Fast charging in hot weather, slowdowns

[AndysComputer]

I made a comment on another thread that fast charging does not slow due to hot weather, but my experiences yesterday now suggest otherwise…
In the past I have only needed to fast charge once in a day as I hasn’t travelled that far, but yesterday I needed to cover over 400 miles.

I left home with a full charge and travelled via highway to a distant charger arriving with 7%. Or I would have if I had not missed the exit and had to u-turn at the next one which resulted in me arriving in 0%!
On the first attempt I got a time out error, but on the 2nd at the same machine it worked and I charged up eventually hitting 49kW as I approached 80%.

I unplugged and drove at speed on the highway to the next charger, arriving with 15% where I plugged in and it worked first time but only hit 32kW. After charging up to 45% I switched machines but got the same 32kW which did not increase even to 80%.
I left, driving back ti the original charger, arriving with maybe 17%. I used the original machine which after 3 attempts would not start charging due to a ground fault. I switched to another machine which would not read my card in 3 attempts, so switched to yet another machine which had no card reader. Using the app instead it initialized on the first attempt but again I never exceeded 32kW.

I left there on 80%, hit the highway for a spirited drive to the final charger, arrived on 19%, and after initially pulling up at a down machine, initiated a charge on the 2nd, again at a 32kW peak all the way to 80%.

From there I drove home, arriving with 4%.

The whole day was 39/40degC, around 102-104f, and the shutters were open with fans running when charging.

So only the first charge was at full speed…

 

[Puppethead]

So only the first charge was at full speed…

An air temperature of 104 ºF isn't really unreasonably hot. I suspect it's more likely the chargers that are slow, not the SE. I don't know if you were at EA chargers, but I know they have coolant in the cables, that's why they are so thick and heavy (other fast chargers may be similar). And if the black cables are really warm from being in the sun I could see the coolant not being able to dissipate all of the built-up heat. Also, the Texas power grid is not one of the most reliable.

 

[AndysComputer]

The reliability of the grid doesn’t come into it, especially as all the charging was in Oklahoma.
The first charger was a 200kW unit belonging to a Francis Energy and the car charged at full speed.
The second was an Electrify America at Walmart, a 150kW unit. It would not exceed 32kW, and a second 150kW unit at the same site was the same.
The third session was the same site as the first and while a different unit was also rated at 200kW but the car only got 32kW.
The fourth session was a different Francis Energy site and was again a 200kW unit but again, only 32kW.
If the EA site did better I’d accept it was an issue with all the Francis Energy machines or sites. But the fact EA had the exact same speeds leads me to believe the car is the problem, not the site or machine brand.

 

[Aquavir]

Is it possible that the utility has the option of throttling the chargers during peak demand? I have that setup with my home EVSE (got/get a rebate for letting them have access). When they are throttling is like a level 1 charger.

 

[teslarati97]

The reliability of the grid doesn’t come into it, especially as all the charging was in Oklahoma.
The first charger was a 200kW unit belonging to a Francis Energy and the car charged at full speed.
The second was an Electrify America at Walmart, a 150kW unit. It would not exceed 32kW, and a second 150kW unit at the same site was the same.
The third session was the same site as the first and while a different unit was also rated at 200kW but the car only got 32kW.
The fourth session was a different Francis Energy site and was again a 200kW unit but again, only 32kW.
If the EA site did better I’d accept it was an issue with all the Francis Energy machines or sites. But the fact EA had the exact same speeds leads me to believe the car is the problem, not the site or machine brand.

Francis Energy should be using BTC Power's HPCD1-200 dispenser. While the dispenser is rated at 200kW, the power box cabinet is 150kW (3 x 50kW modules) and would only allocate a single 50kW module to your MINI. Factor in all the heat and efficiency losses and you would be for sure less than 50kW received by your EME during your DC fast charging session.

It's really stupid how you can say the dispenser can handle 200kW to 350kW but the big cabinet only has 150kW available!

 

[Not me]

Is it possible that the utility has the option of throttling the chargers during peak demand? I have that setup with my home EVSE (got/get a rebate for letting them have access). When they are throttling is like a level 1 charger.

Not likely. You'd be seeing a lot of news about all the 200+ kW car owners in an uproar if that ever happened. I also saw a max of ~32 kW from an EA charger yesterday in 100°F heat, so if I had to guess it's a temperature switch in the car.

Not sure what day you were charging but if it was yesterday (Sunday) that daily peak is much lower than any weekday peak. To grid operators, even a dozen EVs pulling 150 kW at a station is peanuts compared to what some of the C&I customers pull.

 

[AndysComputer]

It was yesterday I experienced this, yes.

Good suggestion, but...

While site power can be a limiting factor, I was the only one there.
So I would assume a site with 4x200kW (actually 4x 150kW as helpfully pointed out by @teslarati97 ) with only one person there should have no trouble providing 50kW total to that person. Even if they were throttling the site due to grid demand, going from conservatively say 500kW at the site to 32kW seems a bit much, what's that a 93% drop? Seems excessive and would cause uproar.

Also, the EA site had two cars in it at one point, me on a 150kW unit and a new Mercedes EQS on a 350kW unit (after I helped the new owners out). I Was getting 32kW when they plugged in and they were getting 170kW so at the EA site at least there was no throttling I could see.

I am convinced the car cannot keep its small but hot (I am assuming it was hot or at least very warm when I arrived) battery cool enough to pump 50kW into it (and they are pouch cells which are not as easy to cool as cylindricals I think?). The fact it worked on the first charge is interesting as it was probably 2pm when I charged it so it was already hot in the day, so I'm thinking it was able to handle it but the battery which was probably not hot when I arrived, was by the time I left. And with the cars cooling loop working hard to keep the cabin cool it didn't have much spare capacity to bring the temperature of the pack down as I drove at 75mph to the next charger. That's as far as my thinking takes me anyway...

 

[teslarati97]

So I would assume a site with 4x200kW (actually 4x 150kW as helpfully pointed out by @teslarati97 ) with only one person there should have no trouble providing 50kW total to that person

For greater clarity it's 1 cabinet (3 x 50kW modules for 150kW total) in the "fenced off area" which supplies to 2 dispensers (either 4 CCS1 OR 2+2 CCS1/CHAdeMO rated at 200kW) per BTC Power. In theory only a single vehicle DCFC session (no other cars charging) could hit 150kW, but Francis Energy can prioritize how the 50kW modules get distributed between dispensers.

 

[Puppethead]

You'd be seeing a lot of news about all the 200+ kW car owners in an uproar if that ever happened.

Do any BEVs actually charge at rates that high for more than a few minutes? One thing I think the SE has going for it is the really good charging curve, achieving really close to the full 50 kW for a significant part of the charge.

 

[Not me]

Yeah, we're on the same page, I'm talking about a theoretical dozen EVs at a site not making a dent in a grid's capacity - some C&I customers pull hundreds of megawatts without toppling the grid, & no charging station would ever be constructed that could possibly pose a risk to the grid. I was also the sole car charging yesterday & saw the same thing, although I left the AC off & sat in the shade. You're right, t's definitely our car limiting the charge, but it's a mystery as to exactly what conditions that'll happen (e.g. what temps of what components while running/not running climate control trigger the reduction).

In any case, the best informed action we'll get to take is "expect slower charging speeds when it's hot". At least we know how much slower to expect.