Odd Voltage behavior

Ray B

Ray B

Active Member
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.

OBD_Voltage Anomalies.webp
 
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I will offer a theory here... It could be totally wrong.

Since the time of Henry Ford, cars had alternators (generators). Simplistically, the battery voltage was either 12V (when the engine was off), or 14V when the engine was running. Loading had little impact on the voltage (unless the battery became depleted).

With the Clarity, there is no alternator. It seems like Ray is seeing two different voltages (~12, and ~14) that likely correspond to the condition when the battery is being charged, and the condition when the battery is not being charged. Instead of the straight-forward legacy scenario that charges whenever the engine is running, the Clarity has some kind of computerized charge controller that draws from the traction battery when it feels that the 12V battery needs a few more joules of energy.

As such, I think these two states you are seeing have nothing to do with the operation of seat heaters, headlights wipers, etc. (other than those loads do deplete the battery and ultimately cause the charge controller to toggle back and forth between 'charge' and not). I think the 11.5, and 12.2 both represent non-charging conditions (perhaps with different loads), an the 13.5 condition is the charge controller in it's active state.
 
As I was reading your account I came up with the same theory as MrFixit. I think your use of power from the 12 volt battery is triggering the DC-to-DC circuit and increasing the system voltage.
 
Thanks MrFixIt and MNSteve - makes sense.

I wonder what you think about the first stint in which the EV battery seems to be recharging the 12V battery, and as the car is shut off it drops by 1.3V, and over the course of the next 4 minutes (including 3+ minutes of the car being off) where the SoC drops by 4%. The car also gave the beep warning when I shut the door during the stop indicating that something (nothing?) was still on. After HV mode was activated and the engine sparked up, the Voltage dropped to 11.5V - so it seemed to stop recharging, but I'm not sure what may have been active.

It would be nice if there was a way to trace what is using up power when the car is off.
 
MrFixit said:
I will offer a theory here... It could be totally wrong.

Since the time of Henry Ford, cars had alternators (generators). Simplistically, the battery voltage was either 12V (when the engine was off), or 14V when the engine was running. Loading had little impact on the voltage (unless the battery became depleted).

With the Clarity, there is no alternator. It seems like Ray is seeing two different voltages (~12, and ~14) that likely correspond to the condition when the battery is being charged, and the condition when the battery is not being charged. Instead of the straight-forward legacy scenario that charges whenever the engine is running, the Clarity has some kind of computerized charge controller that draws from the traction battery when it feels that the 12V battery needs a few more joules of energy.

As such, I think these two states you are seeing have nothing to do with the operation of seat heaters, headlights wipers, etc. (other than those loads do deplete the battery and ultimately cause the charge controller to toggle back and forth between 'charge' and not). I think the 11.5, and 12.2 both represent non-charging conditions (perhaps with different loads), an the 13.5 condition is the charge controller in it's active state.
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The intermittent charging is designed around 12v battery life.
Constant charging at 14v from belt driven alternators in typical cars reduces 12v battery life, especially in hot weather.
It's a quick and dirty (and robust) method to replenish the battery after starter draw down and simultaneously power accessories
On the other hand, hybrids have better control over 12v battery charging and can be optimized for loads that don't include high amp starters by implementing cycled charging.
Interestingly, Chevrolet had trouble with this logic in the Bolt.
There are multiple reports of dead 12v batteries in Bolts (including my personal experiences) where the 12v soc sensor and associated logic missed cycles.
Haven't had the issue in six months, so it may be fixed.
No issues like this with the Clarity.
 
Ray B said:
I wonder what you think about the first stint
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Ray:

It looks like you were steadily in charge mode up until around 07:00 (perhaps including during the 3 minute shutdown). I can understand why the system might continue to charge the 12V battery for a bit even after shutdown. That could explain a corresponding drop in SOC, BUT...

A 4% drop in SOC of the traction battery is way too high. That's ~0.5 kWh which would be like dumping thousands of amps into the tiny little 12V battery during that short time... Not possible.

The only load I can think of that would approach this would be the main heater (~7kW * 0.05 hours = 0.35 kWh). You said the main heater was off while you were shut down, but perhaps somehow it hadn't turned off yet? A 4% loss in 3 minutes is quite a loss.
 
MrFixit said:
Ray:

It looks like you were steadily in charge mode up until around 07:00 (perhaps including during the 3 minute shutdown). I can understand why the system might continue to charge the 12V battery for a bit even after shutdown. That could explain a corresponding drop in SOC, BUT...

A 4% drop in SOC of the traction battery is way too high. That's ~0.5 kWh which would be like dumping thousands of amps into the tiny little 12V battery during that short time... Not possible.

The only load I can think of that would approach this would be the main heater (~7kW * 0.05 hours = 0.35 kWh). You said the main heater was off while you were shut down, but perhaps somehow it hadn't turned off yet? A 4% loss in 3 minutes is quite a loss.
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Interesting thought. Perhaps it doesn't like to be turned on and only run for 2 minutes and then shut off. Maybe wants to complete the full heat-up cycle, even if it is shut off before it is finished. This could explain why I get the unexplained beeps when leaving the car. If the cabin heater is in the middle of a heat-up cycle during shut down, the car will give a warning that it is still drawing power. I don't use the heater all the time - usually when I pick up others who complain about how cold it is - so I will need to keep an eye on this and see if it explains the angry beeps.
 
