Good technical SC explainer?

[kman42]

Is there a good technical explainer on super chargers? One that describes how the charging rates of the different versions are impacted by being crowded? I know the basics of how two neighboring stalls will reduce charging speeds if both are being used, but I can’t find a good explanation of the whole infrastructure from the supply to the charging experience for each version of SC. I tried searching here and google, but must have a brain block on how to find what I’m looking for as I’m sure there are some great articles and posts out there providing minute detail. I just can’t find it. Thanks!

The impetus for my search is that I was at a crowded supercharger and was only getting 30kW at about 30% charge. This is much lower than I expected, even for a crowded station. The Primm, NV station I was at has 32 chargers up to 250kW (v3?) and 10 up to 150kW (v2?). I thought I would get a minimum of 75kW at 30% charge.

 

[RayK]

My understanding is this (if I'm wrong, I know someone will correct me):

• Urban (72kW): dedicated power
• V2 (150kW): shared power, but not always split 50-50 as it depends on who's there first
• V3 (250kW): dedicated power

 

[RTPEV]

It's not just the utilization of the site, but there are other factors as well including your vehicle's battery temperature (is it too hot or too cold), state of charge (charge rate slows down at high SOC), and of course the health of the charger itself (are there charging modules that are down?) and total site utilization.

But concentrating specifically on the Supercharger architecture itself, I'll try to summarize some of the key architectural issues. Hopefully someone will correct me if I get a detail wrong.

For V2 Superchargers:

As you know, each pair of pedestals (e.g. 1A/1B) is served by a single charger. Inside the charger are 8 18kW charging units (actually I think they may be able to each hit 19.2kW, but the math is easier if we assume 18). Those 8 units can be allocated individually to each of the two pedestals, so for example, if there are two cars plugged in, each calling for over 72kW of power, the charger should allocate 4 units to each of the pedestals, giving each 72kW. If one of the cars is nearing completion and drops below 54kW of demand, it can then allocate 3 units to the slow car and 5 to the faster one so they make best use of the available power. There may be cases where the first car connected gets more power, but it's supposed to split the power fairly.

If the total site utilization exceeds the capacity of the grid feed, each of the charging station pairs will curtail the amount of power delivered. For example, if there is a 750KVA (i.e. 750kW) transformer at an 8-stall site, and there are 8 cars plugged in all calling for 100kW+ of power, the site will only be able to deliver a max of 94kW per vehicle (probably less due to losses). More on this in the V3 discussion below.

For Urban Superchargers:

Urban Superchargers are similar to the V2 Supercharger except that each pedestal has its own dedicated 4 units (I don't know if there are actually 4 18kW units, but conceptually it's the same). That means that there is no sharing with adjacent vehicles, but you're going to top out at 72kW.

The same site utilization limitation applies.

For V3 Superchargers:

V3 Superchargers are arranged so that each charger cabinet services 4 pedestals, and can deliver up to 250kW to each pedestal. But, there are limitations!

First, each cabinet has hardware in it that can pull in 350KVA from the grid and convert it to DC. If there were a hypothetical 4-stall V3 Supercharger, it's only going to be able to supply a total of 350kW to the 4 cars plugged in (barring any on-site solar & battery--more on that in a second). An 8-stall V3 Supercharger could hypothetically supply up to 700kW to the 8 cars plugged in (so as you can see, this is far below the 250kW simultaneous capacity that most people think V3 Superchargers have, but statistically it's rare that 8 cars would all be requesting 250kW at exactly the same time).

Now up to 7 V3 Supercharger cabinets do share a DC bus. That means that any excess power brought in from the grid and be shared with other cabinets. So if there are 4 cars all plugged into 4 stalls served by the same cabinet, and all requesting 250kW, the cabinet can pull power from other potentially underutilized cabinets (and any on-site solar & battery). Each cabinet is capable of pulling in 575kW from the shared DC bus, putting the total power that the cabinet can supply to its 4 pedestals at 925kW, just shy of the 1000kW needed for simultaneous 250kW charging. That is, if there is enough excess capacity on the rest of the site.

And as mentioned, on site solar and batteries can supply power to the shared DC bus as well.

And finally, as with the other Supercharger types, there is the total site capacity. A utility will only authorize and install a transformer (or transformers) of a certain size. This is usually the limiting factor if there is excessive utilization.

Hope this helps!

 

[Rocky_H]

Wonderfully, thoroughly explained! I just have a couple of notes:

The V2 sharing methodology seems to have shifted some, so you might hear the "old wisdom" or the "new wisdom". It used to be very much that first come priority, where the first car to arrive got as much power as it wanted, and the second car got the low power leftovers, but I think a minimum of about 30 kW. It wasn't really announced anywhere, but people started to discover in the last few years that it seemed to switch over to an even half and half split if a second car plugged in.

