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I haven't seen the document being referred to elsewhere, but I highly doubt that there's anything fundamentally new under the sun. The industry tried this before but got stuck in a first-mover-disadvantage situation, which doesn't affect Tesla as severely because they have relatively few parts in common with other cars in the first place. So put me down in the "wherewithal" column. That's not to discount it at all. There are some real challenges; most automotive fuses for instance, are only rated for 32-volt operation. (Fuse voltage has to do with the length of the gap opened when the element blows, and the structure's ability to withstand or staunch any arcing that may happen.) Telephone fuses would work here but they're not exactly cost-optimized, I'd love to see what they do in this space. Switch and relay contacts too, may need different or thicker coatings to reliably break 48 volts at the number of cycles needed, but they'll be doing so at much lower currents so I think it's a net win. (Contact wear isn't my field of expertise, though.) However, mechanical switches are decreasingly relevant in the power path anyway, and FETs will definitely do better with the lower currents. One thing I saw talked about last time, which is completely irrelevant now, is alternator load-dumps. You know, due to the lack of alternators. But in the past, with an accessory belt spinning an alternator, the power produced by the machine was dictated by the current in the field winding. Regulating the output was a simple control loop, sensing the system voltage and servoing the field current accordingly. The field winding has significant inductance so its field can't change quickly, but with a big battery sitting on the bus that didn't matter. However, if the battery lead became disconnected, and the power draw on the system decreased, the alternator would suddenly be producing too much current and unable to rapidly reduce its field, and with no battery there to absorb the overage, the result is the system bus voltage spiking as high as 120 volts, or at least that's what the load-dump test spec says you have to withstand for 400 milliseconds. In practice with incandescent bulbs and some other linear loads around, they'll typically clamp the transient to 40 volts or so, but that's still pretty harsh for stuff that's working at 14-ish. The concern was that a 48-volt alternator could produce some truly terrifying load-dump transients. (Although I think this is also overblown; it's running at lower current so the field winding would be weaker and should be able to decrease its field faster, no? Hmm. I should do some math...) But now that the 12v or 48v is produced by an electronic DC-DC converter running from the traction battery rather than an alternator spun by the engine, it's completely immaterial. |