Mwagers
Posts: 3
Joined: Wed May 22, 2019 10:32 pm

Re: Problem: Full charge capacity dropping

Thu Jun 06, 2019 3:57 pm

I contacted Chevy and I have an "advocate" who is supposed to help me get this resolved. I will wait to see how Chevy handles this, but I am not satisfied so far; the car could have been diagnosed by now and the battery order placed if not for the failure of Chevy's dealer service model.

Strange comment from @neilblanchard about using the guess-o-meter, since almost everyone here has gone beyond that. I'm wondering if you are a dealer, since this has been their de-facto response to my problem; your failure to provide a way to better estimate the battery capacity is also similar to the dealer response.

@SeanNelson's method of charging to full and driving to empty is a good first pass method to get a rough estimate of capacity (though I'm not clear how the infotainment system accounts for regen, but that should only be a small amount of energy). I am using the amount of energy added to the battery from the charge station over a known range of state of charge (SoC) i.e if I plug the car in at 10%SoC and charge to 100%SoC only 27 kWh goes in; it should take ~54kWh (0.9 * 60kWh).

I understand how EV efficiency works. I keep my tires at 50psi, and on my most recent trip I was driving on level roads (200ft maximum elevation change according to abetterrouteplanner), with the AC off, 70F outside temp with two passengers (250 lb total) at 55 mph; just about the ideal driving conditions. My efficiency was 5.5 mi/kWh. Up until now, at 5.5 mi/kWh, I have gotten--as the car should--280 miles out of 85% of 60 kWh battery (60*5.5*.85), I got closer to 140 miles before I stopped to charge at 15%SoC.

I have also been using TorquePro and I see that cell 29 is 3.85V with all of the other cells at 4.1-4.2V (I did not note the SoC for this reading). My version of TorquePro does not have "HV Capacity", but the "!Battery Level Guess" from Torque is near 60kWh, so I'm not sure what's going on there. I also notice that the "SoC Raw" diverges from the "Battery % DIC" as my capacity approaches zero (at 100% they are almost the same, but near 0% DiC the SoC Raw is near 50%. I'm almost certain Chevy has a bad algorithm that is failing to throw a code for this failure. I hope none of you have this problem because it is impossible to deal with Chevy. Also, when I fast charge, the rate drops from 55kW to 35kW at about 25% (it should drop at 55%) and drops again from 35 kW to 25kW at about 50% (it should drop at 70% or75%?), so it seems to be using SoC Raw to determine the charge rate cutoffs. The OP had the same problem with no code. Does anyone have any ideas what is going on based on the symptoms in Torque? Any help is appreciated!

SeanNelson
Posts: 1437
Joined: Tue Jul 05, 2016 2:43 am
Location: Vancouver, BC

Re: Problem: Full charge capacity dropping

Thu Jun 06, 2019 6:38 pm

Mwagers wrote:@SeanNelson's method of charging to full and driving to empty is a good first pass method to get a rough estimate of capacity (though I'm not clear how the infotainment system accounts for regen, but that should only be a small amount of energy).

If you go down a long hill you'll see that the "Energy Used" kWh value on the Energy Detail screen drops as regen adds energy back into the battery. So it appears to account for regen in the way that you'd expect.

Mwagers wrote:I am using the amount of energy added to the battery from the charge station over a known range of state of charge (SoC) i.e if I plug the car in at 10%SoC and charge to 100%SoC only 27 kWh goes in; it should take ~54kWh (0.9 * 60kWh).

You have to be a bit careful of the energy shown by the charger because charging is not 100% efficient and the car's own systems can consume of of the energy as well. For example if the car is turned on with the heater running while charging then up to 6kW of the power from the charger will be going into the heater instead of the battery. And if the car needs to control battery temperature it can run the heater or A/C even if it's turned off.

Another thing to watch out for is Hilltop Reserve mode - if you're charging from an L1 or L2 charger then the car will complete the charge cycle at a state of charge well under 100%. And I haven't seen any DC Fast Chargers that do this, but it wouldn't surprise me if there were some out there that cut off at 80%, which seems to be a pretty widely agreed "recommended stopping" point for DC fast charging.

That being said, 27kWh seems awfully low if it really added 90% of charge to the battery.

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