# Tesla pyrofuse



## boekel (Nov 10, 2010)

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


----------



## boekel (Nov 10, 2010)

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?


----------



## Duncan (Dec 8, 2008)

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


----------



## boekel (Nov 10, 2010)

Duncan said:


> 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


Yes, and yes Nice solution, I wonder how long the batteries will last.


----------



## kennybobby (Aug 10, 2012)

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?


----------



## Kevin Sharpe (Jul 4, 2011)

kennybobby said:


> 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


----------



## boekel (Nov 10, 2010)

kennybobby said:


> 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)


----------



## electro wrks (Mar 5, 2012)

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?


----------



## boekel (Nov 10, 2010)

electro wrks said:


> 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...


----------



## Duncan (Dec 8, 2008)

boekel said:


> 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...


So on your triggered fuse were the two small fuses blown??


----------



## electro wrks (Mar 5, 2012)

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.


----------



## kennybobby (Aug 10, 2012)

boekel said:


> 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.


----------



## GoElectric (Nov 15, 2015)

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.


----------



## boekel (Nov 10, 2010)

Duncan said:


> So on your triggered fuse were the two small fuses blown??


Yes, they are blown



electro wrks said:


> 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



kennybobby said:


> 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.



kennybobby said:


> 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.


----------



## Duncan (Dec 8, 2008)

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


----------



## boekel (Nov 10, 2010)

Duncan said:


> 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.


----------



## kennybobby (Aug 10, 2012)

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.


----------



## Solarsail (Jul 22, 2017)

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.


----------



## GoElectric (Nov 15, 2015)

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.


----------



## GoElectric (Nov 15, 2015)

kennybobby said:


> 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.


----------



## Solarsail (Jul 22, 2017)

Go Electric, do you have a link to your module conversion?

The Tesla module being 86p will receive 700/86 = 8.14A per cell, assuming uniform distribution. This is 2.4C which doesn't seem so high. I do not know what the cell fuses are rated, but I think it is over 10A.


----------



## Karter2 (Nov 17, 2011)

Solarsail said:


> The Tesla module being 86p will receive 700/86 = 8.14A per cell, assuming uniform distribution. This is 2.4C which doesn't seem so high. I do not know what the cell fuses are rated, but I think it is over 10A.


 .? 700 amps is only about half the current the P100D draws when in full power mode.
Its been suggested that the cells are discharging at 5-6 C at times.


----------



## kennybobby (Aug 10, 2012)

This was Jason's comments after opening a P100D tesla pack:

"... the BMS reports a max discharge current of 1,760A for the P100D Ludicrous pack. The normal Ludicrous P90D/P85D packs report 1,520A. This makes perfect sense with scaling, since it's 74 vs 86 cells per group..."

ref. https://skie.net/skynet/projects/te...nd+Info:+Inside+the+Tesla+100kWh+Battery+Pack

So that looks like 20.5 Amps per cell.



Tesla patent application related to Pyrotechnic High Voltage Battery Disconnect (pyro "smart" fuse) can be found here: http://www.patentsencyclopedia.com/app/20130154352 


i found another patent application from 2002-2004 timeframe, it is not Tesla's, but was filed by Delphi, Battery Circuit Disconnect Device, US20040041682 A1. 

from paragraph 10 of the invention summary:
Another embodiment of the present invention includes designing the overall electrical resistance of the bus bar conductor to a known resistance and incorporating a means to measure voltage across a length of the bus bar electrical conductor. The circuit disconnect device acts as a shunt resistor for measuring current in the protected circuit. In this embodiment, the circuit disconnect device further includes a control unit or means to communicate with an external control unit to activate the separator mechanism when the voltage differential across the bus bar electrical conductor exceeds a threshold amount. This allows the device to monitor for over-current conditions without the need for a separate current sensor.


----------



## Solarsail (Jul 22, 2017)

Hi kennybobby and thanks. I was reading about your event. Would you say that within that low-voltage group of 86p (or 74p) cells, there was one cell that was not exactly a short but was stuck internally at let's say 5 ohms. So it was cooking and heating up its adjacent cells getting all ready for a blowout, and the prolonged charge just pushed it over the top? I would think an active BMS would have caught this kind of anomaly in time, even before charging had started? 86p is a huge number. What do you think is the risk for a 10p group to go bust?


