Cars, cars and electric cars

Discussion in 'Just Talk' started by joinerjohn1, Jul 26, 2017.

  1. Lol...

    Yes, it's a consequence of the fan belt being slightly loose, and this can be fixed by re-tensioning it, but I trust you understand that the belt will only slip when there's a greater load on the alternator?

    Once the battery is fully recharged, the belt will not slip as the alternator is easy to turn.

    Yes?
     
  2. fillyboy

    fillyboy Screwfix Select

    Yes.

























    [​IMG]
     
  3. Thank you for agreeing.

    And, yes, my very first car was an Anglia.

    Damn, I wish I still had it. :)
     
  4. Mr. Handyandy

    Mr. Handyandy Screwfix Select


    No. The alternator runs at the same speed of the engine always. It does not get harder to turn when more power is needed, it charges the battery at a constant voltage. The squeal you may hear is just waiting for the lubrication of the bearings in many components to get going(crank, water pump, power steering, alternator etc)

    And my scenario does not add anything to the car.
     
  5. Mr. Handyandy

    Mr. Handyandy Screwfix Select


    Yeah, that probably had a dynamo!
     
    Deleted member 33931 likes this.
  6. fillyboy

    fillyboy Screwfix Select

    I hate to say this but DA is right in that an alternator will cut in where required placing an additional load even though it's turning at the same speed as the engine, on the older dynamo, that would just turn constantly with no additional load but at a lower voltage.
     
    Deleted member 33931 likes this.
  7. P J Thompson

    P J Thompson Active Member

    Lenz law.
    The current draw from the alternator affects the load on the engine. More current = more load
     
    Deleted member 33931 likes this.
  8. fillyboy

    fillyboy Screwfix Select

    I used to know a mechanic called Len, wonder if it were the same bloke.
     
    btiw2 likes this.
  9. chippie244

    chippie244 Super Member

    Wrong, you are well out of your depth mate.
     
  10. btiw2

    btiw2 Screwfix Select

    Yes. I understand that the metal sheet was an example - a thought experiment.

    So we have three options.
    1. Steel plate with no hole
    2. Steel plate with a hole
    3. Steel plate with a hole and a turbine

    Let us compare the pairs of options in turn.
    PJ identified a special case when you deliberately want to bleed energy - specifically if a car accelerates down a hill.
    I'm considering the normal cruising situation.

    "Steel plate with no hole" vs "Steel plate with a hole"
    Steel plate with a hole means less air resistance. Steel plate with a hole wins this round.

    "Steel plate with no hole" vs "Steel plate with a hole and a turbine"
    Steel plate with a hole and turbine generates power and wins.

    Okay. So either option option 2 or 3 beats option 1.

    The interesting bit is to consider:
    "Steel plate with a hole" and "Steel plate with a hole and a turbine"
    The turbine slows the air down (that's how they work - it's where they get their energy from) so it has more air resistance than just the hole. (1 point to hole without turbine).
    But, the turbine generates electricity for our batteries (1 point to turbine - now for the tie breaker).
    The 2nd law of thermodynamics tells us the energy that the turbine generates will be less that the air resistance.
    So the "Steel plate with a hole" beats "Steel plate with a hole and turbine".

    Final ranking:
    1st place: Steel plate with a hole
    2nd place: Steel plate with a hole and a turbine
    3rd place: Steel plate with no hole

    So if you can find a place to make a hole in your car to reduce air resistance (which sounds like a pretty big if) then do that, but don't add the turbine.
    When your car is cruising along the turbine will cause more resistance than the energy it will generate.
     
  11. Mind if I change your ranking a wee bit, btiw2?

    Thank you.

    It's:
    2nd place: Steel plate with a hole
    3rd place: Steel plate with a hole and a turbine
    4th place: Steel plate with no hole


    1st place goes to:
    No steel plate regardless of hole, no hole or turbine - leave the bludy car alone.
     
  12. Please don't hate to say it. :oops:
     
  13. Mr. Handyandy

    Mr. Handyandy Screwfix Select


    But the alternator is not harder to turn, it doesn't make the fanbelt squeal when more power is required. The engine may struggle to find electricity but there is no extra force needed to run the alternator. It runs relative to the speed of the engine, regardless. When the alternator needs more power, the fanbelts and alternator pulley do not struggle to turn, so they don't slip.
    So DA is wrong.
     
  14. Mr. Handyandy

    Mr. Handyandy Screwfix Select


    But not as much resistance as a flat solid part of car that already exists. It's free air.
     
  15. fillyboy

    fillyboy Screwfix Select

    What you're saying is true for a dynamo, but not an alternator.
    Similarly, an aircon compressor, belt is permanently attached and the compressor turns as the engine turns, with the aircon switched off, the compressor is free wheeling (almost), switch on the aircon and watch the revs drop. An alternator, although turning all the time, only kicks in when a charge is required, extra force is required to turn it, innit.
     
  16. Mr. Handyandy

    Mr. Handyandy Screwfix Select


    No it's not. The air-con is free-wheeling because it uses a clutch which is disengaged when not in use. The alternative runs regardless. It is always engaged and charging.
     
  17. NC500

    NC500 New Member

    You're such a nerd :D
     
  18. Mr. Handyandy

    Mr. Handyandy Screwfix Select


    Aye, it annoys some people!
     
  19. NC500

    NC500 New Member

    Ha! I'll bet it does.
     
  20. P J Thompson

    P J Thompson Active Member

    No, sadly you are wrong. In drawing more current there is an effect on the electromagnetic field created by the winding spinning relative to the stator (more inertia is created). That effect leads to there needing to be more effort put in to spin the moving coil in the alt. This is observable when you do something like let the engine idle and turn main beam on....the revs will dip slightly. To get the revs back up, guess what, more fuel has to be injected.

    You're arguing against established science that is built into the electrical systems of everything from car alternators through to wind turbines and power stations :)
     

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