Winter 2021 Onboard - planned timeline
This term, the battery box mini-project will be mandatory for all team members.
The project will be more relevant to the car to have members understand the importance of the mini-project
The purpose of the mini-project is to configure a battery pack based on certain specs, there will be a good amount of handholding (i.e., help will be provided when asked so be proactive!)
The project will last for two weeks following Thursday, Jan 14th, 7:30 PM general
End of week 1 | Thursday, Jan 21st: First presentation of findings thus far, including thought process and questions
End of week 2 | Thursday, Jan 28th: Final presentations of solution
@mentors should be more proactive, please hold check-in conversations weekly if possible on Slack to lead new members.
To get everyone started on the battery box team, it would be good to through the basics of designing a simple battery pack. This exercise will help you understand what you are contributing to this term!
You’ll start by reading up on some of the battery pack details and manufacturing methods, and then move to design a simple pack to understand how to put everything together and then provide a recommendation for a battery pack for a car similar to MSXIV.
This is the exact same process that we go through when starting to design a new pack for the car (or any battery pack for that matter) - so this is all required knowledge for building battery packs.
Step 1
Read through these PDFs about designing and building a battery pack. These compile a ton of information - don’t be scared to read them, but be sure to spend the time to understand them. If you have any questions, then message the #mech-battery-box channel on slack and someone will get back to you!
Read these first
Thanks Alwin George for pointing out that some diagrams are missing in the PDFs - the original web pages are here:
Part 1: https://www.electricbike.com/introduction-battery-design-1/
Part 2: https://www.electricbike.com/introduction-battery-design-2/
Part 3: https://www.electricbike.com/introduction-to-battery-pack-design-and-building-part-3/
And read “Inside 18650 Cells”: https://www.electricbike.com/inside-18650-cell/
Then read these for some more in-depth background for battery packs
Step 2
We’ll start with a simple pack - here are some of the specs that we want for this project:
Item | Spec | Notes |
|---|---|---|
Amount of Energy Stored in pack | 100Wh minimum | We also want minimum weight while meeting this criteria. Minimum weight is a hard requirement (must be met). |
Cell Nominal Voltage | 3.635V | |
Cell Nominal Capacity | 3450mAh | |
Operating Voltage | 6-18V | Must stay in this range for the entire discharge. At any charge state (from fully charged to fully discharged, the pack voltage should be more than 6V and less than 18V). |
Single Cell Min, Max Voltage | 2.5V, 4.2V | At the full charge and full discharge limits |
What do you recommend for the number of cells in series and parallel, and why did you choose those numbers - we’re looking for an answer in the form of XPYS, where X is the number of cells in parallel and Y is the number of cells in series, along with a justification.
Step 3
Draw a diagram of the cells, how they are connected together, and where the main battery terminals are for the battery configuration calculated for Step 2.
Step 4
Now that you should know how to design a battery pack, we’ll get you to run through the process of choosing a battery configuration for a car, given the following parameters (chosen to loosely represent Midnight Sun XIV):
If you think there’s info missing here, message Micah Black on slack and I’ll first make sure I didn’t make a mistake in the info provided, and then help you out to make sure you’re on the right track!
Car Specs:
Item | Spec | Notes |
|---|---|---|
Race Distance | 3000km | |
Car Average Velocity | 60km/h | Assume average velocity for the entire duration of the race, and that the path is flat. |
Power Consumed travelling at Average Velocity | 1005W | Per Motor |
Peak Motor Power | 5000W | Max power that the motors will draw (per motor) |
Number of Motors | 2 | Motors on each of the 2 rear wheels |
Motor Controller Min, Max Voltage | 50V, 165V | |
Single Cell Min, Max Voltage | 2.5V, 4.2V | At the full charge and full discharge limits |
Nominal Cell Voltage | 3.635V | Average voltage of a cell over the full discharge curve |
Single Cell Capacity | 3450mAh | Assume all cells are perfectly balanced |
Max Discharge Current of Single Cell | 10A | |
Solar Power Input | 800W | Assume the sun is always shining for the entire duration of the race |
What do you recommend for the number of cells in series and parallel, and why did you choose those numbers - we’re looking for an answer in the form of XPYS, where X is the number of cells in parallel and Y is the number of cells in series, along with a justification.
Step 5
Submit your answer to the Battery Lead (Micah Black ) through Slack and then we can discuss some more in detail about your answer. I’ll make sure that you understand what you will be contributing to this term!
Extra Info
How does the Solar Work?
The solar panels on the Midnight Sun Vehicles provide power directly into the High Voltage system, which powers the motors - it's another power source for the car and will lighten the load on the batteries.