Standby Power

I saw a small blurb in my recent Kiplinger’s magazine about the waste of standby power from devices like TV’s, VCR’s and computers when they are not being used.  These devices consume a little bit of power when they are plugged in and off, and that adds up to quite a bit of wasted power when you consider that they are not being used most of the time.  There was mention of a device from Smart Home USA called the Smart Strip that cuts power off to devices that are not in use.

That made me wonder how much standby power my house is using and what the biggest consumers of it are.

I turned everything off all the lights in my house and went to my circuit breaker panel and measured the current on both incoming 120 V feeds to my house with a Tenma True RMS AC/DC Clamp Current meter.  Here’s the results.

left feed = 1.98 A
right feed = 1.59 A

Total current consumption = 3.57 A

At 120 V rms, the total power is 428.4 W rms.

Assuming that everything is off and not used an average of at least 15 hours per day (probably an under estimate), the total power used per day would be:

6426 W hr / day

Total power wasted per year would be:

2345.49 KW hr / year

At a cost of about 0.10 per KW hr, that would be a waste almost $235 per year.

Description	Standby Current Measured (A)	Standby Power
Total Standby for my House	3.57	428.4
Basement TV + DVD / VCR combo	0.29	34.8
Basement Computer (in standby) + Printer (Printer alone was 0.13 A)	0.143	17.16
Cable modem and router (with no network activity)	0.153	18.36
Living room TV	0.0119	1.43
Living room entertainment center (including cable box)	0.57	68.4
HDTV 1	0.02	2.4
Radon fan	0.414	49.68
Office Computer (in standby) + Printer	0.243	29.16
Office speaker amplifier (on but not being used) and external USB hard drive (off)	0.065	7.8
Aquarium	0.2	24
Garage door opener	0.035	4.2
Bedroom TV / VCR	0.094	11.28
Sunroom TV / DVD VCR Combo	0.146	17.52

(1) This is in low power mode.  The TV is a DLP and it takes longer to power on in lower power mode (20 s vs. 1 s).  In fast power on mode the TV has a standby power of 0.48 A or 57.6 W

The total standby power that I have accounted for is:

2.385 A
286.2 W

That leaves the following amount unaccounted for:

1.185 A
142.2 W

I’m a little surprised at how much I didn’t account for yet.  I believe some of it can be explained by various night lights and clocks that we have around the house, but the majority remains a mystery.  Larger items that I haven’t checked yet are the oven, microwave, furnace, water heater, washer, and dryer.  The next step of this project is to figure out how to reduce some of this standby power loss.

DC-DC Switching Converter Noise Performance

I’m not a power supply designer, but as a high speed digital design engineer the importance of the power supply is obvious.  Noisy power supplies translate into signal integrity problems.  There was an article in a recent EDN magazine discussing the different DC-DC converter topologies and their noise performance [1].  This is a good starting point reference for understanding DC-DC converter noise at the architecture level.  At least I can refer to this and ask intelligent questions of the power supply designers on my next design project or help influence the choice of DC-DC converter architecture for noise sensitive portions of the design.

[1] Marchetti, Robert. March 1, 2007. “Comparing DC-DC Converters’ Noise-Related Performance.” EDN Magazine.

NASA Master Clock

NASA is currently developing a new system for distributing timing reference information over long distances.  The new system will replace an older system called the Deep Space Network (DSN) frequency and timing subsystem (FTS).  The new system will be more modular, expandable, and easier to maintain.  The heart of the system is a master clock assembly (MCA) that creates time signals synchronized to a 100 MHz reference signal from an atomic frequency standard.  The MCA creates a timing signal called a system time code (STC) that is sent via fiber optic cable to a distribution assembly (DA).  The distribution assembly reconstitutes the signal and sends it either to another DA for additional fan out or to a time-code translator (TCT) also via fiber optic cable.  The TCT compensates for the delay in the signal from the MCA and creates time codes or pulse rates as required; the TCT is the interface to the end user of the timing signal and can be distributed as an electrical signal or optical signal as necessary at this point [1].  More information can be found in the Technical Support Package at www.techbriefs.com/tsp under the Electronics/Computers category.  I had trouble navigating to this information on the Tech Briefs web site, but was able to find it with a Google search of the article described in [1].

[1] NASA Jet Propulsion Laboratory. May 2007. “Master Clock and Time-Signal-Distribution System.” NASA Tech Briefs.

