Page Comparison

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Q5:

We seem to be focusing a lot on thermal runaway for the next pack during the module design sprint. Our last one had cells very close together is there a reason I missed why we are changing this?

A5:

In our last pack, I'm pretty sure that thermal runaway would have propagated from one cell to the next if one did happen to heat up too much.
For production packs in EVs, etc. the consensus is that the pack should be designed to deal with thermal runaway WHEN (not IF) a cell goes into thermal runaway, as there will be so many packs on the road, it is bound to happen.
For our pack, it is possible to monitor it and test the cells/modules regularly to evaluate degradation and temperatures, but there is always some risk.
I wanted to go with a thermal runaway tolerant design for MSXIV but none of the solutions that I found matched our timeline, budget, or space and efficiency constraints (placing  cells further apart, machining heatsinks for the cells, using PCM material, etc.). I focused more on keeping the pack compact, well-monitored (voltages and temperatures), well-cooled (airflow channels between cells rows, and more fans than I think we actually needed), efficient, and easy to manufacture.

Q6:

Are there any situations where might want to heat up the batteries? If we do, is that gonna be something involving strategy?

A6:

I'm assuming you've seen the track mode preconditioning for the lucid and tesla plaid cars, and that's why you're asking, correct? We don't care about power output that much to install a whole heating system - wastes too much energy to generate the heat. We might as well just be driving to heat up the batteries through the internal resistance.

The internal resistance of the batteries does go down a little bit with increasing temperature (up to a point) from what I've read, so this can give us a bit of an improvement. But allowing cells to heat up decreases the margin for cooling, and we may need a better cooling system to get up the hills (i.e. smaller temperature rise before we hit the max temp).

The best way to take advantage of the lower resistance at higher temperatures would be to strategically cool the batteries at specific points so that we get low resistance (slightly higher ambient temp) for most of the race, but still cool the batteries more before a large hill so that we don’t risk overheating as we climb.

The solar panels do get hot and are more efficient when they are cooler, so there could be a potential solution to transfer heat from the solar panels to the battery to get the best performance. Generally though, we are already close to max temp for the batteries - 30 degrees ambient in the middle of the desert in the US on the route typically, then 5 or 10 degree rise for normal operation puts us pretty close to the 45C limit on some of the cells.

I would see this as an optimization issue to try and tackle once we have a working vehicle. We can make some modifications if we have time, but our focus should be on creating a reliable system first.

When the battery’s resistance drop with increased heat, we can pull more current because the resistance is lower, but we'd blow our fuses well before that extra current would be helpful - we can already hit full power even without the lower resistance.