Fun with Watts up

In keeping with the "energy saving" theme of the first posts, here's another gadget to help you keep on top of your energy use, this time we'll focus on electricity use.

Ever wonder how much running that PC all the time is costing you? How about that window air conditioner in the summer. Is my refrigerator running efficiently? The Watts up? power analyzer measures the power consumed by just about any device that you can plug into it. It can keep a running log measuring power in watts, line voltage and current and power factor. If you tell it what your electric rates are, it will tell you how much that device is costing you. A free software package available at the website puts this data in graphical form. If you purchase the upgraded software you can do long term real-time logging with one data point per second speed, instead of being limited to the 1000 data points in the Watts up? memory.

Let's try some (un)common household items and see how much power they use. Here's a standard 32" flatscreen CRT TV. (Just click on the graphs that follow to see a larger version)



Nothing out the ordinary here, fairly constant at about 90-100 watts. One of the features of the Watts up, is even though the best logging rate you can get is once per second, it actually measures much faster than that and will store instantaneous maximums. So let's turn on the max watts trace on the graph.



Yikes! The spike in the beginning is so large, the scale of the graph has been changed. Why the spike? I have a feeling in a couple of years, when most every set will be either plasma, LCD or DLP, people won't remember the "thump" their TV made when it was turned on. A coil of wire is wound around the CRT inside the set, which is energized momentarily when the set is turned on, to demagnetize the CRT. Your CRT computer monitor's "degauss" function is the same thing. One problem with this particular model set is that this degaussing circuit was not well designed, and eventually it would fail and the set's fuse would blow. We're talking a surge in the range of 10 Amps here, and the set's fuse is only 6 Amps. Mine's already blown once, but we don't use the set any more.

Here's a chart for our replacement 32" LCD set.

The set was only running for a few minutes so you see the vertical bar. Notice the power draw is constant around 115 watts. The power consumption of a CRT based set will vary as you saw in the above chart as it draws more power for brighter scenes, where an LCD set has a backlight that has a constant brightness.

Let's try some household appliances. How about a coffee maker.


This is a Cuisinart Grind-n-Brew, where it grinds the coffee beans for you then brews the pot. In the beginning you can see the short time where it's grinding the coffee, drawing about 100 watts. Then you see much more power consumption as the heater turns on to brew the coffee. When the coffee is done, the heater is only turned on once in a while to keep the pot warm.

Here's a typical front-loading washing machine.



Front-loading washing machines are very energy efficient, not only because they use very little water, but instead of the motor constantly turning an agitator, the drum only rocks back and forth. You can see each individual spike during the wash and rinse cycles where the drum rotates in one direction, stops, then rotates in the other direction. Where the spikes are not as pronounced you can see where the water is being pumped from the washer. At 12:35 on the graph you see the point in the rinse cycle where the drum is continually spinning. At 12:45 the washer is in the spin cycle and you can see the power draw increase as the spin speed increases. The largest spike is a very high speed spin that only lasts a few seconds, then at the very end you get a gentle rocking motion to free the clothes from the side of the drum. Since the Watts up knows how much my electricity costs, lets see the graph.


From this I can tell that it cost just about a penny's worth of electricity to do that load. Unfortunately, I don't have access to an older type washer to do a comparison, but I can assure you it would be using much more power.

Let's go back to the fun & games and measure an XBox360.



I expanded the vertical "power" scale of the graph a bit here. For the first 4 hours, I was playing "Test Drive Unlimited" so you can see the power vary as processing needs vary. For the next 4 hours, I downloaded a game demo through XBox Live and from then on the XBox was idling. So it was drawing 135 watts even when doing "nothing". How much did that cost me?



Hmmm About 5 cents to play the game, another 4 cents to download the demo and a bit more than 5 cents of wasted power. Maybe Microsoft could add a patch that shuts the unit down when a download is finished?

Now we go back in time, to when radios had little glowing glass bottles in them and you had to wait for them to "warm up". This is a Philco 8 tube 9-band shortwave table set from 1953.



Notice that over about 3 hours the power consumption rises from 75 to 95 watts. The first thing to consider is that it takes 25 watts just to run the heaters of those 8 tubes. I guess that 25 watts of heat comes in handy in the winter. These radios certainly weren't designed to "Energy Star" standards.

I'm not really sure yet why this is happening. Possibly as the radio warms up something is drifting off and causing the extra power drain. For all I know this could be normal. First thing would be to run the set with the back off and see if it still drifts. In any event, if I were to use this set daily, I'd do a restoration (replace all capacitors and check everything else) before I trust to leave it unattended.

