Why can't we use non-electrolytic capacitor ?

We knew that all the Aluminium Electrolytic capacitor having shelf
life of 5 year
according to the mfe standard.( Due to crystaline in the material). Is
that mean any electronic product if you do not use more than 5 years
will not fuction properly ? Hence why can't we use non- electrolytic
capacitor to substitute ?
Can any person know the reason ? Thanks.

 

Properly derated, good quality electrolytic capacitors, (temperature,
temperature rise, voltage) can last a lot longer than 5 years. Poor
quality caps that are running at several of their maximum ratings can
have a very short life.
One of the wear out mechanisms is loss of electrolyte through the seal
material. I do not know what you are referring to by, "Due to
crystaline in the material".

 

You misread the situation. People don't use electrolytics becasue
of some special characteristic, they use them because that's the only
feasible way to get larger capacitances. Find a non-electrolytic with
a value of 1uF or more, and it gets rather large. But switch to electrolytic
and they become much smaller. It's the construction of the electrolytic
that allows the higher capacitance within a reasonable package.

So you will find that virtually all the capacitors over 1uF or
so are electrolytic. The exceptions are when there is a very specific
need for something else, such as specific value (electrolytics don't
come in tight tolerances). There is little other reason to justify
the size and cost of non-electrolytics in those larger values.

And once you have that path, then people simply live with any drying
out of electrolytics.

Michael

 

Hi thank all for the response, I read from some book ,is just like lead acid
battery if not use for a long period the plate in the battery will be polarize.

 

It is like a battery only because it involves chemistry. In
electrolytic capacitors, one of the plates is metal (aluminum for
most, tantalum for some) and one plate is the conductive electrolytic
solution surrounding that metal. The insulation that separates them
is a thin layer of oxide that is made of the metal and oxygen released
by driving current through the electrolyte in one direction during the
manufacturing process. If the unit sits around for years, there is
some degradation of the oxide, reducing its insulating properties.
There is also a possibility that the electrolyte will escape and there
will be no conductive plate opposite the metal. Both these aging
problems are much improved since I started electronics, 40 years ago.
But long periods of hot storage or operation will eventually wear out
any electrolytic capacitor. It is only a question of how hot and how
long. That is why capacitors are life expectancy rated based on
several conditions (temperature, voltage, ripple current). Sitting on
the shelf, they last much longer, generally.

 

Thanks John for your explaination. I have another question. A ceramic
disc
capacitor is cheaper than any of the polyester film capacitor, If
both having the same value why can't i use the ceramic disc instead of
polyester
film capacitor if the cicuit is user in a 20w fluorescent light dc to
dc
driver by car battery, is this some thing to do with working frequency
of the capacitor ?
Best Regards

same value o

 

It may be possible to use the cheaper capacitor. No capacitor is
perfect, and you have to decide if the imperfections of a particular
type will be a problem in a given application. Ceramic capacitors
made to be small and cheap have very strange dielectrics that change
capacitance with temperature and also with applied voltage. They also
act as transducers that produce voltage when force is applied to them
and change dimensions when voltage is applied to them. They also tend
to get warmer than film capacitors when charged and discharged rapidly.

Here is a web site that explores many of the details of the various
kinds of capacitors.
http://my.execpc.com/~endlr/index.html
There is a lot to know.

 

Hi John
Thank for your reply, it take sometime to understand the capacitor topic
Best Regards

 

Here is a web site

The last item on the page
is a comment by the site owner about his employment status.
It contains this link:
http://my.execpc.com/~endlr/will_design20_.jpg

 

Oh crap!