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Discussion Starter #1
Let's make a separate post on this...

So this is a pyrofuse as I found it in a battery pack.






There are two 30/50 amps (can't find more info on this rating) fuses parallel with the pyrofuse, might be to provide some power to regen / slowly drive after crash?


The connector with the yellow insert is the pyro part (blast cap?)


Bottom of the circuit board.








other side of the shunt-part
 

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Discussion Starter #2

Pyrofuse opened


sorry for the bad cellphone pictures...





The fuse is powered by two batteries, and has no connection with the outside world. Only wires from the board are to the shunt, and to the blast cap.

So I guess the fuse blows above a certain amperage, and probably also when above a certain G-force (crash)
In the event of a crash, the two small fuses can still provide about 40kW to and from the battery, this might be enough to keep control over the car until standstill?
 

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So it has blown that black tongue out snapping the conductor?

As normal fuses take forever to blow unless you are massively overloading them that seems like a neat solution
 

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Thanks for sharing pictures of the pyrofuse, did all of the modules blow?

Wonder what the 'reset' does on the circuit board. i noticed two big FET devices Q2,Q3 --likely switching both high and low side of the batteries. So it takes both to fire and a single failed-short fet won't accidentally trigger it.

Why do you suppose they had to add these--do Euro electric car regulations require such a cutoff device?
 

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Why do you suppose they had to add these--do Euro electric car regulations require such a cutoff device?
Musk said in relation to 'ludicrous mode' -

"While working on our goal of making the power train last a million miles, we came up with the idea for an advanced smart fuse for the battery. Instead of a standard fuse that just melts past a certain amperage, which means you aren’t exactly sure when it will or won’t melt or if it will arc when it does, we developed a fuse with its own electronics and a tiny lithium-ion battery. It constantly monitors current at the millisecond level and is pyro-actuated to cut power with extreme precision and certainty."

http://jalopnik.com/the-tesla-model-s-just-got-upgraded-to-ludicrous-speed-1718577723
 

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Discussion Starter #7
Thanks for sharing pictures of the pyrofuse, did all of the modules blow?
what do you mean by modules?

Wonder what the 'reset' does on the circuit board. i noticed two big FET devices Q2,Q3 --likely switching both high and low side of the batteries. So it takes both to fire and a single failed-short fet won't accidentally trigger it.
I'd say to reset the electronics when installing a new pyrofuse...or maybe just prior to assembly...wouldn't be nice if these things went off when someone drops a crate of fuses ;)

Why do you suppose they had to add these--do Euro electric car regulations require such a cutoff device?
I think ludicrous mode indeed, a 700A fuse would be prone to blowing...going higher would mean the cell-fuses would blow before the 'normal' fuse (I think)
 

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Interesting stuff. It doesn't look like there was much of an arc when it blew. Does the cover, or other parts, have a magnet to blow out the arch? I wonder if the escaping gases from the pyro charge are directed to blow out the arc?
 

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Interesting stuff. It doesn't look like there was much of an arc when it blew. Does the cover, or other parts, have a magnet to blow out the arch? I wonder if the escaping gases from the pyro charge are directed to blow out the arc?
This might also be the (or a) function of the two small fuses...they'll blow a fraction of a second after the pyrofuse, so no arc there...
 

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Thanks for doing this! Could you do close-ups of the front area of the pack around the 2 stacked modules? The place where the fuse goes, BMS mother board (if any), contactor, and other parts, wiring, and shields.
 

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what do you mean by modules?
From your picture in the other thread i mistakenly thought there were 16 of these pyrofuses--one in each module of cells. After doing some search and reading i see how they replaced the big 700A fuse with this "smart fuse". Is there an access cover for the pyrofuse so it could be easily replaced?

The copper portion of the buss connection looks like it has a welded-in piece, or a laser-trimmed portion, that is used as a calibrated current sensor with the red and black wires. It looks similar to the current sensor on the buss bars in the motor inverters shown in jackbauer (damien's) diy tesla inverter thread.

