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Step 2It is not just Environmentally Green
,
My Honest Admission - The so-called Green aspect to saving electricity never even crossed my mind until the project was completed. But then if you need an environmentally friendly science project idea?
Then a light went on above my head.
Figuring that LEDs are getting cheaper and brighter all the time, I would try using a group of LEDs, but I needed a circuit. At [www.DiscoverCircuits.com DiscoverCircuits] I searched for LED and found this interesting article, with some pix.
AC Powered White LED Strings
designed by David A. Johnson, P.E. May 14, 2007
A while back a guy by the name of Ken Schultz sent me a simple drawing of how he connected a string of 30 LEDs, to make a nice under the counter accent light, powered by 120vac. He wired the strings in two series sections of 15 LED each, but wired in opposite directions. He then used just one capacitor to limit the AC current through the two stings. I looked at the circuit and decided that it seemed quite reasonable. The only change I decided to make was to add a metal oxide resistor in series with the capacitor, to act as fuse and to limit the peak current, should there be a voltage spike on the AC line. With the two strings of 15, the current is first pumped through one series string, and then as the AC line polarity changes, it flows through the second string. Since the capacitor acts as a constant current source, you can use other string numbers. The capacitor value shown keeps the current limited to about 20ma for the LEDs. In Europe and Australia, where the line frequency is 50Hz, you may see a noticeable strobing of the LEDs, if there is substantial separation between the two different polarity strings."
"Soktha from France (soktha@free.fr) sent me his version of this circuit, using two strings of 14, for a total of 28 white LEDs. He mounted the LEDs onto a wood stick. When powered up from a 240vac 50Hz source, the devices provided a nice white light.
Seems it does not matter how many LEDs are used if they are somewhat balanced. As well a bonus, is it should works worldwide on wall power. The schematic is a pdf file.
My Honest Admission - The so-called Green aspect to saving electricity never even crossed my mind until the project was completed. But then if you need an environmentally friendly science project idea?
Then a light went on above my head.
Figuring that LEDs are getting cheaper and brighter all the time, I would try using a group of LEDs, but I needed a circuit. At [www.DiscoverCircuits.com DiscoverCircuits] I searched for LED and found this interesting article, with some pix.
AC Powered White LED Strings
designed by David A. Johnson, P.E. May 14, 2007
A while back a guy by the name of Ken Schultz sent me a simple drawing of how he connected a string of 30 LEDs, to make a nice under the counter accent light, powered by 120vac. He wired the strings in two series sections of 15 LED each, but wired in opposite directions. He then used just one capacitor to limit the AC current through the two stings. I looked at the circuit and decided that it seemed quite reasonable. The only change I decided to make was to add a metal oxide resistor in series with the capacitor, to act as fuse and to limit the peak current, should there be a voltage spike on the AC line. With the two strings of 15, the current is first pumped through one series string, and then as the AC line polarity changes, it flows through the second string. Since the capacitor acts as a constant current source, you can use other string numbers. The capacitor value shown keeps the current limited to about 20ma for the LEDs. In Europe and Australia, where the line frequency is 50Hz, you may see a noticeable strobing of the LEDs, if there is substantial separation between the two different polarity strings."
"Soktha from France (soktha@free.fr) sent me his version of this circuit, using two strings of 14, for a total of 28 white LEDs. He mounted the LEDs onto a wood stick. When powered up from a 240vac 50Hz source, the devices provided a nice white light.
Seems it does not matter how many LEDs are used if they are somewhat balanced. As well a bonus, is it should works worldwide on wall power. The schematic is a pdf file.
LED strip 0 light schematics pdf.pdf(792x612) 11 KB| « Previous Step | Download PDFView All Steps | Next Step » |
I got a question regarding the resistor, its driving me crazy. To me this is how a resistor is used (quick googlezia result) http://unclean.org/howto/led_circuit.html
Volts = Icurrent Rresistance
so lets say if I take resistor out and measure voltage drop with a multimeter between cap and leds and if I do the same measurement between cap, leds and resistor v drop will be greater, ohms laaaaww, right?..oh and after resistor current is..wait, zero or pretty close to?
thx
the capacitor is not polarized ( 400V capacitor, 0.22uf ) the resistor is a metal oxyd ( 1K 1W ).
also for the second experimentation, i've put 72 Leds ( always followed the provided diagram ) the lamp works fine.
diagram and detail : http://www.discovercircuits.com/H-Corner/AC-Powered.htm
Again, thanks to David A. Johnson.
Soktha
http://library.thinkquest.org/10784/circuit_symbols.html
This link shows the symbols I'm used to as far as capacitors go anyway.
Because of the written circuit description that I found I went with a non-electrolytic. I believe it is because an electrolytic would not work properly as the current limiting while on AC.
Thanks