Keeping Track of My Plug-in Prius' Battery Pack

By Bill Moore

Posted: 13 Nov 2009

The screen captures you're looking at were taken off my Macbook Pro laptop computer display. They depict what the Java-based application looks like that is used to monitor the state of Plug In Conversions Corporation's battery pack. The top image shows the SOC in the morning after our plug-in Prius (LIVN GRN) has been charged overnight in our attached, two-car garage. The image below is a second display screen showing a more general summary of the vehicle after a day of driving, just before plugging the car in. This display would show more detailed performance data if the car were moving, but it does indicate battery pack voltage, state-of-charge, and battery internal temperature at around 11 PM at night, when I plug the car in.

Of more interest to me is the top display depicting detailed information about the battery pack, including the voltage levels of the individual cells in the pack. You'll notice that with the battery fully charged -- PICC leaves a 11% SOC buffer [89%} rather than charging it all the way to 100%. The number 74 represents the typical Toyota battery buffer which is what the car's control system looks for. After charging the car, the internal battery temperature is always at a consistent 68-71 degrees F. You'll also notice from the end-of-day display that the lower SOC buffer limit is around 23%. At this point, the PICC system resumes operating like a normal Toyota Prius, and fuel economy drops back to the 50 mpg range.

The 999 MPG figure would change as you're driving along: this number simply indicates the car is stopped. It's also the number you'll see when driving in EV and PHEV mode. The 0 MPG is an artifact of this early beta version of PICC's display. It should be MPH and got mislabeled MPG.

Once integrated into the Prius, the display will be touch-screen activated. For the time-being, I have to connect my laptop to the canbus plug under the dash to retrieve the day's performance data. Because the display runs only in Windows at the moment, I run VMware Fusion that allows the Mac to run Windows applications. It's a bit cumbersome and if I had the money, I'd go buy a small netbook-type computer and permanently keep it in the car. Maybe Santa will be kind this year.

In the meantime, I am gradually developing a database of day-to-day performance numbers that I hope will help PICC and other researchers better understand the impact and opportunities plug-in hybrids offer, especially in the Upper Midwest region of the United States.

A year ago I would never have dreamed I'd be conducting important research like this. Now my daughter isn't the only researcher in the family!

PICC plug-in display showing battery and vehicle performance data

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