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Document status | Status | title | DRAFT
Developers | QA | Karl Ding
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Goals
Pack
- Design a matched battery pack that consists of balanced Li-ion cells
- Design a battery pack and enclosure that provides adequate cooling for the Li-ion cells
Battery Monitoring System (BMS)
- Design a BMS that is robust to electrical noise found from sources in and out of vehicle
- The BMS is robust and reliable to vibration, elements, and users
- The BMS provides test points for scrutineering
- The BMS is calibrated appropriately
- Provides at least the minimal active protection requirements for the Li-ion battery pack
- Over-voltage
- Under-voltage
- Over-temperature
- Over-current
- Design mechanically isolated modules that can be removed
- Determine how the pack will be mounted to the car to minimize or dampen vibrations
Background and strategic fit
Battery Pack
The Battery Pack in MSXI consisted of Panasonic NCR18650 Li-ion cells that provided 120 V to our electrical systems. From a high-level perspective, the pack is charged by the solar array, which in turn, provides the power necessary for the car to move. These cells must be pre-approved by race officials. This will consist of a pack built from the 18650 (18mm by 65mm) class of Lithium-ion cells (which are similar in size to AA batteries, which are also known as the 14500 class).
In addition, we need to design an enclosure that allows the battery to be removed and impounded at the end of a race day. At a race, the box will be fitted with tamper-seals provided by the race officials, and should not allow access without removing these tamper-proof seals. The enclosure should also provide mounting points points that should be shock-resistant.
Moreover, we should take into consideration what procedures we need to have in place, in the event of a battery incident (along with items that we need to keep in stock in our battery incident kits).
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The Battery Management System (BMS) is responsible for monitoring the state our Li-ion pack, ensuring that the battery is operating within its Safe Operating Area, calculating secondary data, reporting that data, and balancing it. It consists of AFE chips that allow the board to grab pack data, and then take appropriate actions.
Assumptions
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Requirements
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These are requirements driven by the Rayce regulations.
World Solar Challenge 2017 Regulations V1.1: https://www.worldsolarchallenge.org/files/1504_2017_bwsc_regulations_final_release_version_11.pdf
| # | Title | User Story | Importance | Notes |
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Any AC input charging system must meet following requirements
● the charger must be used with a residual current device
● the charger must be either permanently connected to the energy storage system, or connect to the energy storage system using an appropriate connector
● the output of the charger must be electrically isolated from the ac input
● the charger must stop charging automatically when the energy storage system is full or if a fault occurs.
Spill-proof barrier must be present between energy storage system and occupants. If energy storage system is capable of spilling
Energy storage packs must be constructed to be sealed using tamper-evident plastic seals similar to 3x100mm plastic cable ties.
Said ties cannot be removed after scrutineer has been completed
Energy storage packs must be protected by a fuse or circuit breaker to interrupt the short-circuit fault current of the pack
Must be mounted in or on the energy pack
Batteries used only to
● power a real time clock when the solar car is turned off; or
● retain data when the solar car is turned off; or
● power wireless tyre pressure monitors
are not considered part of the energy storage system (max 2.0Wh)
● Energy storage system must remain in a safe state when disconnected
● Team must provide a lockable box for storing the energy storage packs
HV parts outside of driver, passenger and luggage compartment must be designed to exclude fingers (Ingress Protection rating IPXXB).
Test for IPXXD
A probe is required. The probe consists of an insulated handle about 100 mm long and about 10 mm in diameter which ends in an insulated sphere (stop face) of 35 ± 0.2 mm diameter. On the opposite side of the sphere is a metal rod 100 mm long and 1
+0.05-0 mm in diameter. The live parts in the enclosure are connected together with wire and connected in series with a lamp, a suitable ELV supply and the 1mm diameter metal rod of the probe.
The tip of the metal rod is pressed gently against the opening. If the rod goes in there must be adequate clearance between the rod and the live parts i.e. the lamp should not light up. Tests must be made with the rod in all possible positions. The lamp must not light up.
The full diameter of the insulated sphere (stop face) must not be able to pass through the opening.
Internal Requirements
These are requirements driven by Midnight Sun.
- Must allow for reasonably easy installation that won't be very time consuming
| 1 | Matched battery pack | Build a pack with balanced |
| cells | Must Have | |
| 2 | Cooling |
| Designing a battery layout and enclosure that accounts for cooling requirements | Must Have |
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Questions
Below is a list of questions to be addressed as a result of this requirements document:
| Question | Outcome |
|---|---|
| Are we going to run the pack at a higher voltage? Can we even run the pack at a higher voltage? |
| Yes. The goal will be to reach a maximum 160V. |
| Are we still planning on using |
| 18650 cells? | Yes |
Not Doing
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| Are we still going to use the Panasonic NCR 18650? | No. We are using the LG MJ1 per testing. |
| How are we going to mount the pack in a way that provides shock-absorption? | |
| What will the dimensions of the battery-box be? |