Chevy Bolt EV Forum banner

1 - 20 of 37 Posts

·
Registered
Joined
·
307 Posts
Discussion Starter #1
I got lost (embarrassing) on a return from Denver airport to my house at 9500 feet and did 25 extra miles. Stupid error. So on the 6000-foot climb to the tunnel I had to drive very cautiously. I was down to the dreaded one flashing orange bar as I was within a few miles of the 2-mile long (gently uphill) tunnel at 11000 ftl. Dying inside the tunnel would have been a disaster. But once through it, I knew the amount gained on the 2500 ft downhill would get me up the 800 feet to my house. I answered YES to "low power mode?" so I could not see the center display and did not know how many kWh I had left. Now, each bar represents 3 kWh (with small error). So I thought I was down to 1 kWh or so. When I got home, I still saw only the single flashing orange bar, but when I rebooted, I saw that there were 5.4 kWh remaining. So it would appear that the bars, when down to 1 or 2, do not accurately reflect the 3 kWh per bar rule. So, just like fuel gauges, this appears to be nonlinear! Does anyone know exactly what happens in terms of kWh remaining as one gets down to one or two bars? I would have been much happier if I had not gone down to low power mode so I could see how much is left, as the truth is important. As far as I can tell, the bar-kWh ratio is just about a perfect 3 for the first 15 or so of the 20 bars. Is it reasonable to think that there are a few kWh more than one would naturally think, or am I making a mistake there.

Aside: On 25000 miles I am averaging 4.4 kWh on the display, but it is really more because I gain 0.7 whenever I leave my house and that is not recorded when starting with full or nearly full charge. So it is about 4.5 in truth. As noted, the lower air resistance here at 9000+ feet is the likely reason for the good rate.
 

·
Registered
Joined
·
365 Posts
What you have likely observed is the battery settling down after a long discharging session and its voltage shifting a bit. Since the remaining charge is derived from the measured voltage, a change leads to a different reporting of the SoC. I’ve seen a deviation of up to about 2% after turning the car off and back on, which is sufficient enough to move the bar up or down a notch since its resolution is coarse.
 

·
Registered
Joined
·
307 Posts
Discussion Starter #4
There is no display on the Bolt showing kWhs remaining...only kWh used. Where are you getting this number?
Sorry: I just subtract from 60. Imperfect, but the ratio of 3 to a bar is very close (except at end),
 

·
Registered
Joined
·
3,676 Posts
Sorry: I just subtract from 60. Imperfect, but the ratio of 3 to a bar is very close (except at end),
OK. So you had used 54,6 kWh when you were down to one bar. That means you have no more than 57.6 kWh usable. Not at all surprising. Most, if not all, EVs have lost 5% of usable capacity by the first year.

Don't feel bad. You have what we had when we drove it off the lot.
 

·
Registered
Joined
·
46 Posts
Nobody has actually answered the OP's question: what happens when you run the main battery down to zero. A quick search of this forum turned up another thread with the same topic. Perhaps a bit more info can be found there about "What happens...".

 

·
Registered
Joined
·
307 Posts
Discussion Starter #7
More thoughts. Maybe it said 55.5 used. So, yes, one explanation is that I had only 57 or so to start.
As for the voltage settling down: I restarted within five seconds of arriving in garage.
Well, it would be nice to see the kWh used display when, about once a year, I get this low. Is it reasonable to NOT go into the low power mode? Seems like some bravery is needed for that, since every Wh is useful at that stage. I will look up that other thread. Thanks, TexBolt.
 

·
Registered
Joined
·
3,676 Posts
More thoughts. Maybe it said 55.5 used. So, yes, one explanation is that I had only 57 or so to start.
As for the voltage settling down: I restarted within five seconds of arriving in garage.
Well, it would be nice to see the kWh used display when, about once a year, I get this low. Is it reasonable to NOT go into the low power mode? Seems like some bravery is needed for that, since every Wh is useful at that stage. I will look up that other thread. Thanks, TexBolt.
I have done this at least three times now. You don't need to agree to shut down the center screen. You can accomplish the same thing manually. When I get down to two bars, I turn off the outside lights with the knob to the left of the wheel, turn radio down to zero, turn the dash lights all the way down, and of course turn off the fan and HVAC system. You can see your SOC remaining with the MyChevy app, or Torque Pro. I can say that our Bolt will maintain at least 55 mph at power reduced, at least down to 1.6% SOC.

After shutting down the car, and reopening the driver's door, you will again see the info on the DIC. I have seen miles remaining jump up by one or two miles. This is because, with no loads on the battery, the voltage, and estimated SOC goes up slightly.
 

·
Registered
Joined
·
365 Posts
Back when a Redditor did a battery-related data dump (I think it was from the MyChevrolet app), there was a mention about the Bolt going "negative" in the displayed SoC to let the car drive a bit more as the battery is run down. Basically, it claimed that you can tap into that 4-5% buffer at the bottom end in an emergency. I have no wish to intentionally test this, though.
 

