In article , (GregS) wrote:
In article , Geoff Schultz
wrote:
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

I would try to add some capacitors across the 9 volt. Get what fits,
maybe a 100 uF electrolytic 25 volt. This does not rule
out a defect in the design circuit, which a dc/dc converter
may not fix.


A thought. That circuit should allready have the necessary capcitance
on the output. It "should". Adding input filtering may be required
to the domes. Boat power may be noisey, but we are just guessing.
Gradual dimming is usually the result of driving too hard. They also
short term dim when too hot.

greg

I have been fooling with various high power leds. I had no problems
with the Lumiled devices, but some Cree devices wen bad
after I attached to the power supply. There is some kind of spike
that takes out these leds which are supposed to handle 1 amp peak.
There are nice leds with a nice warm glow. The warmest I have seen.
http://ledsupply.com/creexre-ww.php

greg

(GregS) wrote in news:gv1m1f$dqm$1
@usenet01.srv.cis.pitt.edu:

A thought. That circuit should allready have the necessary capcitance
on the output. It "should". Adding input filtering may be required
to the domes. Boat power may be noisey, but we are just guessing.
Gradual dimming is usually the result of driving too hard. They also
short term dim when too hot.

greg



Why not just use a 7809 regulator IC, or something heavier duty if it draws
more than 1A? The output will be EXACTLY 9VDC, no more no less, no matter
what the battery does, with 5.2V of overhead space to play with. You won't
even see the engine start dimming them unless the battery is dead or all
the terminals are corroded up.

On the cheap, let the regulator drive a big NPN power transistor if you
need more current cheaply. The LEDs will run fine on 8.4VDC steady from an
Emitter follower with 9V on its base.

What a boat DOESN'T need is another digital electronic transmitter like a
DC-DC converter for stupid simple lighting making a racket in every RADIO
aboard.....Let's keep it analog and QUIET.

7809's are about 20 cents.....2N3055 power transistors give you 15A for a
couple bucks....Remember the case is at + battery voltage on the collector.




--
-----
Larry

If a man goes way out into the woods all alone and says something,
is it still wrong, even though no woman hears him?

In article , Larry wrote:
(GregS) wrote in news:gv1m1f$dqm$1
:

A thought. That circuit should allready have the necessary capcitance
on the output. It "should". Adding input filtering may be required
to the domes. Boat power may be noisey, but we are just guessing.
Gradual dimming is usually the result of driving too hard. They also
short term dim when too hot.

greg



Why not just use a 7809 regulator IC, or something heavier duty if it draws
more than 1A? The output will be EXACTLY 9VDC, no more no less, no matter
what the battery does, with 5.2V of overhead space to play with. You won't
even see the engine start dimming them unless the battery is dead or all
the terminals are corroded up.

On the cheap, let the regulator drive a big NPN power transistor if you
need more current cheaply. The LEDs will run fine on 8.4VDC steady from an
Emitter follower with 9V on its base.

What a boat DOESN'T need is another digital electronic transmitter like a
DC-DC converter for stupid simple lighting making a racket in every RADIO
aboard.....Let's keep it analog and QUIET.

7809's are about 20 cents.....2N3055 power transistors give you 15A for a
couple bucks....Remember the case is at + battery voltage on the collector.

Its all about efficiency. The best way is use 4 high power devices in series
and you will need nothing else. Might be too bright.

greg