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| Question | Outcome |
|---|---|
| Do we need a microcontroller? | Ideally, no. We don't need to broadcast any CAN messages. |
| What kind of protection do NiMH battery packs need? | Under voltage over the entire pack only. We will charge the NiMH cells at a constant C/20 rate such that they will self-balance over a slow charge cycle. Ideally the auxiliary battery will not be run for a long time so discharge balancing is not a concern. Overvoltage in NiMH at C/20 is not a concern. Temperature protection is not a concern. |
| How do we charge the auxiliary battery pack? | The auxiliary pack will be charged from the LV (12V) DC power rail in the car. A charge controller IC will be needed that will provide a NiMH charge profile. |
| What is the NiMH charge profile? | |
| In what conditions will we use the auxiliary battery pack? How long will it be used? What is the current draw? | The auxiliary battery pack is used in cases when the main battery/12V DC-DC is not active or in a fault state. This includes vehicle startup (before HV battery is active), and battery isolation conditions (e-stop, BMS fault). Ideally the auxiliary pack will not be used for long, and will have on the order of 1-2A drawn from it at once. The auxiliary battery pack should have a capacity of >2000mAH. |
| What kind of communication does the auxiliary battery pack need with the system? How do we know when to switch in/out? How do we notify the system that the battery level is low? | The switching should be controlled directly by the power distribution. Refer to architecture for details. |