Odd Supercharger Behavior

[stevezzzz]

I arrived at the Cheyenne Supercharger today just as a couple of other Model S were leaving; they did not report any problems I have an early Sig 85 with the A pack, and arrived with 18 miles Rated range remaining. On plugging in (stall 2B; all the others were empty) I watched the charge ramp up to 86 kW (251A @ 344VDC) and then in very short order (at about 23 Rated miles) it dropped back to 60-61kW and stayed there until it hit about 100 Rated miles, then dropped slowly to 58kW and stayed there until I unplugged and drove off with 171 Rated miles. Late in the charge another Model S arrived (VIN 30nnn) with 25 Rated miles and plugged into 1B: his charge rate ramped up to 120kW, as expected.

Since this was the first time I've arrived at a Supercharger with such a low SOC, I don't really know what to make of this. I've seen 90kW at a Supercharger before, though, so my car is (or was) capable of 90kW Supercharging. Does anyone know if this is necessarily a Supercharger issue, or could the car's battery management software be limiting my charge rate for unknown reasons? I did notice that the car would not allow me to turn on the climate control early in the charge (the app said climate control was disabled at such a low SOC).

 

[TurboFroggy]

I am guessing it was very hot and your car was telling the Supercharger to turn down while it could cool your battery pack. Was your car making a very loud hum with the fans all going full blast in the front? Also did it seem like the air conditioning didn't work so good while your were charging? This is all signs that it was very hot and your car was diverting all the cooling it could muster to keep your battery pack cool.

 

[Owner]

I don't think it has been very hot as I'm somewhere in the area (sort of)

I suspect your stall had issues. I've seen this from time to time. I always wait till it starts charging and check the number, if it is slow I'll jump over to another supercharger.

 

[stevezzzz]

OAT was 73° F., breezy and cloudy. All four of the cars had made the run from Lusk, WY; the two who left just after I arrived reported no charging anomalies (they'd been using pedestals 1B and 2A) and the one who plugged into 1B just before I pulled out ramped up to 120kW without a hitch (he charged from the other SpC cabinet). My car had just begun to limit traction power as I pulled up to pedestal 2B with 18 miles Rated range, and there were no loud cooling fan noises coming from up front as we started to charge. All these data seem to argue against an SpC cabinet issue; I suppose it could have been a problem with the pedestal itself, but there's no intelligence in the pedestals, that I know of (Cottonwood, are you there?).

I suspect the car was limiting charging power, but I don't know why it would have needed to so I'm left wondering if there's a fault in my car. I did call it in to the Supercharger team.

 

[stevezzzz]

But, OTOH...

I have a snapshot of the Charging screen from Lusk earlier in the day showing that I ramped up to 90kWh; I don't have any others showing intermediate charging rates, but I do recall checking the app several times and being unsurprised by the charging ramp-down. The odd thing in Cheyenne was that it was pretty much a step function: started at 86kW and dropped almost immediately to 60kW, and stayed there (+1/-2) until we unplugged at 171 Rated miles.

So I've changed my mind: it's probably a SpC anomaly. Or is there reason to suspect an imperfect electrical connection between the charging wand and my car's charging port? I've had problems in the past making the initial connection just so I can start charging, but never anything like this, where the car did not complain but the charging rate was lower than it should have been.

 

[FlasherZ]

Tesla really needs a way to indicate some sort of a fault, or something a bit more verbose as to why charging is restricted... A simple message indicating any condition that would be classified as a "back-off" would go a long way.

"Supercharging at reduced capacity (Call Tesla Supercharger Service)"
"Charge rate reduced - battery too hot (Rate will increase as battery cools)"
"Charge rate reduced - battery too cold (Rate will increase as battery warms)"
...etc...

 

[Cottonwood]

OAT was 73° F., breezy and cloudy. All four of the cars had made the run from Lusk, WY; the two who left just after I arrived reported no charging anomalies (they'd been using pedestals 1B and 2A) and the one who plugged into 1B just before I pulled out ramped up to 120kW without a hitch (he charged from the other SpC cabinet). My car had just begun to limit traction power as I pulled up to pedestal 2B with 18 miles Rated range, and there were no loud cooling fan noises coming from up front as we started to charge. All these data seem to argue against an SpC cabinet issue; I suppose it could have been a problem with the pedestal itself, but there's no intelligence in the pedestals, that I know of (Cottonwood, are you there?).

