led diode resistance

Silent Shrill

Hi, advice needed.
I wish to install 4 seperately coloured led's to replace the warning lights on my motorbike. All work independently. Turn signal, oil, high beam, and neutral. I have led indicators at present with an led flasher unit, so they work fine.
Voltage from bike is usually 12-14v.
I'm making a custom housing for the 4 led's and original setup is going.
Will I need in-line resistors, heatsink, one way diodes, etc?
Bill

paulheu

THIS would probably be a good start.

TheChizler

Did the LEDs come as a prebuilt unit for a bike? If they did just check the spec. If not you'll have to say exactly what you bought and the way you plan to use them.

Silent Shrill

TheChizler wrote: »

Did the LEDs come as a prebuilt unit for a bike? If they did just check the spec. If not you'll have to say exactly what you bought and the way you plan to use them.

Unit custom made by myself. Led's are 5mm, 3v and 20ma, 2 pin. They will only light when either using high beam, oil becomes low, neutral gear, and indicator working.

TheChizler

Silent Shrill wrote: »

Unit custom made by myself. Led's are 5mm, 3v and 20ma, 2 pin. They will only light when either using high beam, oil becomes low, neutral gear, and indicator working.

Do you have the datasheet for the LEDs? Are you connecting the 4 of them in series or parallel?

Edit: sorry I thought you were replacing the turn signal indicators, not the 'dash' indicators. If each LED has a junction voltage of 3 V, and a nominal current of 20 mA, and a supply voltage of 12 V, then you'll need a resistance of (12 - 3)/.02 Ohms rated for a power dissipation of that squared times 0.02 W in series with each LED.

Silent Shrill

TheChizler wrote: »

Do you have the datasheet for the LEDs? Are you connecting the 4 of them in series or parallel?

Only data I have is in previous post.
Each led is wired to seperate systems. All share earth/neg.

whizbang

To get 20mA, Take 13v minus 3v for led, that leaves 10V, Divide by 0.02Amps = 500Ohms.

Common standard values would be 470 or 510 Ohms.

At .02Amps multiply by 10V, gives a Resistor Power of 0.2Watts, or common standard value is 1/4 Watt

As the Led's won't be on all the time, these upper limits are safe to use.

So 470 Ohm, 1/4 Watt resistor for each LED. Nothing else needed.

Silent Shrill

TheChizler wrote: »

Do you have the datasheet for the LEDs? Are you connecting the 4 of them in series or parallel?

Edit: sorry I thought you were replacing the turn signal indicators, not the 'dash' indicators. If each LED has a junction voltage of 3 V, and a nominal current of 20 mA, and a supply voltage of 12 V, then you'll need a resistance of (12 - 3)/.02 Ohms rated for a power dissipation of that squared times 0.02 W in series with each LED.

Thanks.
So a 500 ohm resistor rated at 1/4 w should be ok?
Would I need a heat sink? And would I need a one way diode on the indicator warning led?

Silent Shrill

Cheers lads. It seems you get a post in as I'm replying to another. My fingers are obviously slower.....haha.
Anyhow, my question has been answered very proficiently.
Many thanks

whizbang

500 is bang on, 1/4w is so small, you would need 100 of them bunched up to feel any heat at all.

If the rating for the reverse breakdown voltage is lower than 12v, then you may need to use blocking diodes.

but no, nothing else needed.

gctest50

Silent Shrill wrote: »

Hi, advice needed.
I wish to install 4 seperately coloured led's to replace the warning lights on my motorbike. All work independently. Turn signal, oil, high beam, and neutral. I have led indicators at present with an led flasher unit, so they work fine.
Voltage from bike is usually 12-14v.
I'm making a custom housing for the 4 led's and original setup is going.
Will I need in-line resistors, heatsink, one way diodes, etc?
Bill

if there is only one turn signal warning light it might be wired this way :



you'd need to add a few diodes :




( resistor not shown - you'll need one as above )