RE: LED at 60 HZ? (was RE: Radio Shack Strobes)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

On 24 Feb 2004, at 18:32, Tesla list wrote:

 > Original poster: "explorecraft" <pariah-at-explorecraft-dot-com>
 >
 >
 > Anyone here tried wiring an LED straight off the mains with
 >   a capacitor <in series> chosen for its reactance at 50 or 60 hz?
 >
 > I thought choosing a cap with a reactance to drop the
 >   current down to the 40 mA level would do the trick.
 > (I wanted to do something like that to drive my planned
 >   primary, a flourescent circular tube, matching the cap
 >   reactance at the resonance to limit tube current)

Not a good idea. The non-conducting half cycle will apply a damaging
reverse voltage across the LED.

Malcolm

 > <My next fireworks show, perhaps>
 >
 >  > -----Original Message-----
 >  > From: Tesla list [mailto:tesla-at-pupman-dot-com]
 >  > Sent: Wednesday, 2004 February 25 06:45
 >  > To: tesla-at-pupman-dot-com
 >  > Subject: Re: LED at 60 HZ? (was RE: Radio Shack Strobes)
 >  >
 >  >
 >  > Original poster: Jerry Chamkis <jchamkis-at-bga-dot-com>
 >  >
 >  > It's true- an LED will work fine.  Regular LEDs turn on and off >
 >  plenty fast > for this application but there might be some question
 >  about > -some- white LEDs > that use a UV-excited phosphor. > > Two
 >  things to keep in mind though- > > 1.  You must protect the LED from
 >  reverse voltage.  You can > either put a diode > in series or a diode
 >  in parallel facing the opposite way of the LED. > > 2.  You must
 >  limit the current through the LED so a series > resistor is also >
 >  required.  You may get away with powering it directly from a (very)
 >  small > transformer because it can't supply a huge amount of current,
 >  but that LED > won't die of old age!  You can probably get away with
 >  50 - 100 ma peak > current through a full-size LED and of course it's
 >  perfectly acceptable to > use multiple LEDs for increased brightness.
 >  > > Jerry > > On Tuesday 24 February 2004 02:10 pm, Tesla list wrote:
 >  >  > Original poster: "Daniel Kline" <daniel_kline-at-med.unc.edu> >  >
 >  >  > An engineering friend says a high-brightness LED on a >  >
 >  low-voltage transformer, like 6 Volts, connected through >  > a
 >  suitable resistance, should flash at 60Hz in sync with >  > the 60Hz
 >  mains. (50Hz for you all over there :) >  > It seems too easy to
 >  me...he thinks that the LED may have >  > a "persistence" issue. In
 >  other words, just because it >  > turns off quickly doesn't mean it
 >  stops emitting quickly. >  > Comments? >  > Thanks, >  > Dan K > > --
 >  > Jerry Chamkis > jchamkis-at-bga-dot-com > > > >
 >
 >
 >