[pure-silver] Re: RE-FORMING ELECTROLYTIC CAPACITORS IN STROBE PACKS
- From: Dana Myers <dana.myers@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Wed, 28 Sep 2022 12:37:51 -0700
On 9/28/2022 12:24 PM, Tim Daneliuk (tundra) wrote:
On 9/28/22 14:15, Dana Myers wrote:
Some additional info about reforming caps. As I recalled, the issue is
protecting the
cap from high charging current as the oxide layer is reformed.
That is exactly right, but - I think - only part of the story:
- The charging circuits in the flash unit/head should have some
level of current protection in them to avoid this problem.
I have never seen a cap reforming surge take out a flash power
pack or head unless ...
Indeed. The circuit that charges the capacitor is inherently current-
limited by the characteristics of the components used. Fast-recycling
strobes are designed specifically to provide more charging current.
It's possible, or even probable, that the charging circuits are designed
to tolerate a short-circuit/high-current load for a brief period, and the
current delivered in this case is intentionally limited to avoid damaging
the capacitor.
- If caps get old and leaky enough, anything is possible. I've seen
HV caps (not in electronic flash, thank heavens) offer themselves
up in smoke and fire when power up after years of non-use and
deterioration. It doesn't sound like that's remotely the case
here though.
Interesting case - a truly old, dried-out capacitor is probably less of
"pop!" hazard than an old not-yet dried-out cap.
P.S. I spent some years working on seagoing RADARs for commercial fishing
boats in Alaska - the kind you see on "Deadliest Catch" on TV. This
equipment was just loaded with high voltage all over the place to
power the modulators and transmitters (magnetrons). You learn
very quickly to not wear metal watchbands after a 50,000 volt
arc jumps from the electronics cabinet and throws you across
the wheelhouse. This is called "learning the hard way" ;)
I was amused to discover the HV cap in my microwave oven has an inherent
10M bleeder resistor. I did do the math to make sure it was discharged
adequately
before probing with the DVM to make sure. Oh yeah, I once got a replacement
magnetron from GE under warranty and installed it myself.
CRTs were fun; it doesn't matter to me how old a TV is even today, I still
discharge
HV port before touching anything.
Dana K6JQ
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