Resistor calculator

[scubado]

Hey guys, several months ago someone posted a link to a website that calculates the resistor needed to drop a voltage along with the current needed to drive an LED. I thought I had saved the link, but it's gone and trying to do a search brings up too many threads to weed through. Can someone please repost the link for me?

Thanks.

[Guest guest]

I believe one of these websites are what you're looking for:

http://home.cogeco.ca/~rpaisley4/LEDcalc.html

http://ledz.com/?p=zz.led.resistor.calculator

One of these will give you what you're looking for.

The second won't allow voltages higher than 32 volts DC, the first one will do 120V calculations.

Good luck!

[scubado]

Thanks Orville! That's what I was looking for.

[Guest guest]

scubado wrote:

Thanks Orville! That's what I was looking for.

Glad I could be of help!



I prefer the first one because I do use 120V applications in some of my projects. But it gets a little more complex because I have to use(add actually) a Full Wave Diode Bridge to convert the 120V ~AC~ current to 120V DC current or additional circuitry to drop the 120VDC down to a lower voltage depending on what I'm constructing and how many LED's the project will require. Most often I try to use 3VDC, 5VDC, 9VDC and 12VDC adapters (wall warts, as many call them) for smaller or projects that don't use but 4 to 8 LED's..

[scubado]

I'm installing 3W blue led's in my van for interior lighting and needed to figure out which resistor I need.

I try to avoid wiring leds in series. I seem to have higher failure rates.

[Guest guest]

scubado wrote:

I'm installing 3W blue led's in my van for interior lighting and needed to figure out which resistor I need.

I try to avoid wiring leds in series. I seem to have higher failure rates.

What you probably have is one LED getting too much current and burning out, and of course, if it's wired in series, one goes out, the entire string goes out, I try to wire my LED's in parallel when possible or practical. Sometimes it needs to be in series, but whenever possible I always try to use parallel, that way, if one LED does happen to burn our or have an issue, it doesn't affect the others in the circuit.

Good luck with your interior lighting project. Where I am blue or red lights of any kind on or inside a vehicle(with the exception of brake/tail lights) that are visible from the outside are illegal and can get you a nice citation or jail time for supposedly "impersonating a police officer(car)". So I use Green, Amber or White LED's on and in my vehicles.

[scubado]

We're not supposed to have blue exterior lights. Mine won't be on while on the road. I have seen a couple cars recently that had blue exterior lights, I wonder if they get stopped for it.

[Guest guest]

I had one of those night runner (knight Rider) style lights mounted on the rear of our '87 Firebird, it looked like it was put their by the factory, mounted under the spoiler, fit perfectly. It only came on with the brake lights and indicated which way you were turning. Because it was "animated", I got stopped by some gung ho rookie State Trooper and told me you can't have "animated lights" on your car anywhere. (I had put in a connector for easy disconnect) And he told me I had to immediately disable it or face going to jail for 30 days! He wante me to cut the wires, I opened the vehicle and said, look it came this way, see the installation was a factory install. Had the same connectors a factory would use, but he insisted it was illegal because it flashed one bulb at a time. I said what about the old Cougars? There rear turn signals are like this, said he never saw one and never heard of a factory making any such thing.



So he gave me a "citation" for the lights, at the time and if I recall, the citation was around $300! *OUCH* Even though I disconected it, he wanted me to CUT the connectors off and the wires short so it could not be reconnected, which I would not comply with. But because it was "disbaled" and non-functional, that part I complied with, that's why he wrote the citation instead of taking me to jail, which later I could have gotten him on a wrongful or false arrest!



I did take it to court and the judge at first was going to throw the book at me until I convinced him to take a short recess and look at the installation and how the lights functioned.