·
Registered
Joined
·
1,371 Posts
Back when a Redditor did a battery-related data dump (I think it was from the MyChevrolet app), there was a mention about the Bolt going "negative" in the displayed SoC to let the car drive a bit more as the battery is run down. Basically, it claimed that you can tap into that 4-5% buffer at the bottom end in an emergency. I have no wish to intentionally test this, though.
The actual text is:
Code:
// empty battery level (SoC) - used for the battery-empty indicator and for defining the point at which a route/destination becomes unreachable (0% uSoC / 4% hvSoC)
// note: the car will continue driving until reaching -3.2% uSoC (equiv. to KeOOER_Pct_OOESOCFinalwarn = 1% hvSoC), which gives some additional buffer.
// At -3.2% uSoC the contactors will open and the car will go dead. In that state the car will not restart until it is recharged back to 0% uSoC (4% hvSoC).
So yes, it's at -3.2% that the car will die. That said, there is no guarantee that this point really corresponds to 3.2% of extra energy since the calibration might be much more inaccurate at the bottom end of the range.
 

·
Registered
Joined
·
307 Posts
Discussion Starter #11
Well, that is interesting. Short of buying new equipment to measure things, I suppose one thing I could do next time I get to one bar, is to repeatedly go up and down a hill outside my garage that would be safe. Wait: Why not just leave it in the garage and turn the heat up high. A lot simpler. It does seem like this is a reasonably important piece of information as it directly affects how one drives when is low and home is a few miles away.
 

·
Registered
Joined
·
3,676 Posts
Well, that is interesting. Short of buying new equipment to measure things, I suppose one thing I could do next time I get to one bar, is to repeatedly go up and down a hill outside my garage that would be safe. Wait: Why not just leave it in the garage and turn the heat up high. A lot simpler. It does seem like this is a reasonably important piece of information as it directly affects how one drives when is low and home is a few miles away.
Going up and down the hill, with the heat on high, would be even faster. It would be helpful if the hill heads down to the garage. :)
 

·
Registered
Joined
·
307 Posts
Discussion Starter #13
Yes, it is purely downhill into the garage so I could coast home. But I can try this only when the car is down, and we always hate to let that happen. We'll see.
 

·
Registered
Joined
·
3,676 Posts
So yes, it's at -3.2% that the car will die.
This will depend on how closely your 96 cells (actually 288) are matched for capacity. My cell 70 will trip the BMS before the others reach bottom. This is where Tesla has an advantage. I have seen screen shots of the voltage variation across the thousands of cells in a Model 3, and they are much closer than the cells in the Bolt.

12-29-18-3.jpg
 

·
Registered
Joined
·
4 Posts
This will depend on how closely your 96 cells (actually 288) are matched for capacity. My cell 70 will trip the BMS before the others reach bottom. This is where Tesla has an advantage. I have seen screen shots of the voltage variation across the thousands of cells in a Model 3, and they are much closer than the cells in the Bolt.

View attachment 27589
huh that's interesting...I wonder how much of that is because of physical properties of the cells and how much is because of individual cell management in a tesla keeping the voltage variation lower through better charge/discharge cycles of each cell.
 

·
Registered
Joined
·
3,676 Posts
huh that's interesting...I wonder how much of that is because of physical properties of the cells and how much is because of individual cell management in a tesla keeping the voltage variation lower through better charge/discharge cycles of each cell.
I believe it is because of the extremely automated, and precise nature of manufacturing small cylindrical cells, compared to production of large format pouch cells. If there is a small imperfection in a 3 Ah cell it can be readily spotted, and discarded. A tiny imperfection in a 60 Ah cell might go undetected for some time.
 

·
Registered
Joined
·
331 Posts
This will depend on how closely your 96 cells (actually 288) are matched for capacity. My cell 70 will trip the BMS before the others reach bottom. This is where Tesla has an advantage. I have seen screen shots of the voltage variation across the thousands of cells in a Model 3, and they are much closer than the cells in the Bolt.

View attachment 27589
I'm not sure how much credit to give low cell variation or what to read into cell variation at low SOC. I've seen people report that the cell variation was very low on their Teslas all the way up to the point where the pack failed and had to be replaced. Plus on a Tesla, you have to worry about balancing thousands, not hundreds, of cells.

Mike
 

·
Registered
Joined
·
3,676 Posts
Plus on a Tesla, you have to worry about balancing thousands, not hundreds, of cells.
Nope. Once they are attached in parallel, you have 96 cells, just as the 288 cells in a Bolt become 96. There is no functional difference between a single 1000 Ah cell, and 1000, 1 Ah cells once they are attached in parallel. The difference is in the level of granularity which you can test and sort them before assembly.
 
1 - 20 of 37 Posts
Top