Supercharging Pairing and throttling- What am i missing?

[Gregsbeach]

This seems so stupid I must be missing something. I pull into a crowded supercharger with 70 miles remaining on my Model s 85.
There is no unpaired supercharger, so I have to plug in and the system throttled me at 35 KW for the first almost 30 minutes. So I sit in a completely full supercharger taking up one of their precious spaces and charge only an additional 40 miles in this 30 minutes. (I needed 70-90 additional miles to get home safely). Then the supercharger kicks in and starts at 65-85 KW, but then as the miles start rolling it, it starts to throttle me again as I get above a 60% charge. (I know this is to protect the battery and etc). But this means it takes an hour to get a charge to get home.

My Question is: Why doesn't the supercharger let you get MAX KW when you are empty and first pull in? I could have gotten 80 miles charge in 20 minutes (or less) and been gone with no throttling from the supercharger or the battery safety technology.

Instead, we have all these overcrowded superchargers.

In this example, Three cars could have charged in the time I spent charging if they could reverse the pairing/throttling protocol. This alone would triple the capacity and speed of the use of these super crowded superchargers, wouldn't it?

 

[richrootes]

That is a good point - particularly in locations where you are billed by the minute as opposed to per kWh

 

[David99]

What you experience is unfortunately how Superchargers work. If the other car (on the paired stall) is low on the battery, they will draw a lot of power for a while and the other car, in this case you, will get just 36 kW (in theory). The first car gets the fastest rate the car can take (or close to it), the second car gets the leftovers. Once both cars are filling up, the combined power to both cars is probably lower than the cabinet could do and the capacity is lost because it can only share between the two stalls.

The idea of pairing stalls was fine a few years ago. Back then, supercharger sites were hardly busy. Pairing didn't happen all that much. But also the batteries were different. The early batteries had a different charge curve. The power peaked at up to 25%, then it dropped down as the battery filled up. At 50% SoC you only get 65-70 kW. There was a good amount of power left for the second car. In those rare occasions where you had to take a paired stall, the impact wasn't so bad.

Today the situation is different. All newer battery packs keep a high charge of over 100 kW rate all the way up to 60%, leaving only the minimum for the second car. Tesla needs to increase the total power shared by two stalls. The majority of cars today charge at a higher rate. I hope the Supercharger V3 will fix the issue.

But honestly the reason why superchargers are more and more full these days is just the number of cars on the road. Tesla has been selling more cars than they have added superchargers. Hopefully they will catch up and hopefully other charging networks will install EV chargers in large numbers like Tesla does.

 

[derkan]

The other thing they could do today is to consider the target charge level of the paired cars when determining how to allocate power. If I pulled in first and need to charge from 30% to 100%, and am given an estimate of 60 min.. then someone else pulls in and they need to go from 10% to 40% to be on the road again, the system could take that into account.

Also if they want to continue the first come first served method, and I'm about to choose an empty spot on paired stalls they could simply tell me how many minutes are left on each car so I can pick the spot accordingly. Otherwise it feels like russian roulette.

 

[ewoodrick]

Tesla decided, and it does make sense, that a paired Supercharger configuration makes a lot of sense and can help provide fault tolerance if one of the pedestals breaks down.

While I forget the exact number, I'll say that the transformer is built for 140 kW. This is probably dependent on some of the configurations available from the power company and the cost of transformers. (getting a 1000 kW transformer is really expensive). Also, when working with high current applications, you often use a bunch of smaller systems paralled together. Tesla, I believe uses 4 35kW modules to control power.
So, since a limitation was part of the engineering requirements, what should be done? Do we just split in in half? That means that if the site is empty, we are slowing down any car. Do we give one 100% and the other 0%? Not a bad decision, but lots of issues. So, knowing that charging slows down over time, they ended up with 105kW for the first connection (3 modules) and then 1 module for the next car. As the first car starts to slow charge, it releases one of the module and assigns it to the second car, so your charging jumps to 70kW. And then the final one switche

This seems so stupid I must be missing something. I pull into a crowded supercharger with 70 miles remaining on my Model s 85.
There is no unpaired supercharger, so I have to plug in and the system throttled me at 35 KW for the first almost 30 minutes. So I sit in a completely full supercharger taking up one of their precious spaces and charge only an additional 40 miles in this 30 minutes. (I needed 70-90 additional miles to get home safely). Then the supercharger kicks in and starts at 65-85 KW, but then as the miles start rolling it, it starts to throttle me again as I get above a 60% charge. (I know this is to protect the battery and etc). But this means it takes an hour to get a charge to get home.

My Question is: Why doesn't the supercharger let you get MAX KW when you are empty and first pull in? I could have gotten 80 miles charge in 20 minutes (or less) and been gone with no throttling from the supercharger or the battery safety technology.

