John Fields wrote in
:

On Wed, 07 Oct 2009 22:27:31 -0500, Lostgallifreyan
wrote:

DaveC wrote in
l-september.org:

What was the existing cap?

DaveC wrote in
:
It's a Mallory FP119A.

Any clear indications as to why or how it failed?

No. Guesses: Old age? Heat?



Old age isn't a mechanism. Heat could well be right. Also accelerated
loss of electrolyte. Did the cap look like it had burst from inside
earlier than any final appearance of internal gubbins? Another
possibility is the voltage it saw. When you say 110 volts, you mean the
mains, right? If so it will be rectified and that cap will be seeing the
peak value, not the RMS, so around 125V when under no load, so you
really do need it to have a higher voltage rating than that.

---

peak = RMS * sqrt(2) = 110 * 1.414 ~ 155V

JF


Agreed. I even knew the formula and entered exactly 1.414, no less, so I'm
still wondering what the hell else I wrote into the Windows calculator this
morning to get an answer of fractionally over 125V. I'll put this down as yet
another reason to aim for safe margins if the cost doesn't prevent it.

(Actually I found it. I typoed as 1.141...)