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Class 8 trucks going down mountains with full battery

Discussion in 'Technical' started by constraint, Sep 24, 2013.

  1. constraint

    constraint Member

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    #1 constraint, Sep 24, 2013
    Last edited: Sep 24, 2013
    I was discussing the electrification of Tractor Trailers as an academic exercise with one of my friends the other day and we came up with a question that neither of us had a good answer for. For an ICE truck, when going down hills everyone knows that semi's use engine breaking as to not overheat their brakes. Now in a series hybrid or full EV configuration using engine breaking is impossible but regen could be an acceptable alternative. But as most Tesla owners know, there are certain situations where regen is disabled or reduced (full battery, cold battery...).

    Now trains to my understanding use a large resistor at the top of the locomotive to dissipate regen energy as there is no battery to store that energy into. This seams like a doable solution but maybe not ideal in a semi configuration. One solution that I thought of (dont know if its possible) is to use the EV motor in "reverse" to slow the tractor trailer while going down the mountain. Can an electric motor be used like that?
     
  2. Anarr

    Anarr Member

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    Trip planning is serious business in trucking and i'm pretty sure this situation would be incredibly rare, but yes you can use motor power to actively slow the vehicle. An electric semi is a fascinating idea as with no massive engine to squeeze in, the design could be quite radical. You would more than likely need dedicated battery swap stations and superchargers to make it viable for really long hauls.
     
  3. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    I'd have thought you could do it, but it'd need to be computer controlled.
     
  4. constraint

    constraint Member

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    I rode around with my friend for a day (who is a regional driver) and we got to talking when he filled up his rig with Diesel. We came onto the topic about electric cars (go figure) and started figuring out what it would take for a Class 8 to become a BEV. In a long haul scenario the energy requirements are pretty big and the only way we could see it working is with battery swapping as any fast charger for the numbers we were looking at could brown out the local grids if there are any number of truckers charging at once. Also battery swapping would allow you to stop once or twice a day with minimal turnaround time thereby allowing the packs to be smaller and therefore cheaper. My rough estimate of an 11 hour work day was something like 2-3 MwH for long haul.

    I know there are some yard BEV's in ports in California and I have been hearing some good things about them. My guess is we will start seeing these in the pop/beer class 6/7's first where they report back to a central location at night.
     
  5. drees

    drees Active Member

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    Long Beach has been testing Balqon trucks, but unfortunately Balqon appears to be in financial trouble and only has a few months of cash left unless they can get additional funding or sell a lot of trucks.

    Balqon Interview With Balqon CEO Balwinder Samra (video)

    Too bad, as electrifying trucks, especially around ports would have very large health benefits in addition to reduction in CO2 emissions.
     
  6. stopcrazypp

    stopcrazypp Well-Known Member

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    That is kind of sad. The problem is there's only a couple of ports (mainly in California) that care enough to invest in this. And they are up against competition from Tyrano (the hydrogen truck) which got lots more public funding.
     
  7. wycolo

    wycolo Active Member

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    Edwards, INC (Kansas City MO) makes big BEV trucks & tugs. Short distance only but beauty part is when they move into a shed and the doors are closed there are no fumes emitted indoors. Tremendous torque too.

    Running an electric drive motor 'in reverse' while going down a grade - this is the same as a Tesla motor in regen mode. No difference. When an electric motor is running at a stable rpm and you then try to increase the rpms by applying energy to it, the back voltage is now > the applied voltage resulting in the 'generation of power' (sending that extra power back to the source). This transition is seamless - what makes driving a Tesla so special.
    --
     
  8. constraint

    constraint Member

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    Ouch... just looked at balqon mx30 day cab Tractor specs. 380kwh for 90 miles of loaded range. Guess my 2-3MwH for a long haul day wasnt to far off.
     
  9. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Not surprising. Big rigs use a lot of energy.

    The main problem that a BEV has as a truck is the weight of the batteries. Axle weight is regulated for a certain maximum load--typically 18,000-22,000 lbs/axle depending upon the jurisdiction--so every pound that the vehicle weighs reduces the payload (and income) by that much. Of course, there are some types of haulers, such as furniture vans, that are limited by volume rather than by weight, so BEV would be fine for them but the majority of trucks on the road are limited by weight.
     
  10. Vexar

    Vexar Member

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    I'm curious about this subject, I have a relative in the trucking logistics business. Details, please? It will make the holidays much more interesting to be ready with the information. Based on what I've seen so far, it sounds to me like a hybrid platform where the metal-air battery is what gets swapped makes the most sense. Then the "Flying J" truck centers would be where the recharging occurs, and all the drivers really need to do is take care of themselves and relax. I would still rather see Hyperloop deployed for freight. Unfortunately, the problem of that is the classic "square peg" of a shipping container and "round hole" of a hyperloop tube.
     
