Re: gEDA-user: Capacitors

[Bert Douglas <bertd@xxxxxxxxxxxxx>]

It seems that nobody says anything good about electrolytics.
I remember one automotive box I built.  I used some tantalum caps.
They lasted about 3 months, then they died.  Short circuit.
After some careful reading of some (surprisingly obscure) app notes I 
learned that tantalums have a strict limit to dv/dt (or current) and 
that exceeding this limit results in short circuit failures.
So I switched to electrolytics (several in parallel to get lower esr) 
and it has been operating for 10 years now with no further problems.

The specs on electrolytics vary widely.  You really have to read the 
data sheets to know what you are getting.  A one line figure of 10uF or 
100uF means almost nothing by itself.

The only thing that bothers me about electrolytics is that they are only 
guaranteed to work for 2000 hours, typically.  But if you choose higher 
temperature and voltage ratings than needed, then you can get much 
longer life.


Hal2000 wrote:
> Marc Price wrote:
>
> > I read the section on capacitors in art of electronics and got to the 
> > part where electrolytics are maked as awefull ghastly & terrible.
> >
> > Marc :)
> ha :-)
> They are horrible over temperature, especially cold.  Got into an 
> argument with older engineer about this.  He said electrolytics lose 
> 50% value when cold (-40C).  Checked it out, and they don't.  It's 
> more like 10%-15%.  He was remembering from 30 years ago, maybe.  
> Point is, they've gotten better (but still suck :-)