EcoFit Lighting Thermal Test Report

Transcription

1 EcoFit Lighting Thermal Test Report November 2009 Prepared by J. Bloomfield and K. Warren Advanced Manufacturing Institute Kansas State University KTEC Center of Excellence 510 McCall Road Manhattan, KS T F

2 Contents Executive Summary...3 Introduction...3 Testing Equipment...3 Test Procedure...4 Thermocouple Placement...4 Testing Conditions...12 Measured Data...13 Summary and Conclusion

3 Executive Summary The primary purpose of the tests performed for this report was to determine the steady state operating temperatures of the EcoFit streetlight modules over a range of outdoor temperature conditions. To complete the tests the light fixtures were placed in a thermally controlled chamber and operated at 5 C increments from 0 C to 35 C. The data were then recorded and compiled into the tables showing steady state temperatures and steady state temperature differentials. The measured steady state temperatures were utilized to calculate LED junction temperatures at each tested temperature setting. The combination of outside, ambient and junction temperatures measured during the testing process provide the basis for determining L70 LED longevity under a variety of outdoor temperatures, based on LM 80 data provided by the LED manufacturer. All testing procedures are consistent with ENERGY STAR Program Requirements for SSL Luminaires Version 1.1 (December 2008) and ENERGY STAR Manufacturer s Guide for Qualifying Solid State Lighting Luminaires Version 2.0 (October 2009). Introduction The Advanced Manufacturing Institute is a part of Kansas State University College of Engineering and a Kansas Technology Enterprise Corporation Center of Excellence. AMI develops products and processes, analyzes product performance, improves manufacturing efficiency, optimizes equipment design and discovers new technologies for a wide range of industries. EcoFit Lighting approached AMI to develop test methods and procedures to independently test and establish the steady state operating temperatures of various points on five of their LED streetlight module product configurations. The tests were performed in a thermal chamber at Kansas State University, with the streetlight modules operating in a controlled temperature environment ranging from 0 C to 35 C in 5 C increments. The product configurations tested were: 30 LED, 350 ma 42 LED, 350 ma 42 LED, 525 ma 63 LED, 350 ma 63 LED, 525 ma Testing Equipment The following equipment was used to perform the test as well as process the data collected: a) Thermal Chamber at Kansas State University Institute for Environmental Research b) Omega TXDIN70 Signal Conditioners c) 30 AWG type T Thermocouple Wire d) NI LabVIEW application for Data Acquisition and processing 3

4 e) NI USB 6251 Multifunction Data Acquisition device f) Microsoft Excel for post processing Test Procedure The following section illustrates how the thermocouples were mounted to the light fixture as well as the conditions of the tests that were performed. Thermocouple Placement The data acquisition device allowed for the use of sixteen analog channels. With one channel reserved for the chamber temperature, the streetlight module assemblies were instrumented as follows: 1) Bottom of Light Engine (i.e. light emitting side pointing downward toward the ground, directly exposed to the external environment) a) Channels 1 5: Five on the LED circuit board including the four corners and the middle (see Figure 1, #1 5); these thermocouples were soldered directly to the printed circuit board (PCB) aluminum core (surface material was removed) immediately adjacent to the mounting points of the LEDs (see Figure 2 for example); the resulting data were used to calculate the temperature of the PCB/LED solder point (T sp ). b) Channel 6: One inside the acrylic cover immediately above the LEDs (see Figure 3, #6); this thermocouple was used to directly measure the ambient temperature in which the LEDs operate (T a ). c) Two on the external aluminum heat sinks directly exposed to the external environment. i) Channel 7: One on the tip of the external fins on the power supply side (see Figure 3, #7). ii) Channel 8: One in the valley of two adjacent external fins on the opposite side. (see Figure 3, #8). 2) Top of Light Engine (i.e. side encased within the light fixture). a) Channel 9: One on the driver heat sink tip located over the FETs. (see Figure 4, #9). b) Channel 10: One inside the polycarbonate cover of the driver board (measuring air temperature within the driver compartment). (see Figure 5, #10). c) Channel 11: One on to the bottom of the driver compartment in the main casting. (see Figure 6, #11). d) Channel 12: One on the temperature of the outer lip of the main casting that contacts the cobra head housing. (see Figure 7, #12). e) Channel 13: One in the ambient air to measuring air temperature inside light fixture housing. (see Figure 8, #13). f) Channel 14: One on the middle back aluminum heat sink (tip of fin) (see Figure 9, #14). 4

