This page is not yet finalized, and more discussions are still to happen.
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No Lithium based secondary batteries are allowed per regs.
LiFEPO4
No Lithium based secondary batteries are allowed per regs. I'm really hoping that ASC changes their minds on this, as the main issue with Lithium batteries is thermal runaway, and LiFEPO4 batteries are not susceptible to thermal runaway. For now, this may be out of the question.
Other Strategies to eliminate AUX issues
There are several other approaches we are also analyzing to avoid all the AUX issues we have been having as well.
- Properly analyze the minimum voltage for switchover on the DC-DC power path IC. Choose the resistor divider accordingly.
- Add a time delay filter on the voltage measurement circuit if it does not impact any other switchover time characteristics significantly.
- Use thicker wires and nickel strips in the construction of the AUX battery (not the cause of the issue, but it can certainly help).
- Shorter wires for the AUX current path (don't go from battery to driver AUX Switch then back to battery - too much resistance and voltage drop).
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We are going to be using the NiMH 10S 1P battery made from Turnigy cells bought from Hobbyking.
This AUX battery will sit inside the battery box.
Capacity - 5000 mAh
The max discharge rate of 8A has pushed us to go with larger cells that support this current, as well as have lower internal resistance to keep a low voltage drop during higher load currents (such as the lights, fans, and display).
We aim to be able to power the car during debugging. 5000mAh cells give us around 70Wh of capacity, so with our LV target power consumption of 80W, around 1h of debugging is possible which I think is reasonable.
Chemistry - NiMH
Reason: Lightweight, allowed by regs, high safe discharge rate, and readily available.
We will also be using a similar auxiliary battery to power the horn and driver ventilation fans, possibly with increased capacity.