[pure-silver] Re: Speedotron 2401A
- From: "Dana H. Myers" <dana.myers@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sun, 01 Oct 2006 20:06:13 -0700
Jim Brick wrote:
> At 04:00 PM 10/1/2006 -0700, you wrote:
>
>> I think the capacitors are formed when you fire them - not just
>> letting them
>> sit there with the power on.
>
>
>
> Capacitors are formed when voltage is applied and they take on a charge.
> When turned on for the first time after a long idle time
> (weeks/months/years) the power should be left on for several minutes
> before firing for the first time. This will allow the capacitors to form
> completely. They are de-formed when fired, that is, all electrons
> rapidly leave, or leave slowly over time.
Well, sort-of. Electrolytic caps form the insulating layer where the
charge stored (called the "dielectric") when DC voltage is applied,
via electrolytic action between the "plates" (electrodes) in the
capacitor.
It's possible for the dielectric to deteriorate when the capacitor is
not powered, but, as long as the capacitor still has electrolytic paste
still present, the cap will reform when DC voltage is applied.
> Strobes should never be turned off with de-formed capacitors. One should
> ALWAYS charge the capacitors and when they are ready to fire, then turn
> the power off and store the unit. Those folks who fire their strobes
> just before turning off the power are ruining their capacitors. The
> useful life of the unit will be noticeably shortened.
I think it's better to store a device with the caps charged, but that's
almost meaningless if the equipment is stored for very long. The charge on
the cap leaks off (electrolytics are notoriously leaky) and they become
discharged after a fairly short period of time (likely measured in weeks
or months). So the issue really isn't really about storing caps in a
charged state if the time between uses is more than a few weeks to a couple
of months.
What usually kills electrolytics is drying out. Older caps, like, those
made before I was a kid, have a pretty strong reputation from drying out
on their own and becoming essentially inert. Drying out is accelerated
by temperature, and a reforming electrolytic experiences a current surge
before the dielectric forms that heats the electrolyte, thus accelerating
the drying-out just a teeny bit. One techique used by restorers of very
old radio equipment is to ramp up the supply voltage slowly so as to limit
the in-rush of current to aged caps, so they can form dielectric before
cooking-out the scant remaining electrolyte.
However, modern caps are a lot better than the caps from even 40 years
ago^H^H^H^H^H^H^H^H^H^H^H^Hmy childhood and usually dry out much more slowly
as long as they're stored in 'reasonable' conditions (below 80F, for the
most part).
> I used to repair strobes as a business.
You ever abuse an electrolytic until it explodes? I learned that lesson
pretty early myself... sure made a mess.
Dana K6JQ
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