NEW PCS (Power Conversion System) Failure & Replacement News

[Eka]

There are 2x 24AMP AC-DC converters. If one fails, the AC (home) charging will be limited to 24 amps. If both fail, then only DC (Supercharger) charging would be available.

The PCS does NOT handle Supercharging, only AC (home) charging.

Yep, but the high voltage side of the PCS is directly connected to the pack voltage.

Yeah for some reason I can’t supercharge either after AC charging went out so I thought might be related somehow.

Keep in mind that the two power pins on the NACS carry either AC or DC current. There is no mechanical disconnect, so the AC and DC pathways are always conjoined.

The PCS's FETs can fail in a way that causes DC fast charging safety checks to fail. So Supercharging fails.

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[mongo]

Keep in mind that the two power pins on the NACS carry either AC or DC current. There is no mechanical disconnect, so the AC and DC pathways are always conjoined.

Sort of
There is a set of contactors that engage for DC charging. The ACJB also sits between the PCS and the charge port. So only the charge port/contactor/ ACJB inlet see both AC and DC (my best guess).

The PCS's FETs can fail in a way that causes DC fast charging safety checks to fail. So Supercharging fails.

But how can they fail in a way that prevents DC charging, but still allows HV system operation for driving?
I think there may be a logic issue in software.
Or PCS is used during precharge... in which case, do the outlets drop out momentarily when starting a DC charging session?

 

[Eka]

But how can they fail in a way that prevents DC charging, but still allows HV system operation for driving?
I think there may be a logic issue in software.
Or PCS is used during precharge... in which case, do the outlets drop out momentarily when starting a DC charging session?

Well, we know the PCS make 48VDC from the main battery pack. So it must have some sort of connection.

 

[no%X#XMVk65v#cq]

Yeah for some reason I can’t supercharge either after AC charging went out so I thought might be related somehow.

Don't let someone that is confidently incorrect tell you that you're wrong about your actual experiences. Many here report PCS failure prevents any kind of charging. Its very clearly related.

 

[mongo]

Well, we know the PCS make 48VDC from the main battery pack. So it must have some sort of connection.

Sure, HV connects from the pack to the PCS. My curiosity is what kind of fault prevents DC charging but allows driving. Unless the PCS is used to precharge the DC cables, a fault bad enough to prevent DC charging should also prevent activating the HV bus entirely.

 

[Eka]

Sure, HV connects from the pack to the PCS. My curiosity is what kind of fault prevents DC charging but allows driving. Unless the PCS is used to precharge the DC cables, a fault bad enough to prevent DC charging should also prevent activating the HV bus entirely.

I suggest reading up on FET fault modes. They can fail fully open to fully closed, or anywhere in between. Usually if they fail anywhere near fully closed they can splatter metal and silicon particles everywhere, and those particles can then cause leakage currents.

 

[mongo]

I suggest reading up on FET fault modes. They can fail fully open to fully closed, or anywhere in between. Usually if they fail anywhere near fully closed they can splatter metal and silicon particles everywhere, and those particles can then cause leakage currents.

I'm well versed in FET failures and have caused them myself (sometimes purposely).
The question I have is how a FET or other PCS failure would allow activating the HV bus, but prevent connecting that same HV bus to the charge port.
Assuming the ACJB is still functional, then the only part in play is the DC fast charging contactor.

 

[NSCyber]

So if it fails and we can’t get appointments for a couple weeks out then the car just dies and that’s it? Got to then get it towed?

 

[mongo]

So if it fails and we can’t get appointments for a couple weeks out then the car just dies and that’s it? Got to then get it towed?

Yeah ‍
Unless you use the last of the power to get it to the service center to wait for parts. (Which SC may or may not appreciate).

 

[Jager]

Tesla can't - well, they could, but it would be pretty unwise - do a PCS recall until they have reasonable confidence that they have a fix.

That they haven't issued a recall might very well suggest that they themselves are awaiting longer-term reliability data from the Rev -G module.

That - failures in Rev -G PCS2 units - is the thing to watch, IMO.

 

[Leifmb]

Tesla can't - well, they could, but it would be pretty unwise - do a PCS recall until they have reasonable confidence that they have a fix.

That they haven't issued a recall might very well suggest that they themselves are awaiting longer-term reliability data from the Rev -G module.

That - failures in Rev -G PCS2 units - is the thing to watch, IMO.

Solid logic-agreed!

 

[hyperpunx]

are all CT affected by the PCS failure or just the early builds?

 

[Eka]

are all CT affected by the PCS failure or just the early builds?

I'm worried they haven't fixed the issue yet. I think the problem is their soldering process leaving the FETs' top surfaces not parallel to the PCB and cold wall.

 

[EWELON]

are all CT affected by the PCS failure or just the early builds?

it seems like just early ones from the posts that are out there. EDIT: im adding… “maybe”…. thats another reason why Tesla hasnt done an official recall. maybe they knew it was going to happen and fixed it preemptively in later builds.

 

[CyberGus]

I tried reading the Wiring Diagram, but can't make sense of it. I'm a software engineer!

Q: How many software engineers does it take to change a lightbulb?
A: None. That's a hardware problem

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