Instead, we have all these overcrowded superchargers.

In this example, Three cars could have charged in the time I spent charging if they could reverse the pairing/throttling protocol. This alone would triple the capacity and speed of the use of these super crowded superchargers, wouldn't it?

Tesla decided, and it does make sense, that a paired Supercharger configuration makes a lot of sense and can help provide fault tolerance if one of the pedestals breaks down.

While I forget the exact number, I'll say that the transformer is built for 140 kW. This is probably dependent on some of the configurations available from the power company and the cost of transformers. (getting a 1000 kW transformer is really expensive). Also, when working with high current applications, you often use a bunch of smaller systems paralled together. Tesla, I believe uses four 35 kW modules to control power.

So, since a limitation was part of the engineering requirements, what should be done? Do we just split in in half? That means that if the site is empty, we are slowing down any car. Do we give one 100% and the other 0%? Not a bad decision, but lots of issues. So, knowing that charging slows down over time, they ended up with 105kW for the first connection (3 modules) and then 1 module for the next car. As the first car starts to slow charge, it releases one of the module and assigns it to the second car, so your charging jumps to 70kW. And then the final one switches.
For urban chargers, often in malls and parking garages, they decided to change the behavior and always allocate 2 modules to each vehicle.
If you do some math, you'll find that at a standard Supercharger, the first car will always charge at full pace. The second car will take no longer than if the power was equally split. So while the second doesn't charge as fast as a single, it generally does charge faster than an urban charger.
Moral of story: Always study the drivers at a full Supercharger and see who seems to

​

 

[David99]

While I forget the exact number, I'll say that the transformer is built for 140 kW. This is probably dependent on some of the configurations available from the power company and the cost of transformers. (getting a 1000 kW transformer is really expensive). Also, when working with high current applications, you often use a bunch of smaller systems paralled together. Tesla, I believe uses 4 35kW modules to control power.

A Supercharger site usually has a 500 kVA or larger utility transformer. 140 kW is less than one cabinet serving two stalls needs.
Inside the superchargers are smaller chargers working parallel. They use 12 kW chargers in groups of 3 to ensure that all three phases have equal load. There are 12 chargers in each cabinet in 4 groups of 3 each. A group of three is switched together 'as one'. That'w why we see limitations of 36. 72 and 108 kW when paired. Urban Superchargers have a fixed split of 2 groups of 3 each = 72 kW.

How pairing at Supercharging works

 

[ucmndd]

My Question is: Why doesn't the supercharger let you get MAX KW when you are empty and first pull in?

If you were only pulling 35kw, it's because the car next to you was also very low on charge and was running basically full-tilt, but that car had priority because it arrived first. You got what was left, handed over in ~36kw increments (as described by @David99 above).

I suppose we can debate the merits of whether or not the charger should bleed some power off of the person who got there first to give you a bigger boost, but I don't see that doing much to ease congestion and adds all sorts of complexity to the "first come first served" model that everyone can at least intrinsically understand.

The Urban Supercharger sort of addresses this - 72kw for everyone. Maybe switching the high-powered sites to a similar model, such that all stalls get at least 72kw instead of at least 36, is an idea to consider. But again, I'm not sure it would actually do anything to ease congestion and get the majority of people on their way sooner.

 

[David99]

I believe the urban chargers have the 72/72 split because they are used mostly by locals to fill up while shopping. People are using them frequently. The lower peak power is probably easier on the battery and the slower overall charge rate matches more then typical length of someone shopping in a mall. Long distance superchargers are supposed to deliver the highest possible charge rate to make the stop as short as possible. But as we see, even the superchargers along major travel routes are getting congested. The power sharing starts to become more of an issue. This has been discussed many times here. You can optimize power delivery, queuing, give drivers more info to avoid slow stalls and so on, but at the end it comes down to not having enough power for the amount of cars needing to charge. Now the problem compounds. The system slows down because of the high demand. The throughput or cars slows down, making the problem even worse.

Power sharing between two stalls doesn't make sense any more when one car can draw 90% of the total power for the majority of the time it needs to charge. A LR Model 3 or a 100 Model S/X plugging in at a supercharger with a low battery will render the paired stall painfully slow. If a second car arrives shortly after the first one, it gets aprox 1/4 of the charge speed for the next 20-30 min totally defeating the idea of a supercharger. Splitting the power differently doesn't help at all. What you gain for one car is taken away from the other. Only higher power per stall can help in this situation.

 

[animorph]

Tesla could have made unpaired Supercharger stalls. You could have waited in line for an empty stall (half as many) and received 0 kWh during your wait. Or they could have made it an urban charger and given everyone 72 kW. Paired stalls are not terrible and do provide redundancy. But as noted the newer batteries can charge at full power for quite a while.