March 8th, 2019 by Dr. Maximilian Holland
On Wednesday night, the eagerly anticipated Tesla Supercharger Version 3 (V3) technology was unveiled, allowing the Model 3 Long Range to receive peak charging power of 250 kW! That’s well beyond the power levels expected by seasoned Tesla tech analysts (myself included). What does this all mean? Let’s dive in and discuss this new Supercharger technology.
In this article I want to outline some initial analysis of V3 and discuss some of the implications. I’m going to look separately in a coming article at what it means in practical terms for charging times on road trips and the like. In short — Tesla is obviously giving us EV technology that smooths away residual friction for fossil-driving folks considering whether or not to make the jump to an electrifying transportation life.
Estimated Charging Curve
Let’s dive in first with some modeling of what the charging curve of the Model 3 Long Range on Supercharger V3 might look like (and compare it with the maximum charge power recorded on Supercharger V2):
Allow me first to note that I’ve called this an estimated charging curve, and called the current Supercharger parameters “Beta.” There are a couple of reasons for this: Tesla’s blog article about V3 makes it clear that the company considers the present hardware and software settings to be a public beta, and it is looking to “review and assess” the early results before rolling out more hardware and potentially tweaking the software and parameters next month. The other reason for sticking on labels of “Beta” and “Estimated” are that the announced (and 3rd party documented) Supercharger V3 parameters have come as a big surprise to me and other Tesla hardware geeks. One well known and highly regarded Tesla community geek and detective (whose name we will gracefully not speculate on) said to me “how is that possible?” Personally, I was predicting peak charging on Model 3 of not much more than 160 kW, and “never” more than 175 kW! I’m going to have to stick some small print on my Tesla hardware predictions from now on. 😉
The charge curve I’ve modeled above is based on what we know so far:
- Maximum peak power is 250 kW on the Model 3 Long Range.
- This corresponds to a peak of “up to” 1000 miles added per hour charging.
- 5 minutes of (sweet spot) charging gives up to “75 miles” of “peak efficiency” range (likely EPA city range), which is slightly less than gained from 5 mins @ 250 kW and the “1000” rate (above).
- Thus, we can deduce that 250 kW is a short peak lasting a little under 5 minutes.
- Videos (including 3rd party videos) suggest 250 kW peak power starts somewhere before 10% state of charge, and sub-5 minute duration points to likely taper starting not much beyond 20%.
- Videos show that the Model 3 screen estimates charging from low levels to 80% still takes around “27 minutes” and to 90% takes “35 minutes.”
- Thus, we know that after the short peak, there is still significant power taper at higher states of charge.
The curve is a decent fit to all of these parameters (I’ve run the numbers in geek-level detail on the spreadsheet that generated this curve). Obviously, this curve (as well as Tesla’s above factoids) specify peak performance (“up to”) under ideal conditions. You’ll rarely hit all conditions in the real world for perfectly optimal charging — but if you do, the result could be something like this curve.
However, as I noted above, Tesla may anyway tweak the parameters it has so far specified, based on results of the Beta testing. There are also alternative mild variants of the above curve that could give a similarly close fit to the parameters. I should add that charging from the typical 10% starting point to a high of 80% can take just under 25 minutes — significantly faster than on V2 (around 33–35 minutes). Note that the maximum recorded charge power values on V2, as indicated in the orange dotted curve, come from the data gathering and research of our friends over at A Better Route Planner (ABRP).
As a final note on the curve shape, aside from the unprecedented power levels, the profile characteristics (especially the very early peak) do have precedent in a Tesla. Check out the charge profile of the older Model S 70 kWh battery pack (again from ABRP data gathering):
What Does It All Mean?
Designing an early high peak of the charging power is a smart strategy by Tesla for a number of reasons. Most importantly, it is the safest way of charging quickly whilst protecting the battery — the power still tapers steeply back to well established power levels after 50% state of charge, to prevent over-stressing the batteries.
We know the Model 3 Long Range battery pack is good for 330 kW of peak power output, so 250 kW (for a short period of under 5 minutes) is within reason. Tesla by now has extensive data and knowledge about the performance of these batteries over long periods and diverse conditions and use cases. The early peak power is more efficient since, on a given charge session, a good proportion of owners will often need only a given amount of additional range to complete their journey — and not need to recharge all the way to 70% or 80% (or more), when 40 or 50% may be sufficient.
Front-loading charging power and added range in this way is more efficient overall than delivering the peak power at 60–80% state of charge as many other EVs do. This happens mainly because most non-Tesla EVs spend the majority of the charging cycle at power levels that are in fact limited by the maximum current (amps) of the charging hardware, and the pack voltage — which cannot be adjusted post-hoc — is gradually climbing throughout the charge session. Recharging a battery is by definition lifting its voltage back to maximum potential difference (volts). As a consequence, on a charger whose current is maxed out for most of the charging session, the peak power is necessarily somewhere in the second half of that session, when the voltage is closing in on its peak. Newer and more powerful public chargers are improving this by moving to much higher levels of current (amps) delivery, up to 500 amps in many cases. This may allow some EVs to change the shape of the charging curve. Tesla designs both the vehicles and the chargers, so can have a more coordinated approach to this optimisation task than any other EV maker can.
