Very slow DC charging

[Yves]

I have already done that. No error codes or other obvious reason.

If I remember correctly you see the voltage of all modules are they all the same?

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[chrisk]

If I remember correctly you see the voltage of all modules are they all the same?

Right now, after "rebalancing", all cells are between 0.71v and 0.73v at 80% SoC and 25C temperature. That looks pretty balanced to me. If you can get data from your car, it would be nice to compare.
Before the rebalancing some cells were at 0.2v. Still that does not immediately explain why the slow DC charge...

 

[Yves]

Right now, after "rebalancing", all cells are between 0.71v and 0.73v at 25C temperature. That looks pretty balanced to me. If you can get data from your car, it would be nice to compare.
Before the rebalancing some cells were at 0.2v. Still that does not immediately explain why the slow DC charge...

0.69v both high and low at 61% SOC … 0.2v seems a lot normally the imbalance is measured in mV … anyway I do not really trust the numbers I see out of the app, but it’s an indication.
I would let it be diagnosed by Porsche …

 

[Rocketair]

New data point for me - today I charged for a bit at an EA station (after doing a PCM reboot, which not surprisingly did nothing of note...)

Charge still limited to ~34kw, though i did enable compatibility mode and it moved up to ~39...) My charge session was for 14.4 kWh, and my SOC both car and EA station showed it moved from 39% to 63%. So 14.4 kWh=24% of battery, meaning it thinks there is an effective total of ~ 58kWh. Making an appt with the dealer, but will be interesting to see if this is hardware of software. I still bet on software, but we'll see.

One other thing I noticed, and may have always been there, but now I am looking at it closely - when I start the car in the morning the 12V battery meter goes from ~13V to 14.4 in the first 30 seconds and the screen actively shows it rolling up to that number over the time...

 

[chrisk]

0.69v both high and low at 61% SOC … 0.2v seems a lot normally the imbalance is measured in mV … anyway I do not really trust the numbers I see out of the app, but it’s an indication.
I would let it be diagnosed by Porsche …

It is actually 0.02V i.e. 20mVolts, which is about 2-3% imbalance. Internet wisdom suggests the Taycan BMS triggers rebalance if it detects 2% cell difference.
At 60% SoC the imbalance was 0.69v highest vs 0.68v lowest cell. After I charged to 75% it is 0.73v highest vs 0.72v lowest. Down to 10mVolts.

Anyway battery rebalancing seems to have fixed the slow DC charging for me. I charged much faster today, about 150kw at 50% while before the rebalancing I was getting 33kw max at same charger and same conditions.

 

[Yves]

It is actually 0.02V i.e. 20mVolts, which is about 2-3% imbalance. Internet wisdom suggests the Taycan BMS triggers rebalance if it detects 2% cell difference.
At 60% SoC the imbalance was 0.69v highest vs 0.68v lowest cell. After I charged to 75% it is 0.73v highest vs 0.72v lowest. Down to 10mVolts.

Anyway battery rebalancing seems to have fixed the slow DC charging for me. I charged much faster today, about 150kw at 50% while before the rebalancing I was getting 33kw max at same charger and same conditions.

Yeah I miss read that in my head somehow Anyway a 20mV is that a lot or not ... nu clue. I should check my iX but if memory serves me right it was in the order of 2, 3 mV ... forgot the name of the app but it was first for BMW cars and was way more correct and useful.
Good to know balancing worked. Quite strange that procedure is 95% and not a 100% as for example with my BMW I really see it balance ones reaching 100% and then keeps on charging until it eventually stops ...

 

[chrisk]

Yeah I miss read that in my head somehow Anyway a 20mV is that a lot or not ... nu clue. I should check my iX but if memory serves me right it was in the order of 2, 3 mV ... forgot the name of the app but it was first for BMW cars and was way more correct and useful.
Good to know balancing worked. Quite strange that procedure is 95% and not a 100% as for example with my BMW I really see it balance ones reaching 100% and then keeps on charging until it eventually stops ...

The procedure is something I read in a Taycan TSB and which was saying to charge to at least 90%, so I did 95%. Then the magic happens while it is unplugged. You have to leave the car unplugged and undisturbed for at least 6.5 hours.

I suspect that the Porsche chooses to discharge the highest voltage cells until they match the voltage of the lowest. But the BMW chooses to charge the lowest voltage cells until they match the highest.

 

[nulled]

Does it fix the issue? Mine also maxes out at 30kwh and ruined my road trip plans for the week. No errors on the dash, just refuses to fast charge on multiple chargers. I have only street parking, so I can't charge at home...

 

[FirstEV]

Side note. My dealer said that if I am to leave the car for more than two weeks I need to have it connected to an external battery charger, otherwise the battery will discharge completely. You had yours untouched for three weeks?

That’s not stämmer at all. I’ve had my bil at the återförsäljare for almost 3 months without it being touched and it still started. It really shows how the dealer is so uneducated on their EVs.

 

[nulled]

Porsche dealer said the issue was software not hardware. They said that they've updated the software and it should be fine. The battery was split in half and the system thought it was reaching 100% that's why charging speed slowed down.

 

[Wivenhoe]

The battery can split when on 400v charger so it takes 2x 400v. Sounds like that had developed a fault.

 

[xmlguy]

I am having this exact issue — capped around 35kw at three different EvGo stations by my house. It’s also limiting my range to around 150 miles, which I guess would be consistent with one of the two banks not charging…

 

[xmlguy]

Car went into the dealer for a week. Below is the summary of the fix from Porsche, in case others have this problem.

Customer states vehicle is not charging correctly, charge speed is slower than normal and stuck at 35kw. Notices the estimate range that appears on the cluster is showing incorrect data after unplugging vehicle. Vehicle will not charge past 150 miles of range. Customer charges using the supercharger (DC charger) and 110v charger (AC charger) and notices the same result. check and advise.

Internal cell module software causing the cell modules state of health to be read incorrectly. Created PRMS ticket: 3898368, and was informed to follow SY 9301 (SY 248/24) for this concern. After performing the SY and charging the battery in increments, got the charging speed to return to normal 90-110kW versus the 35kW max it was charging at. No signs of improper charging by the customer, or any kind of influence that would have caused this concern

Hooked the vehicle up to DC charger and verified the vehicle would not charge over 35kW. Created VAL and checked faults. No faults related to concern. Noted battery cell module state of health had a 35% difference between the lowest cell module (Module 1 at 65%, Module 10 at 100%).

Created PRMS ticket 3898368, and performed instructions as per SY 9301 (SY 248/24) for re-commissioning the cell modules. After performing this step the modules all read 100% state of health. Creates another VAL as per PRMS request. The cell modules did not balance as was hoped, so i was instructed to, and performed a charge cycle, while actively monitoring the cell module voltages to be sure the difference between the min and max modules did not exceed 250mV. After a full charge, found a difference of 170mV. Created a post VAL showing the results. Concern is remedied at this time, and the HV battery will continue to balance the cells as discharge and charge cycles are performed. Advise customer to perform full 100% charge cycles for the next couple weeks to ensure proper cell balancing

 

[chrisk]

Car went into the dealer for a week. Below is the summary of the fix from Porsche, in case others have this problem.

Your dealer did a good job with the diagnosis and recovery.
Their diagnosis confirms my suspicion and the data from Car Scanner app that shows the issue is due to battery cell imbalances. It also means there is a bug in the Battery Management Module that lets the cells get to this state.
Next time you can solve it without a dealer visit by following the charging procedure mentioned a few posts above.

@Rocketair did you get your car back? If not you can point them to the post right above for the steps the other dealer followed.

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