deep look into charging a cold battery

[rs38]

I like to provide some facts about charging Taycan I just was able to log.

Here you see an approx. 7 month old MJ21 Taycan with quite cold battery while charging at a 300kW HPC from Alpitronic, quite common in Europe.

Checked upfront: "fast" State of Health says 93% with only 7000km on the odo.

I'm still working on the nicer display, but I will explain a bit more:

Start of charge was at:
16,3% SoC displayed, while the internal BMS value was at 21%, which is also a nice hint for net/gross capacity.
695V HV- and 3,5V cell voltage and 17°C battery temp.

At that time BMS allows a maximum of 90A (63kW) under that medium cold conditions.
The battery heating starts (see cooling inlet and outlet) and rises to 25 degrees while increasingly using the PTC heating up to 10 amps. (and burning quite some energy).

Small way point at about 21°C battery and 29% SoC display (32% internal): now the BMS did enough active heating and switches off the heater. Inlet and outlet become more and more equal, still a rather little charge current is allowed (110A)

Reaching max. charging power for that session at approx. 150kW and 195A in a jump at 27 degrees battery temperature. SoC 44 vs. 46%.
This speed lasts until 53/54% SoC, battery is now at 30 degrees celsius and then abruptly drops to about 100 kW (130A). I am not quite sure if a power limitation at the quite big carging station occurred.

Reaching batt temp of 32°C active cooling started. Nice to see, keeping Inlet < Outlet and no more PTC current. Also the A/C compressor is clearly audible in the car.

At 66% SoC we stopped charging only to see if other (better) max charge current would be allowed on a restart. Obviously not in that case.
Nice to see the cell voltage inertia slowly go down towards OCV after stopping the charge.
https://www.batemo.de/products/batemo-cell-library/e66a/ -> pulse characteristics

Charging continues at 130A until 78% SoC then with continuous decreasing current to 85/86% SoC . Battery temp can be hold at 33°C.

Hope you enjoyed that inside view into a cold battery charging session.

Sponsored

 

[JimBob]

I took the liberty of putting your report in table format so I could understand it better. I hope you don't mind.

SOC Reported %​	SOC Internal %​	Battery Temp Celsius​	Amps/kWh​	Comment​
16.3	21	17	90/63	Battery heating starts, inlet outlet temp unequal
29	32	21	110/	Heater off, inlet outlet more equal
44	46	27	195/	Reaches maximum charging power
53	54	30	130/100	Charging speed drops suddenly to 130A
		32		Active cooling started. Inlet < outlet
78		33		Charging holds steady at 130A then starts to drop
85	86	33		End of test

A couple of questions.

1. Can scaling be added to the x and y axis for easier reading?

2. Can the scanner do a data dump in csv or other format?

3. Is the battery heating that occurs after the heater is off, due to battery heating itself?

4. I can't see how the difference between the reported SOC and Internal SOC is a hint of the net and gross battery capacity as the difference declines throughout the test. Looks a bit more like an artifact of testing.

5. And somewhat unrelated, are you aware of any ODB2 data loggers that work with the Taycan?

 

[rs38]

nice table format and correct interpretation, appreciate it!

1. yes, I will improve it. That lack of proper scaling also makes the SoC net vs. gross look strange, see 4.

2. yes, it actually dumps .csv only and I put not much effort in nice charts

3. yes, there is some tiny PTC on demand heating left but it's mainly for cabin as it was 4°C outside. I'd say 99% heating at that point occured by internal battery resistance, being at ~1 mOhm. P = I² x R = (~130A)² x 0,001Ohm = 17kW heat

4. here is better scaling applied. reported SoC started with 4% less and gets on par at ~65% and is 1% ahead at the end with 86/85%

5. every 5-100$ ebay dongle with 11/29-500 CAN Bus hardware can do it. Only CAN Bus IDs and UDS DID (sometimes similar to many VAG cars) are the trick. I spent some time to reverse it.

 

[Johann55]

Very interesting information on cold battery charging, thanks for sharing. Did you consider releasing your findings for live data as a phone app, maybe sharing Taycan-specific sensors for Torque Pro users?

My Taycan is coming soon, hope to use ABRP via OBD2, but seeing more parameters would be really great.

 

[daveo4EV]

I like to provide some facts about charging Taycan I just was able to log.

Here you see an approx. 7 month old MJ21 Taycan with quite cold battery while charging at a 300kW HPC from Alpitronic, quite common in Europe.

