Project 1 Mechanical design of battery pack

Objective : To design a 250W Lithium Ion battery pack for an e-cycle.

Design calculations :

Mechanical Design:

1. The application selected for the use of battery pack is an e-cycle.
2. According to ARAI, the max power transmitted from the controller to the motor should be 250W incase of low speed electric cycles.
3. Considering the restriction on power requirement, a 280Wh pack design was selected.
4. So, being a application with max discharge current being 1C, NMC 18650 cells were selected for the application.
5. The pack should be lightweight, with excellent operational characteristics, hence cell holders of material ABS plastic have been selected.
6. So, according to the power, the pack voltage was designed to be 36 V, which was achievable by using 10 cells in series. And the capacity being 7.8Ah, was achieved by using 3 cells of 2.6 Ah in parallel.
7. The cells were later connected to each other with help of 0.5mm* 10mm nickel strip.
8. The nickel strip is usually spot welded to the cells for cost effectiveness and ease of operation.

Electrical Design :

1. BMS was decided to place at one of the end of the pack, keeping temperature sensor in the core of the pack.
2. BMS would protect the pack from over currents, over voltage, voltage imbalance and temperature imbalance.
3. BMS should be rigid and not dislocate during vibration, hence proper packaging has been done.
4. Natural cooling mechanism hs been selected for cooling of the cells.

Following are the CAD developed in PTC Creo

1. 18650 cell :
2. Cell holders :

Complete assembly of battery pack :

Isometric view :

Top view :

Side View :