Making string of leds

I bought two sets of 10 light LEDs that use two C batteries each. I hooked up a 4.5 volt adapter to one string and it worked fine. Not too scientific but it worked. First I experimented with a Lionel transformer or low voltage. I think 12 olts would be too much.

Ed, your calculator is actually correct.  If you have 10 LED's in series, even the 2V ones would be looking for 20 volts.

You'll need to wire them in groups of three or four and have each string separate with it's own current limiting resistor.

After you figure the voltage drop of all the LEDs in the string, just multiply the remaining voltage by 50 and that's the resistor you need for that string.  That's a minimum, you can go higher in resistance to add a safety margin, even doubling the resistor will make little difference in the light output.

Thanks for the info.

My application is an 18" tall Christmas tree in my home office.  I bought a box of Lionel Christmas ornaments awhile back and now I wanted to make up a string of orange and a string of blue leds.  I thought it would be as simple as putting a single resistor in front of 10 leds but now I know how it needs to be done.

Thanks,

Ed

You could feed it with higher voltage and use them all in series.

115V should do it, and the flames from the tree will be entertaining as well!

Good one !

I am not an expert on these things, but if you are going to power with AC vs DC, you also need to know the reverse voltage so you don't cause a problem. Effectively, LEDS powered by AC will turn on/off at the frequency (60Hz). I don't know if the flicker would be noticable.

I was joking about the AC, but if you want to power a string of LED's with AC, the simple protection scheme is to connect them in pairs of opposite polarity.  The one that is lit protects the unlit one from the reverse voltage on each half cycle.  The 60hz flicker is not noticeable to 99.9% of the population, though some insist they can see it.  You watched TV for many years with NTSC broadcasts with 60hz refresh rates...

and the flames from the tree will be entertaining as well!

John, your spell checker apparently substituted a "w" for your original "H".  The tree would be just as hot as ....

I'm trying to be good Dale, but it's difficult.

When it comes to sizing LED resistors and designing arrays, I've relied on these two online calculators to get the job done right the first time.

For single LED circuits: Single LED Calculator

For multiple LED circuits: Series/Parallel LED Calculator

Hope this helps!

-John