Integration of a 400W ac dc power supply into a closed system relying only on natural convection cooling

Transcription

1 Integration of a 400W ac dc power supply into a closed system relying only on natural convection cooling How potting an electronic assembly simplifies the thermal management in harsh working conditions

2 Abstract General requirements in the modern residential power supplies installation. More and more often it is required to integrate power supplies in systems operating in environments where forced air cooling is not allowed or available and where the heat transfer by conduction is not practicable or ineffective. There, the unwanted heat, generated by the power conversion, has to be managed and dispelled in a way to ensure adequate operating temperatures not harmful to the proper functioning and reliability of the apparatus and not compromising its service life time. Herein after will be considered a specific thermal management case of a 400 W power supply integrated in a closed system which ambient temperature can be 50 C. The power supply, for its intrinsic efficiency generates W in heat which management requires to be thoroughly analyzed and properly addressed since the early stages of both power supply and system design. A representative example of such installations is offered by Roal Electronics four channel safe energy server, SES400, which integrate the DDP400-US24-SC used as ac-dc converter. This system, is an EMerge Alliance registered product, consistent with the EMerge Alliance, Occupied Space, standard.

3 Introduction About EMerge Alliance An open industry association developing standards leading to the rapid adoption of DC power distribution in commercial buildings. These innovative standards integrate interior infrastructures, power, controls and devices in a common micro-grid platform to facilitate the hybrid use of AC and DC power throughout buildings for design and space flexibility, greater energy efficiency and improved sustainability. The Alliance will ensure that its standards deliver: Required solutions based on market requirements and ecosystem approval Buyer assurance with products evaluated against our standards and registered for public view Increased supply choices in the value chain that spans the needs of different commercial interiors EMerge Alliance is a member of the U.S. Green Building Council.

4 Introduction EMerge Alliance Occupied Space standard Occupied Space: the EMerge Alliance Occupied Space Standard creates a 24-volt DC micro-grid for use in commercial interiors featuring: Safe, flexible, plug&play low voltage dc power distribution Power, infrastructure, peripherals (such as lighting), and controls on a common platform - Hybrid ac-dc power for design efficiency and sustainability Connects directly or through building micro-grid to on-site renewable generation and storage EMerge Alliance Registered Products for the Occupied Space Standard are listed on the Alliance website product registry.

5 Introduction Power Supply on Occupied Space standard AC power must be converted to DC at the device level to power equipment like electronic lighting ballasts, solid state lighting (i.e. LEDs), lighting sensors and controls, HVAC controls and actuators, and myriad variety of computer/it/telecom equipment. The Safe Energy Server is a power supply unit designed to interface directly with the EMerge Alliance distributed DC Power system. The SES400 is ideal for individual offices, classrooms, clouds and lobbies where independent smaller grids may be necessary. One system may be deployed for each 200 to 400 square feet (18 37 m 2 ) of ceiling grid depending on room design and load requirements.

6 EMerge Alliance Occupied Space Standard requirements Safety ROAL s Safe Energy Server (SES400) is designed to power low voltage lighting, building control systems and audio visual equipment in 24 V DC distributed building power systems. The system is compatible within the EMerge Alliance Occupied Space 24 VDC standard and will install and operate seamlessly with other EMerge compliant products. The power system comes as a fully enclosed 400 W power system that incorporates 4 output channels, each providing a regulated 24 VDC which meet the requirements for a NEC Class 2 circuits, Which are only allowed to be powered from a power source with an output power of lower than 100 VA and an output current of lower than 8 A. The power source needs to be listed as an UL 1310 power supply device or must be approved as a Limited Power Source (LPS) according to IEC The NEC Class 2 limits need to be fulfilled even under overload or during fault conditions of the unit.

