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Discussion Starter · #1 ·
I installed a Sense power monitor in the electrical panel of my house. It's a device that measures the current and voltage real time, uploading it to the cloud via wifi and showing it on a neat app (see www.sense.com). After a while Sense learns devices and is able to identify what is running in the house. The machine learning part doesn't work well in practice, but I can easily identify my Volt charging from empty to full in 3:30 hours last night:



A few interesting things:

Every hour there is a short 1-minute period where the charger uses only half of the rated power. Why is that? Is it to re-calibrate the voltages in the battery management systems without a charge current? It's not clear to me. This power dip is always the same and exactly on the 1-hour mark, so it's not to control thermal issues.

At the end of the charge cycle, the power draw reduces gradually over a 10 minute period. That surprises me. Why did GM engineers go to the trouble to program this gradual decline? Is this perhaps done to approach the maximum cell voltage across all 97 groups slowly? That could be, but the normal charge/discharge currents while driving are 10x higher, so it would not make a difference.

Both the above things puzzle me. Anyone has an idea?

From the graph I calculate a full charge at 11.92Kw, which is less than I always had assumed. On average I see 10.2Kw usable in my 4.5-year old Volt, so the battery efficiency is ~86%. The rest is lost as heat in cables and in the charger.



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Discussion Starter · #6 ·
I would expect the Volt to monitor the cell leveling status during the "pause" in full charging. Could be a point where it decides to continue or throw a CEL. The end ramp is where the charger goes into constant (maximum) voltage charge. Another interesting point that I've measured is the ramp at the beginning. Volt doesn't go full on to 3.3KW (or even 1KW L1), but will slowly ramp up to full power over about 10-12 seconds. You can even see this on a Kill-a-Watt meter for L1.
You are right: The ramp-up is indeed about 12 seconds.



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