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12VDC to 100DC is it possible?

Discussion in 'General Electronics Discussion' started by AlenZGB, Feb 28, 2015.

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  1. AlenZGB

    AlenZGB

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    Feb 19, 2014
    I was wondering is ti possible to get 12VDC(more around 14) from cars alternator and boost it 72VDC ?

    Regards,
    Alen
     
  2. BobK

    BobK

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    Yes. The difficulty will depend on how much current you need.

    Also why is it 100V in the title and 72V in the post?

    Bob
     
  3. AlenZGB

    AlenZGB

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    Feb 19, 2014
    thx for fast answer, it should be 72V batteries. 12V put in series. Should be for electric car.
    so i want to make somekind of self charging for the car. but i think i need 108V dc to charge it. if i didnt get something wrong
    Should be around 20A.


    About 100V in title was exedently.

    Regards,
    Alen.
     
  4. davenn

    davenn Moderator

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    Sep 5, 2009

    with a car alternator and the current you want .... no, not possible
     
  5. AlenZGB

    AlenZGB

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    Feb 19, 2014
    What max current will be ?

    EDIT:
    better to charge something then nothing, right?


    Regards,
    Alen
     
  6. hevans1944

    hevans1944 Hop - AC8NS

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    Typical automobile three-phase rectifying alternator can produce way more than 14 volts at normal operating speeds by controlling the field current, but there is no guarantee the diodes won't pop if their peak inverse voltage rating is exceeded. Some folks remove the diodes and just use one or more of the three phases to produce high-voltage alternating current, which you can rectify externally with appropriately rated diodes. All depends on what you are trying to do.

    If this is an electric car running off of six 12-volt batteries (72 volts nominal), what is going to power your alternator? Do you plan to crank the alternator by hand, or is there a small internal combustion engine involved? Or did you have some idea that regenerative braking could be used to re-charge your batteries by mechanically tying the alternator pulley to the car wheels? What, exactly, are you trying to accomplish? Be forewarned, NO "over unity" power schemes are allowed here on Electronics Point.
     
    duke37 likes this.
  7. duke37

    duke37

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    If you use a push/pull invertor running 20A input through a pair of MOSFETs, then you will charge at about 250W so 3A and a bit out. Power above this is beyond my knowledge.

    What is the current output of your alternator?
     
  8. AlenZGB

    AlenZGB

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    Feb 19, 2014
    one side of electric motor should go on clutch and gearbox side and the other should be directly or over some pulley to alternator.
    alternator should be powered by 72V battery on what car would be running. but i still need one 12v battery for accesories in car so from that ill get +12 to alternator and ground.
    I was planning to by pure electric not other engine. eco style



    Alternator if im not mistaking is 90A
     
  9. hevans1944

    hevans1944 Hop - AC8NS

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    So, the electric motor shaft on one end of the motor is connected to clutch/gear box/wheels? And the electric motor shaft on the other end of the motor is connected directly, or with belt and pulleys, to the alternator? And where is the electrical output of the alternator connected? To the 72 volt battery bank?

    How is the alternator going to get mechanical power, necessary to turn its shaft to generate electricity? Can you make a sketch, photograph it, and upload to this forum?
     
  10. AlenZGB

    AlenZGB

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    Feb 19, 2014
    funny drawing .jpg ill try to funny drwa it
    i hope you get what i mean
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    That's just not going to work.

    It will simply cause your battery to discharge faster.

    The only way you can reclaim some of the energy is by regenerative braking. Look that up.
     
  12. AlenZGB

    AlenZGB

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    Feb 19, 2014
    can you explain why this wont work ?

    If i use another battery to stimulate alternator and charge that battery with solar panel on the roof ?
    Will that work ?
    Im not trying to make 100% selfcharging car, just want to make better autonomy of the car.


    Regards,
    Alen
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The power taken from the battery to turn the alternator exceeds the amount of energy you'll get from the alternator.

    That WILL work, because the power to charge the battery does not come from the battery itself.

    However, regenerative braking will deliver better gains because there is no (or insignificant) weight penalty, or additional aerodynamic drag, it works at night, and doesn't require a huge amount of roof space on your car.

    Having solar panels on your roof at home and using them to charge the car makes more sense.
     
    AlenZGB and hevans1944 like this.
  14. hevans1944

    hevans1944 Hop - AC8NS

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    This is a manifestation of a perpetual motion machine of the first kind. Your scheme purports to take energy from the battery to drive the motor, which in turn drives the alternator to replenish the energy removed from the battery.

    This scheme will never work because, along the way, some of the energy taken from the battery to drive the motor is dissipated as heat energy because of friction. This includes ohmic losses caused by electrical current heating the wire resistance, as well as mechanical friction losses in motor and alternator bearings, and windage losses in rotating parts. This lost heat energy can never be fully recovered (for reasons involving the 2nd Law of Thermodynamics) to replace the energy removed from the battery.

    Your scheme neither acknowledges this lost energy nor makes any attempt to recover (some) of it. All your scheme will do is hasten the discharge of the battery. It will not re-charge the battery or make the motor-battery connection more efficient.

    That doesn't even make sense. The electrical power provided to the alternator field winding does not produce any electricity. It produces a static magnetic field through the alternator rotor poles. Only when the rotor is turned, causing the rotor poles to move with respect to the static magnetic field, is a current induced in the rotor windings in accordance with Michael Faraday's law of magnetic induction. The only reason an alternator has a field winding is to control the amount of magnetic induction that occurs. It works just as well with a permanent magnet field, except then the output voltage and current, which are functions of rotor rotation speed and electrical load, are not controllable.

