[sdiy] Failure modes on bypass caps...

[Harry Bissell Jr]

LOL... no a 3300uF electrolytic on 650V...  :^P
  
  (I wish I had saved that photo... maybe I'll see if it is archived)
  
  H^) harry

James Patchell <patchell at cox.net> wrote:  Depends on the capacitor.

Tantalums, can and do fail to a short circuit.  And I have had it happen.

Surface mount ceramics, if not soldered correctly (they can crack), can 
fail to an open...And I have had it happen.

But in general, ceramics "do not fail", so there isn't a whole lot to worry 
about with them.

Shorts across the power supply are probably not much problem.  A 78xx 
limits to about 1.5 amps and has thermal shutdown.  1.5amps isn't going to 
hurt much.  Bigger supplies should have a current foldback, otherwise you 
will be a lot of smoke.

A 470uF Tant that shorts across a 300 amp supply is a sight to behold (and 
I have seen it happen)....

At 01:54 PM 12/6/2005 -0500, you wrote:

>I've been reading up the sage advice on bypass caps, and something started 
>to worry me...
>
>When caps fail, do they fail into "open circuits" or "short circuits?"
>
>If the later, it could be scary if the cap runs from the power supply to 
>ground...
>
>- Aaron, working on the transition form theory to practice
>
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         -Jim
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