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Fuse Rating for Automotive Application

Discussion in 'Beginner Electronics' started by alpha_uma, Jun 14, 2005.

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  1. alpha_uma

    alpha_uma Guest

    I have a regulated DC Adapter with the following specs:

    input: 12V DC (from cigarette lighter socket)
    output select: (3, 4.5, 6, 7.5, 9, 12)V DC, 0-300mA

    Is a "1A, 125V" fuse safe enough to use (for the sake of protecting the car
    battery and the electronics connected to the adapter)? What is a "typical"
    fuse in such an environment for use with portable electronic gadgets? Any
    hard data for typical ranges for current and voltage spikes during car

  2. Landon

    Landon Guest


    A 1 amp fuse is probably the smallest you are going to be able to find
    for automotive usage.

    As far as protecting the battery etc. remember that the cigarette
    lighter circuit already has a fuse in case something goes horribly wrong.

    I wouldn't think that there is a "typical" fuse for anything, it depends
    on what your load is going to be, that is where the "typical" comes
    in. Your total load for the adapter is never going to be above 300mA
    which is less than one amp, your adapter probably has some kind of
    thermal overload built into it that will shut it down if the load goes
    over 300mA.

    Check under the dash for your cigarette lighter's circuit's fuse, it is
    probably 15 amps, as long as you do not plug anything into the cigarette
    lighter socket that exceeds your fuse rating you should be fine.

  3. alpha_uma

    alpha_uma Guest

    Thanks for replying.

    Yes, the car's cigarette lighter circuit already has a 15A fuse under the
    dash. The "1A" fuse (specified by the DC adapter's manufacturer caution
    against fire hazard) is actually inside the DC adapter. It has burnt out.
    I hope so. Is there any relationship--direct or indirect--between the 1A
    rating of the fuse and the 300mA output rating of the adapter? Or is that
    something only the manufacturer's engineers would know? Would a max rating
    of 300mA be enough to power a laptop computer?

  4. Landon

    Landon Guest

    Your adapter has a 1 amp fuse because that is the smallest that you can
    find for automotive uses, there are probably some that are smaller but
    they are hard to find.

    1 amp also equals 1000mA.

    I seriously doubt that 300mA is going to power your laptop, my little
    portable CD player runs on something near 400mA and all it is is a
    little motor, a laser, and a small audio amplifer to power the headphones.

    Check the sticker on the laptop for its power requirements, it probably
    says 120 volts; 50/60 Hz.; and then the amperage is probably something
    between 3 and 6 amps (3000mA and 6000mA), or it may not have the
    amperage and just list the wattage.

    Your best bets for running it from the cigarette lighter jack are
    getting an adpater that was specifically made for your laptop to run
    from the cigarette lighter jack, or getting a power inverter that
    converts the 12 volts DC to 120 volts AC then just plugging the laptop
    into that.

    Good luck.

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