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