5 ms·
> 2.5A primary side fuse (integrated into the AC inlet) did not melt This is a current-limited power-supply right? Test your fuse! Would not be the first time
by alright2565 2y ago
> 2.5A primary side fuse (integrated into the AC inlet) did not melt
This is a current-limited power-supply right? Test your fuse! Would not be the first time a fuse-shaped wire is sold[1]
[1]: https://youtu.be/B90_SNNbcoU?si=HwDCRvz7E-aCR1rQ&t=431 https://youtu.be/B90_SNNbcoU?si=HwDCRvz7E-aCR1rQ&t=431
- stouset 2y agoThere’s a special place in hell for people who sell fuse-shaped wires.
- mozman 2y agoit’s likely the track was weaker than the fuse - and you have long blow/slow blow fuses electricity is lazy it takes the easiest path
- whiw 2y agoThe transformer secondary was maxing out at 4A, 36V. The primary current will be much lower, probably about (40V/240V)*4A, ie about 0.67A.
- stavros 2y agoHow do you test a fuse?
- deleted 2y ago[deleted]
- charlieo88 2y agoTerminally.
- stavros 2y agoI admire your optimism that all the fuses will behave similarly.
- alright2565 2y agoFor a hobby project like this, I don't think you need utmost certainty. And if you're building aircraft, why are you shopping on Aliexpress?
- stavros 2y agoNot utmost, but if I put one in my car, it matters if one burns at 2A and the other at 4A.
- charlieo88 2y agoRight? The best you can do it test a sampling of fuse from a batch, to there failure point, which destroys the fuse.
- jabbany 2y agodestructively
- bitwrangler 2y agoI would use a variable power supply, amp meter and some sacrificial fuses. Slowly turn up the voltage while watching amps on the circuit until it blows? Or simply apply the rated amps (with current controlled power supply) to verify if/when the fuse blows. I have a multiple-fuse assortment kit that was a great (too good?) deal from AliExpress. Now I'm thinking I need to do some of those tests myself to verify their rating.
- coryrc 2y agoGet a set of visually-similar fuses that claim to be the same rating. (Visually because you need the shape to be the same). When testing a few to destruction, record the temperature of the fusing element and resistance and power over time. Also measure the temperature at operating current. Now the fuse you want to have the utmost trust in, test it at at half the time it should fail for a given i^2t. The temperature, resistance, and power curve should match the ones you tested destructively. The temperature at operating current should also be similar. If so, you can expect it to fail the way your destructively-tested fuses did. Now, if you trust the metal composition and fusing element shape, a simple resistance meter will tell you if two fuses will behave the same.
- thsksbd 2y agoHow do i measure the temperature of a fuse?
- noSyncCloud 2y agoThermography should work?
- thsksbd 2y agoSo I need a lab to test my Amazon products. I have a lab. What do 99% of consumers do? This is why the grift works.
- BenjiWiebe 2y ago99% of consumers aren't designing a power supply, at least.
- creer 2y agoYou can destructively test samples out of a box of them. But even then the proper current profile that a fuse is supposed to accept or block is far from obvious or intuitive. Reading the spec helps. And then you still have the problem of supplying an acceptable sequence to get a correct result as you desired. Another option is to experimentally send through various current profiles so that you - more intuitively - get a better understanding of whether your thinking of what you want to protect from, might actually happen.
- exmadscientist 2y ago> But even then the proper current profile that a fuse is supposed to accept or block is far from obvious or intuitive. Reading the spec helps. Right. This. Even if you shove the standards in front of their faces, most engineers don't know what fuses really do (prevent fires) or what they don't (save circuit boards) or how fast it happens (not very). Asking your typical engineer to test a fuse lot is not going to give a useful result. This is why there are so very many safety agency marks on fuses and why even the Chinese often skip the BS and just pay for name brand fuses.
- Terr_ 2y agoYou could... whoah, wait a second... isn't this one of the few places where that interview question of "determine the durability of N objects by dropping them from different floors in a building in a minimum of attempts" may actually be relevant?
- exar0815 2y agoSome weeks ago I also relied on a 1A Quick-Blow fuse to safeguard my project from accidentally blowing up. However, while tuning the parameters for the 10 Amp 5-60V Buck Boost converter (which was only loaded output-wise for 5W at the moment) I got a thermal runaway at one of the mosfets, which instantly vaporized the FET and the FR4 below it. While my error was that the Input PSU was still set to 250W, that fuse was completely okay afterwards. Don't rely on fuses alone. They suck.
- pjc50 2y agoFuses are just not that great. Quickblow fuses cannot keep up with quickblow MOSFETs. All they can do is limit the size of the fire in your enclosure.
- deleted 2y ago[deleted]
- creer 2y agoSpecifically, fuses (I mean actual fuses) have specific specs and MOSFETS have different specific specs. There is nothing wrong with using fuses if you understand and pay attention to that spec. Indeed a "quickblow" fuse will not protect you from everything you can think of - just some things - just because it's "quickblow".
- shadowpho 2y agoThermal fuses (which is what pretty much everyone here is talking about) will blow in seconds for “quick blow”. (There’s a chart for overload vs time, but it’s still slow). If you want protection you can use electrical fuses/load switches that turn off in microseconds (which still might not save the fet but should at least save the pcb)
- userbinator 2y agoThe author appears to be in Europe so that's 240V @ 2.5A, or 600W of power. Even legit fuses can vary quite unpredictably: https://www.youtube.com/watch?v=WG11rVcMOnY https://www.youtube.com/watch?v=WG11rVcMOnY