Path: ...!weretis.net!feeder6.news.weretis.net!feeder8.news.weretis.net!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: liz@poppyrecords.invalid.invalid (Liz Tuddenham) Newsgroups: sci.electronics.design Subject: Re: Survivor! Date: Fri, 22 Mar 2024 11:52:29 +0000 Organization: Poppy Records Lines: 41 Message-ID: <1qqtklp.5n88da1fzufswN%liz@poppyrecords.invalid.invalid> References: X-Trace: individual.net SXBxM0zVt3rZ96LunMBt8gpGLqom3vGuLhPTK2RVLx1rPPbA/O X-Orig-Path: liz Cancel-Lock: sha1:EQqzHNAEuKW269+07hHvmAcusWY= sha256:NTSdcbyGoG1XT4OxMuo3CdzodBK3ZYej57hzhyNcC3M= User-Agent: MacSOUP/2.4.6 Bytes: 2664 John R Walliker wrote: > On 20/03/2024 15:22, Bertrand Sindri wrote: > > Cursitor Doom wrote: > >> Yesterday I had 2 minutes to waste so I blew up another electrolytic > >> capacitor - or rather I *tried* to. A 10uF 10V cap across the output > >> of a variac with Vo set to 240VAC. There was a considerable *pop* > >> but no bang and it turned out the T3.15 Amp fuse in the variac had > >> blown spectacularly - but the cap had survived unscathed! Tested > >> fine for capacitance and ESR! I never would have believed it. Just > >> wondering how the hell it didn't get destroyed... > > > > Obviously it was able to survive the overcurrent situation for long > > enough to blow the fuse in the variac. Since, as usual, you've left > > off all useful information (i.e., make and model of cap) we can't > > comment any further. > > > > The fuse also did it's job, which is to protect downstream components > > from overcurrent situations by blowing before the downstream items > > themselves blow up. > > > > > More importantly the fuse protected the variac. They are > very intolerant of even quite modest overloads. I have successfully protected one with a thermal cutout which has low thermal inertia and has always operated before any damage can occur. It is in a bench power supply that is often used to test faulty equipment, so fuses would not give a quick and easy reset facility. It suffered a lot of nuisance tripping on loads well below the variac's rating until I realised that the isolation transformer, which it fed, was drawing a large magnetising current. I have corrected the power factor of the transformer with a capacitor and the nuisance tripping has now ceased. -- ~ Liz Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk