In article , "WBH" wrote:
You can put led lights in series, but then you always have to switch more
lights on than you need. The whole idea of led lighting is to be more
efficient with DC and that translates to being able to switch lights
individually. The only way to efficiently supply power to leds is by using
constant current regulators, that use PWM (pulse width modulation). Any
other circuitry, be it transistor or Vreg, produces heat and is therefore
inefficient. Cheap led drivers can be found he
http://www.dealextreme.com/details.dx/sku.13553
cheers,
wbh


I am looking through the stuff. Great stuff. They
even have clicky switches.

18 watt LED !!


"Geoff Schultz" wrote in message
. ..
| A couple of years ago I installed DoctorLED
| (http://www.doctorled.com/p24.htm) Mars Dome interior lights throughout
| BlueJacket. This was the first shipment of these to the US and I literally
| had to wait for them to get off of the container and into my hands before
I
| could depart for the NW Caribbean. They may have changed the design since
| then, but this is what I've got.
|
| Anyhow, about a year later I realized that they were getting dimmer and
| dimmer and recently took a failed unit over to a friend who's an excellent
| electronics engineer to determine what had failed. He found 2 problems
with
| the units:
|
| 1) There's a layer of thermal paste which is supposed to conduct the heat
| between the circuit board that the LEDs are mounted on and the aluminum
| backing plate which also functions as a heat sink. For all intents and
| purposes, there was too little paste to provide contact between the two.
| However, after running a working unit for about 10 minutes, there was no
| appreciable heat buildup, so we don't suspect that my problem was due to
| thermal overheating.
|
| 2) The basic design of the circuit is a transistor which limits the
voltage
| to 9V to 2 parallel stacks of 3 LEDs in series. This provides 3 V to each
| LED, which is just fine. However, the transistor is too slow to handle
fast
| transient voltage spikes, and there's no voltage dump circuitry on the
| boards to handle this. A spike probably occurred somewhere along the line
| and fried some of the LEDs.
|
| DoctorLED will sell me replacement circuit boards at about 1/2 of the cost
| of the whole unit, which is still expensive. I plan to do that, but I want
| to protect against this happening in the future. All of the lighting is on
| 2 separate circuits. What can I do to protect against this happening
again?
| I was thinking about a 12 V DC to DC power supply. Any suggestions?
|
|
| -- Geoff
| www.GeoffSchultz.org