5 g) Channel 15: One on the base of the heat sink, directly below channel 14. (see Figure 9, #15). 3) Channel 16: One in the outside air to measure the temperature within the thermal chamber; this thermocouple recorded the simulated outdoor temperature as the thermal chamber transitioned between 0 C and 35 C. The thermocouples mounted to the circuit board core were soldered directly to the board using standard 60/40 rosin core solder after the surface material was removed. The thermocouples mounted to the heat sinks were attached using a fast setting epoxy (JB Weld). The thermocouples measuring ambient conditions within both the lens and fixture housing were suspended in the air space. Channel Name Channel Number LED 1 1 LED 2 2 LED 3 3 LED 4 4 LED LED air 6 7 Outside Qsink tip 7 8 Outside Qsink valley 8 9 Driver Qsink tip 9 10 Driver air Drvr compmt Module lip Housing air Int Qsink tip Int Qsink base Chamber temp 16 Table 1 Thermocouple channels 5

6 Figure 1 Location of thermocouples measuring LED PCB core temperatures. Figure 2 Close up of representative thermocouple measuring LED PCB core temperatures. 6

7 6 8 7 Figure 3 Location of thermocouples measuring air temperature inside acrylic lens (6) and external heat sink fin temperature (7, 8). 9 Figure 4 Location of thermocouple measuring driver heat sink temperature. 7

8 10 Figure 5 Location of thermocouple measuring air temperature inside driver board cover. 11 Figure 6 Location of thermocouple measuring base plate temperature below driver compartment. 8

9 12 Figure 7 Location of thermocouple measuring base plate temperature along external lip. 9

10 13 Figure 8 shows the placement of the housing air thermocouple. 10

11 14 15 Figure 9 Location of thermocouple measuring internal heat sink tip (14) and valley (15) temperatures. 11

12 Testing Conditions Figure 10 Test Setup Performing the temperature measurement required placing the EcoFit light fixtures within a thermal chamber at KSU s Institute for Environmental Research (IER). The tests required the temperature to be varied from 0 C to 35 C in 5 increments. To simulate worst case environmental conditions, no air flow was allowed during the temperature measurement processes, as air currents could serve to increase heat exchange between the test units and the external environment, lowering the measured temperatures. Stated another way, the thermal chamber ensured 0 mph wind speed, which maximizes measured temperatures; any ambient air motion (i.e., wind) could result in temperatures lower than those measured during the testing procedure. A stand was fabricated at AMI to hold each light fixture in approximately the same orientation as in normal operation. The test setup is similar to Figure 10. The power cord and thermocouples internal to the housing entered through the mounting tube in the back of the fixture. The LED thermocouples (channels 1 6) entered through a small sealed hole drilled in the acrylic cover and were grouped with the two external heat sink thermocouples. Previous testing showed that 3 ½ to 4 hours were required to achieve steady state so each temperature increment was allowed at least 4 hours to stabilize before steady state temperatures were recorded. In this manner, three temperature readings could be collected each day with one allowed to stabilize to the next setting overnight and collected the next morning. 12

13 Unit 30 LED, 350mA Measured Data All of the test data have been compiled into Table 2, which shows the steady state temperatures of each channel for each of the five test units at each ambient temperature. Steady State Temperatures 42 LED, 350mA 42 LED, 525mA 63 LED, 350 ma 63 LED, 525mA 16 Chamber temp LED 1 LED 2 LED 3 LED 4 LED 5 6 LED air 7 Outside Qsink tip 8 Outside Qsink valley 9 Driver Qsink tip 10 Driver air 11 Drvr compmt 12 Module lip 13 Housing air 14 Int Qsink tip Table 2 Steady State Temperatures 15 Int Qsink base 13

14 EcoFit 30 LED (350 ma) Streetlamp Temperatures Deg C Figure 11 Steady state temperatures for the 30 LED (350 ma) unit. 14

15 EcoFit 42 LED (350mA) Streetlamp Temperatures Deg C Figure 12 Steady state temperatures for the 42 LED (350mA) unit. 15

