>>Richard 2@mail.vcnet.com
>>Fri, 26 Apr 2002 13:12:30 -0700
>
>> . . . Digi-Key sells 500v-rated
>>100k-ohm, 3w resistors, also mfg by Panasonic, which make suitable V
>>equalizers.
>
>A Mallory engineer back in the 1960's put a non-equalized electrolytic
>string in a published project with the admonition that such R/eq were
>folly since during failure-mode they actually worked against the best
>interests of the individual failing electrolytic cap.
A failed electroytic V-equalizer resistor dominoes the entire string of
caps. A failed-shorted electrolytic can do the same thing if the other
caps can't take the extra potential burden caused by a failing cap that
got too much V because equalizer resistors were not used. A failing
electrolytic is history anyhow, so his argument is codswallop.
I worked at Raytheon when an engineer stated that transistor
V-regulators can not work floating at kilovolts above ground. Management
bought it and the decision cost Raytheon much money. His idea is
cockamanie.
>And even hastened
>the avalanching of the entire series (but don't hold me to this part of
>it). I just remember this as sage advice from someone who should really
>know.
>
>He described failure-mode of, say, one of the electrolytics as offering
>'zero ohms resistance' at turn-on and continuing as such over the ensuing
>seconds when normally it would begin developing a Vb, ie, 'taking a
>charge'. As it persists in this obstinant state it presents a 'short' to
>the string, thus a resistor across it will be of no significance
>whatsoever. And the presence of resistors across the others likewise is of
>no value to them either, good cap or bad.
>
I prefer to replace the whole string since, when one cap fails, the
writing is on the wall.
>If our obstinant cap suddenly pops 'good' it does so on its own.
The fairy godmother twanged it with her magic wand ?
>
>The presence of that resistor does not assist. If it remains 'bad' the rest of
>the string simply remains under the new parameters giving the good caps a
>bit more voltage each. Note, I'm not saying a failed cap will ever 'pop
>good' again- just trying to cover all possibilities.
>
>I noticed in the Gi7b transmitters that the 6m rig HAD R/eq in the ps, but
>that the hf rig did NOT. Odd. Then a bit later I noticed Richard's comment
>above.
>
>Kilo-pardons to all on List if this topic has been hashed out before- a
>global search did not seem possible.
No pardon is in order, Bill.
cheerz
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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