Odd Voltage behavior

[DucRider]

Battery voltage (and hence the SOC%) takes a bit to stabilize after charge/discharge events. Driving in EV mode will do both and the battery quickly bounces between modes as acceleration and regen events occur. When driving, the battery is in a closed circuit state. After stopping, the battery is disconnected (open circuit) and takes a bit to "regroup" and voltage readings are very likely to be different than in an open circuit condition (how much depends on many factors including temperature and internal resistance of the battery cells).
I also suspect the SOC reading you are seeing is buffered a bit and also based somewhat on recent history - a bit like the range estimate. Dropping by a few percentage points after shutdown is likely within normal behavior.

 

[MNSteve]

Battery voltage (and hence the SOC%) takes a bit to stabilize after charge/discharge events.

This is a good point, and we have to remember that we're not measuring the charge by the same way that we would measure it for a lead-acid battery (specific gravity of the electrolyte) but instead by the output voltage. This is a good approximation of SOC for this type of battery, but it is going to take a short time to stabilize after charge/discharge cycles.

 

[MNSteve]

@MNSteve, I too suffered from Chilly Willy Syndrome” for a while. (Boy, does that reference show my age!)
My support group has got me on the road to recovery and now I’m preconditioning (~1-1.5 kW) and using the seat heater since it’s not been all that cold in KY. But I’m still in denial since I don’t use the preconditioning kW in my kW/mile and MPGe calculations. (Yeah, I know that’s cheating)
I’m very glad there are mechanical and electrical engineers on the forum. You guys and gals are our last hope of figuring all this out. My background is biological so I’m a rank amateur stumbling around here.
Keep up the good work.

I bought a level-2 charger just so that I could do meaningful preconditioning. Probably the most expensive warm air on the planet when I divide the cost of the L2 charger by the number of times I'll precondition.

The only engineers who can untangle all the mysteries work for Honda. But I enjoy the challenge of reverse-engineering the systems, while recognizing that the conclusions we reach may be totally bogus because they are based on limited information.

 

[Clarity_Newbie]

Today while it was around 32 F I did some routine driving around on streets and then for 10 minutes on the highway (which was in HV / ECON mode; otherwise in non-HV ECON). I noticed that the Voltage readings on the Torque OBD app were a little odd.

At the start in EV it was at 13.5V and then I decided to turn on the heat along with both seat heaters, the headlights and the wipers within a short period of time. There was hardly any movement in the voltage (maybe went up to 13.6V occasionally).

After a shot stopover I turned on HV mode and when the engine started up the Voltage dropped to 11.5V, and held steady there through most of the rest of the trip. Near the end of the HV mode I again blasted the heat and seat heaters on for a short period of time and this time the voltage jumped up to 13.5V; when I switched them back off the voltage again went back to 11.5V.

In the latter stages of the trip (mostly flat or downhill) I switched off HV mode (voltage remained at 11.5V and again tried the all-heat-on and the voltage jumped to 13.5V; when switched off it again dropped to 11.5V.

For the chart below I labelled the episodes of blasting the heat and seat heaters with a red "A". I added another flag, "B" for when the engine sparked to life not long after HV mode was turned on.

A last weird thing happened at the end of the first stop (labelled with "C"). It was steady at 13.5V and 29% SoC and then when I powered down and got out of the car I got the 'Angry beeps' when I shut the door. I looked at the Torque app and the voltage dropped down to 12.2V. Hmmm... I wonder if something is drawing battery and the beeps are a warning that something is still on. Note that the headlights, wipers, Climate Control, and seat heaters were all switched off after my experiment a few minutes earlier, so it couldn't have been any of those. Another thing that makes me believe that something was still alive after shutdown was that the SoC dropped from 29% to 27% during the 3 minutes that the car was off. And continued to drop another 2% while parked and on (before engaging HV mode). I have no clue what was eating into the battery. No use of the console head unit at all during the trips, and I had my phone only connected by bluetooth - not hard wired.

I welcome any interpretations for all these weird jumps and drops in voltage. I'm not saying they are abnormal, I just don't understand it.

One last note is the drop in SoC during HV mode from 25% when the button was pressed to 22% at the end of the short journey. Probably within normal 'charge sustain' limits, but probably also follows the trends of those that notice a drop in SoC in HV mode. More data is needed. But I am also going to keep an eye on the 12V system voltage readings.

View attachment 3701

Ray B

The 12 V SoC fluctuates similarity to what you describe for both the Clarity I drive and another a friend drives. In round number...12.3 - 13.9 are the measured norms with outliers in each direction of course.

Hope this helps.