On 2005-06-10, TeakSeal wrote:
Do you need zener diodes or something to limit the DC when your motor
starts charging? The LED's are 12v and the alternator puts out 14
something, right? Do people do this for the whole panel? Thanks.

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

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

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 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

On Wed, 8 Jun 2005 09:46:59 -0700, "Gordon"
wrote:

I want to replace all my old fixtures with new led types. 6 spots and 3
puck style ceilings. Where to purchase at a decent price?

Gordon

I have retrofitted some of my reading lights with led lamps from
Superbrightleds.com.
LEDs have a pretty tight beam angle and a blue-white color temp.
I like them OK for a task light or reading light but not for general
area lighting.
You might check out the cold cathode flourescents sold for computer
case and automotive decoration. CCF have a slightly warmer color temp
and are just about as efficient as LEDs. The tubes are great for
under counter use. I have seen circular CCF tubes installed around a
muffin fan but I haven't seen one in white.
IMTRA has some nice marine fixtures that use CCF if price is no
object.

On 9 Jun 2005 19:33:55 -0700,
Peter wrote:
Try these addresses http://www.spectrumled.com/ and
http://www.superbrightleds.com/ I have dealt with both these companies
and can recommend each. Especially interesting is the 12VDC 1156/T10
PCB LED Lamp offered by Superbright. You can remove the bayonet base
from this lamp and wire it direct (observing polarity).


I looked at that light, I was a tad disappointed that the array simply
used a bunch of dropping resistors, to current limit the LEDs rather
than a PWM controller or constant current supply.

I am in the process of "rolling my own" array with some 5000mcd
superbright whites, and a pic based PWM controller, which, theoretically
at least, will give a nice smooth brightness control from 0-100% on,
without wasting power and heat on dropping resistors.


--
Jim Richardson http://www.eskimo.com/~warlock
Every program expands until it can send mail.
....Except Exchange.

On Fri, 10 Jun 2005 06:02:21 GMT,
TeakSeal wrote:
On Wed, 8 Jun 2005 09:46:59 -0700, "Gordon"
wrote:

I want to replace all my old fixtures with new led types. 6 spots and 3
puck style ceilings. Where to purchase at a decent price?

Gordon

Do you need zener diodes or something to limit the DC when your motor
starts charging? The LED's are 12v and the alternator puts out 14
something, right? Do people do this for the whole panel? Thanks.


Most of these bulbs use a dropping resistor to limit the current draw,
there will be no problems using them at 14-15VDC, in fact, some of
them work fine from 10VDC-30VDC. Check the spec sheets for specifics.

The better way is to drive them via a constant current supply, or a
pulse width modulation driver. The latter gives the additional benefit
of allowing you to vary the brightness.

--
Jim Richardson http://www.eskimo.com/~warlock
Don't get mad, get Linux

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.