[rokweom]

In general, people have the wrong idea about how fuses work. They're not supposed to blow at their rated current, they're supposed to withstand it indefinitely, and only blow at much higher currents. Look up any datasheet from a well established manufacturer and see for yourself (like this one from littelfuse: https://littelfuse.com/products/fuses/cartridge-fuses/5x20mm... )

[owenversteeg]

Indeed. There is a slight temperature dependent de-rating, but in general that is correct. To add, Littelfuse is in fact the inventor of the standard automotive blade fuses - they know their fuses if anyone does. I archived a datasheet of some of their blade fuses here [0] - you can see that a 1-amp fuse will run at 1A indefinitely, 2A for 300ms, 3A ~100ms, 4A ~60ms, 5A ~40ms etc. The same datasheet will tell you the temperature derating for their blade fuses is less than 25% at any temperatures you want your electronics to live at.

Another fun fact that is obvious from applying Ohm's Law - you can calculate the current flowing through a fuse by measuring the voltage drop. You can do the math yourself, or there are handy "fuse voltage drop charts" so you don't even have to use a calculator. Yes, this means that with a simple oscilloscope you now have a portable energy meter that requires zero rewiring. Ha, I accidentally brought us full circle :)

[0] https://web.archive.org/web/20240121052239/https://m.littelf...

[rokweom]

Just be careful with that, measuring mains is a bad idea with most oscilloscopes. The ground pin is usually connected to mains earth, so if you're not careful, you might create a short and blow up your scope. If you have one of these battery powered ones, it'll be fine, but the mains powedered ones are usually a no-no.

[owenversteeg]

Ah, I was referring to automotive blade fuses (which have lovely little contacts on top for measuring.) They are only rated to 32VDC so if you are running mains through that you have other issues. Indeed I'd just use my battery-powered oscilloscope to measure mains but if I wanted to use a benchtop scope I'd use an isolation transformer.

[IshKebab]

So you agree that a 2A fuse shouldn't allow 8A to pass for several minutes?

[owenversteeg]

Yes, that sounds like a very poor quality fuse (assuming it wasn't specced that way, which would be unusual.)

[megous]

People also have a wrong idea about how buying electronic components on Amazon/Aliexpress/eBay/etc. works. You buy a few of the same, test them, then use them if they work. Otherwise ask for refund.

Otherwise you're up for a big surprise that all your TL081's are LM356 instead, or that mosfet you bought has 3x the Rds(on) than expected, or that your fuse doesn't work.