LED Wiring

[w0rld]

Okay, so I'm trying to make this helmet, with LEDs in it. The total voltage for all the LEDs is 29.2 DC. Now, I cannot for the life of me figure out how to get enough power to these 10 LEDs to get them to work! I've looked at transformers, but none of them seem to provide what I need. (Read: Input: 9V Output: 30V Current: 20mA) Please help!

[swansont]

If you have 9 V already, then can you wire some of them in parallel to drop the voltage required?

[Spyman]

Okay, so I'm trying to make this helmet, with LEDs in it. The total voltage for all the LEDs is 29.2 DC. Now, I cannot for the life of me figure out how to get enough power to these 10 LEDs to get them to work! I've looked at transformers, but none of them seem to provide what I need. (Read: Input: 9V Output: 30V Current: 20mA) Please help!

If each LED wants 2.92 V 20 mA and you want to supply 10 LEDs with a 9 volt battery then you can make 5 parallel circuits that each have 2 LEDS and 1 resistor in series. The resistors should have the value of (9-2*2.92)/0.02= 158 ohm to limit LED current to 20 mA.

[Joatmon]

As Spyman says you need a series resistor . However if you have 9V available you can buy what are advertised as 9V LED's. These have a resistor inside them that does the job. If you get these you can just connect them in parallel to your battery.

 

LED's operate on DC and transformers operate on AC so I wouldn't go down that path.

 

 

[Enthalpy]

Slightly better than a resistor, you can use an LM317 and a resistor, combined to make a constant current. This makes the light output less dependant on the battery voltage, which varies a lot, and the lower minimum voltage drop permits to use the battery longer. The TO92 version of the LM317 would fit small currents.

 

Maxim must also have complete solutions exactly for this situation, using a chopper to achieve a high efficiency and at the same time squeeze everything out of a battery. But it's more complicated - probably too much.

[w0rld]

Thanks, spyman! I forgot abot the parallel wiring! I'm using 5 sets of 2 leds each with the same color. I completely forgot! Thanks so much! Now I can stop looking for that damned transformer!