ok i know u cant get yellow cathodes so i am goin 2 use lots of ultra brignt leds, i have a 350watt psu, and maybe upgrain 2 a 450 watt does and 1 know what value resistor i should use to protect the leds for the 350watt and 450 watt psu?
Wow, you're really confused about your electronics, so I'll start from the top, and undoubtedly someone will come along and correct me everywhere I screw up. First, your power supply. Power supplies are rated in wattage, as you've already determined, but that is the theoretical maximum they can operate at. Power supplies actually spit out 6 voltages: 3.3v, 5v, 5v Standby (for when the computer's off and the PSU isn't, used for Wake-on-Lan), 12v, -5v and -12v. The load on each of these voltages, or rails varies depending on what your computer is doing. Now, when working with modding, you're most likely going to use the 5v and 12v rails that are on the molex connectors. Now, in your situation, you need to consider if you want to connect the LEDs either in series or in parallel. One thing I need to say before I go on any further: the positive terminal is referred to as the "anode" while the negative terminal is the "cathode" Wiring devices in series starts out with the positive voltage connection connecting to the first devices anode. That devices cathode then connects to the second device's anode, and so on and so forth. In series, the voltage drops of each device add together. For the sake of the argument (which I'll use from now on), let's say that the LEDs you want to use run at 3v@20mA (.02 Amps). If you were to use them in series, you could successfully use 4 LEDs in series (4 x 3v = 12v) without needing to use a resistor to drop any excess voltage. The second option is to wire them in parallel, which has all of the anodes connected together and all of the cathodes connected together. In this arrangement, the currents of each device add together. The amount of LEDs you could run in this arrangement is limited to the amount of current your power supply can handle. Be aware however that you will need a resistor (and a pretty high-wattage one at that when the amount of LEDs increases) to drop the excess voltage. Say you wanted to connect 5 LEDs in parallel. This would give you 3v and 100mA total. To calculate the resistor you'd need, you'll need to use this formula: (Vin - Vf) / I = O Vin: Voltage input (5 or 12v most likely) Vf: Forward voltage or voltage drop (in this case, 3v) I: Current (.1A our example) O: Ohms (Resistance) Units used must be Volts, Amps and Ohms For our example, a (12-3)/.1 = 90 Ohms. The closest standard unit (resistors are commonly sold in values of 12 different values between 1 and 10 multiplied by a power of 10) would be 82 ohms. If you want to be really precise about getting the right amount of resistance, resistors can be added in series (don't worry, they're not polarized, so it doesn't matter which lead is attatched to which) to add up resistances. A 33 and a 56 ohm resistor gets you 89ohms, close enough. 2 27 and 2 18 ohm resistors gets you 90 ohms exactly. The final way to hook up your LEDs would be a series-parallel net. This is basically a combonation of the two. Going down the columns, the LEDs would be in parallel, but going across the rows, they'd be in series. The important thing to remember is that each column must have the same number of LEDs or else some LEDs will draw more than others, eventually blow out, then the remaining LEDs will draw more than the previous ones and blow out in a flash. Burning LEDs do not smell good. The amount of LEDs you could hook up, again, is limited by your power supply, and also by your wallet (those suckers can add up quickly). For maximum efficiency, I'd use a series-parallel network of (drawing from the example) 4 columns and and a whole bunch of rows. More next post
Continuing off... One thing that IMO that can be easily overlooked is the wattage rating of the resistor used. If you use a resistor that is not powerful enough, you'll create a lightbulb for a couple of seconds (no I'm not kidding. Light bulbs are basically a carbon resistor that gets a lot of electricity through it to the point to where the heat from it resisting current causes the carbon to glow) before it explodes. Power (in watts) is calculated P = IV. P being power in Watts, I being current in Amps, and V being voltage in Volts. Refer back to the example in the parallel LED array. The resistor (assuming we're just using 1 rather than multiple resistors in series to get exactly 90 ohms) in that case will drop a total of 9v (12v supply - 3v LED voltage drop). The current it will handle is 100mA or .1A. 9v * .1A = .9w. You're typical resistor can handle .25w, so if you stick a typical resistor in there, you'll create a light bulb for a few seconds. You need to use a 1w resistor in this case to sufficiently handle the full load. In case you need it, here's a diagram of what series, parallel and series-parallel look like. Note that _ is wiring, + is the anode, and - and - are the cathode: Series: Code: 12v ___ + -_+ -_+ -_+ -_+ -_+ ____ G Parallel: Code: 12v __ + _ + _ + _ + _ + _ + G ___ - _ - _ - _ - _ - _ - Series-parallel: Code: 12v ___ + _ + _ + _ + _ + _ + - _ - _ - _ - _ - _ - | | | | | | + _ + _ + _ + _ + _ + G _____ - _ - _ - _ - _ - _ - Damn, ASCII art is tough
