Running the Battery to 0%

[KickingGas]

Lots of interesting technical info on here! More mundane, but circling back to my earlier post, this happened to me yesterday on the opposite side of the SOC spectrum: I charged up to 100% in anticipation of a long trip. I had another errand to do first 7.9 miles away. When I returned home, it still said I was at 100% charge. Not much up and down, calm weather, some country roads then some in-town traffic lights, but clearly I used more than 0% on a 15 mile trip. Each day I feel less confident in judging how far I can actually drive the thing...

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[Box Cat]

What's the thought on the Out of Spec Lightning team losing power with truck still showing 12 miles of range?
To me they should do an update where they reduce the overall range by 20 miles and protect the lower portion of the battery in addition to the 10% top range they are protecting.

Could you post a link? I only found this one which is crazy. As part of the test, the guy not only reaches 0% but also eats up the “reserve” buffer down to 2kWh and the truck dies a few yards from the charging station . Then truck is pushed to the station and he charges at 50kW … insane

 

[RyZac]

Here's links to two
First is a race down the East Coast where they ran out even though they had range (1:48:00)
They were able to push the Lightning to the charger and continue.


Second is a long 4 truck race from Florida to California were they had to get towed in Part 3 (Go to 3:39:37)
Kyle's dad Dave was involved in both cases with this truck and commented on it.

 

[RickLightning]

Keep in mind that these videos are done to drive revenue. Kyle and others bank enough money to not give a crap about battery longevity.

 

[Yellow Buddy]

What's the thought on the Out of Spec Lightning team losing power with truck still showing 12 miles of range?

Thought: I've experienced the same and it' a bit disappointing the first time it happens given so many other vehicles have buffers.

To me they should do an update where they reduce the overall range by 20 miles and protect the lower portion of the battery in addition to the 10% top range they are protecting.

The uproar it would cause...this forum would be filled with torches and pitchforks demanding buybacks.

'

 

[RyZac]

Keep in mind that these videos are done to drive revenue. Kyle and others bank enough money to not give a crap about battery longevity.

I would hope they were just trying to win a race by using the capacity of the battery and not staging a loss of power event.

 

[flypony53]

Thought: I've experienced the same and it' a bit disappointing the first time it happens given so many other vehicles have buffers.



The uproar it would cause...this forum would be filled with torches and pitchforks demanding buybacks.

'

I had a similar issue. vehicle had 1% battery remaining about 400yds from my house and the truck stopped moving. Luckily I could shift into neutral and push, but, the Lightning BMS has some very basic issues reading the SOC of the battery.

 

[Grumpy2]

the Lightning BMS has some very basic issues reading the SOC of the battery.

The BMS may be trying to save the battery from the driver's actions.

 

[flypony53]

The BMS may be trying to save the battery from the driver's actions.

Then do not quote me 1% battery and 3 miles of range...if range is 0 then show range of zero.

 

[hturnerfamily]

I had a similar experience, and while at first I thought I was 'out' of all power, it actually wanted me to put it in PARK, then back into gear, to move forward, even slowly... give it a try next time.

 

[flypony53]

I would hope they were just trying to win a race by using the capacity of the battery and not staging a loss of power event.

In the Finale Video above, they had 13 miles of range left showing on the GoM, yet the vehicle stopped. I have not watched it, but sounds like they had a similar issue in the other vehicle with the same truck. I dont think anything was staged.

I personally only drove to a few miles remaining on my F150 the one time, so I cannot state if the issue is pervasive or simply one offs. Would do this often on my Tesla to ensure the BMS was reading the pack correctly. But, for these examples with Ford, it seems as though the BMS is not reading the pack correctly to understand remaining charge level.

 

[flypony53]

I had a similar experience, and while at first I thought I was 'out' of all power, it actually wanted me to put it in PARK, then back into gear, to move forward, even slowly... give it a try next time.

Tried this as well...interestingly enough, I would put it in park, then back in drive, press the accelerator, and the truck would roll backwards very slowly (was not on an incline).

 

[Box Cat]

By the way, from what I can observe from the video I linked, it seems (but I still need to get my data points to be sure) more like there is a 6% buffer on top, and 4% at bottom (relative to nominal 131, but of all 144 battery) of which 1.5% is not consumed, and 2.5% is used as reserve.

