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Are bikes AC or DC?

Discussion in 'Technical and Troubleshooting Torque' started by JontyG, Jan 23, 2006.

  1. Hi all,

    An ignorant question....

    Does anyone know if the voltage on a VT250C is AC or DC?

    I am guessing it's DC.

    Reason I ask, is that I am having some issues with an electronic LED flasher unit, which is supposed to operate at extremely low loads, but it's not wotking properly when used in conjunction with 4 x 0.7W LED globes (works fine as soon as I replace one of the LED globes with a 10W incandecent globe). The guy at Narva said it may be because my bike is AC, not DC... :?

    Any help appreciated.

  2. well i dont wear the little leather captains hat, so i guess my bike is DC - if you ride with your hairy chest poking out of your leather vest then your bike is AC?
  3. I don’t know about your VT but would be extremely surprised if you could find anything on Australian roads that was AC, and if you do, don’t trip over the extension lead. :LOL: :LOL:

    I would suggest that the LED’s are just not dragging enough current to work your flasher unit. You may have to replace your flasher unit or wire in an extra globe (under your seat) or something to give it more load.
  4. Leds 4x 0.7W = 2.8W = 200mA @ 13.8V
    Globe 10W = 720mA @ 13.8V

    The flasher probably detects anything less than 500mA as a fault conditon, or uses the resistive load of the globe as part of the oscillator (flashy bit) circuit.

    The leds will need a resistor in series with them, if not already fitted. 60 ohms at 2.5W should do it.

    Oh, and its DC. Requirement of the battery.
  5. they are on a highway to hell
    ....that's a good 'un, gotta remember that.

    Your LEDS suck WAAAAY less power than the standard globes.
    Way less resistance....and no flasher-can is auto-adjust.
    By using 1 globe and 1 LED per side, things should work, but....the flash-rate is too fast. 2 Leds...and there's NOT enough resistance, the flasher-can either gets a fit or the flash rate so fast as to appear as a permanent glimmer.
    You need a resistor, best would be one resistor soldered (and heat-shrunk) into the positive output side of the flasher-can (provided you're running LEDs allround)...or.... add sufficient LEDs to each indicator to constitute a similar current-draw as a globe.
    For correct info on which resistor...no idea, really...but things should come clear after googling around a bit.

    Perhaps I shouldn't laugh too hard at the Narva man....some early Pommie bikes ran frame-positive...but AC? :LOL: :LOL:
  7. Alternating current (AC) doesn't have to come from a mains outlet. Of course 240V power from the wall is AC, but so is power coming from an alternator.

    The power coming from the alternator (AC power) is then passed through a rectifier to convert the current from AC (alternating current) to DC (direct current) to charge your battery.

    ....so , there is AC power in your bike, and no, you don't need an extension lead.

    But, of course the power running all of your gear is 12V DC ;)
  8. Thanks for the quick replies.

    lol, i didn't think it was AC...but i'm new to this and pretty ignorant when it comes to electrics...

    This is the flasher unit I have installed:


    (part number: 68245BL)

    It says it should handle a load as low as 1mA per side, and i reckon my 0.7W LED's provide a higher load than that.

    Looks like a resister in line with the +'ve from the flasher unit may be the go.

  9. Thanks for that, good to know :grin:
  10. My basic maths is telling me it should work.
  11. Hi Jonty, Nil and Glitch

    You all know a bit more than me about these things (I know very little
    about these flash cans).. but to add my $0.02, 60 ohm resister seems a
    little high.

    Jonty.. do you have the datasheet for the LED's ?. What is the
    current and voltage drop at their recommended operating conditions ?

    Normal LEDs have a pottential barrier of about 2-3 volts. When
    the LED has more voltage across it than it's BP, then it acts like a
    short out (roughly).

    As glitch and Nil said you need a resistor to limit this current flowing into the
    can.. so that the charge time is within operating conditions and that you
    are not putting to much current through your LED's.

    (Globes on the other hand are current limiters, because the filiment
    heats up and becomes resistive-- these devices have resistance).

    If the datasheet said that your LED's optimal operating condition
    is 2.2V @ 200mA.. then you would work from that information--

    2.2V * 4 = 8.8V

    Using NIl's battery voltage of 13.8V, we have a head room of--

    13.8V - 8.8V = 5V

    Now we use a resister to develop the 5V across it at 200mA (Peak)--

    ohms law: 5V / 200mA(pk) = 25 Ohm resister at--

    Wire Loss Formula: (200mA ^ 2) * 25R = 1 Watt(pk) rating

    I normally have power ratings of 10% greater than my calculated peak
    value, but because current will be flowing roughly half of the time,
    then average power disipation will be roughly a quarter of this.

    Nil... sorry for stepping on your fine work ;)

    Cheers ;)

  12. I've tried installing led light for my beemer 2 months ago and it blew a 10amps fuse!