> A 3A fuse would burn out in a fraction of a second if you tried to do that.
he bought it on Amazon. He has every reason to be worried that it won't burn out. Louis Rossman did a video[0] where he put 8 amps through a 2 amp fuse and left the room for quite a long time, I think it was several minutes with 8a going through a 2a fuse.
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... )
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 :)
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.
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.
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.
Amazon had one of their buildings in California shut down a few months ago by the fire department when a generator started smoking. It was probably due to a bad fuse they bought off Amazon. https://signalscv.com/2023/07/fire-breaks-out-at-amazon/ That's how blinded by their avarice Amazon has become; they can't even protect their own house. Notice how the Nilight fuses (https://amzn.to/3S06G2n) are still listed, even after a YouTube video with 300,000 views demonstrated that their 2 ampere fuse takes 10 amps to blow. I even had an electrical fire in my house recently, due to components that I purchased off Amazon. I know Amazon monitors Hacker News PR closely, since they took down those ChatGPT generated listings within minutes of us posting them here. Yet they do nothing about product listings that put our lives, and their own lives, in critical danger.
> I know Amazon monitors Hacker News PR closely, since they took down those ChatGPT generated listings within minutes of us posting them here.
Like other engineers at Big Tech, Amazon Engineers also read HN and the post in question happened to be on the HN front page around the lunch break of a work day, IIRC.
It’s easy to imagine one or more Amazon engineers internally pinging the team responsible for Amazon listings hence the appearance that Amazon was able to take down/hide those ChatGPT generated listings in less than an hour of it landing here.
I'm not going to watch the whole video but it doesn't seem like it supports the point you're trying to make.
> How long does it take for your 400mA multimeter fuse to blow at 600mA?
> The amazing unpredictability of fusing current ratings at low overloads.
It makes a point of saying that fuses are imprecise, i.e. that a fuse likely won't blow when 600mA of current passes through a 400mA fuse for a few seconds.
What Rossmann discovered was that fuses from Amazon took 4x the rated current for minutes. That's many orders of magnitude out of spec.
The relationship between the amount of overload and how fast the fuse is supposed to blow is quadratic, not linear. As an example with somewhat made-up numbers, at 1x it might take hours to blow, at 2x it might take a minute or two, at 3x it shouldn't take more than a second and at 4x it should be nearly instant.
If it's supposed to blow in 0.1 seconds when overloaded by 4x, then taking 10 minutes is many orders of magnitude in my book. While that fuse is taking its sweet time, wiring or other components are being heated out of spec (16x more heat at 4x the current), potentially posing a fire hazard or damaging the device it's supposed to be protecting.
Sorry, I misread you, didn't catch you meant the time. Also good point about the possible power damage being quadratic on the current.
Thanks for the polite clarification.
Seriously, I think they would refund the fuse since you are not satisfied.
I think the only way for Amazon to stop organizing countraband would be if dozens of people die in each country and it makes a big media mess and public prosecutors finally rule that Amazon is responsible for mingling and smuggling the products in-country.
Which will impact all
marketplaces, requiring Craigslist/Leboncoin/Gumtree to asses the liability of the sellers on the marketplace.
Well yeah, there's that. My assumption about the worry the author expressed was that it was just an "I'm a little uncomfortable with mains power" type worry, not "did I buy a crappy part that's going to explode" type worry. If it was the latter, that's, well... entirely avoidable.
he bought it on Amazon. He has every reason to be worried that it won't burn out. Louis Rossman did a video[0] where he put 8 amps through a 2 amp fuse and left the room for quite a long time, I think it was several minutes with 8a going through a 2a fuse.
[0]: https://www.youtube.com/watch?v=B90_SNNbcoU