Sponsored

Dark-Fx

Well-Known Member
First Name
Brian
Joined
Jul 15, 2020
Threads
96
Messages
9,367
Reaction score
17,765
Location
Michigan
Vehicles
Polestar 2, R1T, R1S, Livewire One, Fisker Ocean
Occupation
Engineering
Clubs
 
Honestly, with some of the weird 12V issues that have happened I'd imagine more than cost savings it just makes sense to unify the 12V subsystems rather than leaving half the truck operating on one battery and the other half on another. Some have said that the jump leads at the rear only work on one battery and not the other for starters. That said, I'd hope they increased the capacity of the single battery to match the twin setup.
The jump leads were probably designed to be able to activate the HV battery and both DC-DC units, but I'm guessing in some cases the HV battery is left disabled from the power loss and it doesn't work until service can reset codes.
Sponsored

 

madgrey

Well-Known Member
First Name
Allan
Joined
Feb 26, 2022
Threads
4
Messages
807
Reaction score
1,083
Location
Fidalgo Island, WA
Vehicles
2022 R1T, 2016 Miata, 2015 Viper
Occupation
Hardware Design Verification
Yep, laptop. He had to physically plug into the "obd2" port under dash to clear the codes. Just like an ICE vehicle. Pretty sure that port has standard CAN pinouts (which are 6 & 14)...though not 100 positive.
Since there's an ODBII, and this is supposed to be a standard connection, messaging format and protocol, I wonder if a standard DTC reader unit can clear the codes?
 

Dark-Fx

Well-Known Member
First Name
Brian
Joined
Jul 15, 2020
Threads
96
Messages
9,367
Reaction score
17,765
Location
Michigan
Vehicles
Polestar 2, R1T, R1S, Livewire One, Fisker Ocean
Occupation
Engineering
Clubs
 
Since there's an ODBII, and this is supposed to be a standard connection, messaging format and protocol, I wonder if a standard DTC reader unit can clear the codes?
ODB-II compliance isn't required for electric vehicles.
 

madgrey

Well-Known Member
First Name
Allan
Joined
Feb 26, 2022
Threads
4
Messages
807
Reaction score
1,083
Location
Fidalgo Island, WA
Vehicles
2022 R1T, 2016 Miata, 2015 Viper
Occupation
Hardware Design Verification
ODB-II compliance isn't required for electric vehicles.
Makes sense since a big part of compliance is due to emissions regulations.
 
OP
OP
Kuro-Rivian

Kuro-Rivian

Well-Known Member
Joined
Apr 26, 2022
Threads
18
Messages
399
Reaction score
682
Location
Minneapolis
Vehicles
1969 BMW 2002
ODB-II compliance isn't required for electric vehicles.
He's right. But I'm assuming eventually someone will have a handheld code reader/clearing tool. Of what capability I don't know. Already saw on here someone has sniffed the CAN-BUS and figured out HV battery temps. It's probably just a matter of time. The only thing is Rivian can easily patch access with constant OTA updates. But I doubt they'll make wholesale changes to their CAN system just cause some dude figured out how to hook up a coder reader to display 12V battery charging or HV batter temps (for example)

There is also lot of room in an OBD2 connector for Rivian specific communications wiring.

Since there's an ODBII, and this is supposed to be a standard connection, messaging format and protocol, I wonder if a standard DTC reader unit can clear the codes?
Rivian R1T R1S What I learned from my 12V battery swap OBD-port-general
 

Sponsored

RexRemus

Well-Known Member
First Name
Chuck
Joined
Sep 27, 2021
Threads
30
Messages
609
Reaction score
1,088
Location
Chicago, IL
Vehicles
2023 R1S
Clubs
 
My fundamental questions is - why the hell are there 12v batteries at all in a car with a GIANT battery in it? What is the benefit vs just stepping down the pack voltage for things that need 12v? the USB ports are likely 5v but USB-C PD can definitely go to 12v or even higher - are those systems working off the 12v batteries or just being stepped down from the pack?

I presume there are very smart people who looked at this and said no, it MUST be 12v batteries - but.. why? It seems utterly insane to me.
 

SourGrapes

Well-Known Member
Joined
Jan 20, 2023
Threads
3
Messages
61
Reaction score
75
Location
Bay Area, CA
Vehicles
Toyota 4Runner; R1T
Occupation
Engineer
My fundamental questions is - why the hell are there 12v batteries at all in a car with a GIANT battery in it? What is the benefit vs just stepping down the pack voltage for things that need 12v? the USB ports are likely 5v but USB-C PD can definitely go to 12v or even higher - are those systems working off the 12v batteries or just being stepped down from the pack?

I presume there are very smart people who looked at this and said no, it MUST be 12v batteries - but.. why? It seems utterly insane to me.
My guess is that many peripherals are designed to work off 12V (not 400V+ of the HV batteries). Perhaps it's cheaper (or more efficient) to have onboard 12V chargers rather than step-down regulators that supply 12V directly from the HV battery. Or, it's possible that the 12V system needs to stay up while the HV batteries can be electrically isolated when not in use.
 