    If you have a solar panel on the roof (of the automobile, presumably) it can fully charge a battery directly... eventually. No alternator necessary or required. All international contest solar racers are powered exclusively by solar panels. Some racers are more efficient than others because some aerodynamic designs are more efficient. There isn't much left that can be accomplished to improve electrical efficiency... unless some genius comes up with room-temperature superconductors. But all solar-powered automobiles share one major deficiency: they don't work well on cloudy days, and they don't work at all at night, except from power stored during the day (hopefully a bright day).

    An admirable objective! But your best bet to increase efficiency is regenerative braking. This will recover some (but by no means all) of the kinetic energy the electric motor imparts to the car.

    To do this you must mechanically connect the alternator directly to the wheels and then, through the "magic" of power electronics, aided by a microprocessor, control the alternator field current to generate power to re-charge the battery, but only when the driver backs off the accelerator pedal and operates the brake pedal.

    With no field current, the alternator spins freely and imposes minimal mechanical friction on the wheels. When the driver presses the brake pedal, a sensor detects the pedal position and increases the alternator field current proportionally to how far the pedal is depressed. You would also need a parallel hydraulic brake circuit for safety and to comply with road worthiness laws, but the initial braking deceleration would be electrical, not mechanical (which simply converts kinetic energy into useless heat energy).

    What I have described is just the rudiments of a regenerative braking system. Use Google or another search engine to discover more details. What if the battery is fully charged and cannot accept more charge from the alternator for braking purposes? The alternator could then bypass the battery and dump its energy into a (wasteful) electrical resistance load, but there is another recourse. Use the alternator output to actuate an electro-hydraulic mechanical braking system, still wasting the kinetic energy of the car as heat, but at the same time improving the overall reliabiity. You could even integrate an anti-lock braking system!

    I hope I haven't discouraged your entrepreneurial spirit. Using an alternator to recover some of a car's kinetic energy during braking is a tried and true method that has been used many times, some even commercially. Recovering kinetic energy and re-using it electrically is the holy grail of electric car design. Earlier designs used a flywheel, spinning in a vacuum, to store kinetic energy. This is fairly efficient using modern composite materials and very high rotation speeds (upwards of 100,000 rpm), but the gyroscopic effect has to counteracted by oppositely spinning flywheels, adding weight and complexity to an already complex electro-mechanical system.

    Perhaps super-capacitors will eventually provide a solution. Unlike batteries, which can only accept a fixed maximum charge, super-capacitors are limited only by their voltage rating to the amount of charge they can accept. And, unlike electro-chemical battery technology, super-capacitors can be charged and discharged indefinitely.
     
    duke37 and AlenZGB like this.
  15. duke37

    duke37

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    Jan 9, 2011
    An alternator is not needed. The motor can be used to drive the vehicle and can be used to brake the vehicle, you just need to make a complex control system. I do not think that you will get enough recovered energy to make regeneration worthwhile, just drive more responsibly.

    Railway locomotives have used resistors to dump energy when braking, it is only recently that power is returned to the overhead line. This can even be done with AC supply.
     
  16. AlenZGB

    AlenZGB

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    Feb 19, 2014
    @hevans1944

    Thanks for the big answer
    Guess ill have to think some other way to get autonomy.


    Was considering that option also, i would need around 2kw panels on roof, to charge cars battery in 5-6 hours.
    Aprox. In year or so ill be finished with car and solar system i hope :D



    Maybe some switch like economic mode, that lover the voltages and bring up the Ah to extend the autonomy at cost
    of performance. From 72V to 60V or something like that, mix of paralel and serial battery connection.


    Regards,
    Alen
     
  17. BobK

    BobK

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    Jan 5, 2010
    Lower the voltage does not help. The motor will need some amount of power to run that car at a given speed under given conditions. It would still need the same power with a lower voltage. In fact, all you would be doing is limiting the speed of the car, which you can presumably already do without lowering the voltage.

    The battery in my Prius is over 200V.

    Bob
     
  18. hevans1944

    hevans1944 Hop - AC8NS

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    My oldest daughter has a Prius. She seems to like it, but it does depend on its tiny internal combustion engine to keep the battery charged. AFAIK, there is no successful electrical car that depends solely on an external electrical charging source. Takes too long to recharge (even with a 220 VAC mains feed at 200 A available) and commercial charging stations are still few and far between, at least in the USA, where petroleum rules for transportation and there is either a gas station or a drug store on every corner. It's coming though: fission power > electricity > supercaps > electric autos. It may take awhile longer to get big trucks and trains weaned from fossil fuels. It's hard to beat hydrocarbons for energy density, which translates directly into range of operation and load capacity. Gotta do things for profit here.:D
     
  19. BobK

    BobK

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    Jan 5, 2010
    Actually, the engine is not tiny, it is 1.8L, and the car almost never runs completely off electricity.

    What Toyota did was use every trick they could think of the get the highest efficiency:

    An Atkinson cycle engine that is run at a constant RPM where it is most efficient when it is not taxed.
    Regenerative braking.
    A brilliant transmission that uses the electric motor / generator to make up the difference in speed between the engine and the drive wheels.
    One of the best drag coefficients of any production car.
    And social engineering: An active display that encourages drivers to make a game out of getting the best mileage.

    Bob
     
  20. AlenZGB

    AlenZGB

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    Feb 19, 2014
    guess its hard to beat prius :D
    but...i like chellange,car is still in planing faze and gathering parts :D

    Have to find another way then.
     
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