On Thursday I published this post on the Black and Decker power monitor:

Stuff that actually works #1 – The Black & Decker Power Monitor

In that post I talked about the “300 watt mystery”:

Then there is a funny thing we haven’t resolved yet. When we turn off everything that is obvious (lights, electronics, TVs, laptops, etc.) and go to bed, the house is still consuming 300 watts. I figured it was the combination of the cable modem/router/Vonage box/cordless phone base – stuff that is on all the time. But I unplugged all that and it has no effect. The power consumption of those devices is so small it does not even show up on the meter. So where is the 300 watts going? The kids and I will try to figure it out this weekend. I’ll add a comment when we discover it.

You might wonder why I care. It’s because 300 watts works out to about a dollar a day, or $365 per year. If we can stop that 300 watt leak, it means we can spend $365 on something else.

So the kids and I did investigate this weekend. It wasn’t nearly as easy as I thought it would be.

The first thing we did was we went around and unplugged everything obvious. That meant alarm clocks, wall warts, etc. We also unplugged the refrigerator and freezer so they would not kick in and mess up the meter. The meter still showed 0.3 KW, or 300 watts. [that is the best that the meter's resolution gets]

Then we went to the circuit breaker panel and cut off everything that might be draining power. That included the furnaces (and therefore their thermostats), the garage door openers (they have radio receivers that are on all the time), the irrigation system and the microwave oven. Still 300 watts.

Then we started killing off the power to the rest of the house room by room. It turns out that if your resolution is only in 100 watt increments, this is not a very good technique. No single room really registers anything. Still 300 watts.

So we investigated harder. We realized that in the guest bedroom there is a CRT TV, an old Xbox, a VCR and a switching box. They are all off all the time, but could there be some standby power being lost here?

There are boxes you can buy where you can plug in appliances and get an accurate watt reading. But I went to Lowe’s and Wal-mart and could not find one. So I took an old extension cord, clipped the hot wire and connected my digital volt/amp meter into the circuit to measure amperage. I then plugged a bedside lamp into the extension cord and turned on its 13 watt fluorescent bulb. The ammeter measured 0.110 amps, and:

120 volts * 0.110 amps = 13.2 watts

So it is accurate. I tried out a couple of obvious things:

- My laptop: 0.40 amps, so 48 watts when running, battery is full
- Leigh’s laptop (newer laptop, bigger screen): 0.65 amps, so 78 watts
- Leigh’s cell phone wall wart (standby): 0.0008 amps, or 0.01 watts
- Leigh’s cell phone wall wart (charging): 0.015 amps, or 1.8 watts
- LED nightlight: 0.011 amps, or 1.3 watts

All of this seems kosher. So we took the ammeter into the guest bedroom and around the rest of the house. Here is what we noticed:

1) Standby power for the TV, etc. in the guest bedroom is 0.140 amps or 16.8 watts. So we put a power strip in there and turned it all off since no one is using it.

2) We found a 15 watt (fluorescent) bulb in one of the attic spaces that had been left on, so we turned it off (the twins have access doors to two attic spaces from their room. Apparently they have been exploring).

3) The humidifier, when it is turned off, has a display that shows the current humidity and the water level. It uses 0.131 amps or 16 watts. Humidifier season is over, so we put it in the garage.

4) The laser printer doing nothing: 0.034 amps or 4 watts. We now turn it off unless we are printing.

5) We also put the “main” TV, which has a Wii and a DVD player connected to it, on a power strip and the kids turn the power strip off at night. That saves another 20 watts.

So those 5 items add up to 72 watts. Our B&D power meter now thinks the house is burning 0.2 kW or 200 watts at night (assuming neither the refrigerator or freezer or furnaces are running) as the home’s base power consumption.

So where is the other 200 watts going? Here is my best guess:

- Equipment that is always on: Cable modem, router, Vonage box, cordless phone base and the UPS that backs it all up. It uses 0.31 amps or 37 watts.
- The security system: 0.15 amps or 18 watts
- The refrigerator: 0.08 amps or 10 watts standby power (for LED display, etc.)
- Nightlights: 10 watts
- Aquarium: 10 watts
- Various devices in recharge mode (cordless phones, cell phones, iPods, etc.): ?
- My desktop computer along with laptops in sleep/standby mode: ?
- Alarm clocks: ?
- Carbon monoxide and smoke detectors: ?
- Furnaces and thermostats: ?
- Microwave oven: ?
- Garage door openers: ?
- Irrigation system: ?
- Sump pumps: ?
- Other: ?

The problem with things like garage door openers, furnaces, smoke detectors and the microwave is that they are hard wired. I can’t simply plug them into my ammeter and see what they draw. I would have to unwire them and hook them up to test them. The things like alarm clocks and laptops I simply haven’t had the time to test yet.

All of that investigation yielded a 72 watt savings. That’s about 20 cents a day, or $73 per year. I had hoped for more, but it is better than nothing. It looks like our house is going to burn ~200 watts all the time.