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.

Controlling the current by a more efficient means would involve a
complicated bit of circuitry.

Andy Repton writes:


The LEDs are themselves need between 1v and 4v depending on colour,
the 12v replacement bulbs must have some sort of internal drop down.
You need to check their spec to see if they can cope with the charging
voltage, but also to see if they can deal with the spikes etc that an
alternator based 12v system can produce.

--
Andy Repton

--

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.

--
Andy Repton

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

Marc Auslander wrote in
:

Controlling the current by a more efficient means would involve a
complicated bit of circuitry.


Yeah, one little IC chip built right into the LED's base. It's called a
constant current regulator. Some of them with this chip in them will run
on any voltage from 6V to 48V or higher. The chip will also rectify if you
choose to plug them into AC. Superbright LEDs has 115VAC/DC led
replacements for standard light bulbs, the most efficient room lighting
known to man. A 3W LED array is the same as a 40W light bulb....

I'd like to see them make an undercounter panel, not these little strips.
You'd stick it up, plug it in, and not bother to turn it on and off.

--
Larry

You know you've had a rough night when you wake up and your outlined in
chalk.

On Fri, 10 Jun 2005 12:23:27 -0400, Larry W4CSC
wrote:

Superbright LEDs has 115VAC/DC led
replacements for standard light bulbs, the most efficient room lighting
known to man. A 3W LED array is the same as a 40W light bulb....

There is nothing efficient about white LEDs. The most efficient
white LEDs produce about 23 lumens per watt. That's barely
better than Halogen at about 18 lumens per watt.

Cold cathode fluorescent (CCF) is where the efficiency is in
small lights-- at about 80 lumens per watt. And, they don't mind
being cycled frequently like their hot cathode fluorescent
cousins.

Unless you require sub-watt levels of light, CCF is the answer,
not LEDs (and they are a hell of allot cheaper than LEDs.)

If you want to play with CCF, check out the kits online. For
example at http://www.elwirecheap.com/coldcathodes.html

--
BRENT - The Usenet typo king.

Brent Geery wrote in
:

And, they don't mind
being cycled frequently like their hot cathode fluorescent
cousins.


Hmm...In my grandmother's kitchen was a dual Circline, hot-cathode,
fluorescent light with a real starter on each tube. As far back as I could
remember, I always loved to see it start flashing as the tubes heated up on
the starters kicking in. When Grandma finally got old enough to move out
of the house and into assisted living, some 50 years later, those same two
tubes were flashing on the same starter many times a day as people came and
went in the kitchen. Thank you, GE, for producing such a fine product,
sometime way back near World War II. There was a GE circle on the chrome
plating in the middle of it.

--
Larry

You know you've had a rough night when you wake up and your outlined in
chalk.