Tesla Semi truck's battery pack and overall weight explored

Discussion in 'In the News' started by turpenaaron, Feb 24, 2018.

  1. turpenaaron

    turpenaaron New Member

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    #1 turpenaaron, Feb 24, 2018
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    The big question on everyone’s mind-at least on the minds of those who understand the freight transportation industry-is how much the Tesla Semi might weigh. If Tesla’s all-electric semi truck is to be competitive at all, it must be capable of carrying the same loads as current-use semi-trucks in the Class 8 field do.

    A big point of contention from nay-sayers and those in the trucking industry who understand logistics was the lack of announcement of the Tesla Semi’s actual weight. Plenty of press was given to the much-touted “80,000-pound capacity” number bandied around by CEO Elon Musk during the truck’s unveiling late last year. That number, however, refers only to the gross vehicle weight (GVW) of the Tesla Semi and is, in fact, exactly the same number used by every Class 8 truck on the road. They’re called Class 8s, in fact, because the 8 refers to that 80,000-pound total vehicle capacity.

    What wasn’t given by Tesla was the gross vehicle tare weight (GVTW) of the Semi. This is a far more important number. Where the GVW gives the total capacity of the truck in terms of how much its freight plus the truck itself can weigh, the GVTW gives just the weight of the truck, sans trailer and freight. This number tells logistics experts how much actual freight and trailer the truck can haul legally.

    For example, a typical “day cab” configuration 18-wheeler with a diesel engine weighs roughly 32,000 pounds with a relatively lightweight box trailer attached and full fuel tanks. That leaves about 48,000 pounds of freight capacity for the truck. That’s important because, although the truck won’t be loaded to capacity every time, it will be expected to be capable of carrying up to about that weight. Most big rigs on the road are capable of hauling 44,000 or more pounds worth of freight, depending on configuration and trailer type.

    Having experience with driving commercial trucks in the past, once hauling a refrigerated trailer that had a freight capacity of 44,500 pounds, I learned that some industries count on freight capacity as part of their logistics costs and will literally fill a truck to its maximum in order to minimize those costs.

    In logistics, weight and total freight capacity are highly important metrics in the overall scheme.

    What We Know

    Thinking about that, then, let’s look at what we know of the Tesla Semi and its potential weight. We know that the truck uses four independent electric motors that are derived from the Model 3, that it has an energy consumption of less than 2 kWh per mile, and that it can be charged to up to 400 miles in about half an hour. We also know that Elon promised 300 to 500 miles of range in total. On that latter point, it’s pretty clear that a “lower range, cheaper option” will be offered as has been done with most of Tesla’s vehicles to-date. So we can assume a 300-mile version and a 500-mile version will be forthcoming for the Semi.

    We also know that the Tesla Semi had eight ports in its charging plug array. We saw this at the unveil in some close-up photos.

    It’s clear to us that even if the Tesla Semi isn’t to become a big player in the trucking industry, the idea behind it will change things forever.

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    What We Don’t Know

    What we don’t know is whether Musk and Co have something up their sleeves for the batteries. Much of the speculation regarding the Tesla Semi has been in regards to Tesla Semi’s massive battery pack.

    In actuality, having a huge battery breakthrough on a vehicle like the Tesla Semi would not necessarily be a good thing for business. If there is a huge breakthrough, then all bets are off and most of our speculation in this article is moot. That would, however, mean that the sales potential of the Semi would be far lower than it would be otherwise because one thing that logistics companies and fleet managers aren’t interested in are flashy new, breakthrough, and (most importantly) untested, unproven technologies.

    To a fleet manager, those phrases mean “breaks often, expensive to fix” and the potential positives will be ignored because of that. No one who wants to keep a job as a fleet manager or logistics purchaser will gamble on something unproven. Like new battery technology for a truck whose primary cost will be in its batteries. Likewise, unless there is a clear benefit in some terms other than pure business (like marketing or potential tax breaks), no board of directors will risk shareholder wrath on new tech either.

