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

 

The voltage rating determines the voltage at which with sufficient current, the fuse will arc, see http://en.wikipedia.org/wiki/Electric_arc.

This article on fuses should answer most of your questions. http://en.wikipedia.org/wiki/Fuse_(electrical)

As for the specifications, there should be some form of markings that provide that information on the fuse itself.

 

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.

 

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.

 

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.

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?

 

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.

 

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?

thank you

 

Yep.......

 

Yep.......

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.

 

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.

 

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)...

 

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.

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. it won't melt :O just for one more voltage.√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√

 

Sorry, if 12 v acid-battery is 75% chraged its voltage accross at about 12.45.