Resist me not?

So I just don't seem to grasp this at all...

I've read about several mods involving just LEDs and a power source (batteries for the most part). Whenever I put an LED (a Nichia for example) into a circuit with just batteries it fries. Do certain kinds of batteries (lithium?) not cause this problem? Hooking an LED up to batteries without some sort of resistance seems to violate anything I ever though I knew about basic electronics.

Any advice/help from the more knowledgeable folks out there would be much appreciated!

AFAIK, DD (direct drive) is only possible whith ample heatsinking and the use of a Luxeon LED... /ubbthreads/images/graemlins/rolleyes.gif

Smaller LEDs like Nichia's cannot take the current of a direct drive by themselves. They have a low resistence and will easily pull enough current by themselves to self distruct. You need a resistor in series to limit the current in the circuit.

As well, voltage and the internal resistance of the batteries supplying the led is important as well.

You will not fry a white Nichia LED if you supply it with 2 cr3023 cells in series (6v), but you will if you supply it with 2xcr123 (6v).

Abe.

You need the right combination. For example, the NoviGear uses seven leds direct-driven off 3AAA batteries. The leds are soldered/arranged to each take 4.5V off the three 1.5V batteries, thereby dividing among them the max current these relatively small batteries can produce. Changing anything, such as using larger (higher current) 1.5 batteries, or significantly lessening the number of leds, may cause led frying.

I'm familiar w/ putting a resistor in series...that's how I thought all simple LED circuits had to be set up.

I appreciate the clarification, everyone.

Thanks!