  11. constraint

    constraint Member

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    #11 constraint, Oct 1, 2013
    Last edited: Oct 1, 2013
    The first question always starts with how much energy do you need (for a typical day). Normally loaded long haulers with an 11 hour work day would need at least 2 MwH's of electricity (Problably closer to 3 MwH's but we were really trying to see if we could make the numbers work). So if we break that down with today's technology and 1 pack to go the entire distance you are looking at 17,500 lbs and $600,000 worth of batteries (assuming 250wh/kg and $300/kwh). Since as been previously posted, truckers make their money by hauling cargo and not battery packs, not only is the pack too expensive, but it compromises the effectiveness of the hauler as you will be hauling batteries vs cargo. So it becomes obvious that even with significant increases in battery technology that 1 battery pack to run the entire day (which is the current case with diesel tanks) is not feasible.

    So my 2nd question comes down to how often is it acceptable for you to stop in the course of a day. If you stop too often, you never get anywhere (and you have to have more infrastructure) but if you dont stop often enough you get hit with your weight penalty (and higher value of the pack on board). The answer to this really comes down to driver/company preference, but for the sake of argument we decided on no more then 4 stops in a given day.

    Now we quickly decided that supercharging with the current battery technology is just not feasible unless a higher C charge can be used as current charging rates and having to stop 4 times a day means that half your day you would be down due to charging. The other issue that a higher C rate even makes worse is the amount of power required to charge a big rig's batteries in a reasonable time could be enough to take up 5 percent of a single coal fired powerplant causing brownouts and grid overloading. As an example if you had a 600 kwh battery bank (1/4 daily need plus buffer) to charge at a simple 2C rate (80 percent full in say 20 minutes which is the rate of charge for a Leaf using CHAdeMO) would require a connection of 1.3 MW. Now 1.3MW is already a lot of power that can only be created near distribution centers, but what happens if you have 50 semi's wanting to charge at a truck stop?

    So as our conversation progressed the only possible way that long haul trucks could make sense (keep in mind there may be many cases were local and regional trucks make sense) is with battery swapping. With today's technology you will still have a 5200 lbs battery that would cost $180,000 (for 600 kwh) which is still north of what most people would find acceptable even if you didn't require a battery swapping station every 200 miles.

    Now there were benifits over the current diesel (noise, shaking, engine idle overnight, removing the cost of the engine) that I didn't account for. We briefly talked about series hybrid's but I have no idea on efficiency and frankly we changed subjects pretty quickly after that conversation.


    So that was my off the cuff conversation.... Took up a good hour of the ride until we switched subjects on stupid car drivers that like to cut off 80,000 lbs of awesome.
     
  12. Vexar

    Vexar Member

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    Thank you for all the extra details, I appreciate it. I truly enjoy having engineers in this community. I think these class 8 trucks are an argument for nuclear-powered vehicles. I think truck drivers are an argument against nuclear-powered vehicles: they get tired, they make mistakes.
     
  13. Ampster

    Ampster Member

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    Public funding from required environmental mitigation funds is what keeps those projects alive. Those trucks don't share much in common wth long haul trucks.
     
  14. constraint

    constraint Member

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    O I'm not an electrical engineer, but I did stay at a Holiday Inn Express last night. Well technically I guess you could say I am a software engineer.

    Nuclear big rigs.... hopefully you are talking about a pb11 fusor and not the fission stuff that has a 17,000 year half life. A more sensible approach may be a series hybrid like the locomotive design's that have been used for years.
     
  15. AMPd

    AMPd Active Member

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    Wouldn't hydrogen make more sense for long haul trucks?
    Too many hurdles to jump over with a battery powered long haul truck, to me hydrogen makes more sense
     
  16. GSP

    GSP Member

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    Why hydrogen? Natural gas HD trucks are an available and proven technology. They can go further on a given amount of natural gas than reforming the CH4 to H2 and using that in a H2 ICE or "fool sell." LNG infrastructure for cross country travel is being installed now, and is at about the same state as Tesla's Superchargers. LNG allow range and refueling speeds similar to Diesel.

    GSP

    One example:
    Natural Gas Trucks with Leading Fuel Economy - Freightliner Trucks
     
  17. AMPd

    AMPd Active Member

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    I was focusing on renewable source of energy
    While natural gas may be a better replacement and yes there's an abundance of it available, it's still a non renewable source. Not to mention the "fracking" method is extremely harmful to the local enviroment

    edit: I know elon calls hydrogen fool cells and I agree it makes no sense to use it in cars as you'd have to build out a huge network of filling stations, it's completely different for trucks.
     
  18. constraint

    constraint Member

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    Why would that be? Hydrogen doesn't store a lot of energy per unit volume which means a lot of space and weight used up by tanks. In addition hydrogen today is more expensive the diesel fuel not to mention the motor today is a lot more expensive then normal ICE's.
     
  19. AMPd

    AMPd Active Member

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    The reason I think it's different from passenger vehicles is because you don't need to build as many filling stations. Instead of having hydrogen at every gas station, you'll only need them at truck stops
    by no means am I saying TODAY hydrogen is a better alternative, however hydrogen prices are bound to fall whereas diesel prices will only rise.
    Again I'm not saying we should switch to hydrogen now, I'm just saying in terms of future fuel source hydrogen makes the most sense. To me at least, I'd love hydrogen powered trucks, with most of the hydrogen made from renewable electricity

    hey a guy can dream can't he :)
     
  20. constraint

    constraint Member

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    If I am dreaming then I want it to run on a p B11 pollywell fusor. Clean, cheap, abundant and theoretical.
     

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