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Car battery -- charging questions

  1. Jun 9, 2016 #1
    Hello,

    I am a Telecommunications student who does not have a lot clue about cars.Does a car charges up its battery when it moves? What power supply is used for lighting in car, the battery? So if car charges the battery when it moves, why sometimes external/additional charging of battery is vital ?
     
  2. jcsd
  3. Jun 9, 2016 #2

    anorlunda

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    The engine in the car spins the alternator. The alternator produces DC energy to charge the battery, and to power lights, radios and so on.

    If for some reason the battery can't start the engine, then external energy must be supplied.
     
  4. Jun 9, 2016 #3
    I appreciate your answer. How many alternators are in the car? 4? or 2?
     
  5. Jun 9, 2016 #4

    anorlunda

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    Usually one. Do you have a car nearby? You can open the hood, see the engine and the alternator.
     
  6. Jun 9, 2016 #5
    Unfortunately, I don't have a car nearby.But how much power does it output so a battery charges?What about its speed ?
     
  7. Jun 9, 2016 #6

    anorlunda

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    A typical alternator can make 50 amps at 14 volts. That's a lot.

    A voltage regulator controls the alternator so the speed doesn't matter much.

    Here is a picture of a car engine. The alternator is the part spun by the rubber belt.

    FQ8FSGTFOVXOSBT.MEDIUM.jpg
     
  8. Jun 9, 2016 #7

    davenn

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    the car doesn't need to be moving ... the engine only has to be running

    around 14V at a few amps. The alternator rotor spinning speed is around that of the engine revs so as the engine revs faster so does the alternator

    have a look at this pic that I put some text on ......

    upload_2016-6-10_7-49-31.png

    the V-belt connects the alternator to the engine crankshaft, so that when the crankshaft turns, it then turns the rotor of the alternator




    Dave
     
  9. Jun 9, 2016 #8
    Thank you so much guys !
     
  10. Jun 9, 2016 #9

    jack action

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    The battery has only one purpose: Powering the engine starter.

    Once the engine is running by itself, the alternator will power the entire electrical system of the car. In addition, it will recharge the battery for the next engine start.

    The size of the alternator depends on the electrical system. If the electrical system is only the ignition system, the alternator will be quite small. If you also have a lighting system, a sound system, power windows, etc., then you need a proportionally more powerful alternator.
     
  11. Jun 9, 2016 #10

    davenn

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    I would have to disagree with that

    I find my car starts to fail quite rapidly if the battery fails during operation ..... the battery has the current capabilities that the alternator/generator doesn't have


    Dave
     
  12. Jun 9, 2016 #11

    davenn

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    didn't realise it was capable of 50A, can that be sustained or only in bursts ?
     
  13. Jun 9, 2016 #12

    anorlunda

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    50 is sustainable, but it is not often needed in a car.

    RVs and boats often install 100 amp alternators because they have big battery banks to charge.
     
  14. Jun 9, 2016 #13

    wirenut

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    I believe Ford has a 130 amp alternator in some of their vehicles.
     
  15. Jun 9, 2016 #14

    jack action

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    50 A was the standard 30-40 years ago. Today, a small car like a Toyota Yaris have an 80 A alternator. A typical car will have one producing 100-130 A. A fully loaded luxury car/SUV can have a 150-180 A alternator.

    Again, it's not as much of a question about the battery size, but the demand of the electrical system.
    The battery may be needed if the engine is idling and you flip on every switch on your dash, but that is certainly not a normal situation. I'm not even sure it is still a problem in today's car.

    The largest (battery) wire in a typical car is a 2-gauge which can withstand a current of 130 A. So the battery will not be able to give more current than the alternator can provide without destroying the wires. You need a https://www.amazon.ca/Taylor-Cable-...qid=1465523617&sr=1-14&keywords=battery+cable for a 170 A current, which is the largest I found in a quick search.
     
    Last edited by a moderator: May 7, 2017
  16. Jun 9, 2016 #15

    rbelli1

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    It will also run all of the electrical equipment when the engine is not running. In many (most? all?) cars you will notice that the lights aren't quite as bright and the motors are a bit slower when the engine is stopped. This is because the alternator runs at the battery charge voltage which is a bit higher than the typical loaded voltage of the battery itself.

    Having a good battery is crucial as often the regulator needs the battery as part of its operation. If the battery is not present or severely worn the regulator can operate at a voltage that may damage the electrical system. I would suspect as you look at newer models this failure mode will be less severe or absent due to improved design.

    BoB
     
  17. Jun 9, 2016 #16

    russ_watters

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    I drive a Kia Optima midsize sedan. It has electric power steering. Googled -- it has a 95A alternator.

    I'd be curious to know what it draws in normal operation. At 14V that would be 1.8HP. I calculated once that at 30mpg and 60 mph, the engine generates about 17hp, so the electrical load would be about 10%.
     
  18. Jun 9, 2016 #17

    jim hardy

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    They've complicated things immeasurably in new cars
    With electrical load getting bigger and engines getting smaller
    Mr EngineControlUnit directs Mr Voltage Regulator granting permission for Mr Alternator to produce high current if and only if Mr Engine has reserve torque available .
    There are dozens of microcomputers chatting over something called "CANBUS" . That's how hackers take remote control of electronic throttle, steering and brakes through the entertainment system.

    I am getting too old to put up with such design shenanigans so bought myself a '68 Ford truck .. It'll outlast me. And appreciate not depreciate.


    http://www.forbes.com/sites/andygre...-with-me-behind-the-wheel-video/#564897ac5bf2
     
  19. Jun 10, 2016 #18
    Look at the fuse boxes to see the maximum load for a particular circuit.
    That will give some initial idea, but what failsafe they have before a fuse blows would have to be factored in.
    Adding up all the fuse rating would ( should ) be more than 95A.
     
  20. Jun 10, 2016 #19

    davenn

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    sounds a bit low ? considering .....

    haven't found a HP rating at a given speed and RPM which would be the quantifying factors


    Dave

    found a maximum power out
    grrrr why quote totally different units for the different RPM ... how confusing !!

    this one for the 1.6L

    Horsepower: 178 @ 5500 RPM


    @russ_watters would be interesting to know what RPM it was doing at your 60mph ?
     
    Last edited: Jun 10, 2016
  21. Jun 10, 2016 #20

    SteamKing

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    Max. HP and max. torque output for a given engine usually occur at two different RPMs, with max.torque occurring at the lower RPM.

    All of the power figures are consistent, as are all of the torque figures given for this engine.

    Knowing the relationship between torque, RPM, and HP, you should be able to calculate the HP output of the engine when the max. torque reading occurs.
     
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