Resistors for LED indicator question,,,non GS

[millard]

I need some help please with this.
I'm making some LED indicators for my old Norton cause they don't draw much current from it's 60w dynamo.
I made up the wee disc which holds the LEDs and mounted 12 of them, so far so good.

However the wiring is all too much to fit inside the indicator bodies I've turned up on the lathe. This is because each of the LEDs has it's own individual resistor soldered to the tail of the LED.
So I happened across some lateral thinking and had the idea to reduce the size of the mini wiring harness at the rear of the LED disc by removing the resistors and placing them further upstream of the indicators and hide them in the wiring harness somewhere, probly in the headlamp shell, along wi it's now shiny HID lamp
So instead of soldering up the 12 tiny wee resistors like this one which I took off one of the LED's

can I just take one wire from the indicator and fit a big resistor to feed all 12 LED's?
If so, what size/value/specytypestuff do I need for the resistor to feed each of the indicators?
Here's the spec of the LED's I got from eBay, can't think of anything else relevant but if anyone can answer and needs more details please ask away.

Luminosity intensity 13,000mcd
Forward Voltage 6v-15v (I'm using a 12v dynamo system)
Power 100mw
Forward current (DC) 30ma
Peak Forward current 100ma


thanks
millard

 

[alimey4u2]

This may help mill....

http://www.theledlight.com/samplecircuits.html

PS, You're going to live a long prosperous life, & have 3 children. I also read in your life line that you need to be careful with soldering irons...

 

[phaedrus]

Another good website is LEDcalc. If you select 'parallel leds' you'll get the circuit to use with one resistor.

Looking at the specs of you LEDs, the forward voltage of 6v-15v seems really high (normal is around 3 to 4 volts). Were these LEDs sold together with the resistors? If so, the forward voltage is probably for the combination of LED and resistor. In this case you can, in a parallel circuit (look at LEDcalc), replace all the resistors with one of the same resistance but with a high power (about 1,5 Watt for 12 LED's).

 

[D6]

if u look on ebay , u can buy some L E D bulbs for around 12 quid,,,,i got some, work well

 

[millard]

Hmmm,,,just when I was patting meself on the back for cracking it wi alimey's help !!!!!!!
Well first thing I did was to put a meter accross the resistor. Each led comes with a prewired resistor. That measured 430 ohms.
Then doing a wee calculation according to the specs of the LEDs as supplied by the eBay seller I came up wi a figure of 0.360 watts. I arived at this as each of the 12 LEDs is 30mw so 30 x 12 = 360mw = 0.360 w (right ? )

So I reckoned that to replace all them wee reisitors wi one big one I'd need a 430 ohm x 0.360w resistor. So I went to RS Components and they had 430 x .0.6w resistors and for the princely sum of 28p I am now the proud owner of a packet of ten off the wee buggers.
However, when I got back home I realised that I misread (****ed up) the power output as it's not 30mw but 100mw..
As RS is now closed I reckon I can bodge it and not waste all that dosh I spent with them by wiring two resistors in series then hook them up in parrallel to another two to give me 1.2w x 430 ohms. Whatdyas think ???????

Digger, thanks, I've got a LED tail/stop lamp in of that type for the same reason, that it draws little current, but I wanted to fashion me own indicators. They're a kinda like a bigger copy of some I bought on eBay a few months back only those ones were far too small and only had one each LED, so next to useless really. But I liked the retro/corny/Dan Dare 50's look of them and thought that if I do have indicators on an old fities bike then they would look kinda cool and in keeping.
here's a few pics to give you ( a larf) the idea
here's the ones I bought hooked up to the bike alongside the new body I turned up.

Here's the LED holding disc being drilled

Here's the discs being parted off

here's the four bodies after polishing.

The half inch thick flange at the pointy end is just for holding them in the chuck and will be parted off when I'm happy wi them.


Here's the specs for the LED's I got.


New
Material: InGaN
Emitting Colour: Amber
Lens Type: Water clear
Reverse Voltage: 5.0 V
DC Forward Voltage: Typical: 12 V Max: 15 V
Wavelength: 585nm -595nm
Luminous Intensity: Typ.: 13,000 mcd
DC Forward Current: 20mA
Viewing Angle: 20±5degree
Electrical-Optical Characteristic (Ta=25°C)

Item Symbol Condtitions Min. Typ. Max. Unit
Forward Voltage VF If=20mA 6.00 12.00 15.00 V
Reverse Current IR VR=5V / / 10 uA
Dominant Wavelength / IF=20mA 585 / 595 nm
Luminous Intensity IV IF=20mA / 13,000 / mcd
50% Power Angle / IF=20mA / 5° / degree

Absolute Maximum Ratings (Ta = 25°C)

Item Symbol Absolute Max. Rating Unit
Power Dissipation PD 100 mW
Forward Current (DC) IF 30 mA
Peak Forward Current IFP 100 mA
Reverse Voltage VR 5 V
Operation Temperature Topr -40~85°C /
Storage Temperature Tstg -10~100°C /

 

[D6]

nice
good to see people making things!its getting to be a lost art/skill
thought u were jus fittin em in standard indicators

 

[alimey4u2]

Nice piece of turning work .....

 

[scots_jon]

Fantastic lathe work, very nice.

However your calculations for the resistor in your LEDs is wrong. The wattage of the resistor is not the citical factor, the resistance (ohms) is. basically each LED will have a voltage across it when it is "on". This voltage will be in the range 2V to 5V and will be differenct for each LED. Your battery voltage is around 14V so you need to reduce that to the 2-5V each LED uses. You do this by adding a reistor that "drops" the extra voltage across it and also limits the current in the LED.

If all your LEDs had the same forward voltage you could wire them in parallel and use only one resistor. However they almost certainly don't all have the same forward voltage,and if you use only one resistor you risk one LED taking all the current until it burns itself out, at which point the next one will start taking all the current until they are all gone.

You basically have two easy options (I'll ignore the more complex ones!).

1. Have a resistor for each LED and place this somewhere there is space.
2. Wire the LEDs into pairs, and have one resistor for each pair.

If you need any help, drop me a PM and I'll explain in a beter way or send you a diagram.

Cheers,
Jon