Checked upfront: "fast" State of Health says 93% with only 7000km on the odo.

I'm still working on the nicer display, but I will explain a bit more:

Start of charge was at:
16,3% SoC displayed, while the internal BMS value was at 21%, which is also a nice hint for net/gross capacity.
695V HV- and 3,5V cell voltage and 17°C battery temp.

At that time BMS allows a maximum of 90A (63kW) under that medium cold conditions.
The battery heating starts (see cooling inlet and outlet) and rises to 25 degrees while increasingly using the PTC heating up to 10 amps. (and burning quite some energy).

Small way point at about 21°C battery and 29% SoC display (32% internal): now the BMS did enough active heating and switches off the heater. Inlet and outlet become more and more equal, still a rather little charge current is allowed (110A)

Reaching max. charging power for that session at approx. 150kW and 195A in a jump at 27 degrees battery temperature. SoC 44 vs. 46%.
This speed lasts until 53/54% SoC, battery is now at 30 degrees celsius and then abruptly drops to about 100 kW (130A). I am not quite sure if a power limitation at the quite big carging station occurred.

Reaching batt temp of 32°C active cooling started. Nice to see, keeping Inlet < Outlet and no more PTC current. Also the A/C compressor is clearly audible in the car.

At 66% SoC we stopped charging only to see if other (better) max charge current would be allowed on a restart. Obviously not in that case.
Nice to see the cell voltage inertia slowly go down towards OCV after stopping the charge.
https://www.batemo.de/products/batemo-cell-library/e66a/ -> pulse characteristics

Charging continues at 130A until 78% SoC then with continuous decreasing current to 85/86% SoC . Battery temp can be hold at 33°C.

Hope you enjoyed that inside view into a cold battery charging session.

there is soooo much awesome in this posting that I simply do not know where to start.

thank you for sharing - this is GREAT data.

 

[Jhenson29]

4. I can't see how the difference between the reported SOC and Internal SOC is a hint of the net and gross battery capacity as the difference declines throughout the test. Looks a bit more like an artifact of testing.

Wouldn’t the difference necessarily have to change throughout the charge as they are on fundamentally different scales? I think what it hints at is where the extra capacity is, at least in this one case. Hard to know if it is a constant or moves around for some reason. Unless I’m misunderstanding what’s being discussed.

 

[JimBob]

Wouldn’t the difference necessarily have to change throughout the charge as they are on fundamentally different scales? I think what it hints at is where the extra capacity is, at least in this one case. Hard to know if it is a constant or moves around for some reason. Unless I’m misunderstanding what’s being discussed.

The problem I had was the difference between Reported SOC and Internal SOC was down to 1% at when SOC was around 85%. Does that mean it gets to zero when SOC gets to 100%? We know that Gross Battery is 93.4 kWh and net is 83.7 kWh so the difference appears to be the buffer. I don't know how Reported SOC and especially Internal SOC relate to this or even what they really mean.

I think it's a question for the OP.

 

[Jhenson29]

The problem I had was the difference between Reported SOC and Internal SOC was down to 1% at when SOC was around 85%. Does that mean it gets to zero when SOC gets to 100%?

OP said 1%, but in the opposite direction, with it being equal at 65%, so I assume it keeps going up (maybe 2% difference at 100%, for example).

Quote for reference.

reported SoC started with 4% less and gets on par at ~65% and is 1% ahead at the end with 86/85%

 

[JimBob]

@rs38

I was wondering if your App could output how the battery is heated and cooled depending on temperature.

Can you output the battery temperature and how the BMS is maintaining that temperature from a low temperature to a high temperature?. Basically when the BMS is kicking in to heat and cool.

 

[rs38]

feel free to pm me to and take a deep look into your BMS!


Reported SOC and Internal SOC deviate much more than 1% if you compare the whole range. I don't know if it changes with life time but my car reports ~96-97% fully charged and 6% SOC if zero range and 0% Display-SOC.

 

[Tom32]

Checked upfront: "fast" State of Health says 93% with only 7000km on the odo.

Wait, do I interpret it corretly as your battery capacity is already only at 93% at full charge after 7000km, meaning it already degraded 7%?

 

[rs38]

not my car (I am at 93-94% with 17000km) but yes, the BMS's diagnostic values stated SoH of 93%, whatever that exactly means. But that should be a learning value that is close to truth.

Sponsored