No more specification other than ampere rating.

Discussion in 'General Electronics Chat' started by Lightfire, Jun 9, 2011.

  1. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    Hello folks,

    I am searching the internet and finally found the fuse that best suits me.

    But sadly, there is no more specification listed in the Web site other than the ampere rating.

    The ampere rating was 500 milliamperes and its size was 20 millimeter.

    Please refer to this link: http://www.rshelectronics.co.uk/product.php?id_product=213

    Any help would be greatly appreciated.

    Lightfire
     
    Last edited: Jun 9, 2011
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You need a fuse that has a voltage rating greater (higher) than the voltage in the circuit that you are using it with. If you are using a 12v lead-acid battery, then that fuse would certainly be rated for at least 12 volts.

    You missed the "quick blow" specification. That would be fine for LEDs, but if you were using incandescent lamps, the fuse may blow when you first apply power. You would use a "slow blow" type fuse with incandescent lamps and motors.
     
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  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    Good chance its rated to 125 to 250V. (most fuses like that are)
    A 1/2A glass fuse is actually easy to come by... (in the US anyways)
     
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  4. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    But how did you know that it is fine to apply with a 12 volt battery? I want to know.

    Lightfire
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    2,536
    You can use a 120VAC fuse with 12V, but not the other way around. This is true of most electronic components, a 35V capacitor will replace a 25V capacitor.
     
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  6. SgtWookie

    Expert

    Jul 17, 2007
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    Fuses need to be rated for a higher voltage than the circuit you are using them in.

    I have never seen a fuse rated for less than 32 volts.
     
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  7. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    Okay. The purpose is to melt down the fuse due to high current flowing through it. It might looks nonsense but I really want to see a fuse melting in real life.:D

    Okay, please refer to the schematic I attached.

    As you may see, there were three lamps rated as 6 volts, 0.5 amperes wired in parallel. So, total all, the three lamps were pulling 1.5 amperes. By that, it will cause the fuse to melt down.:D

    The battery that I will use is indicated on the schematic. And the fuse that I will use would be the one that I have asked.

    So folks, do you think it will happen, I mean will the fuse melt down?

    Lightfire
     
    Last edited: Jun 9, 2011
  8. tom66

    Senior Member

    May 9, 2009
    2,613
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    One of the fuses will melt first, the other will be fine. (It would be unlikely for both to fail simultaneously, unless it was a gross overload.)
     
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    With 1.5A running through it the fuse will blow in approx one tenth of a second (.1 seconds)
    Don't waste your time.. Its not going to be anything more than a really quick small flash of light.. if that.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    It won't be very exciting, but it will be an expensive 1/10 second!

    If you could instead make the income of what the fuse cost every 1/10 second, you would be a wealthy person in the not too distant future. If the fuse cost $0.10 USD, that would be an income of $3,600 per hour or $7,200,000 per year!
     
  11. tom66

    Senior Member

    May 9, 2009
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    I once put about 10A through a cheap multimeter on the mA range and it lit up the casing of the meter very bright, but it did its job (meter worked fine after fuse replaced.)
     
  12. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    Here is a good statement on fuse voltage rating from Littlefuse contained in Littelfuse Electronic Fuse Products Catalog.

    "VOLTAGE RATING: The voltage rating, as marked on a
    fuse, indicates that the fuse can be relied upon to safely
    interrupt its rated short circuit current in a circuit where the
    voltage is equal to, or less than, its rated voltage.
    This system of voltage rating is covered by N.E.C.
    regulations and is a requirement of Underwriters
    Laboratories as a protection against fire risk. The standard
    voltage ratings used by fuse manufacturers for most small dimension
    and midget fuses are 32, 63, 125, 250 and 600.
    In electronic equipment with relatively low output power
    supplies, with circuit impedance limiting short circuit
    currents to values of less than ten times the current rating
    of the fuse, it is common practice to specify fuses with
    125 or 250 volt ratings for secondary circuit protection of
    500 volts or higher.
    As mentioned previously (See RERATING), fuses are
    sensitive to changes in current, not voltage, maintaining
    their “status quo” at any voltage up to the maximum rating
    of the fuse. It is not until the fuse element melts and
    arcing occurs that the circuit voltage and available power
    become an issue.
    The safe interruption of the circuit, as it
    relates to circuit voltage and available power, is discussed
    in the section on INTERRUPTING RATING.
    To summarize, a fuse may be used at any voltage that is
    less than its voltage rating without detriment to its fusing
    characteristics. Please contact the factory for applications
    at voltages greater than the voltage rating."
    ================
    Bold emphasis added by me.

    Another good article is Littlefuse "Fuseology" found in "OE101-C - Automotive OEM Catalog"
     
    Last edited: Jun 24, 2011
  13. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
    90
    Why would you entertain feeding 6 volt lamps from a 12 volt battery?

    Why would you have 2 fuses in series?
     
  14. PatM

    Active Member

    Dec 31, 2010
    81
    72
    As questioned above, only one fuse in the Positive line is necessary.
    No need for 2 fuses in series in that circuit.
     
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