On 10 Jun 2005 14:34:07 GMT, Andy Repton
wrote:

On 2005-06-10, Marc Auslander wrote:
IIRC, the simple way to wire an led is with a series resistor chosen
to give the rated current at the expected voltage. The LED itself has
a very small resistance - as you would expect given its power
efficiency. Most of the power is then comsumed by the resistor.

This is indeed the simplest way, but it is generally only done when the
supply voltage is regulated. The 12v system on a boat is only loosely
regulated and most (well designed) electronics uses active regulation
to protect the circuitry.

Resistance of the LED is not really the issue, the power dissipated by it
is volts times amps. The issue is that dropping voltage across the
resister wastes power as heat. Hence using a switching regulator to drop
the nominal 12v to the lower voltage needed by the LED is doubly
beneficial - it protects the LED from spikes on the 12v and improves
the efficiency significantly.

Perhaps even better_ a two terminal constant current regulator rated
for generous maximum volts to allow several LEDS in series safely....

Brian Whatcott Altus OK