I never said it supplied enough to completely run things, just to reduce the number of cycles on the LV battery.
You're claiming there is a DC/DC in the car that can handle about 5W, but not 12W?
What a weird engineering decision for Tesla to make. I mean, the engineering meeting would have to go like this:
<scene>
Ok, so we've got like 12W of idle power draw to deal with. We had all sorts of issues with cycling Lead Acid batteries in the Early S/X cars. So here's what we're gonna do.... We're gonna design a DC/DC that is super reliable and safe, such that it can be connected to the HV all the time. But we're gonna make it 6W. Not 12W. 12W is too much. 6W will halve how often we cycle the Lead Acid. But this way, we do still use up lead acids, and we do still get to cycle the contactors every day or so, and we still need to design a 12V charge controller since we do need to rapid charge the battery since we are so inefficient when we are charging it. But that all sounds fun, so let's do it.
Yep. That sounds great. You're right, making a 12-15W always on DC/DC that fixes all our problems would just be silly. Go with that 6W! And let's not just make the existing PCS more efficient at low loads with a different switching method. I mean, that's how OTHER EE's do that, but we're Tesla, what they do is stupid. We throw extra hardware at stuff for fun. So I for sure nominate both an inefficient PCS, and then an efficient second box.
Oh, and while you're at it, make sure we NEVER, EVER show this on any parts diagram. It would be awesome to hide it inside the PCS, but the PCS has no power when the contactors are off. So we'll put it in the penthouse, never mention it in any descriptions, and we'll also leave it off the wiring diagrams, even though it has dangerous high voltage going to it all the time even when the HV of the car is disabled. Nobody will ever need to service it, so it doesn't need to be in the service manual.
<end scene>
You can prove this isn't happening easily. You can unplug the wire under the rear seat to fully disconnect the HV. So check the idle current draw on the LV battery. It will be about 6W. Then unplug the interlock. You're saying the current from the LV battery should go way up? We taking bets on this?
Because they have a safety inter-lock to turn off the support "DC-DC" when there is no battery hooked up?
Yeah, those safety interlocks are called the contactors. You can hear them make a big CLUNK when they change state. You can hear them CLUNK on when you access the car via the app. You can hear them CLUNK when the car starts charging the LV battery in a CLEAR cycle where it goes from 0.5A discharge to 8A charge. Why are they ever off if there is a magic low power, high efficiency DC/DC that needs HV via an interlock?
Are you claiming there is a second set of contactors that interlock just this? That are small and you can't hear?
Because the "support" DC-DC can't provide enough power to run the MCU when fully awake.
We're not talking fully awake here. We're talking about a fully asleep car. We know for a fact the car still discharges the LV battery in this state and has to wake up every ~20 hours to recharge the LV battery.
At this point, someone really needs to point out where this special low power DC/DC converter is in the car. It's not in the PCS for a fact, since the PCS is well known to only have a single HV connection, and that HV connection is prov-ably only active when the contactors are closed. So please, what is the PN of this second DC/DC in the car?
I think the FSD computer takes about 72W on top of the 50W that the MCU uses. That accounts for more than half of the ~220W.
Neither the FSD computer or the MCU are running full bore, max TDP in sentry mode. Is sentry mode as computationally intensive as literally driving a car by itself? Is the MCU as busy as it is when it's showing a full FSD display, moving map, spotify, recording dashcams and playing fart noises? Even though the 10W of screen backlight is off?
Like people keep saying, the car is about 230W when in sentry mode. But there's no way more than about 50W of this is actual computational horsepower. Your phone could easily do sentry mode functions and it is only about 10W. So if it's 50W of processing, where is the other 180W of power going?