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Model Forum / Radio Controlled / Air Models / November 2003Help me refresh my electronics knowledge
I want to put together a small lighting system for my parkflier. I bought a pack of LED's from Miniatronics Corp. It comes with 18 LED's and 18 470 Ohm resistors. The recommended voltage is 3 volts for the LED. It says you can use the resistors to prevent the LED from burning out higher voltages. I forgot how to figure out how to use resistors to limit voltage. If the receiver outputs 5 volts, and the LED needs 3 volts how many 470Ohm resistors do I need to limit the voltage to 3 volts. The only equation I remember is I=V/R but that doesn't seem to be enough to figure this out.  SignatureNormen Strobel nstrobel@zoominternet.nospam.net R=V/I I= V/R V=IR Jack > I want to put together a small lighting system for my parkflier. I bought a > pack of LED's from Miniatronics Corp. It comes with 18 LED's and 18 470 Ohm [quoted text clipped - 12 lines] > http://www.newsfeeds.com - The #1 Newsgroup Service in the World! > -----== Over 100,000 Newsgroups - 19 Different Servers! =----- > I want to put together a small lighting system for my parkflier. I bought a > pack of LED's from Miniatronics Corp. It comes with 18 LED's and 18 470 Ohm [quoted text clipped - 4 lines] > resistors do I need to limit the voltage to 3 volts. The only equation I > remember is I=V/R but that doesn't seem to be enough to figure this out. One should be plenty, and probably too much. I=V/R works, but you need to figure in a voltage drop of .7 volts across the diode. So you'd figure 4.3 instead of 5 for V. See what you get, but you may end up having to parallel two of the 470's, or use 220 or less, to get a good brightness level. One 470 is typical for 12V operation (about 25-30mA in this case). Do they give a mA rating for the LED's? No they don't provide a mA rating for the LEDs. I wouldn't doubt if each color is different. From my tests at 3volts the LED's aren't very bright. Would they be brighter if I ran them at 5volts, or would they just die. SignatureNormen Strobel nstrobel@zoominternet.nospam.net > > I want to put together a small lighting system for my parkflier. I bought a > > pack of LED's from Miniatronics Corp. It comes with 18 LED's and 18 470 Ohm [quoted text clipped - 11 lines] > brightness level. One 470 is typical for 12V operation (about 25-30mA in > this case). Do they give a mA rating for the LED's? > No they don't provide a mA rating for the LEDs. I wouldn't doubt if each > color is different. From my tests at 3volts the LED's aren't very bright. > Would they be brighter if I ran them at 5volts, or would they just die. Might die, but you can put 3 in series and try them that way. The voltage each would see would be just a little more than the 3 volt supply on one. These are very low output units. If you are going to try night flying, you need to get something better. I've seen several guys using very bright white led's on the nose and tail and using red and green for the wings. Works real well. Try to find something in a wide angle. I haven't used these, but here's a source http://www.ramrcandramtrack.com/UltraBrite.html Here is another good source for bright LEDs http://www.allelectronics.com/cgi-bin/category.cgi?category=340500&type=store SignaturePaul McIntosh Desert Sky Model Aviation http://fly.mcintoshcentral.com > > No they don't provide a mA rating for the LEDs. I wouldn't doubt if each > > color is different. From my tests at 3volts the LED's aren't very bright. [quoted text clipped - 12 lines] > > http://www.ramrcandramtrack.com/UltraBrite.html > No they don't provide a mA rating for the LEDs. I wouldn't doubt if each > color is different. From my tests at 3volts the LED's aren't very bright. > Would they be brighter if I ran them at 5volts, or would they just die. Run em at between 10mA and 50mA max. Use the resistors to limit the current when run from 5V. If you have been sticking them across 3V and they haven;t blown up, my guess is they have resistors in already. >>I want to put together a small lighting system for my parkflier. I bought a >>pack of LED's from Miniatronics Corp. It comes with 18 LED's and 18 470 Ohm [quoted text clipped - 7 lines] > One should be plenty, and probably too much. I=V/R works, but you need > to figure in a voltage drop of .7 volts across the diode. Not really for an LED. depends on the color. Up to 2V for some. So you'd > figure 4.3 instead of 5 for V. See what you get, but you may end up > having to parallel two of the 470's, or use 220 or less, to get a good > brightness level. One 470 is typical for 12V operation (about 25-30mA in > this case). Do they give a mA rating for the LED's? > I want to put together a small lighting system for my parkflier. I bought a > pack of LED's from Miniatronics Corp. It comes with 18 LED's and 18 470 Ohm [quoted text clipped - 4 lines] > resistors do I need to limit the voltage to 3 volts. The only equation I > remember is I=V/R but that doesn't seem to be enough to figure this out. You are on the right track, however you need to know the current requirement of the LED. Common or garden variety LEDs (ie. not high brightness ones) like 15-20mA. In determining V, you need to account for the voltage required at the LED, 3v in your case. So to run a 20mA LED from 5v would be: R = (V-3)/I = (5-3)/.02 = 100R If you only have 470R resistors, using 5 in parallel will get you 94 ohms. Could be kinda bulky though :) Russ. Norm, The resistors are current limiters. You should be safe using one resistor in series with the LED on receiver voltage. SignaturePaul McIntosh Desert Sky Model Aviation http://fly.mcintoshcentral.com > I want to put together a small lighting system for my parkflier. I bought a > pack of LED's from Miniatronics Corp. It comes with 18 LED's and 18 470 Ohm [quoted text clipped - 4 lines] > resistors do I need to limit the voltage to 3 volts. The only equation I > remember is I=V/R but that doesn't seem to be enough to figure this out. With all do respect Paul, that is an incorrect statement. LED's are current devices. Let us assume that the LED requires 10ma to obtain normal brilliance at 3 volts. At 5 volts, 2 volts must be dropped across the resistor at 10 ma R = E/I or 2/.010 At 6 volts it would be 3/.010 ergo the resistor size varies with the supply voltage. > Norm, > [quoted text clipped - 12 lines] > > resistors do I need to limit the voltage to 3 volts. The only equation I > > remember is I=V/R but that doesn't seem to be enough to figure this out. I understand what you say but you have to vary the resistance if you vary the voltage. Current changes with voltage. SignaturePaul McIntosh Desert Sky Model Aviation http://fly.mcintoshcentral.com > With all do respect Paul, that is an incorrect statement. > [quoted text clipped - 26 lines] > I > > > remember is I=V/R but that doesn't seem to be enough to figure this out. Normen Strobel opined >I want to put together a small lighting system for my parkflier. I bought a >pack of LED's from Miniatronics Corp. It comes with 18 LED's and 18 470 Ohm [quoted text clipped - 4 lines] >resistors do I need to limit the voltage to 3 volts. The only equation I >remember is I=V/R but that doesn't seem to be enough to figure this out. You need one 470 ohm in series per LED. THe equation you need for resistors in series is Rt = R1 + R2. (for parallel it is 1/Rt = 1/R1 + 1/R2 ) Add in V = R * I and power P = V * I one can solve all dc circuits. -ash for assistance dial MYCROFTXXX > >I want to put together a small lighting system for my parkflier. I bought a > >pack of LED's from Miniatronics Corp. It comes with 18 LED's and 18 470 Ohm [quoted text clipped - 4 lines] > >resistors do I need to limit the voltage to 3 volts. The only equation I > >remember is I=V/R but that doesn't seem to be enough to figure this out. you can run high output leds in serries like two and one resistor and have a more eficient system (less current draw (smaller batteries needed)) if they are 3volt leds two can be run off of a 6volt battery in serries and have great output (if they are truly "bright" ) also a note leds have a verry small angle of light pattern (like 15 degrees!!) so a small prism or the like will help with dispurtion Where do I get a small prism? I found Radio Shack had one wide angle LED but all the rest were narrow. SignatureNormen Strobel nstrobel@zoominternet.nospam.net > > >I want to put together a small lighting system for my parkflier. I bought a > > >pack of LED's from Miniatronics Corp. It comes with 18 LED's and 18 470 Ohm [quoted text clipped - 16 lines] > > so a small prism or the like will help with dispurtion Get a 1K pot and put it in series with the LED. then connect the battery and wind down the pot until the voltage across the LED is the required 3 volts. Measure the resistanace of the pot and get the nearest fixed resistor. Simple, ai'nt it! Andy from Oz > Where do I get a small prism? I found Radio Shack had one wide angle LED > but all the rest were narrow. [quoted text clipped - 33 lines] > http://www.newsfeeds.com - The #1 Newsgroup Service in the World! > -----== Over 100,000 Newsgroups - 19 Different Servers! =----- >Get a 1K pot and put it in series with the LED. then connect the battery and >wind down the pot until the voltage across the LED is the required 3 volts. >Measure the resistanace of the pot and get the nearest fixed resistor. >Simple, ai'nt it! >Andy from Oz And after you cook the LED using this method, use a current meter and set the desired current flow for the LED you have, if you what maximum brilliance. Folks, the "D" in LED is diode and in the above scenerio once the forward drop of 1.x volts is reached it will remain basically constant until you destroy the junction. The 1.x forward voltage depends on the color of the LED as they are different. Dan Thompson (AMA 32873, EAA 60974, WB4GUK, GROL) remove POST in address for email Here is the equation you are looking for: Voltage(input) minus LED(rated)voltage Divided by the Led current (in milliamps) example: 5v(input) - 3v(led) = 2v and 2v divided by .030 (guessing about 30 milliamp current some leds are more and some are less) and that all comes out to about a 66.7 ohm resistor. I have used 470 ohm resistors before and I think the conditions were a 12v source and 20ma leds. Hope this helps. Steve > I want to put together a small lighting system for my parkflier. I bought a > pack of LED's from Miniatronics Corp. It comes with 18 LED's and 18 470 Ohm [quoted text clipped - 4 lines] > resistors do I need to limit the voltage to 3 volts. The only equation I > remember is I=V/R but that doesn't seem to be enough to figure this out. Thanks this helps. I think I'm going to end up going to Radio Shack and find some higher output LEDs, and hopefully they will list the mA. SignatureNormen Strobel nstrobel@zoominternet.nospam.net > Here is the equation you are looking for: > Voltage(input) minus LED(rated)voltage [quoted text clipped - 15 lines] > > resistors do I need to limit the voltage to 3 volts. The only equation I > > remember is I=V/R but that doesn't seem to be enough to figure this out. |
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