Single wire CAN on CP Circuit

[ben.martins]

Hello all,

I just wanted to share something that I'd only read about but never seen.

With the introduction of the EV kit it has meant we can now look at waveforms that may or may not have been of interest.

When it comes to EV's, it goes without saying that charging is pretty high up there on importance. This is tricky to diagnose as there are a number of inherent risks with testing. We talk through these risks in the guided test which you can find in PicoScope 7 Automotive software which the latest release can be found here - https://oem.picoauto.com/p7beta/download.

The area I want to talk about with charging is the Control Pilot signal which is under Charger-Vehicle Tests > Charger Vehicle Communications Type 2. In effect the control pilot is actually the same for both Type 1 and Type 2 but for this post I was using the Type 2 version.

The vehicle in question was a 2020 Tesla Model 3 and I had the opportunity to look at some signals from this vehicle in particular the charging communications between the Tesla domestic 'home' charger and the vehicle. This vehicle has a charging ECU which is located near the charge point which the CP circuit comes into. This made connection a little easier! For all those that don't understand the CP circuit then please see the guided test and take a look at the further guidance section.

Once the connection has been made and following the guided test, the capture below was obtained.

From when the charger was connected we can see that the expected PWM signal ranging from +9V to -12V which then momentarily drops to +6V to -12V as expected but then we see something different. When we zoom in a little a closer all becomes clear!

We do in fact see CAN on the CP circuit. This is something I've read about but yet to see until now as single wire CAN grows in popularity especially when it comes to EV charging. CAN is used particularly for Tesla in order to transmit information related to the vehicle when connected to the supercharger network but this will go further with the introduction of V2G - Vehicle 2 Grid. Currently the CP circuit is transmitted by the EVSE in the form of a PWM signal to indicate to the car the maximum amount of current that the EVSE can deliver. The car then switches a number of resistors in order to change the voltage level to signal to the EVSE that it is ready to commence charging. This is fairly basic information but gets the job done. With CAN though, the car can receive more information about charging capability or whether it can take more current, and the EVSE can receive information about the car, such as battery temperature, SOC, SOH and VIN number.

We can even go another step and add the decoder onto this network as seen below -

As with all decoders though we cannot know what this information is without a DBC file or some extensive reverse engineering, but as you can see the packets are there. In the above I've used 35kBaud to decode with, although I'm not convinced that this is the correct speed. Hindsight being a wonderful thing, I should have upped my sample rate, or changed the time base so I could see the exact speed of the network but I'm sure this isn't the last we will see of CAN on CP.

Technology continues to change around us and brings about new challenges. It's these challenges and the thirst for knowledge and understanding will all help us better diagnose the faults that we expect to see in the future.

I hope this helps in someway and if anyone has any further information on V2G or single wire CAN for CP then please share.

Kind regards

Ben

[liviu2004]

That 35 seems too close to standard 33.3 kbits/s, this must be low cost application anyway.

[ben.martins]

You're absolutely spot on Liviu, thank you!

Have just updated the decoded to 33.3kBaud and it's now decoding all the packets.

Thanks again.

Kind regards

Ben

[JJW]

Great work Ben, I’ll have a look with a current clamp if I get chance to dig into a Tesla

[tymcgee]

@ben.martins Hello can you post the file log, I would like to a look at decoding it.

I am a researcher at a university and am involved with SAE heavy and medium-duty standardization for EVs. We are trying to understand Telsa's single-wire CAN protocol better for comparisons.

[ben.martins]

Hi tymcgee,

I've uploaded it to the waveform library so as long as you've got an automotive scope you'll be able to grab it from there. Search under Tesla.

If you need any further information please feel free to send in a message to support@picotech.com and put FAO of Ben Martins and we can always discuss further considering the company you work for.

Kind regards

Ben