SASSquatch

Well-Known Member
Joined
Feb 3, 2022
Threads
34
Messages
1,834
Reaction score
3,563
Location
Washington DC
Vehicles
BMW i3s Ford C-Max Hybrid
Occupation
Semi-Autonomous Yeti
Clubs
 
If Rivian gets one 12v battery to work fine, I think that’s better. The two batteries do not serve as redundancy, and both have to work for the vehicle to work.

If the probability of one battery failure is p, then probability of working is (1-p).

(1-p) is always greater than (1-p)^2, which is the probability that both batteries work in a two battery situation.

So, one battery approach would seem better than two
+1 for, and I quote, “Sciencing the 🤬 out if this” with the maths!
 
OP
OP
Kuro-Rivian

Kuro-Rivian

Well-Known Member
Joined
Apr 26, 2022
Threads
18
Messages
399
Reaction score
682
Location
Minneapolis
Vehicles
1969 BMW 2002
Considering the issues they have had you would think a service center would have these on a shelf ready to go. Mine has been there a week, still not back in my hands.
That's weird. It's a 1 hour job and batteries are plentiful. When mine when down they said they could fix it same day if I could have had it towed to service center 5 miles away. I'd get in contact with someone and shake things up.
 

Sponsored

OP
OP
Kuro-Rivian

Kuro-Rivian

Well-Known Member
Joined
Apr 26, 2022
Threads
18
Messages
399
Reaction score
682
Location
Minneapolis
Vehicles
1969 BMW 2002
My fundamental questions is - why the hell are there 12v batteries at all in a car with a GIANT battery in it? What is the benefit vs just stepping down the pack voltage for things that need 12v? the USB ports are likely 5v but USB-C PD can definitely go to 12v or even higher - are those systems working off the 12v batteries or just being stepped down from the pack?

I presume there are very smart people who looked at this and said no, it MUST be 12v batteries - but.. why? It seems utterly insane to me.
This is the answer. There are some other articles out there that address the question.

https://www.caranddriver.com/features/a38537243/electric-cars-12-volt-batteries/
 
Last edited:

lefkonj

Well-Known Member
First Name
Jeff
Joined
Feb 6, 2021
Threads
19
Messages
649
Reaction score
999
Location
New Jersey
Vehicles
A7/Q3 R1S ordered
Clubs
 
That's weird. It's a 1 hour job and batteries are plentiful. When mine when down they said they could fix it same day if I could have had it towed to service center 5 miles away. I'd get in contact with someone and shake things up.
This is a fun one. I was going to write it up after I had it back in my hands. Quick summary of the problem: Motor to close the charge door was stuck on, not sure for how long. That drained the 12v. They towed it to the Brooklyn service center about 90 minutes away. Had to get the new 12V and new door motor. Layer on top of that the R1S was delivered with poor alignment (they are fixing that) and the onboard charger died. So more than just the 12V but they told me they had to get them delivered and it took 2 days.
 

seatosummit

Well-Known Member
First Name
Austin
Joined
Apr 14, 2022
Threads
10
Messages
261
Reaction score
379
Location
Santa Barbara, CA
Vehicles
'22 R1T, '87 LJ70, 73' Porsche 914 (EV Conversion)
Occupation
Electrical Engineer
Clubs
 
Yep, laptop. He had to physically plug into the "obd2" port under dash to clear the codes. Just like an ICE vehicle. Pretty sure that port has standard CAN pinouts (which are 6 & 14)...though not 100 positive.
No CAN on Rivian's implementation of OBDII -- easiest place to tap into the CAN bus is in the passenger footwell. This is where adapters will likely integrate to pull back vehicle metrics to power apps such as teslax.

Not sure that the protocol is on the OBDII that they are using to communicate with the controller.
 
OP
OP
Kuro-Rivian

Kuro-Rivian

Well-Known Member
Joined
Apr 26, 2022
Threads
18
Messages
399
Reaction score
682
Location
Minneapolis
Vehicles
1969 BMW 2002
No CAN on Rivian's implementation of OBDII -- easiest place to tap into the CAN bus is in the passenger footwell. This is where adapters will likely integrate to pull back vehicle metrics to power apps such as teslax.

Not sure that the protocol is on the OBDII that they are using to communicate with the controller.
Interesting. Thanks! This must be where the guys who figured out the HV battery temperatures where accessing it then.
 

Throwdown

Well-Known Member
Joined
Mar 14, 2023
Threads
0
Messages
343
Reaction score
366
Location
Colorado
Vehicles
R1t launch edition#2650
Occupation
Technician
My fundamental questions is - why the hell are there 12v batteries at all in a car with a GIANT battery in it? What is the benefit vs just stepping down the pack voltage for things that need 12v? the USB ports are likely 5v but USB-C PD can definitely go to 12v or even higher - are those systems working off the 12v batteries or just being stepped down from the pack?

I presume there are very smart people who looked at this and said no, it MUST be 12v batteries - but.. why? It seems utterly insane to me.
The HV system is off when the car is off for safety so it can't be used to power anything.

They dont have be 12v, tesla is about to switch to 48v, but they have to have something smaller than the HV battery so it can monitor and control the HV battery. To over simplify it it works like a relay works, control a large load with a small load. And also there has to be something else that keeps everything else on the car alive while the car is off. When you shut off any electric car the HV contactors open meaning there is no High Voltage present outside of the battery itself. The control of the contactors is all low voltage and it can't get it from nowhere.
Sponsored

 
 




Top