Announcement

Collapse
No announcement yet.

I was just wondering the logic behind this...

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    I was just wondering the logic behind this...

    Ok, we all know that devices that draw huge amounts of current can adversely affect gas mileage... but can someone explain why it does this?

    Lets say that we have hooked up an inverter in our car... that allowed us to use 110AC... and i decided to put a microwave in my car, so i could make popcorn while on the road.

    OR

    Say I hit my head real hard and started doing pointless mods... and hooked up 15 enormous foglights on my car.... as well as 6 12" subwoofers in my car that i play non-stop while the car is running

    now.... all these devices will get their power from the battery... which is continually being recharged by the alternator... which gets ITS power from the crank pulley via the alternator belt
    the crank pulleys speed is dependant on RPM... and nothing more

    my question is... HOW does a high draw device/devices actually add load to the engine? The alternator is directly connected to the crank... regardless of whether or not my microwave is in the car.... so doesent it generate the same amount of power regardless??

    Can someone explain?
    Like, i feel the idle drop when i turn on my defrosters.... i could feel the increased load
    I just dont know why...

    #2
    Draw from the alternator causes it to have to work harder to keep up with the system's demands. In return it takes more revolutions of the pulley on the alternator to get the same amount of juice, thus adversely effecting power output.

    Or at least thats my understanding. Anyone else?
    The T3 BP MX-3 conversion has begun, and is taking forever & will kill me.

    Comment


      #3
      Originally posted by pigeon
      my question is... HOW does a high draw device/devices actually add load to the engine? The alternator is directly connected to the crank... regardless of whether or not my microwave is in the car.... so doesent it generate the same amount of power regardless??

      Can someone explain?
      Like, i feel the idle drop when i turn on my defrosters.... i could feel the increased load
      I just dont know why...
      In a way, you just answered your own question. You noticed the change when the defroster (a somewhat large load) is turned on.
      You can't get something for nothing, so the alternator pulley gets harder for the crank to turn in response to the demand for current (the alternator regulates the voltage).

      If the alternator was always generating the same (maximum?) power, the unused power would have to go somewhere. This would generate uncessary heat, which is the likely byproduct of the wasted power and also be a waste of engine fuel.

      Originally posted by D323
      it takes more revolutions of the pulley on the alternator to get the same amount of juice
      Basically, an alternator is supposed to generate the required amount of power (maintaining a regulated voltage) regardless of engine speed. In practice it isn't exactly that way in low RPM or in high load situations. Engine RPMs depend on how/if the car is being driven, so it would make sense for the alternator to generate power as independently as possible from engine speed.

      Comment


        #4
        Originally posted by pigeon
        my question is... HOW does a high draw device/devices actually add load to the engine? The alternator is directly connected to the crank... regardless of whether or not my microwave is in the car.... so doesent it generate the same amount of power regardless??

        Can someone explain?
        Like, i feel the idle drop when i turn on my defrosters.... i could feel the increased load
        I just dont know why...
        When the battery is fully charged or at a high state of charge, the voltage regulator senses this condition and turns off the DC voltage being sent to the rotating field (the rotor). With the field de-energized, that is, when it is not producing magnetic lines of force that cut through the stationary armature (the stator), and induce a current to flow in it, there is virtually no load, or drag, on the rotating field and little power is required from the engine to rotate it. This also prevents the battery from being overcharged.

        When the battery charge drops below a critical level, the voltage regulator senses that condition and energizes (sends DC voltage) to the field. This greatly increases the load on the field and therefore requires more HP from the engine to rotate it.

        Therefore high current draw devices actually add a load to the engine since they will deplete the battery charge more rapidly and as a consequence cause the alternator to operate in its charging mode for longer periods of time.

        Happy Motoring!
        02 DX Millenium Red - The Penultimate Driving Machine
        MP3 Strut Tower Bar kit; Cusco Front Lower Arm Tie Bar
        MSP Springs, Struts, Stabilizer Bars, Trailing Links, #3 Engine Mount
        Kartboy Stabilizer Bar Bushings; Nyloil Shifter Bushings; Red Line MT-90 Gear Oil
        MP3 Shifter, Knob and Aluminum Pedal Set
        Suvlights HD Wiring Harness; Osram Night Breaker H4 Bulbs; Exide Edge AGM Battery
        Summer: 5Zigen FN01R-C 16 x 7" Wheels; Yoko S.drive 205/45-16s
        Winter: Enkei OR52 16 x 7" Wheels; Falken Ziex ZE-912 205/45-16s
        Modified OEM Air Intake; Racing Beat Exhaust System; Techna-Fit SS Clutch Line
        Denso SKJ16CR-L11 Extended Tip Spark Plugs; Magnecor Wires
        Power Slot Front Brake Rotors; Techna-Fit SS Brake Lines; Hawk HPS Pads
        Red Line Synthetic Engine Oil; C/S Aluminum Oil Cap
        Cyberdyne Digital Gauges: Tach; Ambient Air Temp; Voltmeter

        Comment


          #5
          Originally posted by goldstar
          When the battery is fully charged or at a high state of charge, the voltage regulator senses this condition and turns off the DC voltage being sent to the rotating field (the rotor). With the field de-energized, that is, when it is not producing magnetic lines of force that cut through the stationary armature (the stator), and induce a current to flow in it, there is virtually no load, or drag, on the rotating field and little power is required from the engine to rotate it. This also prevents the battery from being overcharged.

          When the battery charge drops below a critical level, the voltage regulator senses that condition and energizes (sends DC voltage) to the field. This greatly increases the load on the field and therefore requires more HP from the engine to rotate it.

          Therefore high current draw devices actually add a load to the engine since they will deplete the battery charge more rapidly and as a consequence cause the alternator to operate in its charging mode for longer periods of time.

          Happy Motoring!
          awesome reply, makes perfect sense!
          thanks

          Comment


            #6
            And here I thought that the alternator was just a simple dynamo.

            Comment

            Working...
            X