TRIO-CINEMA 1 UCB, 2/08/2010 CINEMA Solar Array Design Review Yashraj Khaitan David Glaser Kevin Jenkins Chris Pasma Space Sciences Laboratory University of California, Berkeley

TRIO-CINEMA 2 UCB, 2/08/2010 Solar Array Design Agenda AGENDA Electrical Design Requirements Schematic Overview Current Calculations Issues Developmental Plans Layer Images Mechanical Design and Assembly Panel Assembly TASC Electrical Tests Encapsulant Array Design (Time Permitting)

TRIO-CINEMA 3 UCB, 2/08/2010 Solar Array Design Agenda Electrical Design

TRIO-CINEMA 4 UCB, 2/08/2010 Panel Size: Each panel covers ~ 8cm x 8cm area with 24 cells on a panel Blocking: Blocking diodes need to be used to prevent back biasing shadowed cells Magnetic Effects: Cells need to be wired to minimize generated magnetic torque Monitoring: Array temperatures need to be monitored during operation. Requirements

TRIO-CINEMA 5 UCB, 2/08/2010 Schematic

TRIO-CINEMA 6 UCB, 2/08/2010 Overview Panel Size: The panels are 3.465” x 3.420” Blocking: SOD-123 blocking diodes are placed on each cell pair to prevent reverse current in shadowed cells Magnetic Effects: Diagonal routing on middle and bottom layers cancels the generated magnetic torque Monitoring: LM is used to monitor temperatures on the board Contacts between cell and PCB: Wide copper traces have been placed to maximize contact area. Mounting holes have been placed on the PCB for epoxy filling

TRIO-CINEMA 7 UCB, 2/08/2010 Current Calculations Via current: The current permissible in the smallest via (12mil) is A Trace current: The current permissible in the traces (12mil wide) is A

TRIO-CINEMA 8 UCB, 2/08/2010 Issues Trace Currents: Trace widths need to be adjusted to handle higher currents (672mA/Panel) Layout software giving trouble with multiple trace widths Testing PCB: Jumpers have not been installed on this PCB to verify current levels of individual cell pairs or particular traces The only way of testing current levels is to not mount the diodes and short those terminal pads Connectors: The connector used on each panel is a 6 pin connector and the one used on the EPS is also 6 pin However, the EPS connects to two panels at a time

TRIO-CINEMA 9 UCB, 2/08/2010 Development Plans Prototype this design with a PCB layout company - Have quote for $520 for 10 boards Test the board by checking current levels, temperature of cells, efficiency of cells under different operating temperatures. Harness needs to be made to connect 6 pin terminals of two panels to a single 6 pin connector on the EPS Interface board with the EPS to test MPPT operation

TRIO-CINEMA 10 UCB, 2/08/2010 Layer Images (All Layers)

TRIO-CINEMA 11 UCB, 2/08/2010 Top Layer: Copper connections with cell

TRIO-CINEMA 12 UCB, 2/08/2010 Middle and Top Layer (Negative Terminal)

TRIO-CINEMA 13 UCB, 2/08/2010 Middle Layer: Negative Terminal

TRIO-CINEMA 14 UCB, 2/08/2010 Bottom and Top Layer: Positive Terminal

TRIO-CINEMA 15 UCB, 2/08/2010 Bottom Layer: Positive Terminal, Diode Mounting

TRIO-CINEMA 16 UCB, 2/08/2010 Bottom and Middle Layer

TRIO-CINEMA 17 UCB, 2/08/2010 THANK YOU

TRIO-CINEMA 18 UCB, 2/08/2010 Mechanical Design

TRIO-CINEMA 19 UCB, 2/08/2010 Panel Size: Each panel covers ~ 8cm x 8cm area with 24 cells on a panel Cells must be glued to panel with structural and electrical integrity Cells should last for nominal 1-year mission duration Requirements

TRIO-CINEMA 20 UCB, 2/08/2010 Basic Approach borrowed from other projects –Custom PCB –Glue TASC Cells to PCB Basic Approach

TRIO-CINEMA 21 UCB, 2/08/2010 Assembly Procedure Option 1 –Start with PCB, with TASC contacts ~1.5mm holes in back for structural epoxy application –Apply silver epoxy to PCB contacts –Place solar cell appropriately on PCB, allow to cure for 2 hours at 80C –Use syringe to apply Scotchweld 1838 epoxy through back-holes Option 2 Scotchweld 1838 may be applied along with silver epoxy, eliminating need for thru-holes and separate cure, if logistics allow. –Issues may include air escape and epoxy mixing After silver epoxy and Scothweld 1838 have dried –Technicians will solder top pad of each TASC rectangle to the adjacent PCB pad.

TRIO-CINEMA 22 UCB, 2/08/2010 Backup Slide Silver Epoxy Electrical DataVoltage (V)Current (mA) More Epoxy (5 drops ~2mm) Less Epoxy (5 Drops ~1mm) No Epoxy (control) Control Cell with Epoxy (5 drops ~1mm) Electrical Performance of Silver Epoxy (Adhesive left over from THEMIS (expired)

TRIO-CINEMA 23 UCB, 2/08/2010 TASC Assembly Jig

TRIO-CINEMA 24 UCB, 2/08/2010 TASC Electrical Testing

TRIO-CINEMA 25 UCB, 2/08/2010 Reference Data for Solar Cell Performance 24 pairs have been chose for first 2 panels

TRIO-CINEMA 26 UCB, 2/08/2010 CV Encapsulant Nusil markets substance as –“for electronic and space applications requiring low outgassing and minimal volatile condensables." –for "...applications such as solar arrays where clarity and low volatility are important." We want to do UV tests soon to determine extent of protection Procedure: Mix encapsulant 1:1 (by weight) and place in vacuum chamber to deaerate Apply encapsulant to finished PCB with camel-hair brush Thickness: "historically our satellite manufactures utilize a >0.005 " bond line." –Nusil technical sales Allow assembly to cure C (manufacturer specification)

TRIO-CINEMA 27 UCB, 2/08/2010 Solar Array Design (If time allows) See SolidWorks Model of CINEMA