Goals
- Design an enclosure that will house:
- batteries
- Plutus
- Chaos
- Design an enclosure that provides adequate cooling for the battery pack
- Determine how to create modular battery strings that are individually removable from the pack
- Determine how to create strings and electrical connections that maintain these electrical connections between individual cells within a module, and are resistant to vibration
- Design and/or evaluate mechanical battery holders that will hold 18650 cells
- Determine how these battery strings will be mounted to the battery box, and resistant to vibration and sliding
Background and strategic fit
A cell is the smallest individual unit in the battery pack. These are comprised of 18650 Li-ion cells, and will be connected in parallel to form strings. The string will be our smallest removable unit from our battery pack, as designing the pack to allow for individual cells to be removable is probably overkill, especially since we will be replacing our battery pack each race. Multiple strings will be connected in series to form the battery pack that provided the required voltage to our electrical systems.
"Battery Box"
In MSXI, the battery box only contained the battery pack, which was actually not in compliance with the American Solar Challenge 2016 regulations. For MSXII, its new "battery box" will contain:
- batteries
- the Battery Protection System: "plutus"
- Power Distribution: "chaos"
- relays
- solar array relays
- battery relays
Assumptions
Requirements
| # | Title | User Story | Importance | Notes |
|---|---|---|---|---|
| 1 | Mechanically connect individual cells to form a module | Evaluate how to mechanically connect individual cells to form a module and maintain their configuration. | Must Have | |
| 2 | Design a battery configuration that allows adequate cooling | The configuration of the individual cells should be laid out in a way that they should never overheat or approach their maximum operating thresholds. Model battery thermal characteristics and | Must Have | |
| 3 | Determine how mounting points |
Designs being Evaluated
18650 Cylindrical Battery Holder
These are sold by various sellers on AliExpress to hold 18650 cells together, are fairly cheap, and interlock together. In addition, there are guides for nickel strips (which makes spot-welding much easier). Since this solution involves spot-welding, it results in the module as the smallest individual unit.
If we were to use these, we would just buy them in bulk off AliExpress, and not bother manufacturing them ourselves. They're cheap and will save us lots of time.
Battery Blocs
These are an interesting concept that allow us to hold 18650 cells together, and allow us to reconfigure the pack as needed. This design also incorporates mounting points into the pack.
Buying BatteryBlocs for the entire pack would be rather expensive, so we would probably look at designs that draw inspiration from these, and whether we can build something similar for cheaper.
Questions
Below is a list of questions to be addressed as a result of this requirements document:
| Question | Outcome |
|---|---|
| How are we going to make electrical connections between individual cells? | Spot-welding individual cells in parallel to create a string. |
| Do they make connectors for 2-gauge wire for a reasonable cost that aren't huge? | |
| Thoughts on the connector? |