Small theoretical question. . .

Discussion in 'Automotive Electronics' started by Redscarf, Jul 2, 2015.

  1. Redscarf

    Thread Starter New Member

    Jan 28, 2015
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    Hey guys I'm a bit new to the electronics and automotive scene, but I just wanted ask you all, theoretically if some one wanted to make a small automobile that use a solar energy to charge the batteries to power the car. how big of an array would have to be used and how much watts would be needed to power the car to about 50mph max? I would love a reply, thanks.
     
  2. #12

    Expert

    Nov 30, 2010
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    Google is your friend.
    It's been done. Look it up.

    That is not a small question. It's an engineering balance that people have worked on for decades.
     
    Last edited: Jul 2, 2015
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  3. ian field

    Distinguished Member

    Oct 27, 2012
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    Someone in Australia actually did it - the article was published in Silicon Chip quite some years back.

    There's an archive of SC floating about online somewhere that includes that issue.
     
  4. Redscarf

    Thread Starter New Member

    Jan 28, 2015
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    Oh wow, thanks guys but i'd never imagine it'd be this big of a deal, i'll see if i can replicate in a smaller form and work my way up. . .
     
  5. ian field

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    Oct 27, 2012
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    There was an international competition years ago for various uni students to construct solar powered go-carts. The progress and end results were widely published both in paper magazines and online, they may also still be floating about the web somewhere.

    AFAICR: Elektor magazine made a big deal about the contest preparations. I think there were articles about it over several issues.
     
  6. #12

    Expert

    Nov 30, 2010
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    I was thinking about the Australian competition, but couldn't remember its name. :(
     
  7. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    Modern engines can put out an equivalent of over 100 kilowatts. But that is to get up to speed at a normal rate, not allowing for the car to be able to take a full minute to reach 25 mph.

    When there is no specification for how fast it has to get up to speed on a level road, it probably takes very little power because it's almost the same problem as the space ship that uses only a little energy to build up speed over years. The only difference here is you have to be able to overcome the friction when you start out, and some of the power goes for that after it is moving too.
    Note that one person can push most cars at least a little ways. It takes quite a push to get it going but then it gets easier.
     
  8. Redscarf

    Thread Starter New Member

    Jan 28, 2015
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    Oh I see so i'd need one big initial burst of energy to get moving and then from there a lesser amount to maintain speed.
     
  9. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    Yeah something like that, although it may not have to be too big of a burst. Depends on how well you design the car itself too, how much sticking friction there is, and if there is going to be a hill or reverse wind, and how much air drag there is.
    If there was no sticking friction, no hill, no reverse wind, then a mouse could move the car any distance, it would just take more time to get going. Remember the old formula:
    F=M*A
    or rearranged:
    A=F/M
    where M is the mass of the car and F is the force applied, and A is the acceleration. So even with a huge mass and a small force, the right side of this is never zero, so there is always some acceleration although it could be very small and therefore take a long time to get up to speed. That's if there was no sticking friction, moving friction, wind, hill, air drag.
     
  10. Redscarf

    Thread Starter New Member

    Jan 28, 2015
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    Wow that sure is a lot to think about. . . I guess i should brush up on my physics skills. Also I have yet another question if i were to build a smaller version that worked in the same vein as a smaller robot and upscale it to a larger size would it be in any way practical?
     
  11. ian field

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    I've had a few petrol cars that needed the pedal to the metal just to keep up on a motorway.

    The solar go cart competition was pretty much the same time period as a competition to see who could drive the furthest on a very small measured portion of fuel. Overcoming the initial inertia and then just making up for rolling resistance, is a valid strategy for that type of exercise.
     
  12. Redscarf

    Thread Starter New Member

    Jan 28, 2015
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    cool, but what would be the most efficient way of overcoming the initial inertia, aside from probably pushing it own a hill every time i want to get moving?
     
  13. ian field

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    A 2 ton flywheel gradually spun up to 27,000 RPM by a flea-power electric motor, then dump it into the drivetrain with a dog clutch.
     
  14. Redscarf

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    Jan 28, 2015
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    That actually sounds both fun and terrifying at the same time. xD
     
  15. ian field

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    You have to mount the flywheel right up at the front, so its weight stops the cart doing too much of a wheelie all at once.
     
  16. Redscarf

    Thread Starter New Member

    Jan 28, 2015
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    Hahaha okay okayXD, but back to the realm of feasibility( in my case), so how big of a battery would be needed if wanted to travel about 40mph for four hours or so?
     
  17. ian field

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    You can probably get some sort of guesstimate by number crunching the technical specifications published by the manufacturers that make all electric cars.
     
  18. Redscarf

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    Jan 28, 2015
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    Ah cool, any specific recommendations?
     
  19. ian field

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    The car manufacturers advertise to the point of being irritating.
     
  20. Redscarf

    Thread Starter New Member

    Jan 28, 2015
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    I've found out that the Tesla model S uses a 85kWh our battery, also I've been doing some thinking about how to get the initial speed that i need when moving from rest and have played around with the idea of relatively high powered capacitor that could provide the burst of speed and then letting the battery take care of the rest.
     
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