Mechanical Design
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Mechanical Design

The main element of the mechanical design is a center carrier with a cavity for holding the various circuits (DC power supply, infrared receiver, relay logic/motor control, PWM dimmers, current regulators and wiring matrix).

This is a sizable complement of devices and requires quite a bit of real estate.


Wiring Matrix & Current Regulators









Relay Logic - Motor Control

Infrared Receiver




Center Tray with Mounted Electronics

Eight arms extend from the octagonal center tray. The LED assembly is mounted at the tip of the arm. The photo below shows the finned heatsink, the wiring disc and the collimating lens. The actual LED disk is obscured by the lens.


The arm show is actually the second incarnation. The first design extended in its full thickness all the way to the heat sink and cradled the heat sink over half of its circumference. However, this inhibited the airflow around the heat sink to a degree where the LED temperature rose to unacceptable levels.

The temperature limit of the LED junctions is 125˚C. The thermal resistance of the LED cavity is about 2.6˚C/Watt and the heat sink in free air adds about another 2˚C/Watt. Since the airflow of the heat sink is somewhat limited by the mounting method, the latter figure is optimistic. Dissipating 7.6 Watts at full power, the heat sink temperature was measured at 52˚C. This makes the estimated junction temperature about 72˚C, a save value.

The heat sink is mounted to an aluminum bar and directly to the wood. This bar contributes to the heat dissipation.

The photo below is a close-up of the LED assembly. The purpose of the printed circuit board disk is two-fold. It forms the interface between the six-conductor cable coming from the center through a tunnel and the six solder pads of the LED disk. Note the thin curved wires. They are flexible and do not exert any force on the fragile ceramic disk. Again, an earlier design used very stiff and short wires and promply peeled off the metal landings on the LED disk.

The tubular baffles (not shown here) will be glued to the PCB disk. The baffle hides the circuitry,protects the lens and shields your eyes from seeing the intense light on the lens surface.

The raw LED radiates with a 120 degree dispersion. Since I was interested to get most of the light onto the table below, a lens was added to cut down the dispersion to about 40 degrees.


LED Assembly Close-Up

Finally, all things are coming together as shown in the photo below.


Almost completed light fixture, showing some of the baffles already installed.

Finally, the cover is closing the center tray and power is applied. Note the center opening with grille hiding a small fan to move a minute amount of air through the tray. The small dark hole contains the infrared receiver diode.


Completed Light Fixture under Power

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