It brings back fond memories from the late 70s. As a kid, I had picked up a few red LEDs from Radio Shack, without really having a use for them. Until I looked at my slot-car set. The cars had grain-of wheat incandescent headlights, but no tail lights. I measured the track voltage range, which varied with the hand-throttles, then I found the maximum current on the package somewhere. I worked out the resistance needed using Ohm's law, drilled some holes, glued them in, and voila. Tail lights on my slot-cars. Since an incandescent bulb is a regulator of sorts, I could have wired the LEDs through the headlights to stabilize the LED light levels throughout the range of voltages somewhat. Since resistance is very low when the bulb filaments are dim, and high when the filament is hot, it would have allowed higher current to the LEDs when the car was going slow, and limited current when the headlights were bright, and the car was going faster. I'm not sure if the voltage drop would have been sufficient, so perhaps a shunt-resistor may have been required. I remember that if you accidentally got the polarity wrong on those LEDs in those days, they burned out immediately. Thankfully not the case any more.
Very good video, simple and easy to understand.. I'm little bit ashamed because I never did the calculation, I always used any resistor in the 270omhs range and if the led was too bright or too dim, I changed the resistor :-)
Great video. How did you do it without injecting annoying background music into the video? I thought it must be a RU-vid rule that electronic content videos must have annoying and unnecessary background music injected. Thank you very much for you doing it the right way.
There is even simpler method which is U=(R1 +R2) * I . R1 is the resistor R2 is the led résistance.. If you want to know which resistance to use just do R1= R2- U/I
Great video. When you were explaining the reason for the same resistance value in the parallel circuit as opposed to the series circuit, the current was doubled but the voltage drop across the LED's is one half the value of the series circuit, not double. That is the why the resistance value is the same. E is directly proportional to R, while I is inversely proportional to R.
I got confused by this. It seems back-to-front to me. Now that I "get it" watching it back I see where it goes wrong. He doesn't state the value on the datasheet for max continuous current, so when its value comes up much later (0.02A) I didn't know what or where that value came from without use of a meter/measurement. This tutorial, and others like it, led me to build up an wonky mental model that the current in the circuit is somehow a property of the circuit and its components and the supply, perhaps the type of LED happens to draw 0.02A, and that I need to therefore determine the *correct* resistor for that current with the voltage drop of the LED according to its datasheet. The right way to look at it is that you're choosing a resistor in order to limit the current in the circuit to prevent the LED from pulling too much and burning itself out while remaining as bright as you'd like it. So the value I (current and thus brightness) is determined by your choice of resistor, not the other way around; we're trying to find a value of R that gives I. It's not that we have I and we need to "figure the value" for R.
I am trying to build a 20 LED voltage checker for the leisure battery in my camper van. I watched a video where the guy made one with only LEDs and resistors, but his was only ten LEDs. Could you make a video explaining how to figure out the correct resistors needed for each 5% increase? Even after watching your video I can’t figure out how to do it. As the voltage rises, more LEDs slowly come on and vice versa. I have read conflicting numbers for what a fully drained battery is ranging anywhere from 10.5V to 11.4 V and 12.8 to 13.6V fully charged. Does that affect resistor size? Thanks for making this video, I learned something...
Don't worry about all the calculations. Gone on line and you will find charts that give you the resistance value for various voltages plus different colours require different resistance. Different colour LED's require different value resistors. The project I am working on operates at 3 volt. The yellow LED requires a 47 ohm resistor while the blue LED requires a 10 ohm resistor. If I get the resistors around the wrong way I will blow the yellow and the blue will not come on, Down load a resistor value chart and pin it on the wall.
@@imho2278 Hi, the different colour LED's have different voltage ratings, you will have to check a data sheet for the voltage rating. When I know the voltage rating I then look up the resistor required for the supply voltage, his could be 3v, 6v, 24v. When I know the resistor vvalue, say it is 220 ohm I add a little bit extra resistance. The LED will last forever.
There is a app called wova in the Google play store that will do the math easily. To find the wattage of the resistor just multiply the voltage drop across it times the current to get it. Twenty milliamps would be .02 when entering.
