means a plug-and-play solution. You’re going to have to do some coding, and perhaps some soldering. Undaunted? Read on …

I really like the Blue Line Innovations PowerCost Monitorâ„¢ (aka the Black & Decker Power Monitor EM100B). I bought one long before the OPA started to give them away free to Ontario households as part of their peaksaver PLUS program. It’s a little device that clamps to your hydro meter and sends instantaneous power readings to a display.

Wouldn’t it be so much better if you could log and analyze these data? So a day’s power consumption might graph to something like this:

Yup, this is my real electricity consumption, as logged from the PowerCost Monitor. You can see the fridge cycling on and off, and I think the big mid-day spike was either the AC or the dryer; someone was home on that Monday. The rather blocky green line is Toronto Hydro’s hourly smart meter data. It really hasn’t got the resolution to show really detailed power use.

That spike at 06:30; what’s that? Let’s take a look:

That’s me boiling the kettle. You can see that the time resolution is better than a minute, and the power is to the watt. Mmm, coffee …

All of this is recorded using a simple Arduino-based solution, originally cooked up by Bryan Mayland. I’ve forked his code and added some instructions: scruss/Powermon433. Here’s the rig I’ve been using to log data over a USB serial link:

That’s a particularly ugly rig, due to the limitations of the 3.3 V receiver board I was using. There are other options that work with more normal Arduino boards up on github.

Here’s a sample of the data I’m logging, including the kettle incident:

Datetime	Elapsed_s	Energy_Wh	Power_W	Temp_C
2014-09-29T06:27:44	23241.7	25876	289	15
2014-09-29T06:28:16	23273.6	25876	290	15
2014-09-29T06:28:48	23305.5	25876	291	15
2014-09-29T06:29:20	23337.4	25892	294	15
2014-09-29T06:29:52	23369.2	25892	286	15
2014-09-29T06:30:24	23401.1	25892	277	15
2014-09-29T06:30:56	23433.0	25892	357	15
2014-09-29T06:31:28	23464.9	25892	1844	15
2014-09-29T06:32:00	23496.8	25892	1836	15
2014-09-29T06:32:31	23528.5	25952	1829	15
2014-09-29T06:33:03	23560.2	25952	1818	15
2014-09-29T06:33:35	23592.1	25952	1836	15
2014-09-29T06:34:07	23624.0	25952	1836	15
2014-09-29T06:34:39	23655.8	25952	1836	15
2014-09-29T06:35:11	23687.7	25952	1848	15
2014-09-29T06:35:43	23719.6	26048	1832	15
2014-09-29T06:36:15	23751.5	26048	2000	15
2014-09-29T06:36:46	23783.4	26048	2000	15
2014-09-29T06:37:18	23815.2	26048	2000	15
2014-09-29T06:37:50	23846.9	26048	368	15

You’ll see that I’m recording:

• a system timestamp
• the elapsed logging time, from the Arduino’s clock
• instantaneous meter readings in watt-hours. Note that not every row has an update
• the average power since the last record. The product of this and the time between records adds up to the energy consumption
• the outside temperature in °C. This is not very accurate (in full sun it over-reads vastly) but better than nothing.

Compare that to the smart meter data:

DateTime	Hour	KwhUsage	Cost	Rate
2014-09-29 05:00:00	5	0.29	$0.02	$0.075
2014-09-29 06:00:00	6	0.31	$0.02	$0.075
2014-09-29 07:00:00	7	0.59	$0.04	$0.075

Not much data there, is there? Certainly not enough resolution to tell if a kettle has been running.

Even though this interface is homebrew and cheap, it is accurate. Here’s how four days of continuous readings stack up against Toronto Hydro’s meter:

Â	Power Monitor				ndToronto Hydro Smart Meter
Day	First Reading / Wh	Last Reading / Wh	Total Consumption / kWh	No of readings	Daily Total / kWh	No of readings
2014-09-29	23896	43668	19.772	2711	19.77	24
2014-09-30	43668	52500	8.832	2710	8.82	24
2014-10-01	52500	68004	15.504	2711	15.51	24
2014-10-02	68004	81996	13.992	2712	13.99	24

The difference looks to me like aliasing; THES’s reporting is much more granular.

I’m going to develop this further to turn it into an easy (or at least, easier) to use logging platform. It’s taken us a few years to get here, but there’s nothing quite like a project finally working!