How do Telsa cell level fuses work?
Can they protect against short circuits and internal cell fusing?
How is the current distributed throughout so many fuses? A total of 200 amps could pass through the 400 volt end, devided between all the fuses up to the 0 volt end?
What are the physics of that kind of electrical specification?
Are there fuses on the + and – of all cells?
What is the ideal specification of fuses for that use?
For the Tesla Model S:
- 7104 cells.
- Panasonic 3400 mAh at 3.6V. capacity of 7104 * 3400 * 3.6 = 86.95 kWh.
- The cells are arranged in 96 groups of 74 cells each.
- The 74 cells in a group (also called a "brick" in the Roadster are wired in parallel so that the batteries are balanced amongst
themselves. Each group as one large approximately 4.1V cell with a
current capacity of approximately 230 Ah. - The 96 groups are connected in series, rendering a pack output of 403v at 230Ah.
perhaps unreliable: "Model S' optimal speed in comparison is about 140-160 km/h, with 118 kW peak power and 76 kW average to 80 %"
Best Answer
I was waiting for someone else to answer this who knows more, as I have forgotten most of what I once learned of the Tesla fuses.
From what I remember, they are only on the positive side. To clear your confusion about the function of the fuses and how is so much curreng/voltage passed through the fuses - only the current from the individual battery that the fuse is attached to passes through the fuse. That current joins with the current that has just passed through the neighbour's fuse and so on for all 74 in series and then joins the 96 groups in series, not passing through any more of those fuses you are asking about. There are other fuses, but they are different.
The function of those fuses in your picture is to protect the 74-in-parallel batteries from a single or several batteries shorting or catastrophic failing. For example, one of the batteries develops some sort of internal short such that it no longer holds a charge and the remainin 73 batteries in parallel see it as a piece of metal in circuit that they can discharge their entire charge into. The fuse connecting that battery will blow and the current will stop flowing from the remaining 73 batteries, saving them from going into thermal runaway which would be the likely scenario without the fuse and you would lose the whole bank of 74 and likely have a fire.
From tests done on the fuses by a guy who disassembled a model S battery pack, they consistently blew at 25 amps. They are not a complicated mechanism, just a thin wire than burns through at a certain amperage.
Edit: from re reading the blog of the fellow who took apart a model S battery pack, it appears from the pictures that the fuses are on both the positive and negative which seems a little redundant.