It wasn't mentioned in the video but generic LEDs come with a set of generic numbers for typical forward Voltage (R:2v, G & Y;3v W:3.8v, blue:4.5v) and Current (usually always 20-30mA). These are only approximate, when you buy the listing should give actual - but it's usually good enough. then always round resistor values up not down, the higher the resistance the longer the LED will last (but it will be dimmer). Google "current rating of led by color" to see typical ratings. If you work with "ordinary" LEDs and common voltages (3, 5, 9 &12v) the resistances are pretty standard and quite forgiving 56, 150, 390 and 470ohm are pretty common values. google "LED resistor calculator" or visit led.linear1.org/1led.wiz this site does the job for you
Youve quoted what's wrong - Shame you didn't take the time to give the figures you think are correct. I'll take the currents, had a brain fart! I was thinking in mA and then entered it longhand - I've amended that to mA. I did say that the voltages were ballpark numbers - often white is quoted at 3.4@20mA I'd usually work with the numbers I quoted because I find they work. As I said intended to be approximate with a safety margin I'll stand by them. Unless I'm particularly pushing as I also said I'd always round up and put a generous resistor into my stuff, things last longer that way. Feel free to give your take - none of the numbers are set in stone - and I'm sure we all have had different experiences.
Am using a 12v automotive lead acid battery and it can output around 10A consistently (it can light 130W 12v halogen without any issue). So to light a single 3V led from it, do I need a 0.9ohm resistor.?
Lets say that my power supply for example is 50vdc, Can I still use this to power my led? 50vdc-3vdc=47vdc 47vdc/.02amps = 2,350ohms / Would this OK for the LED?
A quick average I use is 1000 ohms per volt for about 10ma and 500 ohms for about 20ma. It doesn't calculate the resistor power dissipation, doesn't work well for voltages below 5 volts, becomes inaccurate with a series string of LED's, becomes more accurate the higher the voltage is, and doesn't really work for the blue or white LED's. It's only good for getting you in the ballpark.
I am using 66 yellow led light for making series with 3 resistors of 100 ohm and it got burn .... I even tried using 6 resistor but same problem occurred...can you please help me??? Where am I getting wrong
Howdy, Brother! What resistor should I use if I have a yellow 10mm LED Emitting Diode (1.8-2.2V) powered by two AA Batteries? I will have an on/off switch in the loop. Will 47 ohms work? i tried 100 ohm resistor but the batteries were getting hot. I'm not even sure if I asked the question properly . Thanks for any assistance.
If there is a large voltage to drop across the current limiting resistor, it may be better to use a driver circuit. This is true with higher power LEDs because a driver circuit adds complexity and cost to the circuit.
hey I got this lithium 12V battery(16Ah) for small scooter or some outdoor electronics. If I want to make a new LED fixture and buy a single 12V LED with current max at 1.25A and run it with the battery that I have, do I need any resistors? I want to make an outdoor camping LED lighting and want to use this 12V 16AH battery to power this for a long time. I heard as long as the voltage is same 12V, the LED will only draw the current that it likes and will not draw more than it can. Does it mean I do not need ANY current resistors? because 16AH sounds like a pretty heavy force for 12V LED with 1.25A current-max to be connected.
I find it strange that this info is so simple and easy to find and yet I STILL frequently find retail packs of LEDs that don’t give me the specs I need.
Emmett Turner If you own a multimeter, you can measure the voltage across both leads of the LED while powered up, then recalculate and pick a more optimal resistor value to pair with the LED. The maximum current is usually rated at 30 mA, but if you target around 10 mA, you'll still get very good illumination and longevity.
If you have to add resistance to a circuit in order to run the LED, does that counteract the energy savings? Do the resisters plus the LEDs burn up the same power as the standard bulb, but instead of having the energy loss through heat in the incandescent bulb, the heat is now generated in the resistor?
Thanks for the video, it was most helpful. Newbie question: Does the resistor need to be in font of the LED? The reason is I have designed a circuit with three LEDs but only one is powered at any given time so I joined the ground ends of the LED's and connected a single resistor between them and the ground. However I am now doubting the correctness of this approach.
