wiring up an LED

I wanna put an LED on the back of my bike just to customise it a bit maybe my initials lol. How would i do it so that it only turned on when i turned the ignition on, i need extreme detail and maybe pics if difficult lol

Cheers LJ

[dirtydog]

Firstly I wouldn't just wire it to the ignition i'd also put a seperate switch so you don't have to have it on all the time.

Depends on what sort of LEDs you intend to use? You can get 12v ones which would make it less work

yeah 12v ones so what would i do, i'm a proper dud when it comes to electrics lol

......

[dirtydog]

On an LED you'll have 2 tails coming down from the bulb one is a +positive the other is the -negative if you've got a few wire all the +positves together and do the same with the -negatives then i would fit a switch to the +positive side of it all loads of different types of switches about so it's upto you what type you use. Then wire the -negative wire from the LEDs to a -negative or earthing point ie the battery negative terminal.
Then you need to find a live feed which there are a few options, you could find an ignition wire so they only come on when ignition is on or you could use the lighting circuit so that they come on with the lightsor you could run them straight to the battery

thank you, sorted

If its just a LED on its own and not a complete LED lamp you will
need to limit the current with a resistor or it will most likely go pop.

Assuming 14V for the battery volts with the engine running.
A volts drop of 2V for the LED with a current of 20mA.

14 - 2 = 12 the voltage across the resistor.

12 / 0.02 = 600 the resistor value for a 12v drop at 20mA.

Closest resistor value you can get to this is 620R (620 ohms value).
For half the current double the value to closest value 1K2 (1200 ohms).

The shortest lead on the LED is the positive I think. You can experiment with the resistor value for the correct brightness but don't go lower than 620R unless you know than the LED has a max current greater than 20mA.

There are some LED's with a built in current limit that can be connected direct to the battery but they maybe low light output types.

its a series of LEDs, how would i connect it to the lights so that it would only come on when the lights are on as i think that is my best bet?

[dirtydog]

Originally Posted by ljharmitt

its a series of LEDs, how would i connect it to the lights so that it would only come on when the lights are on as i think that is my best bet?

You'll need to tap into a live feed for either the front or rear light depending on where you want to put the LEDs

Typical voltage drop for a red LED is about 2.3V
so with four in series it adds up to 9.2V

14 - 9.2 = 4.8 which will be the voltage across the resistor.

4.8 / 0.02 = 240 for the resistor value to give 20mA current.

A 270R or 240R will do or a higher value for less light.

You could put five in series but 2.3 * 5 = 11.5 a bit too close to the 12V
battery voltage, the engine would need to be running to light the LED's.

It could be done using a constant current circuit but then it gets complicated if your not familiar with electronics.

If you need more LED's then use series of four and connect into your lighting wiring to come on with the lights.