what components comprise the "electronic fuses" in a Tesla? - Page 1
Forum section: electronics / general

author: k8943
author_rank: Regular Contributor
timestamp: March 02, 2023, 05:02:30 pm
content: Tesla investor day just happened and something came up about "electronic fuses". See attached image.Also found an article perhaps mentioning the same thing:https://teslatap.com/articles/fuses-and-current-protection/What components are used for these "electronic fuses"?

author: ejeffrey
author_rank: Super Contributor
timestamp: March 02, 2023, 06:50:43 pm
content: I'm not sure what they are specifically using, but generally an eFuse is a big MOSFET plus a controller that integrates the current sense, gate drive, and reset mechanism. The MOSFET needs to be rated based on the needed interrupt rating and any inductive load kicks.

author: Algoma
author_rank: Frequent Contributor
timestamp: March 02, 2023, 06:59:10 pm
content: It does state beside the lineNo Moving parts... (Solid State FETs)Hopefully a really good quality Solid State Relay(s), considering the energy levels of an EV. Using FETs seems exceedingly expensive way build a fuse. While certainly more mechanically rugged than mechanical relay. I worry a bit considering how the cheaper 12V jump starter battery packs tend to overheat and blow out their MOSFETS in a cascade failure after a few uses.

author: uer166
author_rank: Super Contributor
timestamp: March 02, 2023, 07:17:28 pm
content: I was involved in the design of the eFuses. The answer isa lot of components

author: uer166
author_rank: Super Contributor
timestamp: March 02, 2023, 07:21:24 pm
content: Quote from: Algoma on March 02, 2023, 06:59:10 pmThe Venn diagram for Tesla eFuse system and 12V jump starters looks like a set of boobs. They've had this since Model 3, this is nothing new and likely just marketing wank.

author: SeanB
author_rank: Super Contributor
timestamp: March 02, 2023, 07:42:23 pm
content: Rather beefy MOSFETS with high side drivers for them, in series with the high voltage lines, and backed up with regular bolt in DC fuses as final back up as well. The sensing is done with a hall effect sensor clamped to either a PC board trace, or clipped over a cable conductor, though for coarse reading you can use the voltage drop across the MOSFET, along with a reading of device temperature from a thermistor close by to the tab, and have a compensation table to relate the on resistance voltage drop with current and temperature, also providing as a bonus switcvh temperature, so that a fault that causes heat will cause the BCM to show the battery shutting down soon warning, followed by turning off the battery pack before it rises too high in temperature. The isolation is still provided by having DC contactors inh there, plus precharge resistors that also are switched in for a half second to charge up the rather large DC bus capacitors, prolonging relay life, and allowing the fuses to be derated for surge, as they do not have to carry capacitor charge current.

author: Gyro
author_rank: Super Contributor
timestamp: March 02, 2023, 07:46:37 pm
content: They appear to have left out... Fuse: Fails Open, Electronic Fuse: Fails Closed!I'm not 100% comfortable with the concept of a "Firmware Resettable" fuse in the context of an EV (or power wall) either.EDIT: Basically, you still need the fuse anyway. In that respect it's marketing wank.

author: ejeffrey
author_rank: Super Contributor
timestamp: March 02, 2023, 09:27:24 pm
content: Also: I can't really tell from the links, but it looks like they are maybe talking about replacing the conventional 12V auxillary fuses and 12V automotive relays with electronic fuses? This is a whole different order of magnitude than the traction battery cutoff fuses which protect against a fault in the motor/inverter.

author: Psi
author_rank: Super Contributor
timestamp: March 02, 2023, 09:39:15 pm
content: Have a look at the power distribution switches, load drivers section on Digikey.There are many types, but often they're- N-Fet based (so high side with low rdson)- Gate boost driver built in so it can drive the nfet without you needing to supply higher voltages.- Internal current sense- OverTemp shutdown- OverCurrent shutdown- Current sense output pin (so you can roll your own shutdown logic)So you can drive a load with that chip as a high side driver and the chip will automatically shut down if the load draws a current that is too high or it gets the chip too hot. And since you have the analog current sense output line going into your MCU you can shut it down at whatever current you want to. So you have basically a electronic fuse that you can control and which never needs replacing all in a single package.eg, like the VN5T016datasheetSome of the bigger ones have buit in transiant protection for driving inductive loads. But often you are best to add your own anyway.

author: uer166
author_rank: Super Contributor
timestamp: March 02, 2023, 09:49:36 pm
content: Quote from: Gyro on March 02, 2023, 07:46:37 pmNo you don't. This is true for traction system (HV stuff), but not for 12V body controls. If people want to try to figure out how it works, I suggest getting a VCFront, VCRight, or VCLeft on Ebay and reverse engineering. Here is an actual teardown:Quote^90% of this is nonesense, the eFuses are for 12V LV from the context (and picture). There are no hall effect sensors for this either.

author: k8943
author_rank: Regular Contributor
timestamp: March 02, 2023, 11:41:34 pm
content: Thanks.Another video from the same guy offers more detail on the e-fuse zone of the board. Starts around 7mins 50 secs.Here's a zoom of an e-fuse zone. So what's not clear are what the two ICs are in this zone. (Distinct from the huge ST microcontroller that pilots the board.)

author: thm_w
author_rank: Super Contributor
timestamp: March 03, 2023, 12:43:21 am
content: Quote from: k8943 on March 02, 2023, 11:41:34 pmThe guy is explaining to you what they are in the video, did you listen to him?We cant see the exact part numbers of those chips, so you'd have to find a higher resolution photo to determine what they are.

author: k8943
author_rank: Regular Contributor
timestamp: March 03, 2023, 08:02:06 am
content: Unless I missed something he doesn't explain what they are, merely suggesting that one of them is "monitoring".If I were to guess it would be that one of them is a voltage amplifier (because the voltage drop across the copper "resistor" is going to be small: though have too many pins for that!) and the other has both an ADC function (to send a reading back to main uC) and a switching function (to be able to trigger the mosfets itself).

author: k8943
author_rank: Regular Contributor
timestamp: March 03, 2023, 10:01:18 am
content: Found this (attached) comment in the comments.... So if the "monitoring" ICs are custom then they must have a corresponding schematic in discrete components...

author: Psi
author_rank: Super Contributor
timestamp: March 03, 2023, 10:45:54 am
content: Quote from: k8943 on March 03, 2023, 08:02:06 amEither you 'roll your own' with a mosfet, gate driver, Isense resistor, amplifier and analog comparator. Or you use a high/low sided driver IC with some/all of those built in. Depends if you want to do the Efuse protection in hardware or software.Rolling your own is probably cheaper as you can use cheap jellybean parts, but it's a lot of design work.Using MCU code to read the amps and shut off the gate driver is cheaper still but more risks if your code has a bug or the MCU crashes.(unless you use the mcu comp output pin so its done in hardware)

author: ejeffrey
author_rank: Super Contributor
timestamp: March 03, 2023, 05:37:02 pm
content: Quote from: Psi on March 03, 2023, 10:45:54 amAlthough one advantage of a digital controller is that you can have a much more carefully controlled trip curve, and often share duty with over/under voltage lockout, reverse polarity protection, and soft start control. But if you want lots of features this is definitely in the realm where if you aren't 100% sure you have the resources and capability to make a bullet proof controller, you buy one that is.