I agree, the range estimation algorithm/BMS sometimes seem off. Have you guys tried to reset the trip history?

My experience using an LFP rated BMS is that it will “reset” when reaching top and bottom cut-off points.

 

[Box Cat]

Then do not quote me 1% battery and 3 miles of range...if range is 0 then show range of zero.

Definitely the BMS is the culprit. The out of spec guy was able to drive well below 0% (displayed) consuming the buffer.

A BMS would typically use a resistive conductor with very low resistance and very low voltage drop that is then amplified by a differential op amp and sampled at dt intervals by an ADC and consumed by SW. The dynamic v(t)*i(t)*dt is integrated constantly to measure the state of energy of the pack. But all these things have tolerances and as precise as they might be they will accumulate error over time. The reference points for the BMS to reset are at 0 and 100 % cutoff points. And since going down to 0 is far less likely during normal usage, as many people do, charging to 100% every once in a while may cure the problem (unless other things are broken …).
But still to be precise when getting down to zero, the 100% reference may not be enough, and going to zero is needed … unless the system knows exactly how to predict the low point from top with aging, temperature, discharge rates etc.
One thing to note is that you may not need to reach (displayed) 0 and 100 literally.
Depending on what Ford has chosen for a module Vmin and Vmax (say 2.7, 4.2 or else, will measure what the display value are next time I get to 0% and 100%) just getting close to those may give the BMS some information. The V/SoC curve of these cells is quite flat for most of the SoC domain, but slopes quite a bit up and down near the top and bottom, respectively, so one could derive a closer correlation to the actual SoC around those points.

 

[MM in SouthTX]

I charged up to 100% in anticipation of a long trip. I had another errand to do first 7.9 miles away. When I returned home, it still said I was at 100% charge.

I started a whole thread about this observation. I could not fathom an explanation why, after charging to 100%, I was consistently able to drive 6-10 miles and still be at 100% on the display. My only hypothesis was that Ford had unlocked added capacity, allowing the vehicle to charge beyond 131 kWh. So I asked the question on the forum whether this could be, and asking for other possible answers.

What I got in reply was all over the board, but no one came up with an explanation. When I kept asking the question, I kinda took a beating. The conclusion was basically that my observations must be wrong. Ad hominem attacks. (I did get a personal apology from one of them in a DM.) You can read the thread if you wish. (You will see in my first post that my second hypothesis was the correct one.) It was closed by admin but still exists.

Anyway, this was before I had an OBD scanner, and before I knew the difference between actual state of charge (HVB SOC, as read by the OBD scanner) and displayed state of charge (HVB SOC Display, shown on the dash and also by the scanner as the same data). It was also before I knew that 100% charge did not necessarily equate to 131kWh.

I'm having trouble loading images, but here's what I found.

After charging fully, the scanner showed

Energy 126.18 kWh (not 131); HVB SOC Display 100%; HVB SOC 94.83%

I do not recall how far I drove before the HVB SOC Display dropped (on the OBD scanner and on the dash simultaneously) below 100%, but I think it was about 8 miles. At that point it showed

Energy 121.74 kWh; HVB SOC Display 99.5; HVB SOC 92.06%

The findings were that a) the truck thought it was 100% charged when the battery had less than 131 kWh (my second hypothesis); and b) there was hidden energy above the HVB SOC Display reading. I used 2.55 kWh of battery (about 2%) before the display dropped below 100%.

I'm relating this for two reasons. One because several people reported the same finding that I had, but had no explanation. When the thread was closed, I could not report there, so I am reporting here. The second reason is to say that scientific knowledge is not the same as sound reasoning.

I appreciate the contributions of those who have put forth useful information. I have learned a lot here. I have narrowed my "delta" (charging more frequently) in order to preserve battery life. I will avoid going below 20% charge when possible. However, I advise people to take the information given them on the forum and apply your own knowledge to reach your own conclusions and decide how you use your truck.

Best to all involved, and no hard feelings. Not trying to take a victory lap here. Just trying to further knowledge.

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