Help with Resistors ?

Thank you for the information. I am trying to power some LED's. I was able to find what I needed today using the information you provided, which was what I was looking for. In fact I have used the formula for several other lighting projects as well. Hooked a few different things up today and they all work great.

Thanks again

Chris

ChrisGW wrote in news:7bOdnSgX0YDdjyHYnZ2dnUVZ snipped-for-privacy@adelphia.com:

OK, then all you need is a 1400 (1.4K) ohm resistor. With a 14 volt source, that will give you about 10ma of current through the LED. If the LEDs are too bright, you can use a larger value resistor (say, 2000 (2.0K) ohms. or even 2.7K). Or if they are too dim you can go with a lower value resistor (say, 1000 ohms). The things are cheap enough, buy about five values between 1000 ohms and 3000 ohms. Then try each until you get the brightness you want.

FYI: LEDs are current opperated devices (actually all electronic devices are). You use the resistor to limit the current through the LED. As a rule of thumb figure that 20ma is the largest current. and 2 to 10 ma is a good opperating range. Use Ohm's law to figure out the resistor value.

Ohm's Law: Resistor = Voltage divided by Current.

Current in this case is your desired current.

FYI2: THe pureists here will point out that an LED has a characteristic forward voltage drop of 1.5 to

3.0 volts. To be 100% accurate this should be taken into the account in the calculation of the resistor. In actual practice it doesn't really matter. All you are trying to do is light the damn LEDs up. It matters little the the current level is actually a few points lower than calculated.

LEDs require the _current_ to be restricted - typically 15ma maximum. The voltage across the LED is fixed, typically about 2.1 volts. With that information you can work out for any _DC_ supply voltage what value of resistor is required to drop the excess voltage at that value of current. The bigger the difference in voltage between supply and LED requirement the better the current regulation will be so the more constant the light output. It's more complicated than just sticking a light bulb across a suitable voltage, but it's also more versatile.

Regards, Greg.P.

Thanks to all that helped. The info was great!

Chris

Steve Caple wrote in news:1xor8u726ld3s $. snipped-for-privacy@40tude.net:

And if that should offend you, try a few PC varients:

Bad Booze Rots Our Young Guts, But Vodka Goes Well

or

Better Be Right, Or Your Great Big Venture Goes West

or

By By Rosie, Off You Go. Bristol Via Great Western

If a resistor is the correct solution. he didn't specify why he wanted a lower voltage, so a resistor may not even be the best solution -- as couple other posters surmised, suggesting he might find something else entiorely a better solution to his problem.

No, I didn't belittle. I used a smiley, eh?

Er, I don't think that suggesting that someone learn what he needs to know to enjoy this hobby is being elitist. Elitist would be to suggest that he hasn't a hope of ever understanding it, which I don't think is the case at all - he does know that resistors can be used to drop voltage, after all, so he already knows about half of what he needs to know. :-)

HTH

No, he doesn't deserve a beating, and while the responses could have been plainer, about what was missing in the way of information needed, I didn't think them impolite, or trying to infer that he was an 'Idiot' for asking the way he did. (He definitly wasn't in the 'Idiot' category when he thought of this group as a resource for finding the answer.) What I 'flipped' at, was the implied "there was enough information for answering his specific question' tone to your posting. Maybe the first answers 'danced around the problem' enough that the 'communication fog' obscured things a bit, but thats how I read your posting.

Chuck

How many? What kind? What are their voltage and current ratings? Are you powering all at once or one at a time?