Prototype FabricationThe prototype board was fabricated using a toner-transfer copper etching process. Board layout was designed using Pspice, with 6 of the 1.4W LEDs in series, and large copper pads connected to the thermal junction of each LED. A thin (1/64") double-sided copper clad FR4 board was used, with an aluminum backing of 0.063" thickness. The board measured 8.5" by 1.5". The aluminum backing was laminated to the copper board using a two part epoxy (JB Weld), and clamping pressure was applied as the epoxy set.
A thermal experiment was conducted to determine the feasibility of the fixture design. The experimental setup was as follows: One prototype circuit board was manufactured with six (6) of the chosen 1.4W Cool White LEDs mounted to it. The specifications of the circuit board were: 1/64" double sided copper clad FR4 with 0.063" thick aluminum backing, secured with JB Weld*. The board lamination was 1.5" x 8.5", providing a total power dissipation of 0.66 Watts per square inch. Power of 21.6V with 380mA (current limited) was applied to the set of six series LEDs, and the assembly was placed in the empty Hubbell light fixture housing. Temperatures, current and voltage data were recorded and plotted (see attached Excel file). Results are as follows: Ambient Temperature = 22*C Bulk Temp inside box = 24*C Junction temperature of LED (measured at solder joint of thermal junction) = 74*C.
When a computer model of this experiment was run, the results were as follows: Inputs: Geometry and material properties matching those of the LEDs and board lamination Convection on top and bottom surfaces of board lamination with a convective coefficient of h=13 W/mK Bulk Temperature = 297K (24*C) Highest temperature recoreded in the analysis was 71.55*C
These results agree within 2.5*C. The computational model can therefore be used as an adequate tool for evaluation of this system at higher operating temperatures.
A total of three prototypes were developed. The first acted as a benchmark for future fixtures. The final two prototypes were installed on the RIT campus for real world testing.
The budget and spending for the project can be found below.