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    Close-up look at Tesla Semi’s drivetrain from underneath

    We can say, as a side note, that most of the orders that have been placed for the Tesla Semi thus far are from corporations and companies who are doing business in areas where the marketing bonanza and potential tax incentives for laying down those relatively low-cost deposits are immense. Most of the companies involved have already invested heavily (and very publicly) in alternative fuel options outside of Tesla over the past few years. We also note the timing of both the Tesla Semi’s announcement (and order-taking) and the before-2018 rush by potential customers to put in deposits.

    We reiterate that our not knowing if Tesla has some kind of big battery breakthrough announcement is a big “if” in our analysis here.

    What People Smarter Than Us Have Said

    Some people who know more than we do about things like math and engineering science have crunched the numbers on the Tesla Semi’s battery potentials. Over at Engineering.com, John Ewbank broke the results down into layman format. Here’s the gist.

    If the Tesla Semi uses 2 kWh to travel a mile, then a 500-mile range means 1,000 kWh of power. That is not the actual size of the battery, though, as the charging requirement would preclude a huge pack.

    In order to get 400 miles in thirty minutes of charging, Ewbank notes, the charger would have to be 1.6MW to achieve the 800kWh of promised charge in only 30 minutes. Charging at that rate is not possible because the result would be arching in the pack, which would surely be akin to the next Boring Company Flamethrower meme when Semi trucks begin to explode in flames during charging as a regular event. So the charging has to be split up.

    [​IMG]Tesla Semi Megacharger port could support 1 MW of power.

    The answer is simple, of course, and may explain the strange layout of the eight-port charging hub shown on the Semi at its unveil: there are four battery packs.

    Instead of one big pack, four smaller packs (one for each motor, even) are used and are thus charging separately from one another, but simultaneously. Based on Tesla Semi’s Megacharger port configuration, this would likely mean that four of them are positive sides and the other four are grounds. Allowing for a single, huge wire to be plugged into each. The controls for the charging system interface may be plugged in separately (perhaps the oval-shaped black thing to the side?).

    What This Adds Up To

    We add up that bit of information plus what we know about the truck and get an estimated weight. Using the current weight of a Tesla Model S battery pack at 540kg per 90 kWh, we can do some simple math to estimate the Semi’s batteries would weigh about 6,000 kg. We aren’t sure about the new battery weights for the upcoming battery updates, but we can assume a 10-15 percent reduction from several factors (storage density, improvements in chemistry, packaging lightening) without being too aggressive or overly optimistic. Going with the fifteen percent reduction, that 6,000 kg drops to 5,100 kg. That’s about 11,244 pounds.

    A conventional tractor, as we’ve said, has a tare weight of around 32,000 pounds when fully fueled and with a lightweight box trailer in place. Remove the trailer and the truck itself is about 22,500 pounds. It’s difficult to then go to just the weight of the powertrain components and fuel, but they’re considerably less than 11,000 pounds in all.

    [​IMG]Tesla Semi spotted doing a tire-shredding acceleration run down in the wild

    Looking at the shipping weight for a crated engine and transmission for a Class 8 truck, we can see that they weigh about 8,000 pounds on average. Add in fuel and other components and another 1,500 pounds (at most) are put on the truck. We then assume that the rest of the truck (framing, braking systems, air compressor, etc) are about the same for the Tesla Semi in order for it to meet Class 8 standards. So we call those a wash.

    That means that the Semi, under our estimates, is roughly two tons heavier than would be a standard day cab big truck in the Class 8 category. This means the Semi would be that much less capable in terms of freight hauling that’s offset by its unprecedented all-electric performance. That amount, however, is probably not enough to stop the primary buyers of a day cab truck like this from balking at a purchase. The weight difference alone would be repaid in potential fuel savings, tax incentives, green marketing, and maintenance costs.

