Creating an LED array in series circuit using PCB

[B3nchur]

Hello,
I am planning to create an LED circuit using prototype pcb board and a 12v battery source but I am unsure how to go about it.
I read around and with it being a series circuit, won't the resistance increase for every next LED? Does this mean each LED will become dimmer than the last?
I am also confused on what resistor to use within this series circuit as I have tried the calculation and with each LED being at 2-2.2 forward voltage 20ma current, over five LEDs will it change the resistor value I need?

Sorry if the information is vague.

Thanks alot.

 

[duke37]

If each led drops 2.2V, then four in series will drop 8.8V.
That leaves 3.2V to drop by the resistance.
R = V/I = 3.2/0.02 = 160Ω, find a resistor fairly close to this.
You could use five leds but the resistor would be very small and so the current would vary greatly with any change of supply voltage.

Since the current is constant throughout the circuit, then each led will have the same current and will emit the same amount of light.

 

[B3nchur]

If each led drops 2.2V, then four in series will drop 8.8V.
That leaves 3.2V to drop by the resistance.
R = V/I = 3.2/0.02 = 160Ω, find a resistor fairly close to this.
You could use five leds but the resistor would be very small and so the current would vary greatly with any change of supply voltage.

Since the current is constant throughout the circuit, then each led will have the same current and will emit the same amount of light.

That's alright then, I will pick up some 160 ohm resistors soon.
How would I go about making the circuit? Just do the LEDs in a series and solder them onto the pcb? If I use prototype board, don't I have to create a wire link from the positive of one led to negative on the next led using single stranded wire?

 

[Martaine2005]

don't I have to create a wire link

Not if you don't need to.
If the LEDs are close enough to bend the leads and solder them directly.
Also if you are planning on running several series arrays, put a resistor on each of them..

Martin

 

[B3nchur]

Not if you don't need to.
If the LEDs are close enough to bend the leads and solder them directly.
Also if you are planning on running several series arrays, put a resistor on each of them..

Martin

Ok then I will get some prototype board and do it using that then just to keep if neat.

Thanks very much

 

[hevans1944]

You might want to leave each LED a few millimeters "proud" of the circuit board. That way, if one of them fails, you can just snip it out close to the body and have enough lead sticking up above the board to tack-solder a replacement in place. That's a lot easier than trying to un-solder the connection to the other LEDs and less risk to overheating the circuit board and having the "traces" become un-glued. Don't ask how I know this.

 

[B3nchur]

You might want to leave each LED a few millimeters "proud" of the circuit board. That way, if one of them fails, you can just snip it out close to the body and have enough lead sticking up above the board to tack-solder a replacement in place. That's a lot easier than trying to un-solder the connection to the other LEDs and less risk to overheating the circuit board and having the "traces" become un-glued. Don't ask how I know this.

Experience and learning from mistakes I guess haha. Do you mean proud as in space each connection out and use kevlar wire to make the connection to each one?

 

[hevans1944]

No kevlar wire needed. Kevlar is non-conductive BTW. I sometimes use kevlar tape for insulation.

Just don't push the LED down flush with the board when mounting it, i.e., leave it "proud" above the board. Leave just enough sticking up above the board to allow you to slip a pair of flush-cutting diagonal cutting pliers under it so you can cut out a failed LED and tack-solder in a replacement. There should still be enough lead length left after installing the original LEDs to solder everything together as Martin suggested, assuming you don't space them too far apart.

If this is a "permanent" installation and you really want to get fancy, there are available little pin-socket terminals that will allow an LED to be plugged in. They come in all sorts of wire diameters, so measure the LED's lead diameter before going this route. I normally use these pin-sockets for things like "brick" power supplies mounted on circuit boards with machine screws. The pin-spacing on the power supply bricks is not standard, varying according to who manufactured it. I wish I could reference a part number or a catalog page, but there is a huge variety of these things. Here is just one example.

 

[B3nchur]

No kevlar wire needed. Kevlar is non-conductive BTW. I sometimes use kevlar tape for insulation.

Just don't push the LED down flush with the board when mounting it, i.e., leave it "proud" above the board. Leave just enough sticking up above the board to allow you to slip a pair of flush-cutting diagonal cutting pliers under it so you can cut out a failed LED and tack-solder in a replacement. There should still be enough lead length left after installing the original LEDs to solder everything together as Martin suggested, assuming you don't space them too far apart.

If this is a "permanent" installation and you really want to get fancy, there are available little pin-socket terminals that will allow an LED to be plugged in. They come in all sorts of wire diameters, so measure the LEDs lead diameter before going this route. I normally use these pin-sockets for things like "brick" power supplies mounted on circuit boards with machine screws. The pin-spacing on the power supply bricks is not standard, varying according to who manufactured it. I wish I could reference a part number or a catalog page, but there is a huge variety of these things. Here is just one example.

Oh right got ya, that's a great idea actually because I bought some really cheap LEDs and I only expect about 10 out of 75 to work because what can you get for 83p? I just want a couple as a coloured back light for a photography project I'm doing. That's why I've bought all the supplies so cheaply. Chinese posted but I don't need to for a couple of weeks anyway. It does make sense to leave it proud from the board as to cut it out would make much better sense as I can leave the circuit going because the joint is still there rather than if I desoldered it, it would disconnect the series.