He threw out the citation and told the rookie S.T. to take a hike. Told him there was no infraction from the type of installation that was done ann it looked like a factory install to the judge. The judge did ask if it was factory installed or installed later. of course I'm NOT going to lie to a judge and told him I had installed it myself, but wasn't aware they were illegal, which he confirmed, where it was mounted and how it worked WAS NOT as it was in compliane with state laws as a third brake light/turn signal indicator as that was the ONLY time it worked, all other times it was OFF as it should be.

Judge was imnpressed with how I had mounted it and how it looked like a professionally done factory installation on the car.

But I think it really p.o.ed the rookie that thought he was smarter than me.



Now the judge said if it had been mounted on the FRONT of the car, then, yes, I would have been in violation of state laws and that is where he (the judge) thought it was mounted by the report he had in front of him!

I have some cigarette lighter LED items I use and they are also blue, why manufacturers think everything needs to be blue instead of amber, green or white is beyond me, especially when so many states have laws against blue and red lighting that is or could be visible.

[R Weiland]

Scubado; when you use these resistor calculators don't use 12 volts as the battery voltage. I suggest you measure it while the van is running and use that value. Depending on vehicle model and battery chemistry the alternator voltage can be anywhere between 13.7 and 15.0 Volts, enough to over-drive your LEDs if the calculations were done for 12 Volts. Good Luck!!

[Guest guest]

R Weiland wrote:

Scubado; when you use these resistor calculators don't use 12 volts as the battery voltage. I suggest you measure it while the van is running and use that value. Depending on vehicle model and battery chemistry the alternator voltage can be anywhere between 13.7 and 15.0 Volts, enough to over-drive your LEDs if the calculations were done for 12 Volts. Good Luck!!

Excellent point!!!

I always use 15V for vehicle installations, since I have seen the voltage output from my alternator go from as low as 11V to no more thn 15VDC. I prefer to use the higher voltage, just in case the alternator opts to spurt out that much, then I know my LED lights are not going to burn out or worse go POP! And if you've ever smelled a LED that POPPED (exploded), it's not a very pleasant smell at all! Eeeyew.



And I've popped a lot of LED's in my time too.:shock::shock:

[R Weiland]

Orville wrote:

R Weiland wrote:

Scubado; when you use these resistor calculators don't use 12 volts as the battery voltage. I suggest you measure it while the van is running and use that value. Depending on vehicle model and battery chemistry the alternator voltage can be anywhere between 13.7 and 15.0 Volts, enough to over-drive your LEDs if the calculations were done for 12 Volts. Good Luck!!

Excellent point!!!

I always use 15V for vehicle installations, since I have seen the voltage output from my alternator go from as low as 11V to no more thn 15VDC. I prefer to use the higher voltage, just in case the alternator opts to spurt out that much, then I know my LED lights are not going to burn out or worse go POP! And if you've ever smelled a LED that POPPED (exploded), it's not a very pleasant smell at all! Eeeyew.



And I've popped a lot of LED's in my time too.:shock::shock:

Orville;

Yes, electronic components are funny that way, Once you let the trapped smoke inside get out, they don't seem to work they same, if they even work at all!! ..... and there are many ways to let the smoke out. LOL

[Guest guest]

R Weiland wrote:

Orville;

Yes, electronic components are funny that way, Once you let the trapped smoke inside get out, they don't seem to work they same, if they even work at all!! ..... and there are many ways to let the smoke out. LOL

I think my favorites to let the smoke out of are Electrolytic capacitors, when they go POP, esecially in a dimly lit room, that is just so exciting. LOL

I've probably blown up every type electronic part imaginable at some point. LED's, Transistors, Diodes, Capacitors (all varieties), resistors, triacs, electronic relays, all sorts of IC's, even incandescent light bulbs! And each one has its own special scent when that trapped smoke gets let out too, as well as some nifty fireworks at times too. ROFL

[scubado]

I did figure in some cushion. I too have had my share of frying circuits, that's why I won't wear my wedding band. I was working in the back of a live copier and my ring had shorted a couple low voltage pins in a board and put a pit in the ring. Haven't worn it since. Luckily, it didn't hurt the machine.