Quote:
Originally Posted by matt99199
...i just use a master fuse and 12v voltage regulators.
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Then you're not controlling the LED current. For a commercial product that ought to last indefinitely, this is not a good way to do things. Please forgive the continued threadjack, but I think the point is important.
LEDs work because of current through them. There is a specific current that is best. The typical way to set that current is to use a series resistor whose value is chosen based on the expected voltage across it. Let's say you have a 12 volt supply and your LEDs drop 2.2 volts. You can put four LEDs and a resistor in series, and the resistor will see 3.2 volts. If you want 40 milliamps to flow, you should use an 80 ohm resistor. It'll be dissipating just over 1/8 watt, so a quarter-watt resistor is appropriate.
If you use five LEDs in the series string, the resistor only sees 1 volt and should be 25 ohms, and only dissipates 40 milliwatts, but you're getting to the point where imperfect tolerances can cause a relatively large variance in LED current. If you try to use six LEDs, the total voltage drop across them is more than the supply voltage, and no current will flow.
If you use five LEDs and no resistor, you'll be putting as much current through the LEDs as the power supply can provide at 11 volts. This is not how you want to treat the LEDs. With a capable power supply, the LEDs will overheat and die.
Commercial LED lamps often use a circuit that supplies a constant current. That's technically the best solution, though it's probably more complicated and expensive than necessary for a simple decoration.