led series or parallel

[belkin321]

What is the best way to wire leds for models, in series or parallel?
Thanks

[jgoldader]

What is the best way to wire leds for models, in series or parallel?
Thanks

It depends (doesn't it always?). From my perspective, if you've got a few LEDs and want to have the same total brightness, you're going to use the same amount of power: P=IV, where P is power, I is current, and V is voltage. The difference between series and parallel is more or less trading V for I, or I for V.

Series: you only need the current for one LED, usually 20 mA or less, since the same electrons go through each LED. However, the voltage needed to light the LEDs is the sum of the voltages of each individual LED. For example, if you have three reds in series, you can expect to need a power source of 6V or so (figuring 2V or slightly less per red LED) but you'd get by with only 20 mA or less current. Don't forget your dropping resistor, 100 Ohms or so with this setup, though you'll have to experiment to get the brightness and current where you want them. (Maximizes voltage, minimizes current.)

Parallel: you can get by with less voltage, but need more current. Three LEDs in parallel will take the voltage needed to drive one LED (2V for the reds above), but since you're powering three LEDs, you'll need 3x the current, or up to 60 mA if you drive each LED at 20 mA. Again, don't forget your dropping resistor. (Maximizes current, minimizes voltage.)

My experience is very limited compared to others in this forum, but I've used both series and parallel, depending on the situation.

Example: I need to blink 4 LEDs, mixed red & yellow, at the same time. Given the voltage drop from the 555 chip in the blinker part of the circuit, I can't do it all even with a 9V battery if the LEDs are in series, so I wire them in parallel.

Example: I want to have 4 red LEDs always on. I can wire them in series and use a single 9V battery, drawing only 20 mA of current.

Hope this helps,

Jeff

[en'til Zog]

Succinct and accurate. Great!

[belkin321]

Thanks for your explanaton jgoldader....

[jgoldader]

Thanks for your explanaton jgoldader....

You're very welcome, Belkin321. I learned it by doing it. I bit the bullet and bought a solderless breadboard and a bunch of jumper wires, a handful of LEDs, a few resistors, a 555 chip, and a capacitor or two. My initial cost was about $45. Put a couple of AA batteries in a little holder and wire it to the breadboard, and you're ready to go. Experiment! You can't really hurt the LEDs with so little voltage as long as you remember to use a dropping resistor, and 220 or 330 Ohms resistors are very inexpensive. (If you don't use a dropping resistor, I've heard the LEDs can explode like popcorn! )

There are very good calculators out there on-line to help you get started--they'll help you choose your dropping resistors, for example. And when you're ready to make things blink, there are calculators to help you choose your resistors & capacitors for that as well. You can find almost everything you'd want to know here if you take the time to dig through the Lighting forum, and people here are very willing to help out.

Now if only I could be better than pitiful at soldering...

Jeff

[Pat Amaral]

soldering has it's place, I guess but for me, wirewrapping is the way to go. With just a few minutes of practice, you can be an expert at solid, very reliable connections. And if you screw up, you can can easily disconnect without the danger of overheating/damaging anything.

[jwrjr]

Re: soldering - you know the old joke about how to get to Carnegie Hall. Practice, man, practice.

[jgoldader]

soldering has it's place, I guess but for me, wirewrapping is the way to go. With just a few minutes of practice, you can be an expert at solid, very reliable connections. And if you screw up, you can can easily disconnect without the danger of overheating/damaging anything.

Pat,

I bought a wrapping tool and some wiring, and it only took a few tries to get reasonably good at it. I use a bit of heat-shrink tubing to help close the deal. Many of the connections in the D-7 I'm working on are wraps.

I suppose I could use wrapping even with ICs if I made a very thin circuit board out of 0.01 or 0.02" plastic. The IC legs aren't long enough to use wrapping on regular PC boards. Is there a better way than that?

Jeff

[Pat Amaral]

soldering has it's place, I guess but for me, wirewrapping is the way to go. With just a few minutes of practice, you can be an expert at solid, very reliable connections. And if you screw up, you can can easily disconnect without the danger of overheating/damaging anything.

Pat,

I bought a wrapping tool and some wiring, and it only took a few tries to get reasonably good at it. I use a bit of heat-shrink tubing to help close the deal. Many of the connections in the D-7 I'm working on are wraps.

I suppose I could use wrapping even with ICs if I made a very thin circuit board out of 0.01 or 0.02" plastic. The IC legs aren't long enough to use wrapping on regular PC boards. Is there a better way than that?

Jeff

I use IC sockets that have longer legs specifically intended for wirewrap applications. There are a few different designs (ie different pin lengths, numbers of pins, etc.) I'll find some online info and get back to you.

edit: I did a little searching and found an example.

This one seems like it might be a little on the expensive side but I didn't take the time to compare prices with anyone else. Of course, the price will vary with the number of pins, etc.

Incidently, some people like to add a small drop of solder to their wire wrap connections to "lock" things down if they're not completely confident that the wrap will do the job by itself. I don't do it, mainly because I wrap specifically to AVOID soldering. You have to be careful not to use too much solder too because the joints tend to be closer together. I like the heat shrink idea but sometimes there isn't enough room. A little patient planning and careful wire management should minimize most problems.

[en'til Zog]

I always wire wrap directly to my IC's - and then use a touch of solder to make sure they stay that way. I also always solder wire wrap to resistors and capacitors 'cause the wrap doesn't lock too well on round wire.

Wiring directly from component to component is often called 'rats nest wiring' - which I've been using for years.

Pass the cheese, please....