Amp It Up!
Whilst we’re on the topic, this question of current (amps) is the main reason for surprise about the Supercharger V3. Let me explain. The Model 3’s battery pack has a nominal voltage of around 355 volts. Nominal battery voltage is usually somewhere near the midpoint of full charged voltage (high) and fully depleted voltage (low). For lithium-ion chemistry cells, this often varies between roughly 4.2 volts when full and roughly 3.0 volts when discharged, with a nominal value around 3.6–3.7 volts (i.e., the full voltage range is roughly 15–20% above or below the nominal value). For the Tesla Model 3’s overall pack with 355 volts nominal, this suggests that when charge is depleted, the pack voltage is likely around 300 volts, and when full, around 410 volts.
If this is correct, then the 250 kW of peak power is delivered to a nearly empty pack whose voltage is likely somewhere in the range of 310–320 volts. Since watts is a function of volts * amps, to achieve 250 kW at ~315 volts, the peak current has to be somewhere close to 800 amps, which is unprecedented for EV charging! Geek forecasters were under the impression (on the basis of solid evidence) that the Model 3 had hardware limits of around 525 amps. Something approaching 800 amps (even for a very short peak) was well beyond any expectation. Bear in mind that the designed-to-be-futureproof CCS 2.0 charging specification (that the Model 3 in Europe is compatible with) currently taps out at 500 amps. 800 is a big number and a big surprise.
The Supercharger V3 hardware is reportedly also capable of delivering up to 500 volts (though likely not simultaneously with 800 amps). This bodes well for future Tesla EVs that may boost pack-nominal voltages up by 20% or so. If you’re interested in the possibility of Tesla raising pack voltages, I discussed this in another recent article looking at Supercharger V3 (much of which now looks hopelessly low-ball, given what has transpired)! The Audi e-tron and Jaguar I-PACE have nominal pack voltages of around 425 volts.
What else can we say about this elevated peak power? In V3, peak power is assured because the system design gives dedicated power to each stall, not kilowatts at risk of being shared (and reduced) by the back-end power cabinets having to do double duty across two stalls. The Model 3 will also have a pack-preconditioning feature that will attempt to get the pack close to the ideal temperature for high-power charging when the vehicle knows you are heading for a Supercharging session. This allows the pack to receive higher power levels than would otherwise be sensible (for pack health and longevity).
Tesla has said it expects the average Supercharger session duration to be reduced by around half. This leads us to another reason why early peak power is a smart strategy by Tesla. The expectation of halving average charging duration is not because the average charging power has doubled over the entire charging session (it is only double for the first 20% to 30% or so, then gradually approaches the V2 charging regime, and is not much different from V2 from 50% state of charge and above). No, the prediction of average charge duration being halved is because, unlike on V2, early peak power means substantial enough range for a decent onward drive can now be gained in 15 minutes (and then obtained again in another 15 minute break at your next rest stop). On V3, staying much longer is actually not the fastest charging strategy for drivers, compared to getting back on the road taking another short break again later. How much range is added in 15 minutes? If the above curve is roughly correct, when starting from 10%, the Model 3 Long Range can add a little over 54% of battery charge in 15 minutes under prime conditions. 54% translates to 176 miles of range around town (EPA city rating) and even on the highway 54% is close to 160 miles of range (EPA highway rating) in decent driving conditions.
Front-loading the peak power is therefore not only better for the pack and for trip planning efficiency, but it will also encourage folks to move on relatively quickly. After all, the tastiest juice is in the first 15 minutes or so. Much beyond that and you may as well get going and have another quick rest break in 2 to 3 hours. For folks to be happy to move on quickly obviously allows much more use out of each Supercharger, serving many more customers. Smart and efficient.
The Supercharger V3 is more than many of us anticipated. With huge current (amps) capability and a good evolution of voltage, I’m frankly really impressed by it. The power levels that Tesla has managed to push the Model 3 Long Range to are even more surprising. We don’t yet know what power the other Model 3 pack sizes will be capable of charging at, but there’s every reason to expect they will at least regain equivalent percentages of their total pack energy for comparable charging duration, if not the same absolute amounts of energy as the Long Range pack. We also don’t yet know the power levels the S and X will be pushed to on Supercharger V3 (the limitation is evidently not in the V3 charging hardware, but might be in the S and X battery packs).
Personally, I’m optimistic that the 100 kWh battery packs will see a much increased charge rate on V3 (I’ve discussed this previously), though perhaps not quite as dramatic an increase as the Model 3 sees. Given recent events outpacing some of my earlier predictions about V3, I’m not going to make any more forecasts either way right now. Let’s see what more we can learn. No doubt, Tesla will find a way to surprise us again.
If you spot anything here that doesn’t add up, or you have some considered thoughts about all of this, please jump into the comments.
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