Not all electrons are created equal - Fast Charging mystery continues

[TomK]

I"m posting this as an update to a previous thread regarding the effects of fast charging on the perceived efficiency of the vehicle (e.g. miles/kWh).

https://www.mychevysparkev.com/thre...ging-and-efficiency-miles-kwh.9553/post-29923

I have had a similar experience every single time that i had to use a fast charger. Basically, it seemed like someone opened a faucet and the electrons just came flying out after the fast charge sessions. Currently my car shows 15.1 BattCap Est using the OBD2 reader/engine link.

I am starting to suspect that the issue might be the condition of the battery plus the stress that fast charging puts on the battery. I have not delved that deep into battery technology but it seems strange that the method of charging or rate of charge to a certain SoC should result in more or less "usable" energy from the battery. I really can't believe that i would be the only one that is experiencing these issue with fast charging.

For the most part, i have been avoiding DC Fast chargers in my planning as for my vehicle, the range i get out of it seems to be very limited. I recently had no choice to use a fast charger on my way home and the experience was not pleasant. I stopped at the Charger about 24 miles from home with 50% range left. It was 3F outside, so i did crank the heat to get the interior temps up a bit while charging. I charged to 80%, turned down/off the heat and turned off the heated seats and radio.

Here is the histogram for that trip. I went 24 miles and got home with flashing low range indication and the OBD2 SoC said i had 12.88% left. So roughly 2.4 miles/kWh for that trip based on total capacity of 15.1kWh. This is even though i only intermittently turned on the heat at 60F to keep the windows from completely freezing over.
There was no indication that the battery heat or other battery conditioning was running after this and when stationary the HV Amps showed about 1.5A, which is about normal. Batter Coolant temp was 65F and Batt Avg temp was 54F. Seems like the battery should have been happy.



The next day, temps were even lower at -2F, i had to run some errands after work, so i charged on a 110V-20A Level 1 charger at work to 92% before leaving work. Went 36 miles total finishing the trip with 25% remaining - so about 3.55 miles/kWh and 66% of the battery (SoC) utilied for the trip. I even splurged on using heat more frequently but not warm inside by any means. I also had the heated seats going.

Going from 3.5 m/kWh to 2.4 mkWh is the equivalent of losing 1/3 of the range due to fast charging.

 

[TomK]

After doing a bit of reading regarding fast charging and how the vehicle monitors battery state of charge, i think the main issue is that for some reason the car is reporting 80% SoC when i use the DCFC even when it is at much less. Very likely due to losses that happen after measuring how much current has been going into the battery. The last time i used DCFC i monitored the temps and SoC with EngineLink but i did not notice any significant increases in Battery temps (however it was very cold out, so that might result in those heat losses not actually amounting to much as far as temperature of the battery).

I'm guessing once I start driving the computer can calculate better based on battery voltage levels and load on what the actual SoC is and then makes adjustments, which look like rapid drops in the SoC and equate to perceived low efficiency. If that's the case and the battery is really not at 80%. Does it make sense to try to charge for longer when fast charging (maybe 90%) or will that cause more wear on the battery.

Is this something that is expected when using DCFC? Is there some best practice with these to make sure you get a closer to true reading for SoC after fast charging?

I already try not to get in a situation where i need to use fast charging but i cannot always avoid it.

 

[h71]

After spending the last two days reading up about the modules with the car and what is possible by having a subscription to the GM tech network, I'm wondering if there has ever been an update about the DC charge communication systems.

It looks like the updates for various systems are actually dated, someone with the GM subscription and the vcx nano might be able to plug in and scan the modules to find the dc charge setting and check their current version against any possible updates while connected to the GM portal.

 

[Infinion]

Have you ruled out other mechanical issues? Chock your wheels and suspend the rears with a floor jack and one by one give them a good spin with your arms. Now with the car confidently secured, test the play in the wheel, first side to side, then vertically, and take note if there are any differences between the wheels.

I've gotten on top of a recent issue of my own with consumption in the 25-30 kWh/100km range below highway speeds. My RR wheel was locking up causing a sizeable increase in consumption. The crazy thing is, it was silent and I didn't feel any significant difference in drivability besides maybe numbers on the dash being higher. The heat buildup was enormous from 150-300ºC while other wheels remained at 5-15ºC. After inspecting the RR wheel, I could see brake dust in and around the alloy wheel contours, the tire pressure had changed by 4 psi, and after standing still, the click click of thermal expansion could be heard. In other words, the RR wheel was not only permabraking, but it the braking was 95% RR and 5% the rest during hard braking events.

I replaced the brakes and rotors on both sides and that improved the LR by 99% (it was slightly catching) and the RR improved by 30%. Now I'm getting ready to change the bearing hub assembly, which is GM part # 13593156

Several possibilities could include dragging brakes due to seized caliper piston, degraded flexible brake hose holding pressure on the caliper piston, rusted up brake channels so they can't easily slide, seized caliper slider pins, a warped rotor causing contact with the brakes in some or many rotation angles, the e-brake shoes rubbing on the ID of the rotor because the e-brake control module is out of calibration, a degraded wheel bearing that has enough play to allow the rotor to sag close enough to put pressure on the brakes, or the 4 bolts holding the bearing hub assembly are not torqued to spec or damaged, allowing similar bending.

Similar problems can also happen to the fronts. You'll need to be in neutral to test, and the planetary + differential will cause some added resistance. If you secure the car really well, you can put it in L and, while both sides are suspended in the air, have the wheels crawl forward. Then you can walk around and listen for uneven dragging. It should not sound like a chef sharpening their blades on a whetstone.