Can you peel back the white label on one of the little batteries to read the model and size, or measure the diameter--the length appears to be 53mm looking at the xx530? Maybe we can find a datasheet for those cells.

Thanks for sharing your findings.
 

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Hi. Interesting! I like the thought that maybe the small fuses blow after the pyro charge, and make a cleaner interruption of the current, but it doesn't seem like they are blown, so you may be right that they are there to allow some charge to pass through as long as the inverter or something isn't shorted out.

When it blows there may be other circuits which are turned off (inverter), while others stay on for safety reasons, and these fuses allow some supply.
 

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Discussion Starter #14
So on your triggered fuse were the two small fuses blown??
Yes, they are blown

Thanks for doing this! Could you do close-ups of the front area of the pack around the 2 stacked modules? The place where the fuse goes, BMS mother board (if any), contactor, and other parts, wiring, and shields.
You can find pictures of that on a previous pack i disassembled:
http://boekel.nu/foto/17/2017-01-tesla/index3.htm

i'm guessing that those wires run to the main BMS board which can decide to fire the pyro if the current goes over the set point. It's very clever in typical tesla fashion.
No, there is no connection to anything from the fuse.

Can you peel back the white label on one of the little batteries to read the model and size, or measure the diameter--the length appears to be 53mm looking at the xx530? Maybe we can find a datasheet for those cells.
I can do that later

http://boekel.nu/foto/17/2017-09_tesla_battery/2017-09-10 17.51.58.jpg
The fuse has a sealed lid, reachable from the top of the batterypack.
 

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So the fuse is a self contained unit that simply blows instantaneously when it sees a certain current and voltage across the sensing part?

That makes a lot of sense - a normal fuse has a current/time to blow so that even at 100% overload it will take several seconds to blow
 

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So the fuse is a self contained unit that simply blows instantaneously when it sees a certain current and voltage across the sensing part?

That makes a lot of sense - a normal fuse has a current/time to blow so that even at 100% overload it will take several seconds to blow
I think yes, but it might also have other features, like a shock sensor.
 

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i sketched the path for the pyro activation from your photos. It appears that there is a level of fault tolerance and requires both Q2 and Q3 to detonate the pyro.

i'm guessing U1 is an op amp to read the current sensor and U2 is a voltage regulator chip. A simple voltage divider sets the trigger current level and U1 sends the signal to a small transistor Q1 that drives Q2 and Q3. With just a handful of passives and these active components it doesn't appear there is anything but a current sensor, but if i get my hands on one i will trace it out.

 

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Could that odd looking thing to the right of the two batteries be the shock sensor? Note how it is strongly bolted to the PCB. Though you would think a shock sensor would be mounted to the base of the device instead of the PCB.

The two fuses may be to mitigate the effect of the flyback inductive power on the inverter and save the inverter from destruction upon a pyrotechnic event? It would still let the Tesla drive around reasonably at reduced power, as long as the inverter is told not to blow them.
 

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Perhaps I'm stating the obvious, but these are quite necessary for a Tesla because of the cell-level fuses. With a dead-short, if they used a regular fuse which takes seconds to blow, the cells would protect themselves and blow instead, right?

This is why I'm dragging my feet on conventional fuses with my Tesla module conversion.
 

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i sketched the path for the pyro activation from your photos. It appears that there is a level of fault tolerance and requires both Q2 and Q3 to detonate the pyro.

i'm guessing U1 is an op amp to read the current sensor and U2 is a voltage regulator chip. A simple voltage divider sets the trigger current level and U1 sends the signal to a small transistor Q1 that drives Q2 and Q3. With just a handful of passives and these active components it doesn't appear there is anything but a current sensor, but if i get my hands on one i will trace it out.

I didn't have a critical look at it, but nice-job - now somebody go out and make them!! 500 amps, please.
 
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