As of 2023-08-12, revision 1 of the aux battery is no longer sufficient to power the car over a race day of 9 hours due to updated driver fan loads and updated contactor loads.
Supplemental/Aux Battery - Revision 1 Notes
The purpose of this confluence page is so that electrical members may review my calculations.
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Persistent Loads
These loads will be operating over the course of the entire race day. As of right now, the contactor power draw and horn power draw is based off the Systems Integration Meetings - Electrical - Confluence (atlassian.net) page point estimates, which may not be current?
Emergency Loads
These loads will be operating only in the case of a BPS emergency causing the main battery pack to be disconnected. In the case of a BPS fault, as of systems integration meeting 2023/07/05, the LV systems will be powered solely off of the aux battery. The LV systems must be able to hold up until car finds a safe place to park. These loads were based off of the WIP LV power budget as of 2023/08/12. We assume that the horn must run for 5 minutes straight, and the rest of the LV systems must run for 5 additional minutes (?) – MUST CONFIRM.
Load | Description | Energy Demand [Wh] | ||
|---|---|---|---|---|
Persistent Loads: | ||||
Telemetry – Router | Assume 2.5W for a raspberry pi, 9 hr race day | 22.5 | ||
Driver Fans | 2 Noctua NF-F12 iPPC 3000, overvolted to 15V, 5.1W x 2 max tested power draw for 9 hrs
| 91.8 | ||
Contactors (BPS Switch) | 3.5W, 9 hr race day | 31.5 | ||
Total Persistent Loads: | 145.8 | |||
Emergency Loads | ||||
Horn | Horn must be able to be run for 5 minutes in an emergency as per regs | 0.583 | ||
All LV systems – Typical | 91.0 W, 5 minutes | 7.58 | ||
Total Emergency Loads | 8.16300 | |||
Total | 153.96 |
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Contactor Loads
Horn Loads
Chances of being constant 7W is kind of low? What’s peak current demand?
Telemetry Loads
How long do we need emergency power for on BPS fault?
What’s an acceptable S.F?
Are we boosting the voltage coming out of the aux for fans or something? How are we getting 15V from 13.5-10V?
The point estimates I’ve found for these seem pretty imprecise, I’ve gotta ask around and get better numbers?
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10s1p | 10s2p | 10s3p | |
|---|---|---|---|
Watt-hours (rated) | 120 | 240 | 360 |
Watts | 120 | 240 | 360 |
Energy Loads | |||
Persistent loads met? | No | 1.65 S.F. | 2.47 S.F. |
Persistent + 5 mins emergency loads met? | No | 1.56 S.F | 2.34 S.F. |
Power Loads | |||
Typical Phase 2 or 3 | 7.41 S.F | 14.81 S.F. | 22.22 S.F. |
Peak Startup | No | 1.25 S.F. | 1.87 S.F. |
Typical BPS fault | 1.6 S.F. | 3.2 S.F. | 4.8 S.F. |
Peak BPS fault | No | 1.59 S.F | 2.38 S.F. |
Typical BPS Fault & MPS Re-energization | No | No | 1.43 S.F. |
Peak BPS Fault & MPS Re-energization | No | No | 1.1 S.F. |
Runtime [hrs] | 7.4 | 15 | 22 |
Mass (of cells) [kgs] | 1.45 | 2.90 | 4.35 |
Resistance (of cells, nominal) [mOhm] | 18 | 9 | 6 |
Minimum size (assuming square packing) | 171mm x 68.4mm x 70mm | 171mm x 136.8mm x 70mm | 171 x 205.2mm x 70mm |
Conclusions:
It is evident that 10s1p is insufficient to run all aux loads for one race day
10s2p contains enough energy for one race day and can supply enough power for all loads calculated (if loads are correct), however cannot re-energize the MPS if it is de-energized, must power the LV loads and must be re-energized. This is likely not necessary, as the car has to pull over and fix the BPS fault before continuing, as per regs. The safety factor for capacity is 1.65, which may or may not be sufficient, as thermal effects, parasitic resistances, and future alterations to loads may increase the required capacity.
If the loads are correct and safety factor is deemed sufficient, 10s2p will be used.
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