16 EcoFit 42 LED (525mA) Streetlamp Temperatures Deg C Figure 13 Steady state temperatures for the 42 LED (525mA) unit. 16

17 14 Int Qsink tip 15 Int Qsink base EcoFit 63 LED (350 ma) Streetlamp Temperatures LED 4 LED 5 6 LED air 7 Outside Qsink tip 8 Outside Qsink valley 9 Driver Qsink tip 10 Driver air 11 Drvr compmt 12 Module lip 13 Housing air Figure 14 Steady state temperatures for the 63 LED (350 ma) unit LED 3 LED 2 LED 1 Deg C

18 EcoFit 63 LED (525 ma) Streetlamp Temperatures Deg C Figure 15 Steady state temperature for the 63 LED (525mA) unit. 18

19 The following table illustrates the temperature differential of each channel with respect to the environmental chamber temperature setting, which represents the outdoor temperature in field operation. This table also shows that the temperature of the light fixture changes almost linearly with respect to the environmental chamber temperature. Temperature Differentials From Surrounding Air Unit 30 LED, 350mA 42 LED, 350mA 42 LED, 525mA 63 LED, 350 ma 63 LED, 525mA LED 1 16 Chamber temp LED 2 LED 3 LED 4 LED 5 6 LED air 7 Outside Qsink tip 8 Outside Qsink valley 9 Driver Qsink tip 10 Driver air 11 Drvr compmt 12 Module lip 13 Housing air 14 Int Qsink tip Int Qsink base Table 3 Steady State Temperature Differential Knowing the environmental chamber temperature and the operating temperature differential from Table 3 allows for predicting steady state operating temperatures by simply adding the differential to the ambient outdoor temperature. 19

20 Based on the direct thermocouple measurements from solder point thermocouples 1 5 attached directly to the PCB core immediately adjacent to the LEDs (T sp ), the LED junction temperature (T j ) can be directly calculated based on the relationship provided by the LED manufacturer (Equation 1) for the specific model of LEDs tested (Cree XP E). This relationship is defined as follows: Tj = Tsp + Rj sp( Vf I f ) Equation 1 T j = LED junction temperature T sp = Solder point temperature (measured) R j-sp = thermal resistance between the LED and the solder point (9 C/W) V f = Forward voltage across LEDs I f = Forward current supplied to LEDs (350 ma low power; 525mA high power) Because five LED temperatures were collected during the testing procedure, the highest measured solder point temperature (T sp ) at any of the five LED test points was used to calculate the junction temperature (T j ). Example: At a thermal chamber temperature of 15 C with the unit operating at low power (350 ma), the junction temperature Tj is calculated using Equation 1 as follows: T T T T j j j j = Tsp + R j = 55.2 C sp ( V I ) = 44.9 C + 9 C / W = 44.9 C C f f ( 3.3V 0.350A) Based on the solder point/junction temperature relationship defined by the manufacturer, it follows by Equation 1 that each LED junction temperature is 10.4 C and 15.6 C hotter than the measured solder point temperature at low power (350 ma) and high power (525 ma) respectively. The calculated LED junction temperatures are presented in Table 4. 20

21 LED Junction Temperatures Unit 30 LED, 350mA 42 LED, 350mA 42 LED, 525mA 63 LED, 350 ma 63 LED, 525mA Forward Current (ma) Chamber temp LED 1 LED 2 LED 3 LED 4 LED Table 4 Calculated LED junction temperatures based on Equation 1 and measurements from Table 2 21

22 Summary and Conclusion The primary purpose of the tests performed for this report was to determine the steady state operating temperatures of the EcoFit streetlight modules over a range of outdoor temperature conditions. To complete the tests the light fixtures were placed in a thermally controlled chamber and operated at 5 C increments from 0 C to 35 C. The data were then recorded and compiled into the tables showing steady state temperatures and steady state temperature differentials. The measured steady state temperatures were utilized to calculate LED junction temperatures at each tested temperature setting. The combination of outside, ambient and junction temperatures measured during the testing process provide the basis for determining LED longevity (L70) under a variety of outdoor temperatures, based on LM 80 data provided by the LED manufacturer. 22