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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    •  
      CommentAuthorfostertom
    • CommentTimeJun 13th 2016
     
    Posted By: Ed Daviesyou pick up a rented charged trailer which runs your car for a while
    Not unlike the idea of exchanging your battery pack rather than waiting for a charge-up.
    • CommentAuthorEd Davies
    • CommentTimeJun 13th 2016
     
    Indeed - but:

    a) you don't carry the batteries around when you don't need them,

    b) they can discharge steadily to run the motors and/or charge the car's main battery so don't get the variable use which it's better for the owner to decide (performance vs battery life) on

    c) simpler mechanically and could be more interchangeable between car models.

    Would have to have a tow bar and the car electronics might be a bit more complicated to deal with simultaneous operation and charge.
    •  
      CommentAuthordjh
    • CommentTimeJun 13th 2016
     
    Posted By: Ed Daviesyou pick up a rented charged trailer which runs your car for a while

    I like the idea. How much would such a trailer weigh? What is the law currently on being allowed to pull a trailer?
    • CommentAuthorEd Davies
    • CommentTimeJun 13th 2016
     
    Really small cars typically can't (as a matter of type approval). There are rules on the ratio of the car's weight to the trailer's weight depending on whether the trailer is braked or not. Currently, the speed limit is 60 mph and you're not allowed in the outside lane of three or more lane motorways. I think those are the main points though it's a while since I've done much towing.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 13th 2016
     
    Someone better get designing hi-speed trailers which don't upset the car's handling esp rotational momentum about pitch and roll centres (which are key to perception of comfort).
    These cd be almost as heavy as a caravan, to be worthwhile, without the performance and dynamics compromises that caravans create.
    Unless of course by that time we're 'driverless' in which case those things prob won't matter.
    • CommentAuthorskyewright
    • CommentTimeJun 14th 2016 edited
     
    Posted By: Ed DaviesWhy couldn't you extend the range of an electric car by towing an extra battery trailer?

    An excellent idea. The trailer could be designed to minimise drag (& maximise stability).
    Also useful to the intended theme of this topic, i.e. grid storage. If you are just doing a short journey the trailer could stay at home soaking up PV while you were out using the car, then in the evening the trailer's energy could top up the car or the grid as appropriate.

    I'm pretty sure I saw a picture of a battery boost trailer already in practice some where?

    Edit: typo.
  1.  
    The trailer rules we now have are far more complex than simply being braked. It depends on when the driver passed their test, the weight of the vehicle and the weight of the trailer.

    Simply put the exchange battery idea works for trailers less than 750Kg, however give the vast majority of drivers a trailer that small and you will find rear of cars smashed up from jack knifing and broken trailers littering the streets. A small trailer is far harder to reverse than a larger one. Certain cars are very sensitive to hitch weight as well, varying hitch height on cars means this can be difficult to achieve for shared trailers.

    The speed limit is also 50mph on single carriageways.
    •  
      CommentAuthordjh
    • CommentTimeJun 14th 2016
     
    Posted By: Ed DaviesReally small cars typically can't (as a matter of type approval).

    Sorry, it was the rules as they apply to drivers that I was meaning. AIUI, there is no automatic right to pull small trailers on an ordinary licence any longer.
  2.  
    Posted By: djhAIUI, there is no automatic right to pull small trailers on an ordinary licence any longer.


    You can tow a 750Kg MAM trailer on your standard post 1997 cat B license. Depending on the weight of your towing vehicle you may be able to tow a little more - it gets complicated and you need to look at the specific towing vehicle and trailer to work out what would be legal.
    •  
      CommentAuthordjh
    • CommentTimeJun 14th 2016
     
    To expand a little more: Since we're talking about special trailers designed for a specific new type of car, I'm sure the designs can be optimised for whatever criteria we deem important. But the weight of the trailer is of fundamental importance. If the trailer contains batteries that double the range of the car, for example, it will need to be engineered to a similar level to the car and the dynamics will need very careful consideration, especially if it is supposed to be interchangeable amongst a group of vehicle types.