Ray B said:
Interesting thought. Perhaps it doesn't like to be turned on and only run for 2 minutes and then shut off. Maybe wants to complete the full heat-up cycle, even if it is shut off before it is finished.
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I don't have another explanation for the unexplained SOC drop other than a possible measurement error. But I don't like this one. What possible difference could it make to not allow the heater system to come to full temperature? I could understand if it were the ICE, but we don't observe this behavior when the ICE cranks up and we shut down the car immediately after. It seems inconsistent that "off" means "off" for the ICE but not for the heater. Not that this would be the first time that the car's behavior seems inconsistent to us based on the limited data that we have.
 
MrFixit said:
As silly as it is, I guess both you and I would prefer to freeze in the interest of saving a few miles and pennies-worth of electricity !
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Yep. You two are the only weird ones on the forum! [Note for the humor-impaired; this is sarcasm.]
 
In regards to the loss of SOC after shut down; could it be running the water pump and cabin fan to keep the recemtly energized heating element from “slagging down” as a safety feature? As in it will run the water and air until the element cools down to a certain safe temperature? Or maybe it’s trying not to waste the last bit of heat? Would running the fan in med high and beater pump draw enough power to explain your readings?

And have you had the update done that replaces a climate control part along with a software update? Maybe this is one is the things it’ supposed to fix.
Just spitballing along with you here.

This car is truly the best of both worlds in that you can just get in and drive it or go down the rabbit hole trying to reverse engineer it and figure out what and why it does what it does.
It’s kinda like trying to assemble some puzzles you’ve never seen mixed together in the dark while wearing mittens. It can be fun, fascinating, or frustrating; sometimes at the same time. Love this car!
 
KentuckyKen said:
In regards to the loss of SOC after shut down; could it be running the water pump and cabin fan to keep the recemtly energized heating element from “slagging down” as a safety feature? As in it will run the water and air until the element cools down to a certain safe temperature? Or maybe it’s trying not to waste the last bit of heat? Would running the fan in med high and beater pump draw enough power to explain your readings?
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The water pump and fan are powered by the 12 volt battery, so this wouldn't affect the SOC of the HV battery.
 
It just seems like anything else we could imagine (short of the resistance cabin heater) would be small change and couldn't yield a 4% drop in ~ 3 minutes.

Maybe it got down to 29% before shutdown, and when it was turned back on, it re-calculated the SOC with some tolerance in the calculation resulting in an apparent loss that wasn't real. Then there was an additional 2% that occurred quickly after turn-on... More experiments needed.
 
I know they are part of the 12v bus, but could they drain the 12 v battery enough to trigger the HV battery to charge it by DC-DC which as I understand it may not normally occur when off? I know that some posts indicate that high fan speeds w Climate Control will summon HV mode which kind of implies high loads when the battery is cold and can’t deliver full power.
I’m not an EE so I’m just guessing here and throwing out WAGs. :)
 
KentuckyKen said:
In regards to the loss of SOC after shut down; could it be running the water pump and cabin fan to keep the recemtly energized heating element from “slagging down” as a safety feature? As in it will run the water and air until the element cools down to a certain safe temperature? Or maybe it’s trying not to waste the last bit of heat? Would running the fan in med high and beater pump draw enough power to explain your readings?

And have you had the update done that replaces a climate control part along with a software update? Maybe this is one is the things it’ supposed to fix.
Just spitballing along with you here.

This car is truly the best of both worlds in that you can just get in and drive it or go down the rabbit hole trying to reverse engineer it and figure out what and why it does what it does.
It’s kinda like trying to assemble some puzzles you’ve never seen mixed together in the dark while wearing mittens. It can be fun, fascinating, or frustrating; sometimes at the same time. Love this car!
Click to expand...

Good point about the service bulletin. I have not gone back for any of them since I purchased it at the end of August. That could be related - hadn't thought of that.

I should follow up with the service dept and see what needs to be done. I think they may have at least done the HV range fix SB before I got it, because mine behaves normally after about 4 fill-ups.
 
KentuckyKen said:
I know they are part of the 12v bus, but could they drain the 12 v battery enough to trigger the HV battery to charge it by DC-DC which as I understand it may not normally occur when off? I know that some posts indicate that high fan speeds w Climate Control will summon HV mode.
I’m not an EE so I’m just guessing here and throwing out WAGs. :)
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We're all throwing out WAGs, but I actually am an EE, so that makes mine SWAGs. I see two issues here. First, if "off" means "off" then the DC-to-DC converter should not be charging the 12 volt battery when the car is off. Second, the fan and pump draw relatively low power, especially compared to the loss in SOC here, and even if the controller is pumping power from the HV battery to the 12 volt battery with the car shut down, there's just not enough power consumption to explain the power loss in the SOC drop.

But yes, I observed again yesterday when I started the car and the temperature was 11°F that the ICE immediately started. Just in the vein of quest for knowledge, after the engine had run long enough to reach temperature I turned off the heat, and immediately dropped back into EV mode. But I think that this is a case based on the outdoor temperature being so low that the car controller decides that using waste heat from the ICE makes a lot more sense to heat the cabin than pulling power out of a cold battery, not the power draw from the fan and pump.

[My inclusion above of "quest of knowledge" above is meant to exclude me from the elite group here that is willing to forego heat to save a few electrons.]

Edit: There's supposed to be a smiley after "SWAGs". It showed on my screen before saving but doesn't show in the saved response. I don't know why your smileys are working but mine are not. I feel deprived.
 
My WAG is that @MNSteve mentioned the answer to the drop in SOC in a post already; measurement "error". I think it's likely the car could report different SOC readings (within narrow limits) when the car is on vs. when the car is off. The scientists among us don't like that sort of thing, expecting linearity when there isn't any. I wouldn't consider it error, per se, it's just a different reading on-off. So, I wouldn't go looking for things still on after the car is off. I think off means off and it's just a SOC reporting change.
 
@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.
 
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