About Fuse System

Discussion in 'The Projects Forum' started by Lightfire, Mar 18, 2011.

  1. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    Hello,

    Sorry for a couple of questions about fuse-related questions.

    I just want to ask more information about fuse.

    1) For example my fuse was rated as 12 V DC then the electric accidentally goes 13 V DC, is there any possibility to the fuse to have it melted?

    2) Are the size of fuses depending according to its rated specification? (For example, size of 240 V AC and 12 V DC) Because I noticed that the fuse of 12 V DC (glass) is so small (like the fuses in lightning aparatuses in photography) and the 240 V AC (250 V AC instead) is big.

    3) I don't know what's the specification of my fuses. What should I do to have it I know?

    Thank you thank you very much for your effors and time in answering my questions.

    Lightfire
     
    Last edited: Mar 18, 2011
  2. Enforcer83

    Member

    Oct 29, 2010
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  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    1) For 1V over its rating it should not melt.. However if that is the case you picked the wrong fuse from the start. For a 12VDC system I would pick a fuse with a rating of like 32VDC or greater.

    2)Yes the physical size of a fuse is related to the voltage it is designed to interrupt.
    Typically DC rated fuses/circuit breakers are larger that AC versions. The size of the element in the fuse is related to the amount of current it is designed to interrupt.

    3)A fuse is typically specified based on its voltage rating, current rating, interrupt rating, and time curve. Current rating and interrupt rating are NOT the same. A time curve is how fast a fuse will blow depending on the level of current it is seeing.
    For example a 10Amp "slow-blow" fuse might take 15 seconds to blow if exposed to 20 Amps but a "fast-blow" fuse might only take 5 seconds.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Just a friendly warning...
    slow down lightfire... The questions you ask on this forum scare me.. You "seem" to jump into a project without knowing the basics first.. This is dangerous. You seem to have a hundred different projects going on and don't know enough to be safe on any of them.
     
  5. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    No no. :)

    I am not working with hundred of diffferent projects because I'm afraid of it and I don't want to waste my money just for testing it.

    So, I just asking. asking and asking. :) and if i figured it out all, sure, i will do some projects.

    p.s. can you help me?
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    This is one of those subject it is possible to overthink.

    You need a fuse rated for equal or more voltage than you are breaking. Simple, and fundamental.

    Fuses come in slow blow or conventional. The conventional blow as fast as the wire will melt, while the slow blow will allow short surges without doing anything. A power supply with a large bank of capacitors is going to have a startup current surge as the capacitors charge, then it will settle down to a low current.

    When a fuse blows there may already be damage to the circuit. Just a rule of nature. Whatever made the fuse blow probably wasn't right.

    Murphy's Law says the transistors will usually protect the fuse.
     
  7. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    OK. One more question.

    For example, my battery was rated as 12 volts dc and 12 amperes. Then I used fuse that is rated as 12 v dc and 12 amperes. is it ok? :D

    thank you
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    Yep.......
     
    Lightfire likes this.
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Nope.. A 12V battery is typically supplying 13-14VDC.. If your fuse is really only rated to 12V this is NOT okay. This is why ALL automotive fuses are typically rated to 28 or 32 VDC.

    Like already said....Your fuse MUST be rated equal to or "higher" than the "maximum" voltage your circuit will see. 12 is not higher than 14.

    I'd have a hard time finding a fuse that is only rated to 12V though.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    I'll respectfully disagree, it is close enough it would be almost impossible to notice any difference. There really is such a thing as close enough, and fuses are not that precision components.
     
  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    In the professional world if you took a product to UL or any testing agency and your system operates at 13-14VDC with a fuse rated to only 12VDC that would be flagged as a non-conformance and you would need to find a higher rated fuse. Close enough doesn't cut it as far as safety is concerned.

    Regardless I'd have a hard time trying to find a fuse that is only rated to 12VDC anyways.. But still ratings are ratings (amateur project or not)...
     
  12. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    Yes. for lead-acid battery it is more than 12 volts even though in specs it said it's 12 volts. but it's not 13-14. if it fully chraged, it voltage accross about 12.65. if it is 75% it is 12.00 volts. I guess.

    @Bill_Marsden

    Yeah. yeah. yeah. :D it won't melt :O just for one more voltage.√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√
     
  13. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    Sorry, if 12 v acid-battery is 75% chraged its voltage accross at about 12.45. :)
     
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