Signal Integrity Measurement

Making measurements is the most important skill for ensuring good signal integrity in digital systems.  Signal integrity measurements allow the engineer to build confidence in how the design is performing to ensure that it meets not only the functional requirements but is robust.  In addition to improving the quality of the present design, measurements help an engineer build insight into signal integrity and the affect of various aspects of the system on it.  This is the true value of making measurements.  Simulation tools are great, but unless you can get them to correlate well with real signals, they aren’t worth much.  The only way to know is to go and measure!  I would say that training for engineers in signal integrity analysis has improved greatly over the past 5 years.  There are always many articles presented about analysis techniques in trade magazines and at industry conferences and there are plenty of training seminars.  Training and information relating specifically to making and interpreting measurements is still lacking though.  I recently saw an article in Test & Measurement World magazine that supports my view about the importance of measurement [1].  It provides some insights into the types of measurements that signal integrity engineers at several companies are making and what equipment is needed.  The article is pretty high level though.

One example training seminar involving using TDR and VNA that is coming up is presented by Dr. Eric Bogatin (www.bethesignal.com) and is titled Signal Integrity Characterization Techniques.  Based on the description, this would be the perfect class for a digital engineer wanting to develop skills in signal integrity measurement.  I have not attended it yet though and it is only offered once a year.  I can’t go this year.  Maybe next year!

[1] Rowe, Martin. March 2007. “Offensive Channels.” Test & Measurement World. Vol 27 No. 2.

Fluorescent Light Bulb Experiment Part 8

I had the first fluorescent light bulb from this experiment series burn out.  It was the one installed in the basement craft area installed on 1/1/2006.  This was a GE 100 bulb with a guaranteed lifetime of 8000 hours.  The bulb only lasted an estimated 976 hours assuming 2 hours per day usage.  The total power savings of this bulb was only 33.18 kW hr for a monitary savings of about $3.32.  The savings hardly even covered the cost of the bulb!  Here is a table to track the bulbs that have burned out.

Light bulb location	Date installed	Light bulb type	Average hours per day	Power saved per year (kW hr)	Date burned out	Bulb power savings over Current Incandescent	Bulb Lifetime (Hours)	Estimated Total Power Saved (kW hr)	Total Estimated Money Saved ($)
Basement Light in Craft Area	1/1/2006	GE 100	2	24.82	5/4/2007	34	976	33.18	$3.32

 

I have replaced the bulb with a n:vision bulb with the following specifications:

n:vision 100
1600 Lumen light output
23 W
10,000 Hour guaranteed life

Current results of the experiment are summarized in the table on this page.

IPOD Electromagnetic Emissions

I purchased an IPOD charger from Ebay recently.  The charger plugs into an AC outlet and provides a USB connector that you can plug the USB cable that comes with the IPOD into.  The charger provides the 5V supply on the USB connector pins that the IPOD uses to charge its battery.  The charger also has a red LED to indicate if it is plugged in and a green LED to indicate if the IPOD is charging.  It is a very simply device.

Last weekend I was using the IPOD with it’s audio output line connected to the AUX input of a Milwaukee job site radio.  The battery was a little low, so I plugged the charger in as well, to the same outlet that the radio was plugged in to.  Everything was working fine.  I was working in the garage, when I realized that the NFL draft had started, so I switched the radio to an AM radio station.  There was nothing but static on a station that usually comes in very clear.  I tried some other stations, and there was only static.  Wondering what was wrong, I unplugged the IPOD charger from the wall and the static went away.  The ahaaah! moment.

I did some additional investigation tonight and here’s what I discovered.

• The static is not present when the IPOD is connected to the radio but not the charger and the charger is plugged in
• The static is not present when the IPOD is connected to the charger and the charger is plugged in but the IPOD is not connected to the radio
• The static is present, but less severe when the radio or charger is plugged in to the AC outlet of a battery powered inverter while the other is plugged into the house AC outlet and the IPOD is connected to radio
• FM stations are not completely swamped out by the static, although you can still hear it.

It seems clear that noise is conducting from the wall charger through the IPOD on the audio line to the radio.  There also must be some conducting through the power line or ground since it is worse when both are plugged into the same AC outlet.

I’m trying to determine what EMC standards if any apply to the IPOD with respect to conducted noise on its audio line.  Does anyone know?