Onboarding - MS16
Fall 2024 Onboard - timeline
To get everyone started on the Battery Structures & Cell subteam, it would be good to go 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 MSXV.
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 the required knowledge for building battery packs.
This project can be completed largely offline in your own time, but there will be discussions during check-ins and feel free to ask questions on Discord at other times! There is quite a bit of reading in this intro and you’ll come across a lot of words you might not know. But fear not! As an engineer, you’ll 100% be in this situation basically always. Although difficult, you’ll probably learn the most in these situations too! So, don’t be discouraged, search up words you don’t know, and if all else fails skip sections and you’ll likely come back to it later with the information needed to understand it!
Google is your friend and so is this Confluence, search up what term/system/whatever you are confused about on either one and you will find your answer 99.9% of the time
Table of Contents
Onboarding Project
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 leave a comment in your introductory forum post on #bat-onboarding on our Discord and someone will get back to you!
If you have no idea how batteries work, watch this:
https://www.youtube.com/watch?v=PXNKkcB0pI4
If you have no experience with circuits, voltage or current, watch these:
https://www.youtube.com/watch?v=w82aSjLuD_8
https://www.youtube.com/watch?v=8Posj4WMo0o
Battery 101 (Optional but helpful!)
https://www.youtube.com/watch?v=lUZ9l1iAYK8
Start off with reading these: (These are really great!)
Part 1: https://www.electricbike.com/introduction-battery-design-1/
Part 2: https://www.electricbike.com/introduction-battery-design-2/
Part 3 (Optional): https://www.electricbike.com/introduction-to-battery-pack-design-and-building-part-3/
Here is a Video explaining basic electrical calculations (Hint: these calculations will be used in the exercise):
https://www.youtube.com/watch?v=cX4s-bxn4fs
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
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):
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 4
Submit your answer to Nicole Choe or Shem Kim through Discord and then we can discuss some more in detail about your answer
Step 5
After you get your answers confirmed with Nicole Choe or Shem Kim, use SOLIDWORKS to CAD a very simple cell holder for a 5S1P Battery Pack composed of five 18650 cells. This is meant to be a fun project! Don’t over-think it. We want to see a top cell holder, a bottom cell holder, and five 21700 cells in an assembly. If you are having trouble with getting access to SOLIDWORKS, reach out to us and we’ll help. If you are having trouble with making the CAD, there are a lot of tutorials on YouTube, but you can also reach out to us for help. We highly encourage everyone to try figuring it out by yourself though, self-learning is a very important skill that you will need in the team!
Once you are done, send pictures of your assembly design to Nicole Choe or Shem Kim to get it quickly reviewed. Once everything is good, we’ll help you 3D-Print your model and put together your pack!
After finishing onboarding, we’ll have a 1-on-1 meeting where we will be going over what your goals are for the team, what you want to work on, so we know what projects to assign to you! Good luck!
Extra Info
pack design:
https://www.youtube.com/watch?v=2aDyjJ5wj64&ab_channel=LucidMotors
https://www.youtube.com/watch?v=3dD5KmM8ciU&ab_channel=bytesizedengineering
https://www.youtube.com/watch?v=zgHlUwgiARo&ab_channel=ElectricVehiclesSpace
Here is how to arrange the cells to make a battery pack | ELECTRICBIKE.COM,
misc:
https://uwmidsun.atlassian.net/l/cp/uwfmLmmf
reddit I found today: (3) Solar Racing (reddit.com)
data sheet for our cells: PRODUCT SPECIFICATION (dnkpower.com)
asc 24' regulations: ASC2024-Regs-EXTERNAL-RELEASE-B.pdf (americansolarchallenge.org)
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.
https://batteryuniversity.com/articles
And read “Inside 18650 Cells”: https://www.electricbike.com/inside-18650-cell/
Then read these for some more in-depth background for battery packs: