Konstantinos Manos - Accumulator

The accumulator of the vehicle comprises 280 Lithium Polymer pouch cells in a 140s2p arrangement. The maximum total voltage of the accumulator is 588V and it can store 8.2kWh of energy. The cells are divided into 7 removable segments of 20s2p each. The cells are glued into stacks with a flame retardant adhesive. The electrical connections of the cells are made by bending the tabs on a custom slotted PCB and then joining them using an aluminum busbar and a bolt. The BMS cell modules are mounted on this PCB. The accumulator box is air-cooled by fans. The cells were sorted by their internal resistance and the ones with the highest resistances were placed in the most efficiently cooled regions.

Below you can view some photos from the assembly process. (Aug 2020)

Due to the low output impedance of each cell, short-circuits will result in extremely high current values.

The photos to the right, showcase the impact of an accidental short-circuit that resulted to the melting of the cell tabs.

This cell was removed and replaced. :)

The photo to the right depicts a test jig we built in order to test the functionality of the PCBs as part of the whole electrical system, before plugging them in the car.

From top left to right:

DC-link pre-charge and voltage indicator circuitry
DC-link discharge and TSAL (Tractive System Active Light) circuitry
AMS (Accumulator Management System) and IMD (Insulation Monitoring Device) Latching circuit.
Dashboard PCB

Bottom Left: An accumulator isolation relay,
Bottom Center: 320uF capacitance to simulate the inverter's DC-link capacitance.
Bottom right: TSAL flashing red indicating an active tractive system.

Acknowledgement:

The slotted PCBs of the accumulator were designed by Orestis Batsis. The kevlar baskets were designed by Socrates Sallis. The biggest part of the kevlar basket construction was done by the composites-manufacturing subgroup of the team. I was responsible for the cell assembly and testing.

The design of the circuits, and PCBs shown in the test-jig setup, as well as the testing was the result of the collaborative work of 4 students:
me, Vaggelis Psaradellis, Orestis Batsis and Yannis Karampinas.

Back to Formula Student