CAPACITORS

but capacitors would cost more than 5 cents apiece and electronic equipment would last so long that there would no longer be a reason to buy anything new and the whole world economy would collapse.

Electrolytic caps are similar to car batteries in that they store and return charge and they are electrochemical. The most common and low cost ones use a wet electrolyte which, over time, will dry out and cause a failure. Heat exacerbates this process so some designers choose caps rated for 85 degrees C and others choose 105 degree C rated units.

As PhilB stated, economics plays a part in this. Parts can be characterized for useful life by what is called a "bathtub curve" which plots the failure probablility vs time. This starts high and rapidly drops to a low constant value for a long time then rises again. From these data the expected operating life of the part or system can be predicted. So if a manufacturer is producing a product expected to last 5 years the choice of these parts can be based on that. This avoids the added cost of long life parts which is wasted such as putting 20 year life expectancy parts in a product which is only intended to last 5 years, e.g. a computer or cell phone which will be obsolete after that time.

An illustration that "they can make them last a lot longer" is present in my 1936 model Crosley vacuum tube table top radio which still operates with the original electrolytic caps now some 78 years of age. The life expectancy process was probably not accounted at the time for this radio.

Another example is I once worked for a company which made appliance motors and starting capacitors. Clothes washers and dryers were designed for a life of 12,500 cycles and the life of the caps and switches was matched to this as a cost savings. Each penny saved on a unit when 100,000 were made each month is a savings off the top of $12,000 per year.

Neil

Those are interesting factoids about the life expectancy of capacitors.

I guess we are like capacitors in that we are "stamped out from 3d mother printers" and the clock starts ticking.

The planned life-expectancy of light bulbs has always fascinated me... somehow crates of lightbulbs survive the ocean trip from China, bumpy truck trips to distribution warehouses, the shock of shelf stocking... the tiny filaments and fragile components make the trip home to the socket where they last exactly 2-weeks.

Only the electrolytics deteriorate over time(15 years or so), the other components...resistors, coils, other caps, transistors most ic's last indefinitely.

Look at all the vintage electronics on ebay all still working fine from transistor radio's to hi-fi from 50 60 years old.

Small thing to replace a few caps to restore an item to excellant working condition.

The compressor I am using, I got used and had a bit of hum so I replaced the filter caps with a larger value than original and no hum.

Problem with electronics is the lithium rechargable batteries which after 2 or 3 hundred charges and that's it. I get around the built in obselecence by converting MP3 players to work on regular AA batteries so I have days of continuous use and the sandisk one I an using for my station audio source has been running a couple of years now with a micro SD card.

Trouble is to have things made like way back when, things would have to cost a lot more....You can get light bulbs now....LED's that replace a 60 watt bulb with even more lumens of light with a whole lot less power use and the same warm white as before that will last "forever" but they cost $30 a bulb instead of $1.00 a bulb.

Mark

What if we wrote a technical instruction paper "How to Hack Everything."

Less trouble once we know the tricks.

It's well known that electrolytic capacitors in switching power supplies have a high failure rate. As an example search Google for "Samsung TV capacitor problem". Here's one example: http://mix941kmxj.com/samsung-tv-wont-turn-on-affected-models-listed/ . Samsung took a beating on this one by skimping on the capacitor rating.

Low voltage, high current switching supplies stress the filter capacitor with high current. The capacitor's "ripple current" rating is key. If a capacitor with an insufficient rating is used, it will heat up and eventually bulge or burst. This is one application where it doesn't pay to cut cost and skimp on quality, but it still happens. The engineers likely knew better, but management didn't.

Old tube electronics from as much as 90 years ago will likely come to life after a total "re-cap", meaning all the electrolytic and wax impregnated paper/foil capacitors are simply replaced regardless of whether they are still good or not. Often the original vacuum tubes will still be functional, which only highlights the capacitor problem.

Vintage electronics from the 1960s to now don't automatically trigger a total re-cap during restoration, except for electrolytics. That indicates big improvement from the old paper/foil wax capacitors, but not so much for the electrolytics.

Ah yes, the paper/foil wax caps. Made some money back in high school fixing radios and TVs and it was not unusual at all to remove the bottom cover and find drips of beeswax from these. About that time the Sprague "orange drop" caps became available and were quite an improvement.

Back then the usual suspect for failure was the tubes but actually tube failures were rare. Most of the problems were the caps and pots.

One of the strangest things I encountered was with a table top radio. After I repaired the unit (don't recall what was wrong) I noticed that the power cord was quite warm. Thinking this was a hazard I replaced the cord. The tubes lit up like light bulbs and I realized that the series strung filament voltages didn't add up to 120 volts. Turns out that the power cord was made from insulated nichrome wire and served to drop the line voltage to the proper value for the filaments. This is the only set I have ever seen with the ballast resistor in the power cord. Some clever designers back then.

Neil

"Turns out that the power cord was made from insulated nichrome wire and served to drop the line voltage to the proper value for the filaments."

I'll bet there was no UL rating on that baby. 🙂

The vintage radio enthusiasts call them "curtain burners".

There's a well documented trick to replace the dropping resistor in the power cord with a non-electrolytic series capacitor of several uF inside the radio. The reactance of the capacitor at 60 Hz is such that it drops the voltage properly without producing much if any heat.

"curtain burners"

Funny Phil....But makes sense