ImLon2 Posted January 24, 2003 Share Posted January 24, 2003 Ok I cannot take this anymore this should be an easy setup!!! I have even tried this calculator http://www.eworld.contactbox.co.uk/calc/calcled.htm Here is what I have.. What am I doing wrong? I have a Nokia (cell phone) power supply. Out put - 3.7VDC - .35A The LCD bulb I got was from Radio Shack and it is a 5mm 3.7 volts - 20mA 4.7 volts - 30mA But I think that was wrong. Am I right? Could this have just been a bad LCD? It looks fine. Please help!! Link to comment
darkblade Posted January 24, 2003 Share Posted January 24, 2003 Actually, they're right. If your PS is .35A and the bulbs are rated for 30mA MAX, the ps is putting more amps out than the bulb can handle. A resistor would be needed..... or.... Here's what I did. If you have a Pic-n-Save or Big Lots...(same thing)...they have a 3.5 to 12v adjustable ps for 5.00. I hooked up 3 1000mcd 3v blue LED's in parallel (if one blows...the others stay lit), then I can adjust the voltage and it acts like a dimmer. Since the ps adjusts the voltage from 3.5 to 12v, and the total wattage of 3 lamps is 9vDC it's all good. If I lower the voltage, the lights dim pleasingly. You can use a 1000K resistor to drain off some of the current if you think it's too much or buy any Universal adjustable AC/DC power supply. Radio Shack has PS...not for 5.00, more like 15.00 or so and they also have the resistors something like 1.29 for 5. HTH:) Link to comment
ImLon2 Posted January 24, 2003 Author Share Posted January 24, 2003 Thanks for the info. I will have to go up to Big Lots (less than a mile away) But shouldn't my PS work 3.7 with 3.7 LCD? Isn't that all you have to match? Link to comment
ImLon2 Posted January 24, 2003 Author Share Posted January 24, 2003 Okay just got back from Radio Shack. Talk to someone who knew what he was talking about. and said you only have to match the volt. that the .35a is equal to 350ma which was fine. The bulb being 30ma max. He said that is the max the bulb will pull from the PS and that you do not have to match that.. So he gave me another bulb, so when I get off work and get home I will hook this up and hope that it works right this time. Last time I might have hit - + together. I don't think so though. Link to comment
Cami Posted January 25, 2003 Share Posted January 25, 2003 You have to put in a resistor. The total amps the PS can put out is only meaningful if you have a chance of drawing more current than it could put out. Buy a PS rated at 6vdc at 1000ma or more. I can't give you thirty years of electronic training in 1 paragraph so here is the short version. The voltage for the led is fixed by design. An led rated at 3.7 volts will have a voltage drop of 3.7 volts. The 30 ma's is the highest safe current allowed. You have to limit the current by inserting a series current limiting resistor that will drop the remaining voltage (6v - 3.7 = 2.3 ) @ 30 ma. Ohms law is Voltage = resistance * current Current = voltage/resistance Resistance = voltage/current You use the last formula Resistance = 2.3v/30ma Resistance = 77ohms (or the closest value higher) If you use 2 or more LED's in parallel then each needs it's own 77 ohm current limiting resistor. A 6 volt 1000ma PS could lite one of theses LED's or 30 of them. And with 30 of them in parallel , they'd still be using only slightly over 5 watts of power total. Watts = Voltage*Current Hope this helped. I Know alot more about electronics than I know about fish. This seems to be a good supplier for LEDs. Much cheaper than Radio Shack and a better choice of wavelengths (colors) http://www.superbrightleds.com/index.htm Cami Link to comment
stephen Posted February 2, 2003 Share Posted February 2, 2003 so Cami, If I use this power supply: here ...And this bulb: here ...With this resistor: here Will my setup be good to go? I just wanted to make sure before I waste any money blowing up bulbs. : Link to comment
adinsxq Posted February 2, 2003 Share Posted February 2, 2003 umm.... ok so you have a 6v supply, a LED with a forward V of 3.7 and you want to run it at 20ma? i'm calculating a resistance value of 115 (with the next standard resistor being... 120ohm: brown red brown) yes? http://ledmuseum.home.att.net ^^not all LEDs are created equal /me chants nichia! nichia! uno! http://www.nano-reef.com/forums/showthread...=&threadid=6768 dos! http://www.nano-reef.com/forums/showthread...=&threadid=8058 three! (classic) http://www.nano-reef.com/forums/showthread...=&threadid=3691 four! (my favorite) http://www.nano-reef.com/forums/showthread...=&threadid=5845 oh btw, don't overdrive the blue, you'll shorten its life and screw the spectrum Link to comment
adinsxq Posted February 3, 2003 Share Posted February 3, 2003 Originally posted by Satchmo my head is spinning i reached into my fun bag and pulled this out juuuuuuuuust for you... Link to comment
Cami Posted February 4, 2003 Share Posted February 4, 2003 That will work. Three volts won't overdrive the LEDs. I hear, and I can't verify this, that these 470 nm diodes are very static sensitive. Now I've never known this to be true with common red or yellow LEDs but just incase it's true use a ground strap when handling them. Please let me know how it turns out. Cami Link to comment
Satchmo Posted February 4, 2003 Share Posted February 4, 2003 Thanks adin. That's more along the lines of what my electrical abilities can handle. Now the side of the battery with the bump is the positive, right? Link to comment
Crakeur Posted February 4, 2003 Share Posted February 4, 2003 Originally posted by adinsxq i reached into my fun bag and pulled this out juuuuuuuuust for you... you can do that? I didn't know they were good for storage too. Link to comment
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