fuse ratings

Discussion in 'General Electronics Chat' started by mlkcampion, Nov 23, 2006.

  1. mlkcampion

    Thread Starter Active Member

    Nov 16, 2006
    59
    0
    Hey Forum
    I have a fuse that is rated for 250v 4amp, what is
    the rating for this fuse at 24vDC, i.e. what current
    will it blow at?

    Thanks
    Michael
     
  2. PointGiven

    New Member

    Sep 10, 2005
    7
    0
    It will blow at 4 amps.
     
  3. mlkcampion

    Thread Starter Active Member

    Nov 16, 2006
    59
    0
    Thing is the circuit is drawing more then four amps for hours, hence my
    question on the subject?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Many fuses are rated to blow at the stated value after some time interval. The rating is a bit unrealistic is you want a fuse to pop immediately at the stated current. Most want to see 115% of the rated current befre they blow immediately. A circuit breaker will perform better that way.

    Part of your problem is the lower voltage. Fuses fail when they are heated to the melting point by the power dissipated in the element. Power is the product of the voltage times the amperage. Your 4 amp 240 volt fuse will carry more current at 24 volts, as it does not get as hot.
     
  5. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    A 4 amp fuse blows at 4 amps. The voltage rating is there to guarantee there will not be an arc over. You can pick and choose the specifications on a fuse so that it will have zero delay in blowing or will allow small excursions over the rating, the difference between 'fast blow' and 'slow blow'
     
  6. pebe

    AAC Fanatic!

    Oct 11, 2004
    628
    3
    Surely the power dissipated in the fuse = I*I*R. That's not voltage dependant.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    If you figure it by E*E/R, it is.
     
  8. pebe

    AAC Fanatic!

    Oct 11, 2004
    628
    3
    The voltage drop across the fuse(E) will be the same for both circuit voltages
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi Pebe,

    Good point.
     
  10. mlkcampion

    Thread Starter Active Member

    Nov 16, 2006
    59
    0
    Hey Forum
    That discussion bout the power is exactly what i was looking
    for, it was that which was bothering me!! Brilliant!!
    Cheers for that!!!!

    Michael
     
  11. subtech

    Senior Member

    Nov 21, 2006
    123
    4
    Hey mlkcampion
    If you will do a google search using the words "fuse melt data" you will get lots of info on different kinds of fuses and their applications. Bussman, Cooper, S&C and many others provide detailed data and "curves" to help you make the right choices in circuit or equipment protection.
     
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