ATL_R1S
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So while my R1S is still at the service center getting its front drive unit inverter replaced after it failed and left us stranded, I have been lamenting over it but now I've become more interested in knowing WHY it happened. I know that Rivian techs may not take things like inverters apart to investigate the failures at the SC- instead (I'm told) they send them off to an engineering facility to have them analyzed to identify the cause of the failure.
So I've accepted that we'll likely never know exactly what happened in our case, or the others I've read about online, but the similarities I've seen are that a lot of them are happening at relatively low miles. I'm estimating that I've seen anecdotes of this 4-5 times this month. It's rare, but when it happens, it's an absolutely awful, scary, and embarassing experience. There were no leaks or mechanical issues with ours prior to this suddenly happening.
What seems to differentiate inverter failure from drive unit failure is that inverter failure will stop the vehicle in its tracks, throw on the hazards and will not allow it to be driven or shifted out of park at all, even after a hard reset. From what I've read, a drive unit failure may or may not allow the vehicle to be limped around temporarily on the other functioning drive unit.
So in my search for understanding, I've watched the Munro video of them dissecting a Rivian drive unit inverter and I found it super interesting and I wanted to discuss and possibly speculate what is happening to these things to cause them to suddenly fail at such low milage.
Timestamp @ 19 min to inverter section.
Knowing that the MOSFETs are undoubtedly the hottest parts of the drive system as they are responsible for converting the DC energy from the battery to AC to drive the motors, it's easy to understand how they require very robust cooling from the glycol coolant system. This leads to the speculation exercise. Much like a powerful CPU that is water cooled, there are a number of variables that can lead to thermal runaway and failure - such as load, heat exchangers, coolant leaks, air pockets etc.
In a few of the failure stories I've read, including my own, the vehicles were not being driven hard or in super high temperatures, towing a heavy load, or doing anything out of the ordinary when the inverter fails. So we could assume that it didn't fail due to any of those circumstances. My best guess at this point, is that due to an improperly bled coolant loop, an air pocket is collecting in one or more MOFSETs in the first few hundred or thousand miles the vehicle is driven, which creates an instant thermal runaway event and it cooks itself - permanently disabling the vehicle as there can be no more DC to AC conversion to drive the motors. Could also be something failing on the circuit board in the middle. Or a MOSFET gasket failure that allowed coolant to leak into the housing. Or the capacitor has an issue. Until someone attempts an out of warranty repair on one, we may never know for sure.
I'm hoping someone smarter than me with more EV engineering knowledge can chime in here and satisfy my curiosity a little bit because I feel like knowing the cause will give me peace of mind that there is something that can be done to prevent it from happening in the future, and I won't be so nervous to drive my Rivian long distances anymore.
So I've accepted that we'll likely never know exactly what happened in our case, or the others I've read about online, but the similarities I've seen are that a lot of them are happening at relatively low miles. I'm estimating that I've seen anecdotes of this 4-5 times this month. It's rare, but when it happens, it's an absolutely awful, scary, and embarassing experience. There were no leaks or mechanical issues with ours prior to this suddenly happening.
What seems to differentiate inverter failure from drive unit failure is that inverter failure will stop the vehicle in its tracks, throw on the hazards and will not allow it to be driven or shifted out of park at all, even after a hard reset. From what I've read, a drive unit failure may or may not allow the vehicle to be limped around temporarily on the other functioning drive unit.
So in my search for understanding, I've watched the Munro video of them dissecting a Rivian drive unit inverter and I found it super interesting and I wanted to discuss and possibly speculate what is happening to these things to cause them to suddenly fail at such low milage.
Timestamp @ 19 min to inverter section.
Knowing that the MOSFETs are undoubtedly the hottest parts of the drive system as they are responsible for converting the DC energy from the battery to AC to drive the motors, it's easy to understand how they require very robust cooling from the glycol coolant system. This leads to the speculation exercise. Much like a powerful CPU that is water cooled, there are a number of variables that can lead to thermal runaway and failure - such as load, heat exchangers, coolant leaks, air pockets etc.
In a few of the failure stories I've read, including my own, the vehicles were not being driven hard or in super high temperatures, towing a heavy load, or doing anything out of the ordinary when the inverter fails. So we could assume that it didn't fail due to any of those circumstances. My best guess at this point, is that due to an improperly bled coolant loop, an air pocket is collecting in one or more MOFSETs in the first few hundred or thousand miles the vehicle is driven, which creates an instant thermal runaway event and it cooks itself - permanently disabling the vehicle as there can be no more DC to AC conversion to drive the motors. Could also be something failing on the circuit board in the middle. Or a MOSFET gasket failure that allowed coolant to leak into the housing. Or the capacitor has an issue. Until someone attempts an out of warranty repair on one, we may never know for sure.
I'm hoping someone smarter than me with more EV engineering knowledge can chime in here and satisfy my curiosity a little bit because I feel like knowing the cause will give me peace of mind that there is something that can be done to prevent it from happening in the future, and I won't be so nervous to drive my Rivian long distances anymore.
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