Tesla Semi Trucks Supercharging At Rocklin – Here Are The Details

Tesla Semi supercharging


Tesla Semis

Tesla Semi trucks reportedly charging at the Rocklin Supercharger station

It appears the Tesla Semi trucks likely did need a charge on the trip, and here’s why.

Last evening, we reported that the Tesla semi was recently spotted charging at the Rocklin Supercharger station. Rocklin is east of Sacramento, California. On the way from Fremont to the Tesla Gigafactory, Rocklin would be just before Donner Pass, assuming the semi trucks are traveling from Fremont to the Gigafactory.

RELATED Tesla Semi Spotted Supercharging En Route To Fremont

According to an ongoing thread at Tesla Motors Club, the drivers have said that the trucks are both 300-mile range versions. A recent post on the TMC forum states:

“When I spoke to the driver in Rocklin, he mentioned going “back”, so I I took it that he meant back to the gigafactory after dropping off at Fremont. I didn’t feel like interrogating him, they were pretty busy checking stuff out on linked up laptops and what not. He was very clear about BOTH trucks being the smaller battery versions though.”

My engineering partner, Keith Ritter and I developed a computer model for that exact that route. This model was described here in figure 5.

Our modeling shows that the kWh burn to get to the top of Donner Pass is 587 kWh’s. Our numbers seem to agree with what another poster on the TMC thread calculated (560 kWh’s).

We also estimated that the 300-mile range truck has a 510 kWh battery.  That size pack would be insufficient so it seems logical that they would stop to charge in Rocklin prior to going over Donner Pass if they are indeed running loaded to 80,000 lbs. on the way up AND if these are only 300-mile range trucks.

Hopefully, more information will come in soon and we will be able to report on the status of the trip as a whole.

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33 Comments on "Tesla Semi Trucks Supercharging At Rocklin – Here Are The Details"

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Wouldn’t the 300 mike truck need close to 600 kWh?

I wonder if that was Daimler’s point about physics and weight/range. Their electric truck assumes 125 miles on 210 kWh which is a higher ratio than Tesla’s.

There are “back of the envelope” calculations and there are “three pages of spreadsheet” calculations. Our calculations are the latter. We set up a sophisticated spreadsheet-based dynamic modeling tool that calculates aerodynamic drag, rolling resistance, expected accessory kW demand (pumps, power steering, air compressor), and elevation changes where applicable to estimate both instantaneous kW power requirements at various waypoints of the trip and cumulative kWh consumed at various waypoints. It uses vehicle weight, aero drag Cd and frontal area, rolling resistance coefficient, motor HP& torque, gear reduction ratios, tire size, and other relevant specs as inputs.

The model estimated the 500 mile-range Semi kWh consumption at 1.8 kWh/mile – for about 900 kWh of battery. Because the 300-mile-range Semi tractor has a smaller battery, it is about 4,000 lb lighter than the 500-mile range semi. This reduces rig rolling resistance losses which improves the energy efficiency to 1.7 kWh/mile, or 510 kWh battery.

FWIW the Daimler Vision One concept actually claims 215 miles of range off of 300kWh. At that rate 500 miles could be done on a bit less than 700kWh.
The payload would in theory be reduced by the weight of the additional 400kWh of batteries but isn’t it Daimler that has fairy dust and unicorn farts that no one else has access to? Why no claims of snake oil and smoke and mirrors for Daimler? Any explanations other than there are many more dollars shorting Tesla than Daimler?

A 5% weight reduction reduces road load 5%? Hmmm…..

Too much thinking, For in House tesla transporting battery there should make a trailer that transport new battery that are plugged into a trailer as they getting transported so the truck could use power from the battery that is transporting, on the way back use the battery that is in the truck. so as the new battery is getting loaded for transport it charges the truck battery as the truck is on the way to the destination, No charging station necessary. So Truck transporting batteries would never need to stop to get charged. Transported battery for cars would be transported fully charged by solar panels on gigafactory. So that is my idea of dooing it.

Hmmm, très smart! So simple I hadn’t though about it. Wonder how that would fit in with waranties, safety regulation, cooling requirements, etc, … but in principle, a good idea indeed. Send to Elon, I would say.

There’s “back of the envelope”, “3 pages of spreadsheets”, and “real world”.

