A short question about LED's....

[Jacktal]

I have a simple question....for a very specific purpose,I need two LED's to be connected in series but don't know if they'd work.Can it be done?If yes,do I need to double their rated voltage for them to shine properly?Thanks.

[TomDiehl]

Connected in series, yes, but remember they have to be the proper polarity.

LED's in series, if they are both the same voltage rating, then yes, double the voltage of one.

LED's in parallel, only if they are the same voltage rating, and feed them only the rated voltage.

[Anonymous]

Jacktal

LED's can be wired in series. They are silicon diodes and drop about 1.2V, White and Blue LED's can be a little higher. You can put as many of them in series as you want. All devices in series draw the same current. Two LED's in series will drop twice the voltage as one. adjust your current limiting resistor accordingly.

Ken

[Jacktal]

Thanks guys for your kind answers.I knew I could do it with regular bulbs but didn't know about LED's.Now though,it raises another question to my mind....since a LED will drop approx. 1.2 volts,it means that my input voltage has to be 2.4V minimum to start with.I will find any power source that will be needed...no problem there...so my question is...would I be better off if I use the highest possible LED voltages available (let's say 12V compared to 6V or even 3V LED's) or is it of no significant importance as long as power supply and requirements are matched?And while I'm at it...can LED's run on AC?Thanks again,Jacques.

[Seamonster]

It doesn't matter what the input voltage is so long as the dropping resistor is the right value to limit the current through the LED (or LEDs) to 20 mA (milliamps) or a bit less. The quick way to calculate it is to subtract the LED's voltage drop from the supply voltage and divide by 0.02 (for a 20 mA current). For 2 in series operating off, say, 12 volts, it would be 12-2.4 = 9.6 ÷ 0.020 = 480. That's the value of your resistor in ohms. Use the next highest ¼ watt standard resistor value.

Can an LED be operated from A.C.? Yes and no. The standard single colour red, green, yellow, etc. LEDs--no. They need D.C. There are tri-colour LEDs which can be operated on A.C. and D.C. If the D.C. voltage is one polarity, they shine red. If the polarity is reversed, they shine green. If they have A.C. applied to them, they shine yellow. Actually what's happening is that half the time they're shining red and half the time they're shining green. That comes out yellow. There are some tri-colour LEDs that use only D.C. to produce the 3 colours. They can be identified by having 3 leads instead of 2.

Hope this helps.

[pkeppers]

Do led's burn out if you dont have the dropping resistor? I plan on having a bicolor led above each toggle for my tortoise switch machines. I was experimenting a little with a bi color led that is supposed to be run at 3V. A 470 or thereabouts ohm dropping resistor was supplied with it for 12V use. Just to see what happened I ran it on 12V with no resistor and it was a little brighter. I didnt run it real long, a few minutes. Would it burn out prematurly at 12V without a dropping resistor?

[Seamonster]

Yes, an LED will be damaged if it doesn't have a dropping resistor to limit the current. However, it will work fine in series with a Tortoise switch machine because of the resistor that's already in series with the switch machine to limit its stall current. I don't use Tortoise switch machines myself, but I've gathered this information from people who do use them. Perhaps someone who has done this will verify what I've said.