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I have a question for the Volt designers ... not holding my breath for them to answer in this forum, but let's try to guess ourselves.
I've heard that the Volt battery will charge from 30% to 80% state of charge (SOC). I've always wondered where the 80% SOC charge number came from. I'm guessing it is so that regenerative braking would be maintained even when you plugged in at the top of a mountain and then used regen all the way down.
But, how is 80% SOC measured? If there's an electrochemical way of directly measuring anode/cathode charge state, then I haven't heard of it. I always thought that the SOC would just be the integral of power. But the problem here is that you're always integrating an error term, since you don't know the battery impedance exactly. Does this mean that the 80%-30% number might drift upwards over time to 100-50%? Or does the ICE only kick in at 30% based on a small drop in cell voltage? It doesn't seem easy to infer SOC based on cell voltage for a large portion of the discharge curve:
http://www.a123systems.com/#/technology/life/lchart4/
Furthermore, if the battery loses capacity over life, it becomes even harder to calculate how long the charger should run before you are at 80% SOC.
I don't have a solution here - anyone?
I've heard that the Volt battery will charge from 30% to 80% state of charge (SOC). I've always wondered where the 80% SOC charge number came from. I'm guessing it is so that regenerative braking would be maintained even when you plugged in at the top of a mountain and then used regen all the way down.
But, how is 80% SOC measured? If there's an electrochemical way of directly measuring anode/cathode charge state, then I haven't heard of it. I always thought that the SOC would just be the integral of power. But the problem here is that you're always integrating an error term, since you don't know the battery impedance exactly. Does this mean that the 80%-30% number might drift upwards over time to 100-50%? Or does the ICE only kick in at 30% based on a small drop in cell voltage? It doesn't seem easy to infer SOC based on cell voltage for a large portion of the discharge curve:
http://www.a123systems.com/#/technology/life/lchart4/
Furthermore, if the battery loses capacity over life, it becomes even harder to calculate how long the charger should run before you are at 80% SOC.
I don't have a solution here - anyone?