Electronics Final Circuit Revision, Now i need resistor Values (PARRALEL)

Ok Final revision of circuit, hope someone can help with those damn resistor values. thanks

 

what is this circuit for or what doesd it do or supposed to do

 

its a lighting circuit for my motorbike..

BL is brake light
TL is tail light
BAT is battery
LI & RI is left and right indicators

the idea is i can change the light to blue .... for some bizzare reason...

can you help with resistor values?!

 

http://www.bit-tech.net/article/68/ check that out it should help

 

but surely that wont work? i mean.... my LED's are in parralel and there is more than 1 of them ?

 

I am almost sure you are not allowed Blue lights of any sort on the UK roads, car or bike , might be worth checking , be OK if you are just Offroad though..i think lol

 

looking for electronics advice not a lecture cheers

 

well i dont know much about leds and resistors but i would just put a resistor between each led in the parral or just one resistor for all the leds on the parral

 

LED's normally need a 560ohm resistor each in parallel supplied with 12V.

 

A single resistor in series with a load of parallel LEDs is a bad idea for various reasons which you can use the search to find out. You should really have a resistor in parallel with each LED.

560 ohm per red/orange/yellow LED
470 ohm per blue/white/UV/Pure green LED.

Any blue lights are illegal on road vehicles in the UK other than on emergency/police vehicles.

 

soldering a resistor to each led would be a hell of a pain !! why cant i use one big resistor in parralel?

 

Semiconductor devices never operate identically. There will be a slight difference between the characteristics of all of your LEDs you intend to wire in parallel.

It's likely that some of your LEDs will have a marginally higher forward voltage than some of the others. These will draw less current than the LEDs with a lower forward voltage. If you calculated your resistor value to running them anywhere near their maximum current, some are probably pushing their limit. Should one of these LEDs stop working, all your LEDs will draw more current, and the domino effect continues.

Of course, the same thing will happen if one of your LEDs happens to stop working for a random reason, or just because there was a dry solder joint etc.

Your battery voltage on your motorbike is unlikely to be 12V, and will fluctuate quite a bit, this will only aggrevate the situation.

Additionally, I would think for something as important as vehicle lighting, you don't want all your lights to go out if one component becomes damaged - i.e. the single resistor. At least with a resistor per LED, you know that one fault isn't going to take the whole lot out...

 

i see exactly where you are coming from here mate..

Well my idea was to set the resistance values for a 14volt input anyway but wasnt sure it was a super idea just to be on the 'safe side' i rea;;y cant justify soldering 40 resistors though compared with 5, i mean .... thats gonna take all day and i have a crap iron and dodgy hand, not to mention 4 pinout LED's are very close together legs.

i think i have no choice but to go parralel, ive just sorted out a supplyer for the LED's gonna cost me £14 for 12 , 2 for errors lol

 

You should be able to get away with it unless they are cheap crap LEDs, in which case you stand no chance of it working for long .

Just be warned of the effects of a failure

 

ok dude could you throw some numbers at me cheers, like how many ohms for the resistors i could really do with knowing which ones to order, or i could make solder 12 1/4watt ones in parralel that would work right?!

 

The two resistors to the red LEDs should be 120R 2W resistors each. That should give a big enough difference in brightness. If not, 100R (2W) and 150R (1W) resistors would do.

For the blue LEDs use a 56R 3W resistor.

For each set of green LEDs, use 120R 1W resistors.

Make sure you get the correct power rating resistors. Standard 1/4W resistors will fail.

 

so i need

2watt
2watt
3watt
1watt
1watt

from left to right?

and your pretty sure that will work and not blow up my LED's

i would have thought 2 x 1watt for the red but hmm ?

thanks btw

 

If you use two identical resistor values for the red LEDs, it's:

120R 2W, 120R 2W, 56R 3W, 120R 1W, 120R 1W

If you use the 150/100R combo for red LEDs it's:

150R 1W, 100R 2W, 56R 3W, 120R 1W, 120R 1W

The power rating relates to how much power the resistor can withstand, so you could use 120R 2W resistors for the green LEDs for example. (Bigger is fine, but don't use any resistors with lower power ratings that those I've given or the resistors will get toasty and fail )

Those resistor values should keep the current to a maximum of about 20mA, assuming 14V supply.

 

Hi mate

Just thought i'd point out that when the brake light is turned on the current to the tail light still stands, so basicly its like an extra 12v there, not an alternate supply, just the way i read it seems the resistors will get 4 watts is that correct? pah im really confuseD?

 

With just the tail lights on, the power wasted in the resistor is just over 1W, so a 2W resistor should be used.

With the brake light signal on also, the total power dissipation is 2.36W shared between the two resistors. Since the resistors are of equal value, the power wasted in each will be 1.18W, which is why both should be 2W