Unless you know ambient temperature-humidity-pressure along the way, motor efficiency curve + transmission losses (across two different gear ratios for the two pairs of motors), battery temperature, and about a dozen more variables, you’re still shooting in the dark. Remember even rolling resistance changes as tires heat up.

Really only data acquisition across a set of boundary variables is the only way to establish true performance metrics.

125 miles on 210 kWH implies 504 kWh for 300 miles. Their estimated extra 6 kWh could be for the extra weight of batteries.

The trucks were followed to I-80 and they turned West towards Fremont after visiting Rocklin not east to Sparks.

What is still unexplained is why the trailer is different just the day before as the trucks were leaving Sparks. No one seems to have thought to ask if the trucks were carrying a load or empty.

So its 260 miles between the Gigafactory and the Fremont Factory. 40 mile buffer on the first trip with load would make me nervous! Guessing the drivers got some valid range anxiety.
Publicity wise, much better to charge up than to run out somewhere in Fremont.

Reno is 4500′ elevation
Donner summit is 7000′ elevation
Fremont is essentially sea level.

Fully loaded coming to Fremont still has to climb 2500′, and going back the full 7000′
That adds to the range anxiety for sure.

Not to mention if they had a tailwind, or headwind. That could have a huge impact.


But they may be running empty, or at least with only a partial load, on the return trip from Fremont to Gigafactory One. Battery packs go from Gf1 to Fremont, not vice versa. Of course, there may be supplies or parts that need to go from the Fremont assembly plant to Gf1, but I don’t know what those would be.

If the trucks are running empty, or with a light load, then they may not need a stop for recharging on the way back, even with the higher elevation at Gf1.

They are going to the GF loaded? If they were going back empty this would work.

No, I meant the full elevation, not fully loaded. Assumption is they are empty or much less loaded when returning to the GF in Reno, though they could be bringing raw materials up from the ports in the Bay Area.

HAHA, the guy who zzzzzz calls the village idiot told me it was impossible for a Tesla Semi to use a supercharger.

If so, maybe they’re just there for the view.

Zzzzzzz calling anyone the village idiot is the pot calling the kettle black.

Zzzzzzz should just stick with zztops.

I’m not particular: Truth is where you find it.

These are NOT production vehicles. There are no megachargers on the highway now, therefore they set them up to be able to use the supercharger.

I wonder if the trucks are carrying some sort of voltage converter or transformer? I wouldn’t expect those to be installed in the production units, but perhaps they are carrying such units in the cab of these prototypes, if they’re not too big. Or, alternatively, as you say, perhaps these prototypes are built to be able to use Superchargers, if Tesla has not yet installed any Megachargers.

At the Semi Reveal, besides the much focused on, and so often mentioned ‘Megachargers’, Elon also mentioned the Semi would also get its own ‘Destination Charger’ network. Is it not possible this would be a similar slower charger capacity as are currently provided for cars? So, max Destination chargers currently being about 18 kW, vs the current Supercharger at 120 kW, or 15% of SC rate. If the Semi ‘Megachargers’ are at the oft mentioned 1.6 kW charge power, 15% of that would be 240 kW, and so currently, Supercharge rate for Tesla cars is about half of that. Based on this, it seems possible the Supercharger, might be just the right thing to use for now, as they complete a few Semi Destination Chargers, and their first Megacharger. I would bet, since Tesla HAS sold a few private Supercharger units (1st ones in Jordon, maybe 1 in Moscow), that buyers could choose a current Supercharger, or a new Semi Destination Charger, to install at home bases, and if such Semi Destination Charger used the large 8 Pin port, the Semi also has, and may include, a current Supercharger Port, for charging Flexibility! Also, it would be the practical thing… Read more »

My guess is that most if not all Megachargers will be privately owned and operated, not publicly accessible. Trucking fleet owners are going to want to ensure that their own trucks will be able to use them when needed, and not have to wait for others to finish charging. So, I think it likely that the setup for Megachargers will be more like Destination Chargers, altho of course with much higher DC power output.

Interesting about Tesla Destination Chargers for the Semi Trucks. I hadn’t read that before; thanks for the info! I also appreciate you giving figures for charging power in your comments. You are just speculating of course, but it’s well-informed speculation!

