Blog Archives

1st Qtr 2012

(c) 2012 Design/Analysis Consultants, Inc.
Newsletter content may be copied in whole or part if attribution
to DACI and any referenced source is prominently displayed with the copied material

This Issue: NEWS BITE: Creepy Swarming Electronic Insects Are Real! / GOVERNMENT FOOLISHNESS and Incandescent Bulbs / WORST CASE ANALYSIS and the Fukushima Nuclear Plant Meltdown / RISK ASSESSMENT and Lithium Battery Explosions / ANALYSIS QUIZ: Answer To Last Quarter’s Question / DESIGN MASTER 8.2 UPGRADE if you’ve had troubling generating WCA reports on a Win7 PC

NEWS BITE: Creepy Swarming Electronic Insects Are Real!


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GOVERNMENT FOOLISHNESS: Incandescent Bulbs Banned? No Problem, Just Buy A Heat Ball
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From “Upset about Big Brother’s Ban on Incandescent Bulbs? Buy a Heatball!
by Selwyn Duke in the 30 Dec 2011 issue of American Thinker

For earlier Newsletter comments on the absurdity of banning incandescent bulbs, please see “Unintended Consequences: Nanny Engineering” in the 2nd Qtr 2011 issue.

WORST CASE ANALYSIS: What We Learned From Fukushima – Again

“Japan is not a technically backward country  … Its nuclear power plants were designed and built with an acute consciousness of extreme earthquake dangers.

“So how is it, despite that sophistication, awareness, and preparedness, that the Fukushima crisis has nonetheless exceeded worst-case thinking? Here, the story is reminiscent of Three Mile Island and Chernobyl, and the message seems to be the same: Worst-case scenario builders consistently underestimate the statistical probability of separate bad things happening simultaneously, as the result of the same underlying causes. [Emphasis added]
Japan Nuclear Accident Worse Than Worst, Again” by Bill Sweet, 12 Mar 2011, Energywise
Image: http://www.digitalglobe.com

RISK ASSESSMENT: Li-Ion Battery Pack Hazards and our Psychic Prediction

“Internal cell faults continue to lead to thermal runaway failures in Li-Ion battery packs used in the field. Though these events are rare, the proliferation of Li-ion-powered consumer electronics has increased the risk for an event occurring on an aircraft, or at a similarly inauspicious location or time … At present there is no [battery] pack-protection circuitry in commercial use that is designed to continuously monitor the cells for the symptoms of a latent incipient internal cell fault before such a fault causes thermal runaway.”
Detecting Lithium-Ion Cell Internal Faults In Real Time” by Celina Mikolajczak, John Harmon, Kevin White, Quinn Horn, and Ming Wu, in the Mar 1, 2010 issue of Power Electronics Technology

Even though there have been several fires and a few folks have been injured or killed due to exploding lithium batteries, we predict that the risk will be tolerated until a catastrophic explosion occurs. This will be  followed by the usual screaming headlines belatedly warning of the dangers, hind-sight experts suddenly popping up on TV, hand-wringing congressional investigations, and finally, heavy-handed and grossly over-reactive governmental regulatory responses.

ANALYSIS QUIZ (Answer from Last Issue): Adjustable 3-Terminal Regulator Output Tolerance

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An LM317T regulator with 36V input is set for 24V nominal output, using 1/8W 1% 100ppm thick film resistors (10K and 549 ohms). The regulator must deliver 1A and operate from 0 to 50 C for 10,000 hours.


Q: What will be the approximate worst case output tolerance?

-2/+2%        -4/+5%         -7/+6%         -6/+11%         -9/+15%

A: -9/+15%

Surprised? You might be if you only consider initial tolerances, and don’t factor in the effects of temperature and aging. Here are the normalized sensitivities, which gives one a better sense of the significant error contributors:

DESIGN MASTER™ 8.2 UPDATE: WCA Report Generator Bug Corrected

To facilitate the efficient creation of professional worst case analysis reports, Design Master includes an automated Word document report generator, based on Microsoft Office automation technology. We’ve recently had a few Win7 users notify us that the report function is not operable on their systems. Although Design Master has been tested on other Win7 systems with no problems, variations in Win7 system speed appear to prevent the report generator from functioning properly in some cases. Design Master Rev 8.2 allows more tolerance for speed variances, which has corrected the reported issues.

2nd Qtr 2011

(c) 2011 Design/Analysis Consultants, Inc.
Newsletter content may be copied in whole or part if attribution
to DACI and any referenced source is prominently displayed with the copied material

This Issue: NEWS BITE: Miraculous Emergency Landing on Railroad Track! / DESIGN MASTER TIP: AC Rectifier Bulk Capacitor Ripple Current / HUMANITARIANISM: Capitalism + Volunteer Engineering Helps Haitians / UNINTENDED CONSEQUENCES: Nanny Engineering / SHAMEFUL BEHAVIOR: Shanghai Euchips Industrial Co. Used Fake UL Label

NEWS BITE: Miraculous Emergency Landing on Railroad Track!

