[Milsurplus] Electrolytics then and now

[Don Merz]

It would take a lot to convince me that one generation
of engineers inherits much increased capability by
learning from the mistakes and successes of past
generations of engineers. I just don't see it
happening. 

In the context of electrolytic caps, some of the worst
junk ever made was made in the last 15 years for
personal computers while, as this group can all
attest, we routinely see cases where 40+ year old
electrolytics still work fine. 

And don't get me started on stuff like common user
interfaces--for example, why on most cars do we still
have to look THROUGH THE STEERING WHEEL to see the
speedometer and the instruments? That design failure
has propogated itself for almost 100 years of what is
euphemistically called "engineering" in the automotive
industry.

73, Don Merz, N3RHT


--- "gl4d21a at juno.com" <gl4d21a at juno.com> wrote:

> Gang:
> 
> I followed the discussions (arguments?) of
> electrolytic capacitor 
> vagarities with some amusement.  You realize, of
> course, that you are 
> all correct, it is just that no one associated the
> pertinent time 
> frame with their information.  The chemistry of
> electrolytics has 
> undergone several radical transfrmations in addition
> to the ongoing 
> product improvements.  Just take a look at (a
> picture of) one of the 
> old 1930 wet electrolytics of 4 MFd. at say 250 VDC
> and compare the 
> size of it with a modern capacitor.  There had to be
> some changes, 
> not so?  Now, find a similar value device from about
> 1950 or 1960.  
> Near halfway in between for size.  So, the change
> was not one big 
> leap.  Look in your collection for an electrolytic
> about 10 or 12 
> years old, and compare it with a 2006 production
> unit of the same 
> value.  More size reduction.  Lots of new knowledge
> in chemistry and 
> materials engineering in there.  
> 
> Back in the dark ages, when I was specifying
> electrolytics for mobile 
> radio equipment, the capacitance values of standard
> units were +80/-
> 20%, and life was rated at 65°C at the operating
> voltage +10/-25%.  
> You paid more for 85°C products, which we had to use
> because if the 
> heat generated by a dozen or more firebottles in a
> closed box, and 
> paid through the nose for tighter capacitance
> tolerances.  As was 
> pointed out, few if any electrolytic applications
> require capacitance 
> values which are more accurate than the available
> +80/-20%, unless 
> you had an inexperienced circuit designer, and I
> have seen my share 
> of those.  Monte Carlo reliability and performance
> calculations were 
> just coming into use back then, so most of the
> designs I worked with 
> were breadboarded with combinations of max/min
> values to discover 
> problems.  Ah, the good old days.  Don't miss 'em a
> bit.
> 
> 73,
> George
> W5VPQ
> 
> 
>
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