# Automatic kill switch when in a crash?



## Triangles

Does the TM3 have something similar to the fuel shut off inertia switch in an ICE car that disables the car in the event of a severe enough impact? This gentleman was rear ended and the damage looks to be only cosmetic but he had to wait many many hours for a tow and he mentions something about his 12V going dead. 



This seems to indicate the HV battery was disconnected much in the same way the fuel in an ICE car is shut off by an inertia switch in a crash. I'm curious as to what happens to disconnect the HV battery. Is this is a software item that de-energizes the HV battery contactors, pyro-fuse, or what?


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## garsh

Triangles said:


> Does the TM3 have something similar to the fuel shut off inertia switch in an ICE car that disables the car in the event of a severe enough impact?


Yes, it has "pyro fuses" to disconnect the battery from the rest of the vehicle.


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## Triangles

I am well aware of the pyro-fuse but I thought that was intended to to help minimize fire/shock hazard if the battery is physically damaged or short circuited. Correct me if I am wrong but the Pyro-fuse is not inertia activated, it is short circuit activated.


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## garsh

Triangles said:


> I am well aware of the pyro-fuse but I thought that was intended to to help minimize fire/shock hazard if the battery is physically damaged or short circuited. Correct me if I am wrong but the Pyro-fuse is not inertia activated, it is short circuit activated.


I think they might actually be computer-activated. That is, if the car detects a severe enough collision, it fires the pyros to protect first-responders who may need to tear apart the vehicle. But that's just an assumption on my part.


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## Triangles

So apparently I am wrong. Model3man (guy in the video above) confirmed that the impact triggered the pyro-fuse. Battery was unharmed.


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## Guest

Pyro fuse is "airbag module" activated. Same thing on my 2001 BMW. Pyrofuse disables thick red cable and 
only leaves fused circuit live. Tesla uses pyro fuse in HV system and everything on 12V is fused.


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## EarlyBuyer

On the subject of Model 3 and post-crash procedures, this first responders training video is interesting.


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## Magnets!

It is interesting, but not entirely accurate. At one point the presenter states that if the car doesn't have 12v power, then there will be no power to the doors or windows which is not the case.


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## EarlyBuyer

Agreed.


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## Feathermerchant

Also the Model 3 has mo 12V fuses AFAIK. Tesla uses current shunts and transistors. There could be a fuseable link in the battery wire.


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## Triangles

Magnets! said:


> It is interesting, but not entirely accurate. At one point the presenter states that if the car doesn't have 12v power, then there will be no power to the doors or windows which is not the case.


Then what powers the windows and doors? I can't imagine Tesla would be dumb enough to power the doors and windows off the HV DC.


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## Magnets!

Triangles said:


> Then what powers the windows and doors? I can't imagine Tesla would be dumb enough to power the doors and windows off the HV DC.


Elon tweeted recently that there is a backup power system, so I'm guessing yes, it pulls from the HV battery which does have a 12v output (upper right in Garsh's picture in this thread). There's a youtube video (I1Tesla) that unhooked his 12v battery to see if it is true and indeed it is.


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## Triangles

Magnets! said:


> Elon tweeted recently that there is a backup power system, so I'm guessing yes, it pulls from the HV battery which does have a 12v output (upper right in Garsh's picture in this thread). There's a youtube video (I1Tesla) that unhooked his 12v battery to see if it is true and indeed it is.


The 12V you speak of is the DC-DC converter output which performs the same function as an alternator in an ICE car. If the car is on and you unhook the 12V battery, of course you'll still have power to the 12V system as the DC-DC converter is active. Turn the car off, unhook the 12V battery and then check to see if you still have any 12V power. I'd wager a tidy sum you'll have none.


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## Feathermerchant

You may have to do more than turn it off. Put it to sleep so the HV contactor opens.


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## Guest

Feathermerchant said:


> You may have to do more than turn it off. Put it to sleep so the HV contactor opens.


In case of accident contactor is disabled immediately and DC-DC converter is killed immediately. 
After any crash (airbag module registers that) vehicle runs on 12V battery. If 12V battery is disconnected doors windows will not work.


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## Magnets!

Triangles said:


> The 12V you speak of is the DC-DC converter output which performs the same function as an alternator in an ICE car. If the car is on and you unhook the 12V battery, of course you'll still have power to the 12V system as the DC-DC converter is active. Turn the car off, unhook the 12V battery and then check to see if you still have any 12V power. I'd wager a tidy sum you'll have none.


I'll take that bet. Here's the video that tested it.






However as Arnis noted below during an accident this may not work. Although Elon's tweet embedded in this youtube video seems to imply that there is power after an accident.


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## Andress

Hello 
I had accident other day, someone rear end me and rear wheels are blocked
We hve to drag Tesla 3 on to flatbed tow truck.
Official dealt is asking to much money and I found someone for way cheaper but I can move a car due to impact.
Tesla dont wont to deal with that and I assume its need to replace Pyro Fuse?


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