LEDs into gamecube - voltage advice needed

ive been tring to add some leds into a camecube, basically i have 4 x 3.2v leds i want to install, i read somewhere on the intenet it would be possible to run 4 3.2v led straight from the fans 12v supply as all 4 add up to be just under 12v...
does that sound right, if so would i need to run them in parallel or series?
thanks in advance for any advice

 

Better in parallel whith a resistor...

If i've done good my homework you need a limiter resistor of 150 ohm

 

thanks...would the resistor go on the positive side?

 

It's not recommended to use LEDs without a series resistor - what you need to do is find the spec for the LED and find out what the recommended operating current is. Using this LED I just picked at random:

https://www.sparkfun.com/datasheets/Components/YSL-R547W2C-A13.pdf

It gives you a recommended operating current of 16-18mA and an If(max) of 20mA - it also specifies the forward voltage drop as 3.2-3.4V @ 20mA.

So let's say we want 18mA (to make it as bright as possible while still staying in the recommended operating range) and assume that Vf is 3.2V (the low limit on the datasheet).

Using all 4 in series won't work: 4 * 3.2V = 12.8V, which is greater than our supply voltage.

So use 2 strings each with 2 LEDs in it:

2 x 3.2V = 6.4V - so we need to drop 5.6V across the resistor. We already said we wanted an If of 18mA, so using ohms law we get 5.6/0.018 = 311R. The closest preferred value to this is 330R, so use that.

Working backwards, you get 5.6V/330R = 16.9mA - which is right in the middle of the recommended operating range. The resistor dissipation is V^2/R = so (5.6^2 / 330) = 0.095W. So a 1/4 resistor is fine (you could even use a 1/8W resistor, but that wouldn't leave much margin).

So, for this LED, the best way to wire them up would be in two (parallel) strings each with 2 LEDs and a 330R 1/4W resistor in series.

Note that this is based on the datasheet I linked to, so the LEDs you have might not be quite the same (although if they are high intensity white LEDs they will probably be similar).

 

they are 30ma
thanks for the advice, but now im stuck where to find that voltage inside the GC

 

If that the recommended current or If(max)? It seems quite high.

And you can use any voltage you like - you just need to adjust the resistor to give you the correct current - in that example, I was assuming it was running from the 12V supply.

 

ok i think im with you now, i dont mind accepting a slight drop in brightness by using the 12v supply if thats possible, otherwise ill go out and get some resistors tomorrow.

 

4 white LEDs in series connected to 12V should work - although they will be very sensitive to supply voltage variations - they will typically light at 2.5V and can tolerate about 3.5V before they pull so much current they start to damage themselves.

 

You can also get the voltage from the controller ports. I wired 4 LEDs to one controller port and they work fine with no resistors or anything.

 

Guys I have a question regarding the issue. Lets say I have a 12v connector and the fan is plugged and uses the 12v. What if I connect add additional leds which add up also 12v along with the fan wiring. Do they both get the 12v or do they split it so that both gets 6v each?

I'm guessing they split the 12v, but why do I see bunch of people wiring to the gamecube 12v outlet leds that uses the entire 12v. Wouldn't this screw upp the system, since there won't be any addional voltage left to whatever there was connected in the first place?

 

As long as your total load is within the current rating of the power supply, then they will all get 12V if you connect them in parallel. The voltage only gets shared if you connect the loads in series.

Think of it as being like plugging several desk lamps into the same power strip (which also puts the loads in parallel) - as long as you don't plug in so many that you blow the fuse (= overload the power supply), then each of them will get the full line voltage.

 

Thanks, been dying to get this answer!

 

No current stays the same in series but voltage is different based on resistance. Voltage stays the same in parallel but current is different. Basic ohms law.

 

I'm having a lot of difficulty working out exactly what you are arguing with me about here? Your post appears to be simply reiterating what I previously posted, but prefixed with "no". And if the OP had known what Ohm's law was, then he wouldn't have been asking the question in the first place.