Custom LED Lighting

[deLight]

I have started to install custom LED lighting in deLight. Light fixtures are a nuisance. The light is great around the fixture and not so much in the shadows. I had a couple of tube lights strung around the main salon on they provided a nice even light albeit not very bright and highly inefficient.

I decided to replace the tube lighting with custom LEDs. This is a sequence of 3 posts starting with a simple solution ending with a complicated but very nice and very efficient solution.

Note: You need good soldering skills and access to a milling machine. Otherwise, this custom LED lighting project is prohibitively expensive.

The objective  is to replace the brown sponge trim tube in places where we want light with a white plastic tube with LEDs. I used 20mm POMC white plastic tube milled with 2 flat sides at 90 degrees to fit in the corner. A 5 mm channel was milled down the center for wiring. 5mm holes for the LEDs were drilled approximately 3.0 cm apart. See sketch.

 For each piece I measured the exact length and allowed 2.0 cm at each end. then figured the number of holes needed - (Remaining length/3.0 cm). Since we are going to use groups of 3 LEDs, we need to have a multiple of 3. Round the number of holes up or down to be divisible by 3. Calculate the hole spacing by taking remaining length divided by the number of holes minus 1.

Simple calculation: 9.8cm piece (9.8cm -2.0cm - 2.0cm) = 5.8cm,  (5.8cm / 3.0cm) = 1.93, Round to nearest multiple of 3 = 3, Hole spacing is 5.8/(3-1) = 29mm i.e. holes at 20mm, 49mm and 78mm.

Use the milling machine to accurately place the holes. In deLight's main salon, there were 10 pieces with hole spacing between 28mm and 34mm. As long as the holes in any individual piece are spaced identically, the eye does not notice the difference piece to piece.

Next step is to make the LED triplets. I purchased Cree 2500K color temperature LEDs for an incandescent like color. The higher the color temperature, the more white the LED. i used the individual plastic tubes as a fixture to solder 3 LEDs and a 270 Ohm resistor together. Remember each segment may have a slightly different hole spacing.

Insert the triplets into the segment and wire the negative ends together and the positive ends together using the milled channel.

This is the simplest LED setup. 3 LEDs and a resistor wired directly to your battery DC supply. This circuit powers the LEDs with 20ma at 14.4v allowing for battery charging without damage to the LEDs. The downside of this circuit is the lower the battery voltage, the dimmer the light. At my chargers 13.2v float voltage the LEDs receive 15ma. At 12.6v, battery fully charged - about 10ma. Efficiency (Power to LED / Power In) is about 60%

I use this circuit in lockers and storage places that are routinely accessed while attached to shore power. Next, I will describe using a DC-DC converter to have full brightness no matter what the battery DC voltage is.

Max

[deLight]

In my last post, I described a simple LED circuit - 3 LEDs and a resistor in series connected directly to the DC battery supply. The disadvantage of that circuit is that the lower your battery voltage, the dimmer your light.

To solve that problem we can use a simple DC-DC converter. We will still use the same 3 LED triplet only change the resistor to 22 Ohm. We still need a small resistor to prevent thermal runaway and to reduce the sensitivity.

I purchased a small DC-DC converter from Dimension Engineering, an RC electronics company. See
www.dimensionengineering.com/products/de-swadj

I put the DC battery voltage into Vin and adjust Vout to power the LED triplet with 20ma. In my case it is around 9.3v.

By putting the DC-DC converter between the light switch and the LEDs, you have full brightness no matter what your DC battery voltage and improve the efficiency to about 85%. You get a lot of light with very little power.

I use this circuit for areas I need full LED brightness. For example, over the galley sink and the engine compartment.

In my next post we will modify the circuit so it can be dimmed and still be highly efficient.

[deLight]

One nice thing about LEDs is that they are very bright and very efficient. I ringed deLight's Salon entirely with LEDs. 312 of them.
At 20ma each, full brightness you can read or do close work with ease anywhere in the Salon.  Unfortunately, most of the time you are not trying to read the fine print on a prescription bottle or trying to find the needle you just dropped.

Therefore I needed to be able to dim the LEDs. With the DC-DC converter it is fairly easy.  All you need to do is reduce the voltage to the LEDs. The Dimension Engineering DC-DC converter that I used has a screwdriver adjustment. I needed to modify it to use an external potentiometer.

I paralleled the 1K trimmer resistor on the DC-DC converter with a 2.2K Ohm resistor in series with a 20K log taper (volume control) potentiometer. The 2.2K resistor sets the minimum brightness. The 20K potentiometer adjusts the brightness. Turn the brightness all the way up and adjust the trimmer resistor for 20ma (I use 15ma for a margin of error) in the LEDs. Then turning the Potentiometer up and down varies the LED brightness from minimum to full. deLight's Salon adjusts from 1/2 watt to 15 watts. Efficiency is 85%-90%. Easily usable at anchorage without concern. A typical setting uses 2-5 watts.

Photos attached show:

Solder points to attach the resistor and potentiometer to the DC-DC converter. They are extremely small and difficult to solder onto.

deLight's V-berth dimmer. I built an aluminum frame to hold the DC-DC converter which protects it from damage in the locker where it is mounted and helps with the heat dissipation. The V-berth has 147 LEDs which puts the 1 amp version of the DC-DC converter right on the edge of its rated current.

A daytime photo of the Salon LEDs at full brightness.

A daytime photo of the Salon LEDs and minimum brightness.