Key Rule Requirements

• Max segment voltage – 120V (EV5.1)
• Max segment energy – 6MJ (EV5.1)
• Electrically insulated with non flammable material on top and on the side of each segment (EV5.2)
• Segments connected using positively locking, tool-less maintenance plugs (EV5.3)
• Each parallel cell needs to be fused (EV6.6)

Design Decisions:

• 16s3p segment architecture
  • Each ADI BMS IC can handle 8 voltage channels
• Wire bonded fusible links for each parallel cell
  • Fully CNC’d cell connections
• No cooling necessary
• Fiberglass panel insulation on the sides, kapton film insulation on top and bottom
• Cells potted with electrically insulating, thermally conductive epoxy

       

Fusible Links

Power Loads

• 135A max current (6 seconds during acceleration event)
• 55A Continuous RMS Current (150 seconds during autocross)

Design Decisions:

• 63A main fuse (we want this to blow first)
• 35mm^2 / 2 gauge wire
  • Bend radius is 43mm (½ distance between segments) in design, which is 4 times 11mm (wire OD). This is less than the recommended 8 times wire OD so need to keep an eye on cable kink, strain, and wear
• 8mm SURLOK connectors

Fusible Links:

Motivation – Why Wire Bonding?

• No heat interaction with Lithium
  • Compared to spot welding
• Integrated fusing (details in following slide)
• Reduced contact resistance 
• Quick and safe automated process
• Quality Control (Hesse Mechatronics)

Requirements

• Wire bonds rated for max of 1.75x Max cell discharge current (45A cell, 80A fuse)
  • Spec from FSAE Judge
• Specify wire diameter, wire length
• Have Fast and Slow fuse blow out times (160A, 80A)
• 4N Aluminum Wire (99.99 Purity)
  • Impurities change resistance

	Blow Time
Current Level 1 (80A)	30 < t < 300 sec
Current Level 2	5 sec < t < 15 sec
Current Level 3	0.2 sec < t < 1 sec
Current Level 4 (160A)	0.05 sec < t < 0.15 sec

MATLAB Simulation of 1mm Round Wire
Lumped Capacitance Model w/ Temperature Dependence:

Fuse Blowout Times for 42mm wire at various diameters

Test setup: