LED Electric circuit help

[DrewSmith007]

This site will tell you all you need to know about your LED circuits, however you need the datasheet of the LED's you're using.

LED series parallel array wizard

Forward voltage is sometimes listed as voltage drop.

Below is an explanation of how that calculator arrived at its value. You don't need to know this stuff, but I thought I'd put it in there for those of you who want to know it.

The voltage drop is important because it tells you how many LED's can be run on the same strand, called "in series". Voltage drop adds together with each LED in series. If you have a voltage source of 12v, 5 LED's, and your voltage drop is 2.2 for each LED (11V total), then you have a net voltage of 1 volt. This net voltage is what is used to calculate the resistor needed for that strand. If the LED's are rated at 20mA (.020A), with your 1V (net voltage) you would need a resistor value of:

Ohm's Law: Volt (V) = Current (A) X Resistance (Ohm)

Rewritten to solve for Ohms: Ohms = V/A = 1/.020 = 50 ohm resistor

Since 50 ohms is not a common value, you would move to the closest higher value available. This will reduce the current a little, but it shouldn't affect the brightness of your LED much, unless you go much higher in resistance. You don't want to move down, as this will allow more current to flow than the rated 20mA, and could cause the LED's life to shorten.

So, in this case the most LED's you can run in a single strand is 5. If you need more than 5, you just put them on another strand. Remember that if you have fewer than 5 LED's on the new strand, the net voltage will be higher and therefore need's a higher resistor to limit the current to 20mA.

Following these rules will give you the brightest LED's possible, that will last the longest and give the longest battery life. Sure you could do 5 strings of single LED's with a 560 Ohm resistor for each LED, but that requires 5x20 = 100mA of current, which will last 1/5as long for the same result.

 

[Delmustator]

Tip: don't use that heavy 22 or 24 gauge wire that everyone seems to use. It's bulky and gets in the way and really requires that you solder it to the LEDs. Ugh. Use "wire wrap" wire instead - it is more than sufficient to handle the mili-amps of current that you'll be using to run LEDs. EDIT: Don't run more than approximately 140 mA current in the 30 AWG wire wrap. No problem for these little 20 mA arrays, tho.

If you're in the States then go to Radio Shack and pick up a wire wrap tool (see attached photo) and a spool of "wire wrap" wire. It will look too thin, but trust me - this is exactly the stuff that you'll need. Use the wrap tool to produce nice, snug wraps of wire around your LED leads (don't forget to use the included wire stripper to strip off the insulation on the wire wrap!). See the second photo for an LED with the wire wrap around the leads. No soldering required - this is a good, tight fit!

I'm extra conservative in building my circuits, so after wrapping my LEDs I also put some 1/8" heat shrink wrap around each lead and shrink it into place to prevent any accidental shorts in the circuit. (see attached photo) You can get the 1/8" heat shrink wrap at Radio Shack or, a bit more economically, at Lowes or Home Depot in the electrical aisle.

I hadn't seen anyone do wire wrapping since my days in a telco terminal. This is how ALL wire connections are made in a central office on wire wrap blocks. Back in the day, we had thousands of these. It definitely works if you can find a wrap tool. I used to have a wire wrap gun that was electric (kinda like a drill). I could completely wire wrap ABAM cables between a DSX panels and M13 shelves in about 2 hours. If you never seen an ABAM cable, it's 30 pairs of 22 gauge wires per cable.

 

[Troy Downen]

Teleco is about the only place where they still use wire wrap, I believe. But they use the heavier gauge wire. Hard to believe, but some of the Apollo program computers on the ships that went to the moon were connected entirely with wire wrap. Maybe it's a lost art? I dunno... but I'm just now finishing up a Star Wars Star Destroyer lighting project using 30 AWG wire wrap to hook up all the LEDs. It sure makes for fast work.

 

[exoray]

Maybe it's a lost art?

High quality PC boards that can better and more reliably route the signals are more cost effective and can be made smaller and quick, so yeah it's a dying art... When you toss in very high quality stab-lock connections it even pushed the death faster...

It has it's place, but new tech has simply replaced it in almost all application...