7 EMerge Alliance Occupied Space Standard requirements Efficiency Power electronics has become a dominant element in all kinds of technical equipment. Power consumption is crucial and needs to be minimized through highly efficient designs. SES400 Weight [Kg] 4.3 Input [VRMS/Hz] Efficiency [%] No load power consumption [W] Four channels at rated load (23.77 V A) 100 / 60 90, / 60 90, / 60 90, / 50 92, / 50 92, / 50 92, / 50 92,8 4.41

8 EMerge Alliance Occupied Space Standard requirements Ingress Protection NEMA defines standards for various grades of electrical enclosures typically used in industrial applications. Each is rated to protect against designated environmental conditions. A typical NEMA enclosure might be rated to provide protection against environmental hazards such as water, dust, oil or coolant or atmospheres containing corrosive agents Type 2 Enclosures constructed for indoor use to provide a degree of protection to personnel against access to hazardous parts; a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); and a degree of protection with respect to harmful effects on the equipment due to the ingress of water (dripping and light splashing).

9 EMerge Alliance Occupied Space Standard requirements Environment Operating Conditions Natural Convection Cooling. Being the server Armstrong DC FlexZone compatible, conduction cooling would be neither practicable nor effective; Silent Operation (< 40 db(a)) Fully Operating up to 50 C ambient at steady maximum load Auto-recovering operation against electrical and thermal protection Safe from a fire ignition stand point. Test for heat and visible smoke release

10 Safe Energy Server SES400 Sub-parts Description The power system comes as a fully enclosed 400 W power system that incorporates 4 output channels, each rated 100 W at 24 VDC. The power system is comprised of two main sections, bulk AC-DC converter and output splitter limiter. The bulk converter utilizes a high efficiency PFC and LLC resonant technology to provide a single regulated voltage to the output section The output section, MultiLINQ, controls the power from the bulk converter to provide 4 independent channels which meet the requirements for a NEC Class 2 circuit. MultiLINQ is a patented power limiting technology (US patent no. 7,804,189) for low voltage systems.

11 Safe Energy Server SES400 Power Supply Functional Block Diagram BMC: Base-board Management Controller

12 Safe Energy Server SES400 Output Section Control V AC 24 V DC 400 W multiple output, class 2 power limiter and splitter AC-to-DC Power Converter 24 V, 400 W NEC Class 2 Independent Channel 100 VA 100 VA 100 VA 100 VA NO latch The power splitter processes a single input voltage and provides four independently protected outputs, each meeting the requirements of the National Electric Code (NEC 2005) for a class 2 system (100 VA). Each output of the power splitter may then be wired into building infrastructures as a class 2 system without the need for special wiring devices. The power splitter is not a converter that regulates the output voltage. Each output is independently controlled but this does not include regulation of the voltage. Output voltage is dependant on input voltage and voltage losses through the power splitter. MultiLINQ is a patented power limiting technology (US patent no. 7,804,189) for low voltage systems.

13 Safe Energy Server SES400 General Features Universal input ( VDC; 120/240 V AC ) 92% Typical Efficiency 400 W Rated output power Four independent 24 V safe Class 2 outputs Natural convection cooled EMerge Alliance Registered Armstrong DC FlexZone Compatible Partner

14 Safe Energy Server SES400 Input / Output Specifications INPUT POWER: Input Voltage: 120/240 VAC, Hz Input Current: 5 A max Isolation: Meets the UL Reinforced / Double Insulation NEC (Class 2) Input Power Factor: > 0.9 Efficiency: 92% typical 100 VA Limit including over current protection on 24 VDC No operation above 4,16 A, no protection below 3,91 A OUTPUT PER CHANNEL: Output Voltage: 24 VDC +/- 3% Output Power: 94 W continuous (each channel) Output Current: 3.91 A max (each channel) Capacitive Load: Each output will energize a load consisting of up to 1000 µf Output Protection: Each channel is protected against overload, short circuit, over temperature and connection of multiple outputs in reverse polarity. Overvoltage protection is latching; all other protective modes are self-resetting. 3,91 4,03 4,16 A

15 Safe Energy Server SES400 Safety Certifications and EMC ANSI / UL 1310: Class 2 Power Units ANSI / UL 1012: Power Units other than Class 2 CSA C22.2 No (2001): General use Power Supplies CAN/CSA C22.2 No. 223 (1991): Power Supplies with Extra Low Voltage Class 2 Outputs UL2043: Fire Test for Heat and Visible Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces UL2577: Suspended Ceiling Grid Low Voltage Lighting Systems EMerge Alliance Registered EMI: Radiated and conducted: FCC Class A, EN55022 Class A

