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August 24, 2018
Paul Gipe

Peeking Inside the Bolt's Brain Reveals Valuable Secrets


EV nerds, rejoice. You can see some of the communications between various parts of Chevy's Bolt EV and its central computer--the brain that runs the car.

And yes, there are valid reasons why you might want to do so. Monitoring the accessory battery is one. Gauging the capacity of the Bolt's traction battery is another.

Unfortunately, it isn't as simple as it is with Nissan's Leaf EV, but it can be done if you're nerdy enough to tackle it.

All cars today come with an OBD or on-board diagnostic port below the dash near the steering wheel. For the Leaf, there's a commercial app (Leaf Spy) that will communicate via a smart phone with an OBD transmitter that plugs into the OBD port. (See Leaf Spy--an Essential Tool for Serious Nissan Leaf Drivers). Leaf Spy and its supporters have figured out the codes that the OBD transmitter sends and the app provides a nice clear interface for users. Plug the reader in, turn on the app, set up the Bluetooth connection, and begin reading the Leaf's inner secrets.

With the Chevy Bolt it's not as straightforward. Bolt drivers use Torque Pro (Android) or EnglineLink (Apple) to communicate with the OBD transmitter via Bluetooth on their mobile phones. (I use the same OBD transmitter I used with the Leaf.)

Torque Pro works with many different cars. Each car or manufacturer has their own codes. Thus, Torque Pro requires a level of sophistication among its users that's not necessary with Leaf Spy. Torque Pro requires you to load the appropriate codes into the app.

Techs, or what I call hackers, have been reading the Bolt's codes and have created algorithms that they believe translate the Bolt's data into something we mortals can comprehend. They've posted their findings to the web and this information can be downloaded as a file for use in Torque Pro.

While it was simple to download the csv file from Google, I had the dickens of a time finding the correct directory on my phone where to put the file. It's not like I have never moved files from my desktop to my phone or vice versa before. For some reason my desktop wouldn't reveal the one directory or folder that I needed. After several hours of increasing frustration I stumbled on how to copy and paste the file into the correct directory on my BlackBerry android device.

To my surprise, it worked.

That's just the first step. Now you have to go inside Torque Pro and tell it what subjects you want it to display. I found the topics I wanted to view and set up a page where they would display.

EVSE Performance

I've been wondering for some time if the Bolt was drawing its full power from our ClipperCreek HSC40 EVSE that's capable of 7.7 kW.

I monitor our home's instantaneous electrical load with a device that monitors current remotely. This device sends a signal to a receiver so I can visually monitor our electricity consumption during the day.

According to Torque Pro it appears that my Clipsal Cent-a-Meter is off some. I'd been interpolating the display's readout that the Bolt was drawing no more than the 6.6 kW that we saw with the Nissan Leaf. The Bolt's computer says that the car is drawing from 7.4 kW from the ClipperCreek EVSE and delivering 7.1 kW into the traction battery. This is line with the advertised capacity of the Bolt's onboard charger. I feel better now knowing that the car is performing as it should and that the Bolt's big battery charges nominally faster than the Leaf.

Traction Battery Capacity

Chevy's Bolt has a big battery. It's this big traction, nominally 60 kWh, which separates the Bolt from other mass-produced EVs such as Nissan's Leaf. While there's still debate over how much of the traction battery we have to work with in Chevy's Bolt, it seems that the battery is shipped with slightly more than the official 60 kWh. This is important to know if you want to track the battery's degradation over time and use. (Degradation is a serious issue with Nissan's Leaf. See Battery Degradation Two-Year Status Report: 2015 Nissan Leaf.)

Our Bolt was built in March 2017 and we've been driving the car since October 2017. So by mid-August 2018 the car has endured nearly 18 months of Southern California heat. If Sean Graham's algorithms are right--he's one of the hackers-- our car has a capacity of 61 kWh.

I don't know what the battery's capacity was when we picked up the car, but at least now we have a baseline to monitor its degradation--if any. Unlike Nissan's Leaf, the Bolt uses active cooling to protect the battery during charging and when you're driving down the road in hot weather. The Leaf doesn't and has suffered battery degradation in hot climates like here in Bakersfield, California.

State-of-Charge

Hackers have also provided algorithms for interpreting State-of-Charge (SOC). There is no SOC gauge on the Bolt's displays. This is one of the Bolt's weaknesses. The Bolt instead presents a display of 20 bars for the 60 kWh battery that acts like a fuel gauge. Each bar represents 5% of the battery's charge, about 3 kWh.

Experienced EV drivers prefer a SOC meter giving the percentage of the battery remaining. There are several SOC signals from the Bolt. It appears that one signal, dubbed Battery % DIC, represents the signal the Bolt sends to the vehicle's display. This signal best matches the SOC reported by Chevy's app on a mobile phone. Now I can get a reading of SOC directly and continuously without interpreting the Bolt's "fuel" gauge.

Accessory or Starting Battery

One of the weakest links in an EV is the 12 volt accessory or starter battery. Without it, the EV is a dead block of metal. All the accessories operate on 12 volts--not the 400-500 volts of the traction battery. The 12-volt battery also powers up the EV's computer, which then engages the traction battery. If the accessory battery doesn't have enough juice to do this, the EV isn't going anywhere and it may even be difficult to open the doors.

Our Bolt failed shortly after we picked it up. It was dead, dead, dead. (See Our Bolt is Back or How a 12-Volt Battery Can Kill an Electric Car.) The Chevy dealer couldn't find anything wrong, reset the trouble codes, and told us to pick the car up. Since then I've been wary of the 12-volt battery.

For a few months I carried around my trusty Fluke volt-ohm-meter in the car and would check the accessory battery several times per day. Whatever problem had occurred never repeated itself so I put the Fluke away. Yet, I wanted a simple way to monitor the battery's voltage without the fuss of opening the hood.

The hackers found the appropriate code and with Torque Pro provided a measurement of the accessory battery voltage. What I found most useful about this feature is not only the instantaneous voltage, but I can also see when the computer tells the converter to charge the battery. (There is no "alternator" in an EV.) The voltage rises from 12 to 13 volts up to slightly more than 14 volts. That's the way it should be and this little bit of information reassures me that the computer is telling the EV to charge the accessory battery when it should.

All told, Torque Pro and the appropriate codes allow me to track our Chevy Bolt's performance in real time and that was worth the challenge of setting up the app. This information should be at our fingertips, but it is not. And until it is, nerds, such as me, will want to read OBD data despite warnings from GM not to do so.


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