    The law on which drivers can pull which trailers and at what speed will also need changing.

    Again: I like the idea; I just don't think it is straightforward to implement.
    • CommentAuthorEd Davies
    • CommentTimeJun 14th 2016
     
    Posted By: willie.macleod: “The speed limit is also 50mph on single carriageways.”

    Good point. Couldn't remember if that applied to trailers (as it does to many goods vehicles).

    “Simply put the exchange battery idea works for trailers less than 750Kg,”

    My first thought was that that would be plenty but actually Tesla S 85 kWh batteries mass 540 kg: https://en.wikipedia.org/wiki/Tesla_Model_S#Battery though with a “better source needed” annotation, but cromulant with http://batteryuniversity.com/learn/article/electric_vehicle_ev which also says a Nissan Leaf gets 250 km off a 272 kg battery.

    So maybe 0.7 km/kg allowing for the mass of the trailer itself and the reduced aerodynamics but also that it would typically be used for relatively steady high (but not too high)-speed driving.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 14th 2016
     
    Wonder how a rigid 'rear extension' with castor wheel(s) - more a rear platform than a trailer - would work. The castors cd be 'intelligently' steered, to take their share of lateral load under cornering. No backing problem, as long as the extra length is apparent to the driver.

    What's being reached for here is
    a) a universal module attachable to all cars,
    b) instant swopability,
    c) its use optional e.g. to enable uninterrupted long journey one way or another,
    d) can be owned, to sit at home charging, or rented 'on the move'.

    Given that spec being taken up widely, manufs of new vehicles wd I'm sure come up with some protocol that would barely resemble anything we know as 'trailer' today.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 14th 2016
     
    Tom, do you never go out in the Devon lanes in summer when a caravanner is stuck.

    Will also make parking fun, how much extra room would be needed. What will happen to car insurance.

    Probably best to forget the idea of trailers, there is a reason they are making it harder to use one.
    •  
      CommentAuthordjh
    • CommentTimeJun 14th 2016 edited
     
    Posted By: Ed DaviesSo maybe 0.7 km/kg allowing for the mass of the trailer itself and the reduced aerodynamics but also that it would typically be used for relatively steady high (but not too high)-speed driving.

    I think the law would need to be changed such that it was legal to drive those trailers at full speed. I don't believe people would accept a system that required them to drive like a caravan for their holiday or business trip. It would be enough of a struggle to get people to accept the need for an extra boondoggle.

    Oh and what about people who do want to tow a caravan, or a regular trailer (think U-haul)?

    Posted By: fostertomWonder how a rigid 'rear extension' with castor wheel(s) - more a rear platform than a trailer - would work

    Not well, I expect. There has been a lot of work done on articulated vehicles and I expect the solution would come from developing that with the specific parameters for this application. I know I'm not competent to work on that design.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 14th 2016
     
    No, not articulated - rigid laterally but flexible vertically, its overhung weight taken by castor wheel(s). Think not 1 but 2 ball hitches, one at ea rear corner of the car (but wd have to be much easier than that). Close-coupled, it needn't be a long rearward extension. I can see that behaving quite well dynamically.
  3.  
    Perhaps the American square receiver tow hitch system could be used instead of our 50mm towball for adding more batteries - class 1,2 and 3 respectively allow decent tongue weights, simple system which is well known and reliable. Versatile as well, loads of accessories available from bike racks, winches, boxes etc. Ideal for rear extensions without actually trailing anything behind, adding a castor would give even better capacities.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 14th 2016
     
    Why not just make a larger vehicles. I am sure I have mentioned this before when we were talking about the same think.
    I pointed out that as the volume of a vehicle goes up, you don't need to increase the weight by much more (air does not weigh a lot).
    •  
      CommentAuthorfostertom
    • CommentTimeJun 14th 2016
     
