Winter Fall 2021 Onboard - planned timelineThis term, the battery box mini-project will be mandatory for all team members.
The project will
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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!)
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last for three weeks following Saturday, Sept 18th, 1:00 PM check-in
Week 1 | Go through readings and videos to understand battery systems
End of week 1 |
ThursdaySaturday,
Jan 21st: First presentation of findings thus far, including thought process and questionsSept 25th: Bring questions about readings to check-in for Micah and previous members to help with!
Week 2 | Continue readings and begin Steps 2 - 5
End of week 2 |
ThursdaySaturday,
Jan 28th: Final presentations of solution
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Oct 2nd: Bring questions about readings to check-in for Micah and previous members to help with!
Week 3 | Complete Steps 2 - 5
End of week 3 | Saturday, Oct 9th: Have steps done and Micah can walk through the solutions :))
*Remember to ask questions to Micah or Owen whenever you feel stuck!
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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!
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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.
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 Slack 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
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
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Thanks Alwin George for pointing out that some diagrams are missing in the PDFs - the original web pages are here: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
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: 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/
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
Then read these for some more in-depth background for battery packs
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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.
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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 |
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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.
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