FS: Blue LED's (DIY moonlights)

[melev]

Quick question. If I only ran one bulb or two instead of 12, does that change the needed resistor size?

[melev]

Double post.

[jojo22]

Now Dave correct me if I am wrong (as I probably am). But since they are wired parallel the total resistance of his circut is less than 100 ohms. If he uses less shunts then he would need resistors of a lower value to creat the same intensity. So if Marc is useing a 6v supply and is .4 amps then 6/.4 would give the value of resistance. so 6v devided by .4A would be 15 ohms total resistance in the circut?? So 15 ohm resistors would work for a circut of two lights??

P.s. if I am not thinking right please explain and Marc I am sorry if I am hijacking your question and please do not take my answer as valid untill Dave verifies it. I am just learning this stuff in school and want to see if I can convert it into real life use.

[jojo22]

Or am I incorect as the total circut will then have less resistance than the 15 that yours had. I think in my formula the lights would acctually be brighter but I don't know what effect that would have on the LED life or if it would just allow too much current flow and blow them out??

[w7afm]

+ is the short lead, - is the longer

Bob

[dakar]

Quick question. If I only ran one bulb or two instead of 12, does that change the needed resistor size?

Nope the resistors will remain the same if you ran 1 or 12, I just calculated for a reasonable max for your power source, 400mA +/- 10% gave me 360mA to work with. The circuit will only draw as much current from the supply as it can use, so even with a 10A supply you can safely run 1 LED and one resistor.

Now Dave correct me if I am wrong (as I probably am). But since they are wired parallel the total resistance of his circut is less than 100 ohms. If he uses less shunts then he would need resistors of a lower value to creat the same intensity. So if Marc is useing a 6v supply and is .4 amps then 6/.4 would give the value of resistance. so 6v devided by .4A would be 15 ohms total resistance in the circut?? So 15 ohm resistors would work for a circut of two lights??

P.s. if I am not thinking right please explain and Marc I am sorry if I am hijacking your question and please do not take my answer as valid untill Dave verifies it. I am just learning this stuff in school and want to see if I can convert it into real life use.

Joe, afraid to say no... your math is correct, just not being applied correctly. You need both Ohms law E=IR and a little of Kirchov's law P=IE (think they may teach it where V is now in place of E for applied voltage).

The supply voltage is 6V, however these LED's require roughly 3.3V to operate, resistors actually drop the voltage seen by the device (get a meter and measure the voltages between the resistor and power source and between the LED and source.

Reducing the resistance will increase the voltage and the LED will glow brighter, but for a significantly shortened lifetime, 3.6V and up and you'd get about 20 seconds of life, 9V would yeild about 2milliseconds before the smoke flies. They are rated for a max forward voltage of 3.4V, but 3.3V is a safer bet to ensure a longer life, and they will still produce roughly 90% of their rated luminosity.

The only way to get by with smaller resistors would be to run a pair of LEDs in series on each leg, but you would need a power supply of 6.6V or greater.

Hope this makes sense... if not I can start a new thread to draw out the some of the basic electrical laws and how to apply them.

[jojo22]

I get what you are saying but a thread like you talked about would be great!!

[dakar]

I'm sorry to say the cupboards are now bare... even most of my 'private stock'

No worries, I'll be ordering more in a week or two, if anyone wants to jump in early by all means I'll take pre-sales requests at the same price to ensure I order enough at once.

Contemplating a pile of 130,000mcd white 10mm LEDs if there is any interest.

Bob, Marc, Chris & Ivan all of yours will be handed off to the USPS dude in the morning.

[iVgOnMaD]

Contemplating a pile of 130,000mcd white 10mm LEDs if there is any interest.

You already know I am!!

[dakar]

You already know I am!!

Gotcha first on the list! I need to do some serious computations and sort out a conversion of just how to convert mcd ratings into a more recognizable measurement like x number mcd is equivelant to 1 watt. I know these 10Kmcd blues will punch through 24" of water and castt an 8-10" illumated area with no trouble. But the wavelengths of white light will have very different characteristics as it penetrates deeper into water.

I'd love to get my hands on one of those $1K+ fixtures for about an hour...LOL