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daveo4EV

daveo4EV

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once the 12V is dead I'm increasingly of the opinion the vehicle bus is isolated - the ODBII charger wot' provide enough power to "run" the main 12V computer - so it will never wake up - and you're not actually charging the 12V battery because it's "offline" and isolated behind a relay

but that's just pure speculation on my part - see diagram below - you need enough power on the 12V bus to power the main computer to trip the relay to reconnect the 12V battery - not clear to me the ODBII port can accept enough power for that to happen…when the 12V "dies" it goes offline behind the relay for it's isolated safety…

but this is all pure speculation on my part - but 12V power to the "jump post" is the recommended technique to wake the car up at the factory and as part of PDI when dealer receives the vehicle.

[picture deleted - see post #33]
 
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Dave T

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Understood. I also know a bit about electronics and was wondering about a relay like that too. But why do you think there's such a relay? Or why couldn't the charger on the OBDII port power the main computer? Because it draws more than 3 amps?
 
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@Dave T I've revised my picture - ODBII is connected to the can-Bus - so it's not on the 12V "bus"

Screen Shot 2020-09-30 at 10.49.44 AM.png


I believe the 12V is behind a relay based on a conversation I had monday with the service manager - where he indicated once the 12V dies it's isolated and dropped off line - he indicated not all 12V failures are the "same" and not all 12V problems they've seen are due to low battery - but rather the 12V battery isolating itself for fault isolation…and to get it reconnected requires you "power the 12V bus" with enough power to run everything long enough for the 12V to come back online from behind the relay

the ODBII port is NOT directly connect to the 12V bus - but has power leads that can "back" feed power through where ever the ODBII is connected which will ultimately feed power to the 12V - but if the relay is "tripped" that back feed power has two problems:
  1. the 12V is behind a tripped relay - so no power is "hitting" the 12V battery
  2. the power provided by the trickle charger isn't enough to run the systems
but again this 100% pure speculation on my part - but I'll assert it's a reasonable supposition

at a minimum it would take a while to recover the 12V once it's dead given the paltry <3 amp feed via the ODBII port - and you'd have no idea if you are even making progress or how long it would take.

there is some evidence the 12V LiON battery is behind a "safety" relay - because the car is 100% dead as a doornail - and inert in this circumstance - all the relays have tripped and all 3 possible power sources have been isolated from one another:
  1. the main 93 kWh 800 volt DC system
  2. the small 12V battery
  3. the charging ports DC/AC inputs
nothing is connected in circumstance, which is why once you're here neither the power charging ports or 800V battery can even provide power to the main 12V power bus…

reasonable speculation is that this is a "safety" feature to isolate all these systems from one other from a "fault" - once a fault is detected (valid or invalid) everything 'trips' like a breaker and is isolated from one another so that the vehicle can be safely worked on…

providing ample 12V power to the bus is what is required to "reset" all these breakers so that these 3 systems "re-connect" and then they take over running the vehicle…

evidence for this is that other anomalies can cause the 'dead taycan' syndrome even where the 12V battery is perfectly fine and sufficiently charged yet the entire vehicle is still dead…

my speculation is that these systems are simultaneously robust and yet fragile - fragile in that _ANY_ perceived fault will trip everybody offline "for safety" - and then the only recovery possible is an external power-source bootstrapping the car back online via the 12V jumper posts…this speculation makes sense from a safety isolation behavior and fits the observed behaviors we've see for non 12V related failures (bad DC/DC converter is one example, the 12V was fine)

you need to provide power to the main computer via the 12V bus - and during the main computer startup procedures it will reset all the relays to bring the various power sources back online…with out sufficient external power to boot the main computer, there relays' will remain tripped for safety.
 
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r553

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A 12 V LiFePO4 battery with a capacity of 40 Ah is used exclusively as the energy store for
the 12 V vehicle electrical system. This 12 V battery is installed in the body front section
in the technical equipment space and is accessed through the bonnet lid. As with the 992,
the battery contains the integrated battery sensor that records voltage, current and
temperature. The battery also contains a contactor (relay) that disconnects the positive
terminal internally if necessary .
 

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Anyone experience this after the software upgrade? Wondering if I still need to carry all the supplies with me ...
 

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The OP's car is fully updated, and if it was just an update, they would've done that and handed him back his car. Which they haven't.
 
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my car also experienced this after the software update - the software update appears to have improved the situation (@louv can not longer reproduce his specific problem) - but given that we have confirmed cars with updates still experiencing these problems Porsche has not yet eradicated the problem.

this is common with complex software systems - you fix one problem and it now allows other latent problems to be exposed.
 

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@daveo4EV I appreciate the effort to write up this handy instructions on how to get the car back up running. I sincerely hope I will never need to do it, but I have left a printout in my car.

I bought a similar emergency pack as yours but not as powerful, just in case. It comes in a nice storage container see picture belo. I am thinking of getting Porsche to install a bracket on the front of the passenger seat, just like they do for a fire extinguisher, where it could be securely stowed!
0EEE8192-3E30-43B6-A1DE-D5E2EC8A4C4F.jpeg


I also discovered that there is no need to bring a copper wire to use for ground connection. In my case the clip will reach the bolt and assembly for the door hinge, which is securely grounded. I measured and so no resistance between this hinge and the door lock that I think you referred to.
CB98D733-F4EB-4D26-A626-A5CD748FD857.jpeg


In this picture I have not connected the battery pack to the connectors though. Just for test .
 

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@daveo4EV I appreciate the effort to write up this handy instructions on how to get the car back up running. I sincerely hope I will never need to do it, but I have left a printout in my car.

I bought a similar emergency pack as yours but not as powerful, just in case. It comes in a nice storage container see picture belo. I am thinking of getting Porsche to install a bracket on the front of the passenger seat, just like they do for a fire extinguisher, where it could be securely stowed!
0EEE8192-3E30-43B6-A1DE-D5E2EC8A4C4F.jpeg


I also discovered that there is no need to bring a copper wire to use for ground connection. In my case the clip will reach the bolt and assembly for the door hinge, which is securely grounded. I measured and so no resistance between this hinge and the door lock that I think you referred to.
CB98D733-F4EB-4D26-A626-A5CD748FD857.jpeg


In this picture I have not connected the battery pack to the connectors though. Just for test .
This is correct. As a matter of fact, the owner manual does specify that the door hinge, as you pointed out, is the recommended site to place the black negative clip.
As @Daveo4 mentionned, you can also use other metallic part of the car, but you will need a copper extension wire in order to so.
 

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