    The trouble will come with cost differences. If the ROI is not there, most logistics buyers won’t write any purchase orders. But at least we can say that as far as we can tell, the weight differences of the Tesla Semi alone aren’t going to be a huge bar against entry into the trucking industry.

    Article: Tesla Semi truck's battery pack and overall weight explored
     
  2. TslaRcr

    TslaRcr New Member

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    Good article, but looks like there\'s a math error at the end. Your calculated 11,244 lb for Tesla minus estimated 9,500 lb of a conventional truck, that\'s 1,744 lb = 0.9 tons. That\'s less than 1 ton difference and not 2 tons you mentioned. Does not seem that significant.
     
  3. robert_lukefahr

    robert_lukefahr New Member

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    There are four key things this article glosses over (in addition to the math error mentioned above):1) There are significant potential weight savings from other powertrain components beyond the engine and fuel that will further narrow the difference (e.g. the Exhaust stack)2) The photos indicate that Tesla has been working pretty hard to achieve weight saving new materials in the cab design to offset the battery weight3) There are a great many trucking applications where the operator generally \"cube out\" before they \"weigh out\" (IOW they run out of space before they hit the weight limit e.g. DHL) 4) In very short order this discussion - and even the current truck design - will look like a throw-back to a time when people were required to drive trucks and therefore getting the maximum load was a huge cost savings. If one adds a single vehicle platooning ability, for example, then even a 20% disadvantage in freight hauling weight per driver mile on the first truck suddenly morphs into a 60% advantage in weight per driver mile. The real point of this truck is not to electrify the old way of doing things (except as a bridge) but instead to begin a transition to an entirely different way of hauling freight. 
     
  4. lidiavalenti78

    lidiavalenti78 New Member

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    No, it isn\'t true that \"They’re called Class 8s, in fact, because the 8 refers to that 80,000-pound total vehicle capacity.\" They are called Class 8 because they are more powerful than Class 7 for which the weight limit range is 26,001 to 33,000 lbs. Class 8 trucks can have a gross vehicle weight rating GWVR from 33,001 lbs. and up. A different law limits the maximum interstate highway weight to 80,000 lbs., but it only applies to tractor trailer trucks with dual axles on both the tractor and the trailer located at least 36 feet apart. There are plenty of class 8 trucks that are have much lower ratings. For example, an armored cash-in- transit truck is class 8 but has the GWVR of just 35,000 lbs.
     
  5. Roy_H

    Roy_H Member

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    \"...the sales potential of the Semi would be far lower than it would be otherwise because one thing that logistics companies and fleet managers aren’t interested in are flashy new, breakthrough, and (most importantly) untested, unproven technologies.

    To a fleet manager, those phrases mean “breaks often, expensive to fix” and the potential positives will be ignored because of that.\"

    If this is not \"breakthrough\" new design then it will not be superior to any other offering by other truck manufacturers making electric variants of their existing trucks. This in turn means that the Tesla truck would be nothing special, and every other manufacturer would be saying \"500 mile electric? No problem!\". So I submit your basic premise here is wrong. Why would these conservative fleet operators buy into this new and untried Tesla offering? Tesla is offering a 1 million mile warranty, all service included and a guaranteed low cost of electricity at $0,07/kwh. This will go a long way to ease their concerns.
     
  6. Roy_H

    Roy_H Member

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    One thing that is not addressed here is the price of the battery pack. For a long time now it has been suggested that the holy grail point for auto batteries is $100/kwhr which several pundits claim is still several years away. You calculate that this truck requires a 1000kwhr battery pack, so that would cost $100,000 just for the battery. Can Tesla sell the truck for $180k and make a profit? You give the weight of a diesel engine and driveline but not the cost to compare.
     
  7. Richard Kilshaw

    Richard Kilshaw New Member

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    Didn\'t E.M said that a fully loaded Tesla Semi hits 60 mph in 20 seconds and the tractor alone hits 60 mph in 5 seconds?

