Skip navigation
Electronic Design

Bob's Mailbox

Dear Bob:
I've been seduced by your March 4, 1993 column in which you discussed the problem of battery charging for camcorders. I, too, have spent a little time in the woods, some of it in the Sierras down the road apiece from you. Each time I've come out of those woods, I've had to perform a rather lugubrious task at the Redwood City HoJo the night before my plane left for home. The airlines don't like you to have loaded butane cook-stove canisters in your backpack, so I always burn off the remaining fuel the night before out near the pool or on a balcony. Every time I do this, I'm amazed at how long the damn thing burns; there's a lot of energy in one of those lightweight cans. Lots of BTUs, but not easy to convert.

I've been trying to get some time to do the calculations to see how much energy could be extracted from a small steam turbine driven by one of these very large cigarette lighters. Seven watts should be easy. Well, you know how that goes.

Anyway, I thought I'd suggest the solution to you, because you're obviously more obsessed than I am, and probably have more incentive to boot. The only penalty with this solution is using up some water, and often that's not a problem. It might even be possible to steam vegetables or something while you charge your battery. Perfect for Ronco, really.

Let me know if you follow up on this. Not only am I dying to know if it works, but I'm sure we could corner the market together.

I always enjoy your column in Electronic Design. It's one of the few places to share the Joy of Engineering in what has become a vast digital swamp.
Ed Grenda,
Castle Island Co.,
Arlington, Mass.

Next time, give your propane to another hiker! But I don't know where to find a light boiler and steam engine (turbine not piston). Read on.—RAP

Dear Bob:
This is just a brief technical comment on your March 4, Column "What's All This Battery-Powered Stuff, Anyhow?"

I am a French analog IC designer, dealing especially with analog ASICs in the field of military and space applications.

My suggestion is to use a Peltier-Seebeck module to directly convert heat to electricity. It is probable during your trek to have some heat from a burner or fire to convert into a charge current for your batteries.

The tiny Peltier-Seebeck module could be pressed between a copper bar and a heat sink. A careful study, with a proper module selection and a good mechanical/thermal design, could result in a compact power source. Very significant amounts of power can be generated this way. Let's remember that such generators are sometimes used in outer space (some were used to power the data-acquisition/transmission systems Apollo missions brought to the moon, and for flying spacecrafts like Voyager I and II).

That solution may not be very cheap (modules are priced at several tens of U.S. dollars) but could be reasonably lightweight.

Thank you for your column. I enjoy your particular mix of technique and philosophy.
Jean-Francois Debroux,

I have seen some thermoelectric modules, but I recall them being rather heavy, inefficient, and expensive. I have requested literature—and will study.—RAP

Dear Bob:
Regarding "...Battery-Powered Stuff," your cranky generator is probably the most practical solution. However, you might want to consider a few off-the-wall concepts:

Consider the heel impact energy of a person walking on soft soil with 0.5 in. of "give." For a 100-lb. person at a brisk walk of 100 foot-falls per minute, this figures to 0.04ft. x 100lb./0.7 sec. = 5.7ft.-lb./sec., or almost 8W. Convert this at 20% efficiency with boot bellows pumping into an elastic reservoir, supplying a small air motor driving a light-weight high-speed generator, and you can tape for about 1 hour each day. (Not likely!—RAP)

Or consider a typical Sterno can under a pan of rice. Mooch about 1% of the energy flow with a thermoelectric module like they use in 12-V dc pop-can coolers, and charge your batteries while cooking dinner. (Not likely; they're inefficient and you'd need a bonfire.—RAP)

Or consider the heat of formation of aluminum oxide (Al2O3). If you need 120 watt-hours to fill your supply of tapes, you need about 100 KCalories at about 400 KCalories per mode. This means that you would need to carry only about 32 grams of aluminum to supply the whole trip at only 10% electrochemical efficiency. Have you ever come across an aluminum-air fuel cell? (No, not likely.—RAP)

Or revisit the alkaline "D" cells. If you limit discharge current to 100 mA and pull the voltage down to 0.7V, each cell can supply almost 20 watt-hours. Play dc-dc converter games with a small sealed lead-acid battery to supply peak current at a total efficiency of 72% (85% for dc-dc and 85% for the lead-acid battery). You could supply your hypothetical 20-day trip using only 8.4 alkaline D's.
Ben Barnett,
Instrumentation Engineer,
YSI Research Center,
Yellow Springs, Ohio

Now that last paragraph is obscure, but quite feasible! Somewhat promising, and good Engineering! I'm working on a 98% efficiency switcher.—RAP

Dear Bob:
I am tired of hearing in your columns, and elsewhere, "I'm one of those non-degreed engineers 'who gets no respect' monetarily or otherwise." Can one claim to be a medical doctor after learning how to use a stethoscope, or a dentist if one know how to use a drill, or a lawyer if one handled his/her own case in small claims court? How ridiculous a complaint!

