Fw: [Boatanchors] rotor starting capacitor

[Brian Clarke]

Hi Wayne/Horace,

Not so. In a dc electrolytic capacitor, the oxide is not 'deplated', as you
so
innocently suggest; rather the etched surface is damaged and NOT reformed.
The plate forming process and electrolyte in an ac electrolytic capacitor
are
different from their dc cousins'.

I'm having difficulty understanding the scientific reasoning behind your
'heck,
even the correct replacement eventually failed'.  What is the status of this
piece of evidence? Does it mean we know why the component failed? Was
there a mains spike? Was there an over-temperature condition? Was the
accountant more powerful than the design engineer? Was the operating
philosophy in the manufacturer - it's got a concrete guarantee? - ie, it's
guaranteed till it gets onto the concrete pavement outside?

Is following your line a justification for blindly doing whatever happens to
work for a short while? Why do it if in the long run the component will
fail -
what's the logic? Save a few pennies now and cost a small fortune later?

The charm of amateur practice. Humph, indeed. What not do a wee tiny bit
of measurement and get it right? It'll save time in the long run, I reckon.

73 de Brian, VK2GCE.


Wayne chided:

Since the 2 caps are exposed to AC, current in alternating directions,
there is replating as well as deplating going on. The dire consequences are
apparently far enough removed in operating time that the replacement is
considered a successful substitution. Heck, even the correct replacement
eventually failed, right? <g>

This back-to-back caps idea has been in use for many years and handed along
by many people for whom it has served satisfactorily. These are 'practical
experiments' in the field, conducted by these other fellows, showing that
the substitution does work for a long time (an admittedly imprecise
quantity). Their results show that, if the replacement is not exact, it is
of no practical consequence. If it works, it works...that is the charm of
amateur practice! <g>

--Wayne
  WB4OGM