[Ladogaboy]

So, I've been able to get my OBD2 adapter hooked up, and this is what is currently being displayed. It looks as though the Bolt EV does use the same PID as the Volt for SOC. Not sure what you guys can glean from this, but I also included a picture of the recorded usage as displayed.

 

[ClarksonCote]

So is SOC-U what the car shows in the DIC, and SOC-R the "real" state of charge? In other words, they save about 13% of the top end of the battery to preserve it?

If so I believe that's a much larger reserve than what others were assuming thus far.

 

[saghost]

If we're reading the data right, that seems pretty improbable. The folks building from cell level information came up with a total of 64.5 kWh I thought - having user reported 100% charge at real 87% and at least 58 kWh of usable capacity requires a total capacity of at least 66 kWh - and since the bottom end matters more than the top, probably more like 75 kWh.

That'd be great news for degradation, but it doesn't fit with the rest of the available information.

 

[ClarksonCote]

That'd be great news for degradation, but it doesn't fit with the rest of the available information.

Agree. Looking forward to hearing more after this data can get properly decoded.

 

[Ladogaboy]

Ok, so maybe I am missing something. The reason I included the dashboard shot is it seems to align with SOC-U. Is it possible that the SOC-U isn't "usable" but rather what the current SOC is?

I don't know how these PIDs were decided on (I nabbed them from tboult's old Google sheet), so I wasn't really looking at the labels. According to the dash, I used 12.2%. I was adding that to the SOC-U at 86.7%. The remaining SOC should be 1.1%. Wouldn't that be the buffer?

 

[Qinsp]

Over the next year, it would be interesting to map the actual traction array voltage against reported SOC.

This will indicate decay rate and give some insight into how it buffers and charges.

AFAIK, there is no such animal as a SOC sensor or kWh sensor. It reads voltage and load only.

 

[rob]

The Volt spreadsheet shows both SOC-U and SOC-R derive from the same PID (015B). They just get scaled differently. The Volt scaling factors won't be the same as the ones for the Bolt.

For the Volt, SOC-U = (015B - 54 ) / 1.34
SOC-R = 015B * 100 / 255

 

[saghost]

The Volt spreadsheet shows both SOC-U and SOC-R derive from the same PID (015B). They just get scaled differently. The Volt scaling factors won't be the same as the ones for the Bolt.

For the Volt, SOC-U = (015B - 54 ) / 1.34
SOC-R = 015B * 100 / 255

Okay, so SOC-R is an 8 bit SOC number converted to a percentage, and then SOC-U is an artificially created number based on Volt charge ranges?

 

[canehdian]

SOC-U is meaningless - it's hardcoded for volt values. Ignore that.

When your bolt says 100% on the dash (or onstar app, etc), check what the SOC-R value says. That is the upper buffer limit.

Record the car/onstar % and side by side the SOC-R% and we can extrapolate the true upper and lower limits.
Combined with kWh used at each interval, can estimate the full capacity and usable capacity.

 

[wordptom]

Seems to me that any app telling you both the Useable SOC % and the Raw SOC % would need user (or programmer) input telling it some specific vehicle data, such as the size of the useable soc window (and where it starts or ends), to determine the Useable %. Which also raises the question... if the Useable SOC is determined by vehicle-specific data, is the Raw SOC also based on specs for my vehicle’s model year, making in possible for battery degradation to manifest itself in changes in the Raw SOC readings? If a battery degraded from 16 kWh to 11 kWh and was then fully charged (87% of 11 kWh), would it display on the app with a 60% Raw SOC reading (60% of the model year’s 16 kWh), or would it continue to read 87%, i.e., 87% of whatever the battery full capacity is?

 

[canehdian]

Seems to me that any app telling you both the Useable SOC % and the Raw SOC % would need user (or programmer) input telling it some specific vehicle data, such as the size of the useable soc window (and where it starts or ends), to determine the Useable %. Which also raises the question... if the Useable SOC is determined by vehicle-specific data, is the Raw SOC also based on specs for my vehicle’s model year, making in possible for battery degradation to manifest itself in changes in the Raw SOC readings? If a battery degraded from 16 kWh to 11 kWh and was then fully charged (87% of 11 kWh), would it display on the app with a 60% Raw SOC reading (60% of the model year’s 16 kWh), or would it continue to read 87%, i.e., 87% of whatever the battery full capacity is?

We can only go by SOC reported by the computer. That is the SOC-R number.
You could also do a crude estimate based on voltage, but only when very full or very empty (voltage doesn't fluctuate much in the middle).
As the car is brand new, the reported numbers should hint at usable design/capacity.
As it gets older, someone would need to track how the SOC changes vs capacity used.

The very definition of SOC says it should be the latter you listed - 87% of whatever the battery's current full capacity is at the time of calculation.