Shall four to six years of sacrifice and formal engineering study (and up to $80K in tuition) be cast aside so lightly to think that someone who has read hobby magazines and the Radio Amateur's Handbook can be a match for someone who has studied in an accredited engineering program to learn basic fundamentals? How absurd! Does this non-degreed engineer have basic knowledge of higher mathematics, electrical-engineering basic analytical fundamentals, civil-engineering principles (i.e. shear, strength of materials, etc.), mechanical-engineering principles (laminar flow, thermodynamics, mechanisms, etc.), or drafting practices (developments, detail drawings, descriptive geometry, etc.). The "non-degreed engineer's" answer is "I don't have to know that to do my job." That's correct. He has a job, not a profession!

How demeaning it is for the degreed engineer to see someone called a "company engineer" after all the hardship he went through to obtain his degree(s). I have seen "company engineers" perform their assigned tasks well. But ask them to perform a loop analysis or to find the rms value of a waveform, etc., and they look at your with a blank stare.

If all of the advanced study that a degreed engineer is required to go through really is not needed on the job, what a cruel hoax the engineering executives in this country have played on some of the most intelligent people in our society! Apparently, since engineering enrollment is down in our universities, prospective engineers are not only intelligent but have become "smart." Why go through the cost and rigors of an engineering education when others who just know how to slap some chips together can have the same prestige, respect, and salary as the degreed engineer?

In addition, what a hoax was played by corporate management on the degreed engineer by claiming a shortage of engineers that never, ever existed just to obtain an abundance of cheap labor. The "company engineer" concept is another corporate idea for acquiring cheap labor.

What engineer hasn't pondered the thought that he might have been much wiser in his youth if he had sought a career in medicine or law and became a real professional with prestige, respect, and financial reward. Tell it like it is Bob, I dare you to put this in print!
Name Withheld

The IEEE didn't help us much on the "engineering shortage," did they? As for the ability of engineers to handle math, theory, etc., I see a virtually infinite array of capabilities. I don't find all that much correlation between the degree and the abilities. Surely a lot of degreed engineers can't remember how to compute the rms value of a lumpy waveform!—RAP

Dear Bob:
Your articles are usually one of the most interesting features of Electronic Design, and I have so many comments about the last few that it is hard to decide where to start.

First the comments about computers and spreadsheets: I agree with you. It is amazing how upset some "engineers" get when you criticize computers. My philosophy is "If you really want to get something done, don't turn the computer on." Spreadsheets are useful, but they are a keypuncher's dream and can waste a lot of time. Since I am a consultant and get paid by the hour, my clients usually are not willing to pay for too much wasted time.

The same can be said for simulation programs. You can spend hours simulating an RF filter, doing tolerance analysis and changing values to optimize it. Then once it is built, you find out that it is not quite the same as the simulation because of leakages or other factors. The best approach is to first sit down with a pencil and paper and THINK about the problem and what the possible approaches are. Write a few equations, if you still remember how, and see how things look. Sometimes you can even differentiate them, set them to zero, and see if there may be an optimum solution for the configuration. If you can't do that, sit down and review your old calculus book and some basic books from your freshman and sophomore years in college.

Some engineers even think that basic concepts no longer apply in this age of digital circuits and computers. I think the biggest problem with engineers today is that they don't think enough. Their first problem in approaching a problem is to start punching keys and see if they can eventually find a solution by trial and error.

On your article about Compensation, etc.: I have always believed that the best engineers are the curious ones, and it is in the company's best interest to encourage hobby-circuit construction. I was very surprised to find out that NSC sells National parts to employees. I don't know why other companies don't encourage engineers to build circuits at home, because it makes them better engineers at a very modest expense.

On the other hand, NSC has recently made it very difficult for outside users to use their parts. The company hasn't gone to any trade shows where I usually get free catalogs, it only sells them now. If I don't have up-to-date information on the devices, I can't design them into new products. Another problem is that even if something is in the catalog, there is no guarantee that it won't be obsolete in a month or year because a major customer stopped using it. (We're working on that.—RAP) We need a better system for knowing what parts should not be used in new designs. Another thing a manufacturer should realize is that engineers are most likely to use their parts if there are samples in the drawer.

It sounds like NSC is a great place to work.
Jon Grosjean,
Woodstock Engineering,
Woodstock, Conn.

I agree with you about thinking vs. computers. Note, NSC mostly donates parts to employees to design with. But if I want to build my own computer or electric car, they'll sell me the parts. NSC is indeed a challenging place, as we never run out of things that need to be done better.—RAP

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.