Does volt rating on fuse affect the amps at which it blows

[winkinatcha]

Basic question which may have been answered in another thread, apologies if I missed it.


I am using inline auto (12v) fuses as a last resort battery disconnection if something goes closed circuit downline (Ctrlr etc) from my battery.

I am running 24 volt wheels and controllers that are rated at 500w.

In a dead-start, under load condition I have blown a 25 amp 12 volt fuse. I am currently using 30 amp 12volt fuses which have not blown under the same "working" conditions.

Using Old Skool Volts*Amps=Watts

24*25=600w which I reckon is within tolerance and not unexpected to blow under high current work situations.

But I am curious... will a 12 volt rated fuse blow at lower current levels with higher voltages.... Ultimately I guesss wot I am asking is does a fuse blow cos of the wattage applied, or the current or is it not that simple?

Joe

 

[SamTexas]

Good question. I would like to know the answer too. To me only the current matters, so I don't why fuses also have a volt rating.

 

[biohazardman]

My understanding of this subject is that a fuse of the correct voltage will blow at ?A and in ?time. A fuse used at a higher voltage than rated may arc and take longer to blow. So a higher voltage fuse may be used as a substitute but not a lower voltage as I have done. What's up with that? I am bad. Glass tube type fuses have both the voltage and amperage rating stamped on them. I only see an amperage rating on automotive blade type fuses. Most are 12-24V 32V max although there are some 58V available.

 

[amberwolf]

As has been discussed before, the volt rating is the volts at which it is guaranteed to break the circuit. Above that, it might, or it might not.

Also, note that like switches, breakers, etc., AC vs DC also matters, for that voltage.

 

[ZOMGVTEK]

The current rating on the fuse never changes. The voltage rating is the maximum voltage the fuse is designed to handle. High voltage, especially DC, tends to not be happy when you just make a small link go away. It will continue to arc across the path for a long while, basically making the fuse useless and protect nothing. AC isn't as critical, since it cycles past 0, generally 120 times a second. It's hard to sustain an arc when voltage passes 0, so it basically self extinguishes. DC is quite a bit more tricky, so its not just the number you care about, it needs to be DC rated for your voltage to ensure its actually going to act like a fuse. DC of course has power all the time, so an arc can go on as long as the gap is short enough for the voltage.

This kind of stuff is partially why a lot of people with high voltage, high current setups don't bother with fuses. If the bike can draw 200A at 120VDC during normal operation, what fuse are you going to put in there thats actually going to protect much?

Of course you can use a 10000000V fuse on a 1V circuit, thats fine. It simply means its actually designed to absorb the energy required to break that arc, up to the rated voltage. Just don't go using a 32V fuse on a 100V pack and expect it to be perfect, it might be a better bet to just hope your 10 AWG wire melts quick.

That said, ANY fuse tends to be better than none, as far as 'protection' goes. But its far from an end-all protection solution, what it protects is often trivial.

 

[winkinatcha]

Awesome!

Thankyou for the quick replies, and informative content...

Particularly cool to understand the arcing potential at higher voltages

As an FYI, this is a lower voltage (24 v) circumstance, and this "Fuse Protection" I do see as a last resort battery protection for the (I hope) unlikely scenario that I get a complete short downstream.

And of course after AmberWolfs "as has been discussed before" comment I found a bunch of threads that DO discuss this... after posting this'n... Apologies for going over the same old ground, so to speak.

Joe

 

[salty9]

You could make a fusible link by using a smaller gauge wire with the ampacity you want it to blow at. One end could be spring loaded to increase the separation. Spring tension should be strong enough to separate the wire insulation.