Nice vid, it wasn't able to answer a question I have so I'm hoping you can. I bought after market tail light assembly and the brake and day running lights are the same bulb. No additional resistors or capacitors were included. I was wondering how would I go about wiring them so the load will restrict wen not hitting the brakes. Thanks for any help and I'm re using the stock tail light harness.
Paralleling LED's is a bad idea. LED current increases exponentially with LED voltage. Any small mismatch between "identical" LEDs will cause one to draw significantly more current and be brighter than the other. You can add a small value resistor (10 ohms) in series with each of the parallel LEDs to correct for device mismatch, but you would be better off just giving each LED it's own voltage dropping resistor.
From experience, even matched LED's will start drifting apart over time when run in parrallel on a single resistor. I assume it is from uneven heat distribution causing accelerated aging of one of the LED's, which gets worse and worse the further they drift apart.
Thanks for the video. I have a quick question about my third brake light on my car which are LED’s. There are 4 lights in a row on a metal strip with a plastic backing. There are 2 light blue cylinders between each set of bulbs which say 240 J I’m guessing that’s jules. And it says .07 on the same cyclinder. The cylinders are tiny maybe the size of a large grain of rice. Sorry for my lack of terminology I’m trying to learn as we speak. On the far left there is an even smaller black cylinder. All the cylinders have these metal connections on the sides and are connected to the metal strip. The metal strip sticks into the plastic backing and forms a socket in middle on the back of the plastic backing. Sorry I’m typing so much I don’t think I can post pics on RU-vid and I really want to figure out if this is fixable. The lights don’t work and I want to know why. As far as I know the whole light went out all at once. I’m trying to figure out if I can replace some of those cylinders would it fix the light? If you can’t answer I understand thanks again for the knowledge.
hi just want to ask. how can i compute if how many ohms should I use to light up a 40 smd led (blue) which has a 3.2 volts each and 20 ma each using a 12v battery (motorcycle battery) (when charging goes to 13 - 14v) thank you and i will wait for your answer thanks
I have an LED bulb I removed from a "Finger Light" that was powered by three 1.5 volt hearing aid size batteries. There was no resistor in its set up, just a basic on/off switch. I want to install it in the nose of a toy drone that uses a 3.7 volt lipo battery. Do I even need a resistor added to this circuit? Just wire it pos and neg from the drones battery's circuit board terminals?
The "finger light" was relying on the internal resistance of the tiny batteries. The toy drone battery can overdrive the LED, so it is better to use a resistor.
Parallel LEDs in a Red/Green (single LED 2 color LED) pair (street light scenario) would benefit from the last circuit shown. Is there an issue substituting the single color in your example for a 2 color LED (reversing one orientation)? Also - Resistor on cathode or anode normally, and what about on 2 color situation?
hi, nice video will need to watch it a couple of times, but at 4.20 you went on to the calc for Watt, why do we need to know? is it just for the sake of elec consumption or is it for the purpose of using the right parts so no damage is caused? thanks in advance
Please tell me why in my preamp circuit where I include a blue LED powered by the 48 volts from the phantom circuit in my mixer- I can use between 2.2 megs to 5 megs and the blue Led shows up nicely.
What if you don’t know the fwd voltage drop if the LED? Got a bunch of old LEDs, no idea what they are (some IR). So nothing to calculate without that figure, you’d be trying around until you get there...or not?
I've got an LED running off of 5v with a stock resistor of around 350 ohms. can't get this replacement to light up. are these so far off from one another to where that restistor value is way too much?
Calculating the resistance seems the easiest part. Knowing the current and voltage drops takes prior knowledge. You should have provided a source for that info
Im having trouble with a system of mine.. I have avg 3v 5mm leds supplied w/ 6volts of power. Im using a 2.2ohms resistor.. Light seems a bit low luster in my opinion? Am I using or ding something wrong? I tried using the ohms calcualtor law app and it said 2.3 ohms?