----------



## Kevin Sharpe (Jul 4, 2011)

Jehu and EV West had some interesting video during their teardown


----------



## GoElectric (Nov 15, 2015)

Hi - no, I don't, but this thread is here to share and compare. What are you wondering?



Solarsail said:


> Go Electric, do you have a link to your module conversion?


----------



## Solarsail (Jul 22, 2017)

GoElectric said:


> Hi - no, I don't, but this thread is here to share and compare. What are you wondering?


Just wondering what are you converting the Tesla module for? EV, powerwall, e-bike? And how you plan to balance and protect the cells.


----------



## GoElectric (Nov 15, 2015)

Hi. I'm just building an EV. We are planning on using the EVTV Tesla BMS; waiting on Jack.


----------



## Solarsail (Jul 22, 2017)

GoElectric said:


> Hi. I'm just building an EV. We are planning on using the EVTV Tesla BMS; waiting on Jack.


The Tesla module is a 6s74p. That is not going to give you much voltage unless you go up to 60 or 70 kWh and stack up a lot of modules. Don't you need to go down to 20p or 30p? What is your configuration, if I can ask?

I am wondering isn't there already an Arduino based intelligent BMS with software available open source somewhere?

How will you balance and protect the cells? Are you depending on the EVTV BMS to also do protection and balancing? If so, I am afraid you may have to wait for a long time, as that is a major project to funnel everything into one BMS at the commercial level. I think it would be simpler to get off-the-shelf protection and balancing boards, and let the BMS just do the management, monitoring, troubleshooting, heating/cooling if any, etc., and let dedicated hardware do the protection and balancing. In particular if the BMS fails, you don't want the module to be subject to excessive charge/discharge.

Hmmm ... if this discussion does not belong to this thread, I will be happy to take it elsewhere.


----------



## GoElectric (Nov 15, 2015)

Hi. We are running 5 modules at 130V or so on an AC 50, and 6 modules on another project with an AC 51. 

Have a look at the EVTV solution on his website or watch the video - it is simple, but does pretty-much everything. I believe the hardware is open-source, but not Jack's software.

I just wrote a long post on the Working with Tesla Batteries thread which discusses more features (and shortcomings) of Jack's Tesla Battery BMS as part of a discussion about safety. 

I've never seen an online discussion of the above, but we are ordering one, so can report back.


----------



## Solarsail (Jul 22, 2017)

Thanks for the info and pointers. Will take a look.


----------



## jinzo (Sep 26, 2017)

Hi, 

I know I'm quite new here, but I didn't see it mentioned here. The black-with-blue-mesh part of the fuse is actually quite a standard design in never VW/Audi vehicles to blow the "ordinary" battery on crash. But the detecting-and-blowing is of-course done totally different here 
But it's nice to see Tesla using something that looks like a industry-standard part.


----------



## kennybobby (Aug 10, 2012)

Tadiran Batteries makes long-life primary lithium metal cells (non-rechargeable), some lasting 25 years. They are a German company owned by SAFT. The TLM-1530 HPM/TP is a 2/3-AA sized cell (15x30mm) with polarized solder tabs. Many of their cells have passed UN-testing and are exempt from dangerous goods regulations under UN 3090/91.


----------



## kennybobby (Aug 10, 2012)

So my guess was half right on the circuit, there is an op amp but not a voltage regulator. Thanks to Boekel we found that it is just two op amps. The two cells were drained to about 0.6 volts. Maybe it can be repaired.


----------



## Arlo (Dec 27, 2009)

Subscribed


----------



## CRC16 (Aug 31, 2019)

I think there is an error in the schematic above. 
Below is a "more accurate" schematic. Please note that the part numbers for components U2, Q1, D1 and Z1 could not be confirmed. 
Also, all the capacitance values shown are just a guess.


----------



## CRC16 (Aug 31, 2019)

Here is a schematic for an alternate design which allows for trip current setpoint to be adjusted with a 10-turn pot and has a momentary reset switch so this circuit can be re-armed after a trip.




























Parts list for the schematic above:


----------



## Tomdb (Jan 28, 2013)

Did you guts know there is now a version without batteries. 

using a LTC3108 to generate power https://www.analog.com/media/en/technical-documentation/data-sheets/LTC3108.pdf


----------



## iubongda123 (Oct 24, 2018)

Kevin Sharpe said:


> 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


Thank for your sharing, this is my problems lately!


----------

