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Beware the unintended consequences of more-efficient design

Bill Schweber
2/3/2016 11:12:05 AM
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More unintended consequences
Almost started to laugh with the water heater examples given. Had a recent experience with an older water heater being upgraded to a new "efficient" design. Luckily the location for mine did not require major rework of the framing or drywall. A piece or two of trim had to be removed to account for the larger girth. A co-worker had to endure thousands in upgrade costs as his space was not as lucky. He calculated the savings in $$$$ would require the new water heater to be used for at least 30 years before he would see any savings. BTW - That new heater only has a 10 year warranty!

2/2/2016 1:36:24 AM
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He's some unintended consequences
I might have mentioned a few of these before.  I wouldn't list my mistakes.  A few of them would be just as embarrassing as these were.

I worked on a project where the antenna was changed to a quarter wave antenna on a radio to save money.  But, the ground on a quarter wave is the other radiator, so that was probably the reason the RF started to get into all the analog circuitry.  This was very hard to fix and probably saved very little money compared to the effort.

A mechanical boss was added to the housing to make the design stronger. But a ferrite in the radio receiver was moved closer to the input power transformer and the 60 Hz got magnetically coupled into the receiver and rectified.

There was a design where an op amp was changed to another because it was thought the new amp would be better and the design was sent to the customer.  The new op amp had a greater gain bandwidth product and oscillated in the application and it was never noticed.  Sometimes slower amps are more stable and maybe make sure you don't use a digital scope on a setting that filters out high frequency oscillations.

A company I worked for switched to cheaper keypads but they unfortunately the ESD immunity was never considered. Consider the ESD immunity from a mechanical standpoint first, then from the electrical standpoint.

A company I worked for decided to take advantage of very cheap labor in a foreign island and manufacture keypads there. Unfortunately, the favorite lunch there was greasy fish sandwiches and the people don't wash their hands often.  The grease got into the keypads and they had a high failure rate which was never noticed until final assembly.


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