16 Safe Energy Server SES400 Environmental Specifications Operating Temperature: -10 C to +50 C Operating Relative Humidity: 5% to 95%, non condensing Audible Noise: < 40 db(a) at 1 meter Operates in the presence of occasional water exposure from above (NEMA Type 2, equivalent to IP43)

17 Thermal Requirements Analysis PS packaging selection Open Frame - U-chassis Recommended cooling airflow directions 250 W

18 Thermal Requirements Analysis PS packaging selection Boxed built in fan Cooling airflow direction 400 W 250 W

19 Thermal Requirements Analysis PS packaging selection Sealed box w/o heat sink

20 Potted Package Solution Advantages Allowed Output Power 250 W 300 W 50 C Ambient 380 W

21 Potted Package Solution Advantages Internal Temperature Equalization 250 W At 50 C Ambient 380 W At 50 C Ambient

22 Temperature Reference T C Potted Package Solution Advantages Thermal point reference Identification

23 Potted Package Solution Advantages Ingress protection Rating IP67 Rated and Certified By UL

24 Thermal Management Heat sink Function Heat sinks function by efficiently transferring thermal energy ("heat") from an object at high temperature to a second object at a lower temperature with a much greater heat capacity. This rapid transfer of thermal energy quickly brings the first object into thermal equilibrium with the second, lowering the temperature of the first object, fulfilling the heat sink's role as a cooling device. Heat sink consists of a base with flat surface and an array of comb or finlike protrusions to increase the heat sink's surface area contacting the air Heat sink performance, is a function of material, geometry, and overall surface heat transfer coefficient. Use of thermal interface material ensures good transfer of thermal energy to the heat sink.

25 Thermal Management Heat transfer paths Conduction or diffusion: The transfer of energy between objects that are in physical contact. Convection: The transfer of energy between an object and its environment, due to fluid motion. Radiation: The transfer of energy to or from a body by means of the emission or absorption of electromagnetic radiation.

26 Thermal Management Working ambient definition Temperature Reference Point T C < 90 C 50 C 80 C

27 Worse Operating Conditions Thermal Management Heat sink Dimensioning Ambient TA: 50 C Heat Sink: Θ H-A, T H Interface: Θ C-H Temperature Reference Point Tc < 90 C Q: heat generated by conversion 0,90 Efficiency 390 W rated power: 33,33 W

28 Thermal Management Heat Sink Efficacy Verification Test Interface material: graphite composite sheet, electrically and thermally conductive, thickness ± 0.025, absolute thermal resistance 0,1 C/W Section perimeter: 1388 mm Cut length: 103 mm Fin protrusion: 25 mm Weight: 1155 g Thermal resistance: 1.85 C/W Section Perimeter: 1992 mm Cut length: 103 mm Fin protrusion: 40 mm Weight: 1380 g Thermal resistance: 1,00 C/W TC = 90,6 C TC = 88,3 C

29 Thermal Management Heat Sink Efficacy Verification Test

30 Conclusions Electronic assembly potting benefits / hindrances trade-off Hot spots temperature distribution equalization within the electronic assembly by creating an inner thermal path for bulky and not thermally attachable components. Hot spots temperatures homogenization and effective average temperature lowering Thermal reference point detection on case make it easier to work out a privileged thermal path for heat transfer and dispelling. No need to check for every single hot spot temperature. Makes the power supply perfectly suitable and compatible for systems required to be immune against contaminant agent in a polluted environment and operating in the presence of occasional water exposure from above (NEMA Type 2 IP42, IP67) VS Potting process critical: voids, homogeneity, polymerization, cooling shrinkage, curing swelling. Chemical and physical compatibility between resin and components to be tested (UL requirements and tests) Side effects of thermal equalization on secondary components (small electrolytic caps) The values of the stray capacitance distributed over the entire PCB change, being the dielectric properties of the resin different from those of air. This could induce a significant change in EMC performances.

31 Thank YOU Massimo Petritoli, Sales Engineer Michele Simoncini, Designer Roal Electronics 19 September 2013