Wesley's Tool-Box

Lots of companies are hopping on the wave of Internet of Things (IoT) these days, each trying to build an ecosystem of their own. Major Korean mobile carriers (SK Telecom(SKT), KT, and LGU+) are no different, each setting up proprietary efforts. I used to largely ignore them because they required monthly fee, ranging from a few dollars per device to tens of dollars for "unlimited" (discounted with multi-year contract). With many non-carrier solutions usable without fees, I felt this to be undesirable.

However, SKT must have felt that this arrangement was hurting their chances for wide acceptance, because it began offering some of their affiliated products free of monthly fees, charging only a nominal (KRW 5,500, US$4.80) one-time fee included in the sales price since last October. I decided to take the bait and started integrating their home IoT products, sold under the "SKT Smart Home" brand, into my house. The very first one was a smart plug. The one you see here is the one made by Witty.


Over time, I installed several of these plugs around the house and some of them came from another company, Dawon DNS. Because SKT was selling them, lots of things were made to be nearly identical, namely the packaging and the functionality. The frugal-looking brown paper boxes contain the plug and the instruction manuals, all of which look almost exactly the same except for the diagram of the plug. Both companies' plugs are controlled by the one and the same official app, and works largely like as if they are the same product.

Even the price is similar, at around $22.50 to $26, which makes them one of the most inexpensive options. This includes the aforementioned fee, so the pricing is rather aggressive. The deal is made even sweeter by the fact that the plugs do not need any gateways or hubs to operate as some other solutions do (namely that of other carriers'). It will interface directly via Wi-Fi, so if you already have a wireless router at home there's no additional cost involved.

It's been about five months since I installed Seojun Smart Meter at home and took various measures to cut down unnecessary electricity use. Now was a good time to see if the smart meter was recording monthly data accurately, and whether my efforts panned out well. This graph sums up everything that needs to be said.

In terms of accuracy, the smart meter consistently reported slightly lower than the default meter installed in the premise. However, it is more less in line with the advertised margin of error (1%) after the initial month and thus I think it's reliable. This is important because the companion app effectively shows last month's finalized data a full month before it shows up in the bill, and the app also shows the forecast for this month. Now I know that these values can be trusted and I can prepare two months ahead.

Moving onto the consumption trends, my home generally spent around 190 to 200kWh in winter, then fell down to the 170kWh range in spring if the family didn't go out on a vacation. This is already somewhat below average for a 4-person family, but I started making the house even less wasteful starting in February this year by making more efficient use of the appliances and changing the lightings and bulbs to LED. Eventually, it has settled to somewhere between 140 to 150kWh per month now. This is a saving of roughly 30kWh, or more than 15%.

Thanks to this and being much more aware of the consumption in real time, I'm expecting about 30% savings in electricity costs in the summer when the air conditioning is in full operation. Home electricity rates in Korea is pseudo-exponential, so you pay a lot less for seasonal increase if you start out from a lower baseline. Recently, I helped my dad cut down power use at his house by lowering the baseline by roughly 200kWh and I think it'll save him at least US$300 per month during summer. I'm expecting that the money that went into the streamlining will pay for itself in 3 years. Overall, I'm satisfied with the results of the efforts I put in.

As the hunt for even more potential waste of power continued, I brought in the help of thermal imaging technology. By scanning each place with a thermographic camera attached to an iPhone (FLIR One; I'll write about this later) I can find any hot or cold spots that seem to be out of place.

One of such "hot" spots I found was on the side of an air conditioning unit. It wasn't being used, but standby power drawn from the wall outlet was slightly heating up the control circuit and was readily visible via thermal images. I could just pull the plug until summer, but I decided to take a step further.


I replaced the default wall outlet with the one that had an integrated switch. This way, I could cut the power from the outlet with a switch when the air conditioner isn't in use, instead of having to pull the plug. Not only would this be simple to operate, it would avoid the mechanical wear. I should have done this ages ago.

As part of my ongoing data collection, I then tried to measure how much power the air conditioners in the house would consume while trying to cool the house. Sadly, the rooms were not hot enough for them to start cooling the air. I'll have to check them out again when summer comes.

As it is the case with the houses these days, there are lots of electronic devices littered throughout my home, plugged into wall outlets and USB ports. Measuring how much power these consume in their active and idle states would provide a good starting point in how to cut off unnecessary use of electricity. So that's exactly what I did over several days, and the results from the living room and computer/network equipment are now in. I'll be looking at other appliances as chances allow later on.

I tabulated the full results at the end of this post. But first, I'll talk about some interesting observations worth mentioning.

1. Beware of Light-Embedded Switches on the Power Strips

The lights on the switches of the power strips consume as much power as the devices capable of efficient standby - about 0.2 to 0.25W. This seems excessive for an LED, so I did a bit of searching. It turns out that most of these switches use neon lamps because the operating voltage is around 90V, making it relatively easy to integrate into 220V power using a simple resistor. With a nominal operating current of 1mA, the whole neon lamp + resistor assembly would consume 0.22W = 220V x 1mA.

LEDs, on the other hand, operate around 2 to 3V at 15 to 20mA, being about twice as efficient (neon: 90V x 1mA = 90mW, LED: 3V x 15mA = 45mW). But if you use a resistor to meet the voltage requirement, it would end up wasting much more energy (neon: 130V x 1mA = 130mW, LED: 217V x 15mA = 3,255mW). So you need a power converter instead, but they are neither as cheap or small as a tiny resistor. It's easy to see why neon lamps won out.

If your goal is to waste as little as possible, you would need to avoid having these lights on all the time. If six of these switches are always on, it would equate to about 1.3W, or about 1kWh per month of wasted energy. This is something to keep in mind when choosing a power strip for use in a room. If most of the stuff are used all the time or the standby power is low, it would be better to use a simpler power strip.


2. Fully Charged Devices Still Leech Power

There are lots of handheld devices out there, and many of them are conveniently charged when placed on a dock. The problem is that even when the device is finished charging, the charging circuit still draws some power to keep the battery topped off.

For one thing, my electric shaver was found to be sitting idle and sipping nearly 1W for several hours even after being fully charged. Considering that it only takes a few minutes at most to get back to full after a shaving session, this seems to be an unneeded waste. I've changed my usage pattern so that I charge the shaver once every other week or so, and cut the power to the charger once I see that it's done its job.

Then there's the Motoroi smartphone that I've been keeping around its vertical dock as a desktop clock for about five years ever since it was no longer my main phone. The measurement showed that, even though it's kept fully charged, it was drawing about 1.2W from the USB hub all the time because the screen was always on. Like the power strip lights, this is enough to affect the last digit of my monthly electricity usage. So I decided to retire the old phone and replace it with a normal digital clock.

Similar to what was going on with Motoroi and the shaver, smartphones plugged into the dock were also found to sip a bit of power after a full charge. Unplugging it after charging seems to be the "smart" thing to do.