I suspect the car was limiting charging power, but I don't know why it would have needed to so I'm left wondering if there's a fault in my car. I did call it in to the Supercharger team.

As far as I know the pedestals themselves are just places for wiring connections, cord storage, and in the new ones, a place for a lit logo. There seem to be a few extra low voltage wires from the Supercharger Cabinet to the pedestal, so there could be a temperature sensor or something, but I don't think so.

Does the protocol measure Voltage drop between Cabinet and Car? That would be completely possible and would detect high resistance connections. I have no idea, but it is possible for Tesla to do a current backoff based on such measurements.

Let's see if Tesla tells you anything from the logs.

I agree with FlasherZ; a report of the error or limit cause/reason on a screen in the car or the App would be very helpful!

 

[Owner]

There are many imperfect SpCs. Much more likely than a problem with your car. And if you had a charging partner, even worse yet. I was at Fremont once and could only pull 10kW out of one stall and 19kW out of another... more details on my blog.

But, OTOH...

So I've changed my mind: it's probably a SpC anomaly. Or is there reason to suspect an imperfect electrical connection between the charging wand and my car's charging port? I've had problems in the past making the initial connection just so I can start charging, but never anything like this, where the car did not complain but the charging rate was lower than it should have been.

 

[Todd Burch]

My guess is the car detected a high resistance connection. Maybe the plug wasn't fully seated, or there was some dirt/gunk in the plug, preventing a nice full connection?

The car would detect this increased resistance and lower the power output accordingly.

 

[tezco]

It would probably would be helpful for service if in this type of situation we pulled the plug and reset, and then moved another unrelated charging station if the current was still low. That might help them narrow down the problem between car vs supercharger. But, I imagine you guys were giving the Cheyenne station quite a workout. I wonder if the superchargers have a 100% duty cycle?

 

[Owner]

I was just at Cheyenne yesterday. I had the last stall on the right stop on me twice. I don't know why but I was opening the trunk and the frunk.

 

[trigga71]

In the 2 weeks I have had my S I have used superchargers at least 20 times and I get low/slow charger sometimes. I just move to a different stall.

 

[PonoBill]

I'm not familiar with superchargers yet, but I'm pretty familiar with LiPo charging in various chemistries. Since you had discharged the battery substantially it's likely you had a fair amount of battery imbalance. Smart chargers for even 3S or 4S batteries will generally ramp the recharge rate way back when they detect imbalance, and throttle the higher voltage batteries to equalize. I imagine the problem is much more common with the huge number of series connections in a Tesla battery, which I assume is something like 90S for 350VDC.

Ah, I finally found some specs on wikipedia. Looks like 96S 74P for the 85KWH. Hmm, could that be right? Wikipedia says 7,104 cells in the 85KWH pack. If they are 2500MAH cells that's 7104 X 3.7 v X 2500MAH = 63KWH What am I missing here??

 

[jerry33]

Ah, I finally found some specs on wikipedia. Looks like 96S 74P for the 85KWH. Hmm, could that be right? Wikipedia says 7,104 cells in the 85KWH pack. If they are 2500MAH cells that's 7104 X 3.7 v X 2500MAH = 63KWH What am I missing here??

The 7104 number was a guess from a long time ago. I think actual count has changed that number. Wikipedia, Sheesh.

 

[FlasherZ]

The 7104 number was a guess from a long time ago. I think actual count has changed that number. Wikipedia, Sheesh.

It is 7,104 and that's been confirmed by several Tesla folks.

The cells, however, are not 2500 mAH cells. They are, I believe, based off the Panasonic 3100 mAH cells.

 

[Cottonwood]

It is 7,104 and that's been confirmed by several Tesla folks.

The cells, however, are not 2500 mAH cells. They are, I believe, based off the Panasonic 3100 mAH cells.

The final 96S Voltage for an 85 is around 400 Volts, that means each cell is at 400/96 or 4.17 Volts. The average Voltage is less than that, so if you make the numbers work (plausible values), then:

7104 cells x 3.86 Volts x 3.1 Ah = 85.006 kWh​