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Ground-Effect Robot Could Be Key To Future High-Speed Trains” by Evan Ackerman, 10 May 2011 IEEE Spectrum

DESIGN MASTER TIP: AC Rectifier Bulk Capacitor Ripple Current1 


Pretty good estimates of capacitor ripple amps for full wave rectifiers driven by low source impedance can be obtained by using the equations below. Note that an exact solution requires iteration, which can be done automatically by the Design MasterTM worst case analysis software. If you don’t have Design Master, you can get some quick results by first estimating the ripple voltage and solving for tC. Then calculate Vripple to see if your estimate was close. After a couple of iterations you will zero in on good values for tC and Vripple, and then you can solve for total capacitor ripple amps.

A PRETTY GOOD ESTIMATE for BULK CAPACITOR RIPPLE AMPS

1. tC = charge time, sec = ACOS(1-rRIP)/(2*Pi*f)
where
ACOS = inverse cosine function (COS-1)
rRIP = ripple ratio, Vripple/Vdc.
Vripple = ripple volts peak-peak = Idc*tD/C
Vdc = average DC output volts
Idc = average DC output amps
tD = discharge time = 0.5/f – tC, seconds
C = bulk capacitance, F
f = line frequency, Hz
2. Dc = charge duty cycle = 2*f*tC
3. Dd = discharge duty cycle = 1 – Dc
4. ICchg = ripple amps rms due to charge from full wave rectifier
= Idc*SQR(1/Dc-1)
5. ICdis = ripple amps rms due to discharge to load
= Idc*SQR(1/Dd-1)
6. ICload = rms content of pulsed load amps (e.g. input of switchmode regulator) if applicable. If load amps is purely DC, set ICload to 0.
7. ICtot = total capacitor ripple amps rms = SQR(ICchg^2+ICdis^2+ICload^2)

The great thing about analysis, as compared to simulators such as SPICE, is that you can learn a lot by reviewing analysis equations. For example, if you set the ripple voltage ratio to a desired amount (e.g. 15%), and rearrange the Vripple equation to solve for C, you can readily obtain a graph of the required ripple amps rating versus output current, regardless of input or output voltage. Now you’ve generated a general-purpose design guideline to use for numerous applications.

See the example graph below for the capacitor ripple amps requirement versus DC load currents from 100ma to 5 amps, for a 15% ripple voltage and a 60Hz source. For example, for 2 amps of load current, the capacitor will require a ripple current rating of 4.4A

1. Excerpted and revised from DACI Application Note, ” Why Power Designers Need More than SPICE to Avoid Blow-Ups.”

HUMANITARIANISM: Capitalism + Volunteer Engineering Helps Haitians

Non-governmental organizations operating on free-market principles can offer the most effective assistance to those in need. For an example click here.

UNINTENDED CONSEQUENCES: Nanny Engineering

Yes, the government does provide some essential functions. Unfortunately, it doesn’t have the self-control to restrict itself to those functions. The result is that we are plagued by governmental busybodies who like to justify their salaries by telling the rest of us how to behave, in areas that are none of their concern.

For example, as pointed out in Engineering Thinking, there have been numerous regulations passed that restrict our right to choose the products we may want, such as incandescent light bulbs. In that case, the government has deemed such bulbs unacceptable due to low efficiency. But if incandescent light bulbs are inefficient, that fact becomes evident in our electric bill; why do we need the government to tell us how best to spend our money?

Furthermore, perhaps some of us would, regardless of efficiency, prefer to use the incandescent type. But no, the governmental busybodies have decreed that you don’t get to freely choose. Forget about all of the other parameters that might be of more importance to you: short-term cost, color rendering, lifetime, reliability, and environmental hazards. Also, some folks in chilly climates might even appreciate the extra heat that incandescent bulbs provide. But none of these considerations matter to the one-solution-fits-everybody government.

Now, as typically happens following such governmental decrees, we find that they are rife with unintended consequences; e.g. the compact fluorescent lamps (CFLs) that the government wishes us to use instead of  incandescent bulbs have significant disadvantages:  (a) substantially lower lifetimes than expected, (b) may emit hazardous fumes (click here), (c) emit electromagnetic interference (EMI), (d) emit a color that can disrupt melatonin production and thereby cause sleep disorders, (e) sometimes create an irritating buzzing nose, (f) contain hazardous materials that pose significant environmental disposal hazards, and (g) will kill the domestic incandescent bulb industry, and replace it with products that are primarily foreign-made.

Some years ago the government illustrated similar brilliance by outlawing magnetic ballasts, again simply on an efficiency basis. It should be no surprise that the electronic replacement ballasts were more expensive, had shorter lifetimes, were less reliable, contained hazardous materials, and emitted a lot of EMI (so much so that some hospitals refused to use them because of their tendency to interfere with medical instruments).

Recently some smart engineers from China, unencumbered by the U.S. regulatory dictatorship, have created a magnetic ballast whose efficiency is better than electronic ballasts, at lower cost, longer life, higher reliability, using non hazardous materials. [1] Congratulations!

Sad to say, this is the sort of advance that was typically accomplished by U.S. engineers, back before the government decided to play Nanny Engineer.

Note 1: “A ‘Class-A2’ Ultra-Low-Loss Magnetic Ballast for T5 Fluorescent Lamps — A New Trend for Sustainable Lighting Technology,” Hui, Lin, Ng, and Yan, Feb 2011 IEEE Transactions On Power Electronics.

SHAMEFUL BEHAVIOR: Shanghai Euchips Industrial Co. Used Fake UL Label

Details here.