NOTE: My original article was posted in 1999, and updated in 2001. According to the following link at the U.S Consumer Product Safety Commission, at least some of the PowerPlanner units have been recalled for safety reasons. The company, Coast Energy Management, is now out of business. The recall advises discarding or destroying the product. 1-24-06CPSC Recall Notice
Test of the Power Planner(R) Energy Conservation Gizmo
On a recent trip to Home Depot, I was faced with a prominent display of "Power Planner (R)" devices, with a claim of "NEW TECHNOLOGY HELPS YOU SAVE UP TO 35% ON ENERGY FOR HOUSEHOLD APPLIANCES". It is packaged in lots of green. They sell it for about $40. They also have larger versions for use on larger appliances such as central A/C systems.
The display has an unloaded induction motor running, and a meter that measures motor current. You can switch the Power Planner on and see a dramatic reduction in operating current. Unfortunately, as anyone with a knowledge of electrical circuits knows, this is a meaningless demonstration. See the appendix for more discussion.
I decided to buy the gizmo and try it out on my refrigerator, a late model KitchenAid with a high efficiency rating. I have monitored operation of the refrigerator for some period of time, and find that when it starts, it draws about 146 watts, decreasing to a steady state of about 130 watts. I measured the power using a Brand Electronics digital power meter. This instrument measures true power by measuring both the voltage and current, and multiplying their waveforms to determine the power waveform. Over a period of days, it estimated a monthly operating cost of about $2.80. (5-1-01 - this assumed $.08 per kwh, so the fridge uses about 35 kwh per month, or 1.17 kwh per day. At 130 watts when running, it must be running about 9 hours a day, or a third of the time).
Using the Power Planner, I can detect no difference in the power consumption of the refrigerator. Whatever the Power Planner is supposed to work on apparently doesn't exist with my refrigerator.
I decided to try it on my solar water heater, which has two pumps that together draw about 151 watts.
I plugged in the PowerPlanner and read 151 watts. Then a few seconds later I heard a change in the sound of the motors (more hum, which is funny, because the PowerPlanner literature asserts that it makes motors run more quitely), and suddenly read 147-148 watts. So, I suppose it works. It will save me about 2.3 percent. Assuming the water heater pumps run 8 hours a day, this amounts to 6.7 cents a month. It will take me about 50 years to pay back its $40 cost.
I have a box fan that I use in the garage. I tried PowerPlanner on the fan's low setting, at which it normally consumes 80 watts. The good news was that power dropped from 80 to 57 watts. The bad news was that fan speed decreased to the point where the fan moved very little air. This motor produced considerable humming sound when PowerPlanner was engaged.
I took the Power Planner over to a friend's house. He has a 19 year old Whirlpool refrigerator. I first took a baseline measurement, and determined that the refrigerator draws 264 watts when running. I plugged in the Power Planner, and, as with the pumps on my solar water heater, after a few seconds, the power dropped. In this case, the power dropped to about 242 watts, a reduction of about 8 percent. Not quite the 35 percent quoted on the package, but not bad. Assuming that this refrigerator uses about 3 times the energy, on average, of my new high-efficiency unit (I did not have the power meter attached long enough to obtain an actual measurement), the Power Planner might save about $0.70 per month. The payback time for the $40 investment would be less than 5 years. (5-1-01: note assumption of .08 per kwh. Some places in CA are apparently now paying $0.24 per kwh).
Paul Breaux, who owns an off-grid passive-solar house, borrowed the device to check out it's energy saving potential. He is particularly interested in saving energy, because all of his comes from a 2kW PV array. Here are some of his measurements.
Are there some applications for which it will work better? Even save the 35% that is printed on the package? I used the company's web page, technical support area, to relate my experience with the refrigerator, and asked how they would recommend predicting applications in which savings would be the most. Despite the web page's assurance that they always respond within 48 hours, I have had no response in the time since I submitted the query (about 3/24/99).
I thought about taking Power Planner back to Home Depot for a refund. Instead, I it will be fun to try it out in a variety of applications and see what it does. Results will be reported here.
Appendix: Power Measurement
Power delivered to a load is current times voltage, but in the case of AC, you have to consider the relative phase angles of the voltage and current, and toss in an additional "power factor" which is the cosine of this phase angle difference. An unloaded induction motor appears mainly as an inductive load. The current flowing through the inductor is not in phase with the current, so the relative current draw cannot be used as an indication of the power delivered to the motor.
Am I saying that the Power Planner doesn't work? No. I am saying that the demo at Home Depot is invalid. To show anything, they should have a true wattmeter, which will measure actual power being delivered to the motor, by doing arithmetic between the actual voltage and current waveforms.
Despite the fake demo, it seems possible that the Power Planner might work. Induction motors are known to have poor power factors, particularly when they are not operating under full load. The excess current in proportion to the actual power delivered is called the "reactive" current. This current flows through motor windings that have resistance, however, so the current will cause some current dissipation. It is also of concern to the power company, because it causes extra voltage drop in the power lines, because of their resistace.
The classical technique for improving power factor is to attach a capacitor in parallel with the induction motor. Whereas the current through an inductor lags the voltage, in a capacitor it leads the voltage. If the correct value is chosen out, the reactive currents of the capacitor and inductor cancel each other out. This makes the power company happy, but does nothing for the motor.
Still, a lightly-loaded induction motor wastes a certain amount of heat in its windings,due to the reactive current. It seems quite possible that by fiddling with the waveform, they can reduce the loss.
An article in the January 1996 issue of Circuit Cellar Ink described a device that sounds like the PowerPlanner. It was based on a device designed by Microchip, Inc., designated the MTE1122. Microchip does not currently market this device, and I wonder if the design was bought by the PowerPlanner folks.
The basis of the circuit is that an induction motor that is not fully loaded can have it's applied voltage reduced somewhat without significantly reducing motor performance.
The author cites measurements of a washing machine (savings 9% to 45%) and an Air Conditioner fan (savings of 4% to 10%). His conclusion is that the device will be worthwhile in some cases. In particular, it stands the best chance of paying for itself on motors that are lightly loaded and that have a high duty cycle.
I am suddenly receiving quite a bit of mail in response to this article. I suspect that a lot of Californians are getting serious about energy conservation, in response to recent electricity problems.
I have done no new tests on the unit after the original ones. But, I will note here any interesting responses that I receive.
How to Read Your Power Meter
Anyone can read the little dials on the meter to determine kwh. But, it is also possible to get much finer scale measurements using it, by watching the rate at which the little wheel spins. If you look at the meter, you will see "Kh" followed by a number. This number is the number of watt hours that a single revolution of the wheel represents. Mine says "Kh 7.2".
To measure the power being consumed at any time in your house, measure the time, in seconds, that it takes for the wheel to go around once. Then calculate
Kh (watt hours/rev) x 3600 (sec/hr) / time_per_rev (sec)
to get watts. For example, if Kh is 7.2, and it takes 14 seconds for the wheel to spin, you are using 1851 watts. To measure very low power levels, you can count multiple revolutions and adjust your results accordingly.
If you want to measure power reduction in using the Power Planner, do this experiment with and without the Power Planner in the circuit, and compare the results. In general, by carefully switching appliances on and off in the house and noting the difference, you can measure actual power consumption of individual appliances.
I found a web page by Sean Adams describing how he made an automatic meter reader.
If you wish to contact me...