I think this change might have been done by Tesla to shut down the punk move where the owner of the slow secondary car could go over to the primary car, and click the button on their charging handle. This would briefly interrupt it, and then it would reconnect as the secondary car, and the power allocation would reverse. So you could kind of steal someone's charging speed, which would make people angry.

And the sharing locations on V2 aren't always next to each other. It kind of depends on how the contractor thought it made sense. So some were laid out as:
1A 2A 3A 4A 1B 2B 3B 4B
So 2A and 2B are a shared pair, but they are 4 spaces away from each other.

 

[ewoodrick]

My understanding is this (if I'm wrong, I know someone will correct me):

• Urban (72kW): dedicated power
• V2 (150kW): shared power, but not always split 50-50 as it depends on who's there first
• V3 (250kW): dedicated power

And I'd add

Don't assume that the V2 chargers share with the adjacent pedestal. They are all marked with 1A, 1B, 2A, 2B, etc.
Sometimes that are 1A next to 1B next to 2A.
Other times they are 1A next to 2A, next to.... 1B, next to 2B.
Look before parking. And it's always a gamble with the "Who's been there the longest game" because that's the one you want to park next to.

It is not rare to see a pedestal that is underperforming. If you are getting less than expected, feel free t move if another is open.
250kW pedestals should charge at about 1,000mph up to 30-40%
Above that the 250 and 150kW pedestals charge about the same at 500 mph up to about 60-70%
Above that, it's about 200 mph.

But indicating that you are in San Diego and referring to a NM station suggest that you need to get out and test them more.

 

[RayK]

<snip>
But indicating that you are in San Diego and referring to a NM station suggest that you need to get out and test them more.

If your statement is to the OP, then they were referring to the Primm, Nevada Supercharger station, not New Mexico.

 

[ewoodrick]

If your statement is to the OP, then they were referring to the Primm, Nevada Supercharger station, not New Mexico.

Whoops, wrong abbreviation, but my point stands. Not a home charger.

 

[1100MCM]

Now up to 7 V3 Supercharger cabinets do share a DC bus. That means that any excess power brought in from the grid and be shared with other cabinets. So if there are 4 cars all plugged into 4 stalls served by the same cabinet, and all requesting 250kW, the cabinet can pull power from other potentially underutilized cabinets (and any on-site solar & battery). Each cabinet is capable of pulling in 575kW from the shared DC bus, putting the total power that the cabinet can supply to its 4 pedestals at 925kW, just shy of the 1000kW needed for simultaneous 250kW charging. That is, if there is enough excess capacity on the rest of the site.

And as mentioned, on site solar and batteries can supply power to the shared DC bus as well.

And finally, as with the other Supercharger types, there is the total site capacity. A utility will only authorize and install a transformer (or transformers) of a certain size. This is usually the limiting factor if there is excessive utilization.

Hope this helps!

I’m too lazy to look up a source for this but I think the actual number of cabinets that can share the same DC bus is now up to 10. When Tesla started V3 deployment most utilities were using 2500 kVA transformers which would only have capacity for 7 V3 cabinets tied together. Now a lot of utilities can use a 3325 kVA transformer which can support 9 V3 cabinets or 10 if they really want to push that utility transformer to the limit.

 

[RTPEV]

I’m too lazy to look up a source for this but I think the actual number of cabinets that can share the same DC bus is now up to 10. When Tesla started V3 deployment most utilities were using 2500 kVA transformers which would only have capacity for 7 V3 cabinets tied together. Now a lot of utilities can use a 3325 kVA transformer which can support 9 V3 cabinets or 10 if they really want to push that utility transformer to the limit.

Good to know. I figured it was an architectural limit rather than a transformer limit.

 

[israndy]

So 7 cabinets is why there are 28 chargers on the same shared DC Buss and why charge sites when Firebaugh came online were in multiples of 28, so now we can be multiples of 40? So like Coalinga has 80 chargers with the new setup?

 

[1100MCM]

So 7 cabinets is why there are 28 chargers on the same shared DC Buss and why charge sites when Firebaugh came online were in multiples of 28, so now we can be multiples of 40? So like Coalinga has 80 chargers with the new setup?

Some of the earlier large sites like Tejon Ranch Outlets and Firebaugh were built with 7 V3 cabinets per transformer but they did get the two 3325 kVA transformers. This means they left room for expansion and Tesla did take advantage of this since they ended up expanding from 14 to 19 total V3 cabinets at Tejon Ranch Outlets: likely 10 on one transformer and 9 on the other.

Paso Robles and San Bruno - Tanforan were sites built with the 7 V3 cabinets and a single 2500 kVA transformer so there it doesn’t look like Tesla had any future expansion in mind at that same site.