Electronic Design

Bob's Mailbox

Dear Bob:
I have two points to make here.

One: You are absolutely right about spreadsheets telling lies or extrapolating false information. There've been several times I've used a calculator to check values only to find formulae in error. Spreadsheets are great for displaying historical financial data, but when we use them to predict the future, we're in very deep trouble. Perhaps that's why we're in such a mess regarding the national debt.

Two: Tantalum capacitors in audio. Enclosed are data I ran after reading your article. My business is professional audio. I don't believe what I can't measure, but with tantalums the problems are pretty apparent.

Tweakish, molecular audio types are a real cash cow for consumer manufacturers. Fortunately, in the broadcast and recording field there are far fewer tweak heads requesting exotic wire. Keeping product on the air or the client working is the order of the day.

However, the distortion produced by capacitors and op amps is significant when you consider the hundreds in the signal path from microphone, console, recorder, mixer, CD master, CD player, etc. The average solid-state-logic brand recording console contains about 1500 NE5534's!

Mr. Kirkwood's curves show that if you let a tantalum capacitor get biased as much as 0.1 Vdc the wrong way, significant distortion can occur, both harmonic and intermodulation. This can occur with a signal as small as 2 V pk-pk at 20 Hz into a 10 µ\\]F-10kΩ high-pass network. You can avoid this distortion by applying a good dc bias to the tantalum capacitor. Or you can use an aluminum electrolytic, which gives less distortion in the same circuit.—Ed.
Wayne Kirkwood, dba Media Technology Dallas, Texas

I agree. If you know where to look, the errors are not unmeasurable.—RAP

Dear Bob:
After surviving a myriad of hiking and canoeing trips, it has become clear that a short checklist is best. This is especially true for "lug-it-yourself" trips in harsh terrain that last a week or two. Having said that, here are some unusual things from my two lists.

Do bring:

1) a Tyvek clean-room suit and booties for evening relaxation. These are great for mutant-mosquito infested areas like Alaska, Canada, or the Everglades; and they're also good as windbreakers. Don't forget netting headgear and some mosquito impermeable gloves (you won't need repellent).

2) two 3-ft.-long, 1/4-in.-diameter aluminum rods when hiking in desert areas. These can be attached with duct tape to your backpack frame and used as a shade support (bend to suit). Put that flap normally used for pack rain protection to good use and don't cook your head under a hat!

DON'T bring:

1) a Nerf football where marmots may be indigenous. They enjoy converting them into nesting material and aren't very concerned with the environmental impact of man-made material strewn everywhere. (They will also steal one smelly sneaker but invariably leave you the other one.)

2) more than five kohlrabi for personal consumption. Although they have a waxy skin that makes them last forever, you will get sick of them. I have placed kohlrabi out in the open at night but nothing seems to want to eat them. Put a kohlrabi in each sneaker and you may have an excellent repellent, but I won't guarantee it.

I'm also considering using the hollow space in the tubes of my backpack frame for regular or rechargeable batteries (perhaps with a small solar cell array for recharging?). You could power-up all sorts of accessories like a low wattage lamp, a radio, or an animal intrusion alarm. Oh, by the way, also bring several engineers on your trip and you should have everything necessary for fun and survival!
Peter H. Sahm, Sr. Member of Technical Staff Comlinear Corp. Urbana, Ill.

Mr. Sahm: You say you prefer short lists? At least my list avoids Nerf footballs and kohlrabi: For Nicad recharging ideas, wait a couple months.—sRAP

Dear Bob:
In response to your article, "What's All This Incandescent Stuff, Anyhow?," I am sending you a copy of the Engineering Specs from the Sylvania Miniature Lighting products handbook and catalogue. I have guarded this closely because of its contents which include: Theory of Radiation, Theory of Vision, Standards & Nomenclature, and Properties of Tungsten Filament Lamps. I have found this book very enlightening.

You have previously talked about measuring amplifiers and wanting to know how much "funny" they measured when they said their measurements looked "funny."

In your article, you said if you take a 115-V bulb and run it at 125 V your brightness is way up and the bulb life is way down. You also said that if you put a rectifier in series with the bulb, the bulb life is extended enormously.

In the catalogue, the nomograph on page 12 and the graph on page 15 show how much way up and way down and how much enormously.

For example, if you increase the voltage 20%, the current increases 10%, the candlepower increases to 190% (almost double), and the life expectancy goes down to about 12%. Likewise, if you reduce the voltage to 65%, the current drops to 78%, the candlepower drops to 23%, and the life expectancy goes to about 180 times the normal life of the bulb.

If you take this one step further and reduce the voltage to 50%, the current goes to 68%, the candlepower goes to about 9%, and the life expectancy goes to about 4000 times the normal life of the bulb. You might make a good hand warmer with this, but its reduced to the brightness of a night light.

