Why dont you use a full wave bridge rectifier....rather than a half wave?
You can still use the cap as a regulator, although I doubt you need that
large a cap with a full bridge. All your looking do do at that point is to
mitigate the ripple. When you use only a haf wave your ripple is large as
you will only be getting one pulse per cycle. A full wave will invert the
negative half cycle and produce two pulses per cycle or 120hz.
Electrolytics usually have either a stripe down one side or a dot or a +.
Word to the wise....capacitors are able to release all their energy nearly
instantaneously. Which makes them great at shocking the piss out of you.
Especially when charged to potentials high enough to be conducted through
the human body.
----- Original Message -----
From: "Bill Walden" <wdwal...@hughes.net>
To: "Don Cooper" <wavyca...@gmail.com>; <texascavers@texascavers.com>
Sent: Sunday, October 21, 2007 1:57 PM
Subject: Re: [Texascavers] LED Primer
Don, assuming each diode has a voltage drop of 3.6 volts, your series
string of 40 would have a voltage drop of 144 volts at rated current. (I
assume 20 mA) The red dot marks the positive terminal of the capacitor.
At only 20 mA the capacitor may level the voltage closer to the peak value
of the voltage You may want to use a 1000 ohm resistor and two
capacitors - one on either side of the resistor - a pi network filter. Use
a 1/2 watt or greater resistor. Using a multimeter check the current in
the circuit. Meter should be in series with the LEDs. Adjust the value of
the resistor to keep the current at or less than the rated current for the
LED's.
Check the spec sheet for your LEDs for actual ratings.
Best regards,
Bill Walden
.
Don Cooper wrote:
Speaking of LEDs... I'm wanting to use a large capacitor to level the
voltage off half-wave rectification (single std.diode isolating the
capacitor - [k.i.s.]) - for a big series string of 40 white LEDs that are
hooked up direct with a 100ohm resistor in series. It works, but flickers
at 60hz. It is running on the positive side of the sine wave which I
think peaks at 177v (110 RMS). While swinging negative across the
LEDs - the house current is a disconnect. They are diodes after all.
It's a fairly bright and efficient light (probably). Unusually
oriented - the multiple inline elements produce "polarized shadows" (only
vertically aligned objects in the room have defined shadows - this might
make an interesting way to light cave formations!)
Hooked up to AC - the flicker is a bit bothersome. But making it "on"
all the time using a capacitor to reservoir the voltage, it will appear
much brighter. (A beefier load resistor might be in order to maintain
the constant rather than flickering wattage).
QUESTION: I found a big 820uF cap - rated at 200vdc. But it does not
have clearly marked pos/neg terminal. There is red paint on the base
rivet that holds the terminal on.
Is that the Negative or Positive side?
-WaV
A dog. A panic in a pagoda.
On 10/21/07, *Minton, Mark* <mmin...@nmhu.edu <mailto:mmin...@nmhu.edu>>
wrote:
There is a good layman's primer on LEDs and the physics
behind them in the September 2007 issue of Spectroscopy magazine. You
can read it here: <
http://www.spectroscopymag.com/spectroscopy/The+Baseline+Column/Light-Emitting-Diodes/ArticleStandard/Article/detail/457040?contextCategoryId=2324>.
Mark Minton
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