My Cybertruck will not start / power on

[BannedByTMC]

There are at least two 48v sources

Do you mean the battery and DC/DC converter? Because the battery is dependent on the DC/DC and won't last long if the DC dies, and the DC won't work if the traction pack goes offline. So they aren't really independent sources.

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[BannedByTMC]

It's a discussion forum, people discuss things, including engineering design.

 

[CyberGus]

Do you mean the battery and DC/DC converter? Because the battery is dependent on the DC/DC and won't last long if the DC dies, and the DC won't work if the traction pack goes offline. So they aren't really independent sources.

They are independent of each other. That's what makes them independent.

The LV battery does not need to last long in order to provide emergency steering.

 

[BannedByTMC]

They are independent of each other. That's what makes them independent.

They aren't independent, isolated and redundant systems. That would require 2 of each.

 

[CyberGus]

They aren't independent, isolated and redundant systems. That would require 2 of each.

The battery operates without the DC/DC converter? And vice-versa?

(Actually I believe loss of either will trigger the aforementioned "critical alerts" and force you to pull over, but the surviving DC source provides emergency control)

 

[JBee]

I’ve seen designs where the electronic flight controls remain powered by the PMGs that are at the core of the engine-driven generators that normally provide power. And then tiny emergency batteries pick up the load in the landing flare when dead engine stops rotating the PMG. (This is a simplification of the actual design, there was even more redundancy than that.) The point is I haven’t really seen anybody with authority show all the ways the CT steering and brakes can be powered.

You can't be seriously sugessting a $100k truck has the same control redundancy and reliability as a $100 million dollar aircraft that needs to be certified for passenger use by the FAA and requires commercial pilots with hundreds if not thousands of hours of training to operate? You are joking right?

I will re-write how I think it works, based on the shematics, designs and repair info I have gone over, but I doubt it will gain much traction if you want to compare it to a real aircraft FbW.

This is simply not aircraft grade "FbW" at all, in any way.

It is simply a 48V electric assited power steering rack, with a redundant motor (that shares load all the time) and a steering wheel rotary encoder (with 3x sensor redundancy) that tells the redundant rack controllers the commanded steering angle and the controller then calculates the correct rack angle depending on vehicle speed and sends that to the rack to set. In return there's a steering rack linear position sensor that sends back feedback to the steering wheel rotary actuator to make it easier for the driver to sense wheel position by turning the wheel and giving the sensationof torque. Running all of this is a multi module 48V DC/DC converter (3x or more) integrated into the PCS that is supplied by the main pack which also charges the backup 48V battery (6Ah), which by itself also forms a very short term backup due to its tiny size. This arrangement is also setup to be redundant, so different circuits of the SbW have different power supplies.

From the failures described by owners here, it seems that the brake booster is also connected to one of the SbW circuits seeing it fails at the same time which is a very poor design choice.

These Critical Error faults seem to also have different origins, according to the texts recieved by owners from Tesla service where the vehicles are being repaired, being PCS DC converter, rear wiring harness, air compressor etc.

Overall, given the broad range of repairs for the same resulting loss in vehicle functionality and error, there most definitely seems to be a design issue.

 

[JBee]

The battery operates without the DC/DC converter? And vice-versa?

(Actually I believe loss of either will trigger the aforementioned "critical alerts" and force you to pull over, but the surviving DC source provides emergency control)

Specifically "Critical Failure".

No need to water it down.

They aren't independent, isolated and redundant systems. That would require 2 of each.

You raise a good point here which is exactly the root cause if the error is power related.

If you have a DC converter acting as a charger for a battery and it fails to charge because its faulty, you get both a flat battery and a loss of a redundant DC converter at the same time. If you have three redundant supplies, you are already two down.

Now if the battery was charged you would only get useful battery voltage from it if the faulty DC converter is isolated from the battery, but the SbW stays connected to the battery. This has to happen before a short or the like discharges the small battery, or potentially overloads its own BMS seeing its lithium and not lead acid.

The extremely small capacity (2x a USB power bank) doesn’t help here as it has no peak capacity for very long (48V x 6Ah =288Wh X C?), so any short or high load needs to bo isolated pronto to avoid damaging the pack and loosing it as a redundancy.

In these situations the voltages might be low enough to cause brownouts, as it fluctuates under the operational voltages of the control nodes on the 48V ring bus, these will likely trigger the rest of the barrage of errors users saw as they lose power as well.

The crazy thing here though is, why is the electric brake booster sharing a circuit with the SbW and is not on its own independent, or at least be able to be isolated from it if something fails?

Note this kind of interlock switching is done only using relays in power station switchgear, and can easily be implemented on a low power 48V system like this on a PCB to make it work. Sure you can do it on a microcontroller as well and program it, but the point is this is something that s hard to do, and yet it seems the brakes still fail as well with the SbW?

 

[Stuck4ger]

You can't be seriously sugessting a $100k truck has the same control redundancy and reliability as a $100 million dollar aircraft …

You are correct in that I wasn’t suggesting that. I was only suggesting that there was a lot more to the design than so many of the “OMG, Tesla didn’t think of…” posts from folks that really have no clue. You do seem to have a clue but it’s always best to share real data sources (like a link to a service manual) so the rest of us can separate real data from just big talker diatribe.

 

[JBee]

You are correct in that I wasn’t suggesting that. I was only suggesting that there was a lot more to the design than so many of the “OMG, Tesla didn’t think of…” posts from folks that really have no clue. You do seem to have a clue but it’s always best to share real data sources (like a link to a service manual) so the rest of us can separate real data from just big talker diatribe.

NW. Let me know what you find.

https://www.cybertruckownersclub.co...pair-manuals-accessible-online-links-📒.12905/

 

[mark555055c]

For me it's simple, I place my bet on Tesla, the company whose primary goal is beyond five star safety. I don't need to question or armchair engineer things.

If anyone thinks Tesla is going to engineer and build the safest vehicles in the world, but drop the ball on STEERING THE VEHICLE, I just have to laugh.... laugh my way to the delivery center to pick up my CT.

 

[CyberGus]

Specifically "Critical Failure".

No need to water it down.

A reasonable person could infer that a "critical alert" is "alerting you to a critical failure". No need to be pedantic over word usage.

 

[BannedByTMC]

The extremely small capacity (2x a USB power bank) doesn’t help here as it has no peak capacity for very long (48V x 6Ah =288Wh X C?),

I thought it was 4ah?

 

[CyberGus]

I thought it was 4ah?

"Unlike all the other Tesla passenger EVs, the Cybertruck has a 48V low-voltage system instead of a traditional 12V one, and the battery is rated at just 4 Ah."

https://insideevs.com/news/704749/tesla-cybertruck-low-voltage-battery-48v-4ah/


This is published, but unconfirmed. And Tesla changes specifications without notice lol

 

[BannedByTMC]

For me it's simple, I place my bet on Tesla, the company whose primary goal is beyond five star safety. I don't need to question or armchair engineer things.

That's fine, but some people like to know how things work, and why they fail when they don't work as intended. Tesla is not infallible, obviously.

 

[mark555055c]

That's fine, but some people like to know how things work, and why they fail when they don't work as intended. Tesla is not infallible, obviously.

sure, I'm definitely curious to see how this turns out.

I'm sure we'll know the technical of these systems in time also.

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