The power limit is FSAE is 80kW (4.1.1).
| Statistic | Value | Length | Frequency | Notes |
|---|---|---|---|---|
| Max Voltage | 574 | 5 minutes | Super common | Only charging to 4.1 V |
| Min Voltage | 392 | 0 minutes | Rare | Discharging to 2.8 |
| Peak Power | 80kW | 6s | Common | |
| Min Peak Amperage | 150A | 6s | Common | |
| Peak Amperage | 250A | 6s | Very rare (never?) | |
| Mean Amperage | 16.8A | Never | Whole endurance time average | |
| Max Mean Amperage | 18A | Never | Last endurance lap time average | |
| Min Mean Amperage | 10.5A | Never | First endurance lap time average |
https://www.littelfuse.com/media?resourcetype=datasheets&itemid=c77e049e-fb36-4244-9eb4-0f211e503d41&filename=spf-series-datasheet
We have 17 of the SPF30 fuses. Blow time at nominal charge acceleration event, ~40s
Flexible PCB is soldered to nickel strip before spot welding. Fuse and Thermistor bridge gap between cell tab and flex pcb. Flex PCB only needs to be about 6.25 wide to accommodate a flex connector like this. 500 of them ~$75. This gives you plenty of width and traces to do 3A through, even with 0.33 oz copper. 0.5oz copper (one sided board) may be enough. Cost breakdown: Fuses~$100. Flex PCBs (if you order the 3 needed side by side as one panel) ~$120. Thermistors: I think we already have, may be ~$30.
New version: Fuses: https://jlcpcb.com/partdetail/Littelfuse-0451200MRL/C47397
Thermistor: https://jlcpcb.com/partdetail/76369-CMFB102J3200HANT/C75245
High level overview: each cell’s negative terminal has a thermistor soldered directly to its busbar for maximum thermal conductivity. This way we avoid all of the unreliability of using simultaneously electrically insulating and thermally conductive materials which most teams use. However, as we will see, this significantly increases the electrical complexity of the circuit we design. While we are only required to have 30% thermistor coverage, this results in a highly resolution, accurate, real time picture of the accumulator’s thermals. Each negative terminal also has a voltage tap, which must be fused. In a rules clarification, it was made clear that fuses and other such components within the segment only had to be rated to maximum segment voltage,
We use the cheapest possible flex pcb connectors ( see segment board design review) because we need an absurd 500 of them, and getting them soldered in china is a big win.
Since the ltc6813/adbms1818 chips can measure at most 18 cells in series, and we are limited to 28 cells in series per segment, it makes sense to use two pcbs per segment. additionally, each pcb only need to measure at most 14 cells and has 18 slots. We will use this to our advantage in order to measure the thermistors.
The basic idea of the ADBMS chip is that it measures the difference in voltage between C(n) and C(n-1). for all 18 inputs. The S(n) outputs are used to turn on/off discharging. They can be used without an external mosfet, but this can cause heating of the chip and it’s fairly cheap in terms of space and cost to just add an additional mosfet. C(0) is the chip’s ground and therefore it cannot communicate with other chips higher or lower in the stack without isolation. Therefore it uses pulse communication and isolation transformers. Every command is transmitted onward up the stack and all information sent down is passed along as well, allowing for very simple daisy-chaining. For more details, read the datasheet.