I have a question, what if i want to power an LED using a Lead acid 12v battery but of course the constant voltage is not going to be 12v because when it is fully charged it goes up to 13.8v. Do i take an average of that or just stick with 12v. thanks
I would design for the highest voltage so the LEDs aren't stressed from over current if the voltage is that high for long periods or you could use a constant current source driver.
Your last circuit is wrong I think! The voltage drop accross the LEDs is 3 Volts, which means you must have 6 Volts drop on the resistor and that is why you have such a high resistor value and thus higher power consumption. If you supplied the circuit with 5 Volts then you would have R=V/I=(5-3)/0.04=2/0.04=50 Ohms. Hence, P=I^2*R=0.04^2*50=80mW compared to the 240 mW you have on the previous circuit.
I wish this made sense to me. I'm just trying to get my LED diodes to be dimmer. Seems that reducing my power supply to the minimum of 3V might be the easiest.
With the third circuit (powering two LED's) why would you use a 9V power supply?? Two LED's in parallel still only have a 3V forward voltage. The circuit would just require twice the current, the same 100ohm resister and draw exactly twice the power of the first circuit!
Sir my son is 13 yrs he love LEDs his cycle full of LEDs.from the u tube only he learnt to do simple torch he used 12V LED and 9 V battery it worked one day after led finished his life.what to do. In this case we have to use resistor?
I'm sure that it is mentioned in the data sheets but in school, back in the 70s we were told that a typical LED is around 20 Milliamps in the 80s and the 90s the white or blue LEDs it was suggested that a 40 milliamp current would be needed. Not always but myself I rarely ran across one that used a lower current. But since the 00s I haven't been in electronics hardly at all. Can not focus on the small parts.
I have noticed that the resistor used in LED indicators for 220V AC appliances like mosquito repellents uses 100k resistor but according to the formula [Resistance = (Supply Voltage - LED Voltage)/LED Amps] the resistor should be 12k (approx) but why 100k is used?
JohnAudioTech but why 100k... wny not 110k or 200k? how they calculated that it should be 100k? Also the wattage of resistor for 230v should be arpund 5w but why they used 1/4w resistor?
It is not critical. 100K is "near enough" to give the light output they need from the LED. 240v across 100K is about .58 watts. The AC would probably be half wave rectified as the LED would be damaged if that kind of voltage is placed in reverse across the circuit (even at the limited current). This would mean lower heat dissipation from the resistor. I would use a 1/2w resistor.
JohnAudioTech But I want to know how it was calculated that 100k should be used? Also for 100k resistor the wattage should be around 5watts because according to the formula Power = Resistor Voltage * LED ampre = (220-3)*0.02A = 217*002 = 4.34 watts.
The designer connected the LED to a variable current supply and determined the LED was bright enough at 2ma. 217v/.002a=108.5K ohms. 100K is close enough value. 217v * .002a is .434 watts. Your decimal point is in the wrong position.
If i have 20 watt led nd i want to on those all on 220 watt so wt resistence should i use nd if i use with my byck then wt resistance nd wht circuit should i make to start pls help tell me.
Hi , I am going to make a LED light cct for 2000 LED's what would be the best way to the layout? series or parallel? according to your video, I would imagine it was a series.
Are you sure about the current of the LED? I did a quick test with a 3.7V (cellphone battery) and a white LED, the amp meter showed 1.4mA (0.0014A) and using this value in the formula spits out very high resistor values like 2kohms for 4 LEDs at 15V
JAT is correct in what he's showing - You should always design to the figures in the specsheet, that's designed to achieve the optimum (not necessarily the "best"(for you) ) results and protect the LED. In real life other factors such as wire distance/resistance line capacitance/inductance ... la la la may need to be factored in depending on the environment. So when you go to the production stage, adjustments might be needed. If brightness is an issue you can overdrive drive the LED to the point where it only lasts for a few hours rather than the spec rating of 50,000. Actual readings can significantly vary depending on real life requirements. But you still always start from spec.... And in some circuits small differences result in (relatively) big changes in values. 2 v (3->5v) results in a jump from 50 ->150 ohm. That's just the way the fractions work
