Cars, cars and electric cars

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

  1. It's true for both, and you could prove it to yourself if you had one in your lap.

    It's also the concept behind electrical braking and regenerative braking as used in leccy cars.

    A modern car alternator can output an easy - what? - 100 amps if required. (Headlamps, driving lamps, heated screen, wipers, heater fan, flat battery etc).

    If you place that 100A leccy load on it, it'll deliver it. That's a fair amount of power, and it's being provided ultimately by an extra load on the engine and therefore by the car's fuel.

    You can try this - let your car idle, and then switch on all of the above. You will almost certainly hear the additional load that's been placed on the engine.

    Mr Ha - do you think that the alternator is always placing that load on the engine, even when none of these items are on and the battery is fully charged?
  2. NC500

    NC500 New Member

    :confused: I'm gonna leave you boys to thrash it out.
  3. fillyboy

    fillyboy Screwfix Select

    Mmmm yeah but a dynamo can't increase output when more amps are required I thought.
  4. P J Thompson

    P J Thompson Active Member

    Copy cat :p
  5. P J Thompson

    P J Thompson Active Member

    With a dynamo, the voltage drops.
  6. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    When you turn the main beam on, this uses more electricity and the cars ignition system receives less, and that is why the car idle speed drops. It's a drain on the ignition.
  7. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Yes. You try it any time of the day. Test the voltage across the battery when engine is stopped. About 12v.
    Test with the engine idling or revving. 15-16v.
    That alternator is charging always. Lights on, lights off, whatever, it is charging.

    Any time you find that that is not the case, your alternator is duff.
  8. longboat

    longboat Screwfix Select

    What about a diesel engine?
  9. P J Thompson

    P J Thompson Active Member

    Love it.

    Not true, but I love it :D

    (ETA) and if you're alt is charging at 16v in a 12v system, you're gonna have a big problem :D
    14v is around average.
    I made a mistake in the post you quoted btw. Should have said rotor, not 'winding' - the coil winding is what makes up the stator. :oops:
    longboat likes this.
  10. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Yeah, rotor, winding, stator are constant.

    Car charging at any voltage above 12 doesn't matter, that's why we have voltage regulators.
  11. P J Thompson

    P J Thompson Active Member

    It does matter :)
    If that 16v were regularly getting to the car's electrics and battery, you'd get all kinds of gremlins. If you had 16v it'd be a good sign that the voltage regulator in the alt was possibly fubar.

    The rotor isn't constant/fixed. That's the spinning bit that induces the current. The stator is the fixed bit.

  12. When in a hole, stop digging ?
  13. joinerjohn1

    joinerjohn1 Screwfix Select

    Hate to rain on your parade Handy, but in my car, if the engine is only turning over at lets say 800 rpm and there's no load then it runs at a fairly constant 800rpm. If I simply turn the headlights on and turn the air conditioning on (large loads) then the engine now drops it's rpm to around 650 -700 rpm, so as you see , the loading on the alternator , does affect the engine directly. I've also noticed during the summer that if I turn the air con on, then there's a noticeable drop in power output from the engine. BTW, my aircon is electrically operated.
    btiw2 likes this.
  14. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    It's constant as in it doesn't go anywhere different whatever draw is needed.
  15. longboat

    longboat Screwfix Select

    Sound advice.

    What happened to you?
    Not another spell on the naughty step, I just can't imagine it!
  16. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    I just told you that jj. The extra electricity needed to run those components take electricity away from the ignition parts. Like less spark from the coil and the plugs.
  17. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    I'm not digging, I'm filling those people into holes.
  18. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    You would get 14v at tickover, more when revving or driving.
  19. longboat

    longboat Screwfix Select

    The emf in the field winding changes with increased load, an increased load draws more current through the field winding which in turn makes the rotor harder to turn... thus, more load on the engine.
    btiw2 and P J Thompson like this.
  20. P J Thompson

    P J Thompson Active Member

    HA, as fun as this're still wrong on this one. About everything :)
    btiw2 likes this.

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