 

[hvacman]

Let's try this possibility:

SOC-U = the "state of charge% usable" This would be the state of charge % usable for the trip when the "kwh meter" says "0" on the vehicle energy-used display.
SOC-R = "State of charge% remaining" and notes the current state-of-charge of the battery.

The vehicle computer probably has another piece of data (source not yet defined - perhaps another algorithm) that tells it what the battery's available kWh is at 100% SOC-U, then looks at the SOC-R and calculates the kWh used on that trip.

If that is the case, we can derive the battery's usable kWh at 100% charge by subtracting SOC-R% from SOC-U%, then dividing the displayed kwh used by the resulting %.

100-86.7 = 13.3%. 7.3 kwh/.133 = 54.89 kwh usable energy at 100% charge. What is the deepest that anyone has driven a Bolt? What was the kWh used with like 1 mile remaining? I seem to remember in one review where it was really getting low on charge that it was approaching 55 kWh. This would gybe with the total battery capacity of 60 kWh and a 5 kWh buffer.

 

[rob]

Okay, so SOC-R is an 8 bit SOC number converted to a percentage, and then SOC-U is an artificially created number based on Volt charge ranges?

Yes. The raw data for PID 015B ranges from 0 to 255, where 0 = bricked and 255 = overcharged. The BMS is likely responsible for generating the value, but only GM and LG know how it is calculated (until someone dumps and decompiles the Bolt's BMS. Not holding my breath as we're still waiting on someone to do that for the 1G Volt...)

 

[canehdian]

Let's try this possibility:

SOC-U = the "state of charge% usable" This would be the state of charge % usable for the trip when the "kwh meter" says "0" on the vehicle energy-used display.
SOC-R = "State of charge% remaining" and notes the current state-of-charge of the battery.

The vehicle computer probably has another piece of data (source not yet defined - perhaps another algorithm) that tells it what the battery's available kWh is at 100% SOC-U, then looks at the SOC-R and calculates the kWh used on that trip.

If that is the case, we can derive the battery's usable kWh at 100% charge by subtracting SOC-R% from SOC-U%, then dividing the displayed kwh used by the resulting %.

100-86.7 = 13.3%. 7.3 kwh/.133 = 54.89 kwh usable energy at 100% charge. What is the deepest that anyone has driven a Bolt? What was the kWh used with like 1 mile remaining? I seem to remember in one review where it was really getting low on charge that it was approaching 55 kWh. This would gybe with the total battery capacity of 60 kWh and a 5 kWh buffer.

That may be true if GM supplied SOC-U, but they didn't - that is a volt user calculation tailored to the known capacity of a volt.

As I said before, ignore SOC-U entirely for a bolt. It's nonsense until someone does a similar calibrated calculation for it's formula.

SOCR is the raw SOC value reported by BMS. SOC-U is derived from this number using hardcoded values by end users. Even on different volts it was wrong because different model years had different batteries.

 

[Sean Nelson]

Yes. The raw data for PID 015B ranges from 0 to 255, where 0 = bricked and 255 = overcharged. The BMS is likely responsible for generating the value, but only GM and LG know how it is calculated (until someone dumps and decompiles the Bolt's BMS.

Even if you reverse-engineered the code, all you'd be left with is the raw voltage information from the battery - unloaded and loaded voltages (at a particular power level) from which the values are calculated. That just begs the question of understanding how those relate to the maximum and minimum permissible charges. Remember that those are not absolute - they're set by the engineers based on their own criteria for battery longevity, performance, and target range.

 

[Ladogaboy]

Ok, so based on what I'm seeing (I still haven't changed the formulas), both the SOC-R and SOC-U fluctuate as the battery usage changes.

So this morning, I woke up (usage didn't change from what I originally posted) to find these numbers:

This is after 10 kWh used:

 

[Ladogaboy]

This is after 28 kWh used:

And this is when the Bolt EV had been fully charged to 100%:

I don't know if these are useful, but I figured I'd post them up.

 

[saghost]

Well, the 96% of absolute SoC for 100% user SoC makes sense to me. I'm not sure any of the rest does, though.

The difference between going to sleep and waking up could be just the battery temperature change? I don't think the Bolt does vampire drain like a Tesla...

The other two numbers don't seem to make much sense at all from what we think we know.

 

[bro1999]

Success! I think. I loaded the Volt's PID list I found linked on this forum into Torque Pro, and I got the following to display. I had charged my Bolt with hilltop reserve activated, so it was at 87% SOC according to remotelink (normal for hill top reserve). Bolt was still plugged in when I took these screenshots. Ambient temp was 20F.

 

[Ladogaboy]

I'll have to add some of those other PIDs. We can start comparing, but I'd like to see if we can figure out the actual battery capacity. The fluctuations seem weird to me, though.