You can carry bulb saving to extreme. How well can you see in the dark?

I guess we'll have to go back to candles. You can adjust the brightness of the candle by the size of the wick, the thickness of the candle, type of wax, put a little smoke on the inside of the mantle, etc.

As you said, you have to do a little analysis on what you want to trade off for efficiency.

I've always looked forward to your articles that involve a little critical thinking instead of accepting opinions or assumptions as facts. Keep up the good work.

p.s. The price on the current limiters from Digikey have gone up to $1.45 in quantities of ten.
D. Leon Dison, Communications Engineer Radio Communications Bureau

At V = 50%, the GE book predicts 18% candlepower rather than 9%. That's quite dim, but the eye can handle many octaves of range.—RAP

Dear Bob:
I thoroughly enjoy your columns in Electronic Design. They get down to the bare facts and expand the use of engineering knowledge from the dry, esoteric stuff to stuff that can be used in everyday life. And they are fun to read.

In any case, I'm writing with regard to your column that appeared in the December 17, 1992 issue of Electronic Design concerning light bulbs. One issue I haven't seen addressed in utility-company propaganda that promotes the use of fluorescent-light-bulb replacements is the toll taken by turning the bulbs on and off. While it makes sense to use these bulbs in applications where the bulbs are not switched often, it seems that frequent switching will kill these expensive bulbs all too quickly in normal day-to-day use in a home.

So while we might be saving a few megawatts by not wasting energy in the form of heat, we'll be filling up the landfills with phosphorous and mercury (not to mention spending lots of money) replacing these efficient bulbs. I haven't seen any data correlating the frequency of switching to the decrease in bulb life. Nothing is simple anymore. Any ideas?

Also, thanks for the explanation about the Capsylite bulbs. I used one in a reading lamp but was very annoyed by a slight flickering out of the side of my eye. Now I realize that the half wave rectifier you mentioned was responsible.
Gregory L. Tuai, Seattle, Wash.

Your mother told you, don't turn off the light if you are going to be out of the room for only a short time. Your mother was right. For an incandescent lamp, "a short time" is 0.1 second. For a fluorescent, it's 3 minutes, because the start up has a definite wear-out mechanism. If you turn on a fluorescent lamp 3 minutes, 20 times a day, life would drop from 10,000 hours (28 years) to 5000 hours (14 years). But if you run it only 1 hour a day, the payback time is lousy for all those high-efficiency lamps.—RAP

Dear Bob:
Thank you for your article on energy efficient lamps. My home is filled with X-10 type plug-in wireless solid-state lamp controllers, which cannot be used with fluorescent lights. I attempted to get around this problem with X-10 appliance modules that use an electromechanical relay as the switching element rather than a thyristor.

However, all X-10 modules have a feature whereby a lamp can manually be turned on by cycling its on-off switch several times even though it is in the off cycle of its timer period. The problem I found with fluorescent lights is that when they are turned off by the appliance module timer controller, the lamp arc or ballast surge resembles the signature, causing the module to turn on in response to manual switch cycling. Soon after the X-10 module turns off the fluorescent light, it turns it back on!

I had to return to mechanical clock-driven timers for fluorescent lamps. Halogen-IR lamps should solve that problem.

Finally, another candidate for energy efficient lighting is the "E-lamp" developed by Intersource Technologies, which uses radio frequency technology. These bulbs are reported to generate the light of a 100-watt bulb on 25 watts of power, and last 20,000 hours. I don't know whether they can also be used with X-10 controller modules.
Charles Hansen, Allied Signal - Bendix Eatontown, N.J.

I always wondered if there weren't some flaws in systems like the X-10 controllers. Halogens will help solve your problem. "E-lamps" are probably a couple of years in the future.—RAP

Dear Bob:
In your column for November 12, 1992, you report that several readers question "...(now at 260,000), is it right to keep this old car running..."

I recall a college lecture to the effect that two-thirds of the energy ever consumed and almost all the pollution that an automobile ever produces occurs before it is ever driven. That is, the industrial processes that mine, mill, refine, and assemble an automobile dominate consumption and waste.

This suggests that the simplest way to reduce energy consumption and pollution is to require autos to last, say, thirty years rather than a self-destruct design limit of six-and-one-half years. In this context, your preservative instincts appear globally sound.

This would seem to have many interesting ramifications in terms of economic and social policy. For example, if cars are made to last five times longer than they do now, what does one do with the redundancy of capital and employment in that industry?

The demand for improved mileage seems to be aimed to reduce the political pressures on governments to maintain access to cheap fuels. The "cash for clunkers" business looks like a gimmick.
Adam Fritz, Afton, N.Y.

You've got a good point, but I think those proportions (2/3, almost all) are fishy. Who has facts? I'm in favor of reliability and longevity, but I don't want the government ordering me what car to buy.—RAP

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