    Posted By: SteamyTeaas the volume of a vehicle goes up, you don't need to increase the weight by much more (air does not weigh a lot)
    I dispute that!
    Torsional or impact (potholes vertically, joyriders laterally) strength requires the quantity of structural material to increase as about the square of its length.
    A small monocoque can be fantastically light compared to a larger one - try scaling up an eggshell!
    •  
      CommentAuthordjh
    • CommentTimeJun 14th 2016
     
    Posted By: fostertomNo, not articulated - rigid laterally but flexible vertically, its overhung weight taken by castor wheel(s)

    I was trying gently to say that I think your idea is ridiculous.
    Sorry.
    •  
      CommentAuthordjh
    • CommentTimeJun 14th 2016
     
    Posted By: SteamyTeaWhy not just make a larger vehicles. I am sure I have mentioned this before when we were talking about the same think.
    I pointed out that as the volume of a vehicle goes up, you don't need to increase the weight by much more (air does not weigh a lot).

    Err, we are talking about how to carry a large extra weight of batteries. We aren't looking for extra volume.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 14th 2016
     
    Posted By: djhtrying gently to say that I think your idea is ridiculous
    Why? You may be right but not proven from what's been said so far.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 14th 2016
     
    Posted By: fostertomA small monocoque can be fantastically light compared to a larger one - try scaling up an eggshell!
    Yes it can, but so can a large monoque, just look at a bloat.


    Posted By: djhErr, we are talking about how to carry a large extra weight of batteries. We aren't looking for extra volume.
    Have we got very energy dense batteries now? 10kWh/lt would be good :wink:
    •  
      CommentAuthorfostertom
    • CommentTimeJun 14th 2016
     
    I suspect the torsional/impact resistance to weight ratio of a bloat is far less than of an eggshell.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 14th 2016
     
    I shall have to measure an egg, I know the make up of my kayak (2mm GRP, 4m long, 0.6m wide and a volume close to 1m^3.
    Harder to work out the forces, but it can withstand a 12 foot breaker easily.
  4.  
    https://youtu.be/-5NP5dUIpcY

    They already have range extender trailers in France, when I last read about them a few years back they were talking about having a hire network for them, don't know how far that has progressed.

    Seems like a roof box range extender might be better if it were feasible. Would get over trailer speed restrictions.
  5.  
    Bit awkward for handling if you put that much weight on the roof, think rollovers could be a bit of a nightmare as well being in the middle of a battery sandwich.

    Like the wee trailer though, luggage rack and all :bigsmile:
  6.  
    Posted By: willie.macleodBit awkward for handling if you put that much weight on the roof, think rollovers could be a bit of a nightmare as well being in the middle of a battery sandwich.

    Like the wee trailer though, luggage rack and allhttp:///newforum/extensions/Vanillacons/smilies/standard/bigsmile.gif" alt=":bigsmile:" title=":bigsmile:" >

    But the range extender is a small petrol driven generator not an extra battery pack so the weight should be well within normal roof rack capacity, besides in the real world I would guess that the chances of being rear ended are higher than that of being involved in a rollover accident?
    • CommentAuthorEd Davies
    • CommentTimeJun 16th 2016
     
    Thanks for that EP Tender link, Crispy. Yes, it has a generator rather than extra batteries but I had wondered about that, too, as an alternative to a plug-in hybrid. Sort of a PHEV where you can leave the engine at home when you don't need it.
  7.  
    Posted By: Ed DaviesThanks for that EP Tender link, Crispy. Yes, it has a generator rather than extra batteries but I had wondered about that, too, as an alternative to a plug-in hybrid. Sort of a PHEV where you can leave the engine at home when you don't need it.
    I think the idea with the EP tender is that there should be a hire network all over the country so you don't have the capital expense when many people would only require to use it a handful of times a year.

    Any range extender solution should only be a relatively temporary phenomenon until battery technology or in road wireless charging or some other development makes them obsolete.

    Hopefully a 5 year horizon? :-)
    • CommentAuthorEd Davies
    • CommentTimeJun 27th 2016
     
   
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