I'll have more graphs from other appliances in future posts.

Scangauge update

I've used the Scangauge in my Honda for the past 9 months and now have a pretty good idea of what's the best economy I can expect on my commutes. I was able to extend my range to just a little over 600 miles (35 mpg) by holding right to the speed limits. Before I started using the Scangauge, the best I could do was 550 miles. My goal was to be able to get one week's worth of commuting (about 480 miles) for a tankfull. The commute in was always better than the commute home, but not by much (36 in - 34 out).

As the weather got colder, the mileage noticeably decreased, starting to drop as the temperature dropped below 40. With average temperatures routinely in the 20's during the day and in the low teens at night my best round trip mileage is now around 30.

We had a 2007 Ford Explorer 4x4 for about a week while my wife's car was being repaired, so I put the Scangauge on that, just to see how bad it was. I was pleasantly surprised when cruising on the highway, it settled on a constant 25-26mpg, which is on a par with my wife's PT Cruiser. It helps that it had a 5-speed automatic, so the big V-8 is just loafing along at highway speeds. But as soon as you were off the interstate, you started paying the price for moving that hulk around. I couldn't do any better than 17mpg. I never got to do a day's commute with it, but I could see it averaging a little over 20.

Watch your gas mileage

The first Plymouth Voyager I purchased in 1991 had a nifty car computer that gave you a running tally of fuel economy, instantaneous and averaged over the current tankful, and an estimate of miles left to go before you had to fill up. By the time I was ready to replace that Voyager, Chrysler Corp. was setting you up so that if you wanted the nice options you had to either go to Dodge or Chrysler. I liked my dealer so Dodge was out, and the Chryslers were too expensive so I reluctantly had to give up my car computer.

Since 1996, just about all cars sold in the U.S. were required to have an On Board Diagnostics II computer, which would essentially determine if you were going to pass your vehicle emissions inspection. This computer keeps track of such things as your rate of fuel use (hmmmm), speed (hmmmm), coolant temperature, ignition timing and anything else pertaining to the emissions control of the vehicle. Numerous third parties have sprung up offering interfaces to the OBDII computer that a consumer can use, that can either save data or show the information on a computer (PC, mobile PC or Palm) screen or a custom display.

I finally got myself a Scangauge II which gave me back all the things I had with that Voyager car computer (except the compass) and much more. It's like three devices in one. The first screen lets you determine if there are any emissions control issues that will cause you to fail your inspection, so you can get them attended to before you actually take the test. The second screen allows you to select 4 values for continuous display, including battery voltage, current MPG, coolant temperature, manifold pressure, speed, a calculation of engine load and throttle setting. The third screen is your trip computer, which keeps track of cumulative fuel mileage for your current trip or your current tankful, how far you have left on your current tankful, the maximum coolant temperature during that time and distance traveled.

The first thing I did was attach it to my wife's PT Cruiser, which I always suspected of having lousy fuel economy but could never prove it because I couldn't drive it far enough to get a reasonable result. My commute consists of the first half on secondary roads with slightly rolling hills then the rest on interstates like I95/128 (55mph limit) and I93 (65mph limit). I held to the speed limit with cruise control and otherwise tried to drive as lightly as I could (no problem at midnight there's no other traffic to upset by my driving that way) and managed a 30mpg total for the 95 mile round trip. Not as bad as I suspected. I feel part of the problem is because there's only a 12 gallon tank there's an illusion of bad economy as fillups are frequent.

The past few days I put the Scangauge in my 4 cyl manual transmission Honda Accord. I know that if I drive fairly conservatively I can get 1 week out of one tank (about 500 miles). I've always averaged around 31-33 mpg with the car on this commute so I wanted to see how the gauge corresponded to that. Sure enough, the first day I averaged about 33mpg keeping to the speed limit and using cruise control. Good. Yesterday I filled the tank just before I got to work and set the trip computer, then really went to town on the way home to stretch as much as I could - coasting to traffic lights and slowing on the hills, again there was no other traffic to contend with after midnight. I managed 35mpg for the commute home. I'm going to finish this tank trying to conserve as much as possible, then do the next one driving to keep more with traffic and I'll see how much difference it makes.

One thing I noticed that it appears that the engine load is reported differently in the two cars. The Scangauge manual does state that the number may reflect either the percentage of total power available or the amount available at that particular engine speed. It looks like the PT Cruiser reports percentage of total power (around 15 - 25%) while the Honda reports power at RPM since I got readings regularly in the 70% range.