Given your experience with electrical engineering, Bill, perhaps you can make yourself useful (instead of just posting insults) by answering the following question: If these Tesla Semi Trucks had to carry onboard a voltage converter or transformer, one which would allow them to use a normal Supercharger, would that unit be small enough to fit into a storage space in the cab?

“If these Tesla Semi Trucks had to carry onboard a voltage converter or transformer, one which would allow them to use a normal Supercharger, would that unit be small enough to fit into a storage space in the cab?”

Yes, it could fit. But ultimately it is about power. Up convert Voltage can be done easily, but the total power won’t change.

So if Supercharger is pumping out 125kW with 400V and 312.5A, then 125kW is what you will get at the Semi.

If you double the 400V to 800V, then your current will drop by 50% to 156.25A.

That doesn’t even include the copper loss.

What Tesla can do is to charge the multiple on board packs in parallel.

If the battery pack of the semi is essentially a modular assembly of 3 or 4 Tesla battery pack from the car, then each can be Supercharged individually and rebalanced later. (assuming it can reach 4 charging cables at the same time).

(Or if each pack drives each motor individually which would make it modular and cheaper to build).

Pushi: I didn’t insult anybody. zzzzzzz offered his opinion, and I made an objective observation originally that perhaps the SuperCharger network could be used in a pinch. That’s all I said. As far as anything else goes, these days, anything can be economically changed into anything else but to answer your SPECIFIC point here I don’t think anything even as minimally involved as that needs to be done. A semi-analogous situation is the ‘level 2’ chargers in a car for the North American Market will run on 120 or 240 volts without flipping any switches. The car just charges, and most of these units DO NOT have any specialized dual-voltage switching. The Up-converter just works ANYWAY, being turned on and off at a 100 or 120 cycles per second rate depending on which side of the Atlantic the car is being used. The tiny filter capacitor in the unit *IS NOT* large enough to keep riding through zero-cycle operation and is there to filter choke ripple current ONLY. Point of the last paragraph is that the units work ANYWAY. But my basic point that I make on all these comments is SO LITTLE INFO has been publically released regarding Tesla’s… Read more »

Yup, the extreme speculations, gawking, tailgating and filming of a proto semi are mind boggling.

A cool truck but still a truck nonetheless. No reason to ever own one.

Having said that, it stands to reason that if it uses TM3 motors, the pack voltage should be the same. So a Megacharger is probably several Superchargers in parallel. Thus it can Supercharge. Who cares how accurate this is anyway?


Sure, I understand that doubling the voltage won’t increase the kW (power) rating at all. (In fact, there will be a slight loss from inefficiency.) It’s going to take a lot longer to fully charge a Tesla Semi Truck at a Supercharger than it would at a Megacharger. But if Tesla has not yet installed any Megachargers along the route between Gigafactory One and the Fremont assembly plant, it’s understandable why the Semi Trucks would need to stop at a Supercharger station.

You can’t get something for nothing, and Superchargers can’t defy the Laws of Thermodynamics!

I admit to being surprised that Tesla apparently hasn’t yet installed a Megacharger along the route. I figured they would already have done so to support previous road tests.

ModernMarvelFan said:

“If the battery pack of the semi is essentially a modular assembly of 3 or 4 Tesla battery pack from the car, then each can be Supercharged individually and rebalanced later. (assuming it can reach 4 charging cables at the same time).”

Sure, that’s the main reason why I previously claimed that Tesla Semi Trucks would not charge at Supercharger stations. Obviously I was wrong about that, but I still doubt we’ll see pictures of a Semi Truck sitting like a spider at a Supercharger station, with cables extending from four, six, or eight Superchargers plugged into a single truck!

Possible, yes. But rather awkward, not to mention getting Tesla car owners ticked off at them for tying up multiple charging stalls.

Rocklin is not “just before” Donner Pass. Rocklin is just out of Sacramento… not even in the foothills yet. Donner Pass is at the crest of the Sierra Nevada.
Just saying.

“Here Are The Details”

And here I was hoping to learn how they plugged in the superchargers, whether they used only one or perhaps two in parallel, for how long they charged, etc.

Meanwhile, Google’s autonomous trucks are doing deliveries their own data centers:


Seven you seem a little slow as we are taking about electric trucks not autonomous trucks. But when this is the only way you can try and different attention away from Tesla electric semi it just smacks of desperation. Then again most fudds and shorters are pretty desperate and slow to begin with.