LED Electric circuit help

Jedifyfe

Master Member
RPF PREMIUM MEMBER
If I had a small 12v battery and wanted to run (4) 5mm LED's and (12) 3mm LED's plus a small EL sheet, what would the circuit need to look like? I need this in laymen's terms please...maybe even a picture. Thanks!
 

Delmustator

Sr Member
Run them all in parallel. But you will have to step the voltage down with resistors unless everything is rated for 12 volts.
 

exoray

Master Member
If I had a small 12v battery and wanted to run (4) 5mm LED's and (12) 3mm LED's plus a small EL sheet, what would the circuit need to look like? I need this in laymen's terms please...maybe even a picture. Thanks!
Need forward voltage and forward mA of the LEDs to answer that properly...
 

Knightjar

Sr Member
RPF PREMIUM MEMBER
Did you choose 12v to suit the power requirements of the EL inverter? If so, it may be easier to power the EL from a separate supply.
 

robstyle

Master Member
if your a cheap ******* and good at scavenging hit up the local dollar store for a cheap LED flashlight/flasher. Ive seen some with 24 super bright LED's and others with 12, 8, 4... Depending on the size of the EL sheet you should be able to run it as is off the existing scavenged parts. You may need to desolder, add lengths of wire to the board then resolder things but its a cheap and efficient jump off.
 

Dave Porter

Sr Member
the 12v is a small battery. What would you suggest?
Small battery in size, yes, but with a lot of juice.

I have used SR44s in the past. They are 1.5V each, so you chain them together.

You can do it with a 12V but you will need to bring it down or you will fry those LEDs in a second.
 

Troy Downen

Active Member
No, no - the 12V is perfect for your needs. Simply run 4 parallel arrays of 4 LEDs in series and you won't need any resisters. Shoot me a PM and i'll send you a quickie diagram of the circuit.

Why does everyone always want to run individual LEDs in parallel and use all of those resisters? Not necessary...
 

Delmustator

Sr Member
If you need another power source, I have about 50 of these..
18650 Li-Ion batteries



Soon, I'll have enough to power my house.. :confused
 

Troy Downen

Active Member
Okay, I had a request so I'll just post some sketches here. Sorry for the sloppy work, tho. :$

First attached sketch is for running 4 LEDs in an array. The specific request is to run a total of 16 LEDs and an EL sheet. So I sketched two complete LED arrays (the two vertical strings of 4 upside down triangles, which are called diodes - that's what LEDs actually are) and then I got tired of sketching and just drew three more arrays with (...) in each array to represent the LEDs and the EL sheet. See? Sloppy work...

In this first circuit you do not need resistors. Each LED is rated at between 3.3 and 3.5V. So each 4-LED array "wants" to be "fed" between (3.3 x 4 =) 13.2V and (3.5 x 4 =) 14V. You're only supplying 12V, so each LED will run slightly less bright than if you had a 14V battery. EDIT: note that for some LED types you may experience a noticeable degredation in brightness running at less than 3.3-3.5V. For this reason, your preferred choice may be the 3-LED array discussed next. I will confess that I don't know what the spec is for your EL panel, so I don't know if you might require a resistor for it or not.

In the second attached (sloppily drawn) circuit diagram I show a 3 LED array with a resistor. If you're REALLY worried about running your LEDs without enough voltage, you can step down to only running 3 LEDs in each array. Now you'll need to construct 5 arrays each containing 3 LEDs plus another array with only 1 LED, plus another array with your EL panel.

So in this second circuit you DO need resistors. Each array requires a 75 to 100 Ohm resistor. This is because the 3 LEDs in each array only "want" to be "fed" up to 3.5 x 3 = 10.5V. You have to find some way to "consume" the remaining 1.5V (or slightly more if your LEDs are rated at 3.3V) that the 12V battery is supplying, otherwise you'll burn up the LEDs. So that's why you insert the resistor in this circuit. 75 to 100 Ohms running at 20mA current will produce the needed 2.1V or 1.5V. Realistically you can simply choose 100 Ohms (a common rating) and be done with it. Note that I've assumed that each array will be running a current of 20mA. That's typical for LEDs and should be typical for the circuits that you'll be constructing here.

For the array where you only have 1 LED at 3.5V, you'll need a resistor for that array that can provide 8.5V (12V battery - 3.5V LED). So you'll need a 425 Ohm resistor (or thereabouts; anything from 400 to 500 Ohms should work well; your LEDs can run a *little* "hot"). Again, I don't know what your EL panel will require.

For those new to electronic circuits, I've uploaded a third diagram which shows how the second circuit would be wired. Note the polarity of LEDs: the longer lead from the LED is the positive lead. The peanut shaped things at the top of each array are the resistors.

PM if you have more questions. It's not difficult - it just takes a bit of experience and a few "smoked" LEDs to get the hang of things! Good thing LEDs are cheap! :lol
 
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Troy Downen

Active Member
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.
 
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Troy Downen

Active Member
If you run the 4 LEDs per array, that is correct with the exception being the array with your EL panel. You'll need to look at your spec for that element and see what it's upper voltage limit is. If its less than 12V then you'll need a resistor for that element only.
 

Troy Downen

Active Member
I'm going to revise my thinking on this after reviewing some current - voltage diagrams for LEDs this morning. Some LEDs can experience significant degradation in current draw with reductions in supplied voltage. Thus, running the array of 4 LEDs at 3V each might produce a measurably dimmer LED as a result depending on the LEDs used. In light of this, I would recommend the 3-LED arrays with a 75-100 Ohm resistor just to ensure that you get the bright lights that you want. Sorry for the misdirection!
 

Troy Downen

Active Member
Wire wrap makes it SO fast to wire up a circuit. Or un-wire it if needed.

One note, which I've amended to the above: don't run more than approximately 140 mA current in the 30 AWG wire wrap. No problem for these little 20 mA arrays, tho.
 
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