Fuses?!? (Another "wattage" question that's been on my mind)

[sangesf]

Let's say I buy a "DC fuse" and it's rated 32v 15a...

Can I run 100v 2a load through it without blowing the fuse?

Or are fuses able to withstand a certain amount of "wattage" through it before it blows?

Does a "fast blow" or "slow blow" fuse make a difference in this equation?

 

[icecube57]

Fuses dont feel voltage but they feel amps. So you could run 100v 15A through a fuse meant for 32v 15A. Wattage plays no role although the 100v setup obviously has nearly triple the wattage. But if you push it past its amperage blow point and its a fuse that has an exposed element it could arch violently when it blows. Its best get a glass/cartridge style fuse so the arch is contained.

Slow blow fuses allow for quick surges nearly double the amperage rating or more which is well above its blow point to allow power hungry loads to start and the amps tapers off quickly but they will eventually blow if tha high amp load is sustained. But in alot of cases they can run 20-30% of their rated capacity for extended periods.

Quick blow fuses can barely take any amps above its rated without blowing.

 

[sangesf]

But aren't amps a measure of Watts over Voltage?
How can a fuse "tell" amperage without some type of "reference point" like voltage or wattage?

 

[Ypedal]

Icecube is right.

The fuse only cares about " amps " ..

using the highway analogy, the highway does not care how fast(voltage) you are going, but it does care how many lanes wide(amps) cars can travel... the popo on the other hand lol...

Volts x Amps = Watts.

Fuses do have a voltage rating, i believe this has to do with the gap they produce when they burn out, too small a gap at high voltage could cause arcing ( bad ) .. where 100v fuses will burn with a larger gap to prevent the arc at their rated spec.

http://en.wikipedia.org/wiki/Fuse_(electrical)

Rated voltageVoltage rating of the fuse must be greater than or equal to what would become the open circuit voltage. For example, a glass tube fuse rated at 32 volts would not reliably interrupt current from a voltage source of 120 or 230 V. If a 32 V fuse attempts to interrupt the 120 or 230 V source, an arc may result. Plasma inside that glass tube fuse may continue to conduct current until current eventually so diminishes that plasma reverts to an insulating gas. Rated voltage should be larger than the maximum voltage source it would have to disconnect. This requirement applies to every type of fuse.

Rated voltage remains same for any one fuse, even when similar fuses are connected in series. Connecting fuses in series does not increase the rated voltage of the combination (nor of any one fuse).

Medium-voltage fuses rated for a few thousand volts are never used on low voltage circuits, because of their cost and because they cannot properly clear the circuit when operating at very low voltages.[citation needed]

 

[sangesf]

Icecube is right.

The fuse only cares about " amps " ..

using the highway analogy, the highway does not care how fast(voltage) you are going, but it does care how many lanes wide(amps) cars can travel... the popo on the other hand lol...

Volts x Amps = Watts.

Fuses do have a voltage rating, i believe this has to do with the gap they produce when they burn out, too small a gap at high voltage could cause arcing ( bad ) .. where 100v fuses will burn with a larger gap to prevent the arc at their rated spec.

http://en.wikipedia.org/wiki/Fuse_(electrical)

Ok that makes sense....
THAT'S the kind of info I'm looking for when I ask a question...

Thanks Ypedal...
(You can NOW answer my question on my other thread.. [inside joke]).

P.S. Those tiny fuses are HORRIFIC..... I've had one blow and because it was so small, the plastic melted AND "folded" the blown fuse pieces into each other and created a dead short. = Very Bad!

P.P.S. I also read this in the article...

Most automotive fuses rated at 32 volts are used on circuits rated 24 volts DC and below. Some vehicles use a dual 12/42 V DC electrical system[6] that will require a fuse rated at 58 V DC.

Seems to contradict what you just said though... ?!?!

 

[amberwolf]

Just make sure the fuse has a voltage rating higher than your system, and it won't arc across the fuse when it blows.

 

[sangesf]

Just make sure the fuse has a voltage rating higher than your system, and it won't arc across the fuse when it blows.

So for those running 72v+, where do they find a >72v fuses?

 

[teklektik]

There's discussion on this matter on this thread: http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=15225&start=45. This post in particular (http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=15225&start=30#p476065) calls out an interesting main breaker option that looks very promising.

A couple of posts later in that thread I mentioned a similar but lower voltage (50A rated, 62A trip, 65v) marine unit that has been serving me well as combined main protection/main disconnect switch. I also use a 50A MaxiFuse in each of two series battery packs to protect them from indiscretions whether in the bike or out. These fuses have the advantage of a wide contact separation to discourage arcing at the cost of a rather huge socket. A few days ago I smoked a controller and the magnetic breaker quietly tripped but the MaxiFuses were unaffected. A couple of resets and re-trips later, the breaker was still working fine and the fuses still had not blown. Wiring never got hot and inspection showed the CA had burped up to 176A.

It's always dangerous to draw meaningful conclusions from anecdotal evidence, but it this case, the magnetic breaker did a very respectable job of protecting the wiring and other components while outperforming MaxiFuses of the same rating. This is not to diminish the value of a pack fuse for protecting the pack from operator error and inadvertent shorts, but when I move on to a higher powered build I will be looking for a high capacity magnetic breaker instead of a main fuse...