    If the gross vehicle weight is 80,000 lbs:
    80,000 lbs = 36287 kg
    60 mph = 27m/s
    27(m/s)/20s = 1.35m/s2
    f=m.a
    f = 36287 kg * 1.35m/s2
    f=48988N

    60 mph in 5 seconds for the tractor alone:
    60 mph = 27m/s
    27(m/s)/5s = 5.4m/s2
    f=m.a
    f/a=m
    48988N/5.4m/s2 = 9072 kg
    Then the Semi tractor weight would be 20,000 lbs?
     
  8. Null

    Null New Member

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    More likely four  200kwh packs...Also forgot the rather extensive after treatment system and tanks.And cooling systems...And oil tank.Zac Reddix on YouTube did a better analysis on weight of Diesel running gear.
     
  9. Roy_H

    Roy_H Member

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    f=ma of course, brilliant! So this brings the truck in at a little less than conventional trucks. I am sure that Tesla examined every part of the truck to see where they could save weight, and of course, I think they have confidence that by the time the semi is in production, they will be building their next generation batteries that beat your assumed 15% improvement.
     
  10. Jan Kjetil Andersen

    Jan Kjetil Andersen New Member

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    Thank you for an interesting article.

    Another way of calculating the weight of the tractor is to look at the published acceleration figures.
    They have claimed that 80 000 pounds accelerate from 0 to 60 in 20 seconds and the tractor alone in 5 seconds. The full semi uses four times as long time as the tractor alone.

    That means that if the engine uses the same power in both cases, which is a fair assumption, the tractor weight must be one quarter of 80 000 pounds, i.e. 20 000 pounds.

    This means that the Tesla tractor has about the same weight as a diesel tractor, which should be impossible with current battery technology.

    I think the explanation is found in the rest of the tractor. Since Tesla has made the tractor from ground up they may have found ways to optimize other parts of the vehicle. The heavy steel frame needed to carry the diesel engine and transmission is for example not needed.

    /Jan
     
  11. J.Taylor

    J.Taylor Active Member

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    #11 J.Taylor, Feb 25, 2018
    Last edited: Feb 25, 2018
    On a truck weight of 32,000 lb, Tesla has to find the 2000 lb difference in the weight of the battery ...
    some things they can do without ...
    Rad and fluid -
    Exhaust system -
    Drive shaft -
    Extra Seat -
    Using 3 batteries instead of S batteries =5% lighter.
    Now could Tesla reduce the weight of some other components by using lighter weight materials? I think they could. So do the folks who did the acceleration comparison math and seem to agree that the weight issue will be minimal or non existent.
     
  12. johnwall13220

    johnwall13220 New Member

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    So where will Tesla build the Semi? Fremont seems to be full with Model S, Model X and Model 3. Gigafactory makes battery packs and subsystems for the Fremont vehicles, and power packs. With deliveries cited as 2019, it\'s already too late to build a brand new factory from the ground up.
     
  13. joaquimnogueira

    joaquimnogueira New Member

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    You based this on the old model s battery not the new model 3. The 2170 has twice the power with 50% more size and weight. Redo the math and include the components you forgot and you now have a truck lighter then a  diesel.
     
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  14. mcdanielp

    mcdanielp New Member

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    To a fleet manager, those phrases mean “breaks often, expensive to fix” and the potential positives will be ignored because of that. No one who wants to keep a job as a fleet manager or logistics purchaser will gamble on something unproven. Like new battery technology for a truck whose primary cost will be in its batteries. Likewise, unless there is a clear benefit in some terms other than pure business (like marketing or potential tax breaks), no board of directors will risk shareholder wrath on new tech either.

    Hmm, all those preorders for a BRAND NEW,UNTESTED VEHICLE WITH NEW CHARGING STRUCTURE. Totally makes your statement look like it came from an idiot.
     

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