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I like the part where the tantalum blows up and you'll never know if it was installed backwards.... I think that was by design to cover it's tracks.
Date: Tue, 9 Sep 2014 06:33:28 -0700 From: vincemu...@gmail.com To: n8vem...@googlegroups.com Subject: Re: [N8VEM-S100:5177] Tantalum capacitor replacement? On Tuesday, September 9, 2014 8:06:10 AM UTC-5, Crustyomo wrote:
The most "exciting" part of ESR is we're all very used to talking about "ripple voltage" on a power supply, but that obviously comes with an associated "ripple current" in and out of the cap, across the ESR, and the RMS ripple current can be plugged into boring old ohms law with the ESR to figure out how much heat power is getting dumped into the cap. P = I squared times R. So you can imagine the effect of R going up by a factor of a hundred and now something that was stone cold is heating up with tens of watts of heat... but not for long... electrolytics are vented but tantalums always do the ceramic pipe bomb thing once they get hot enough, and kabooooom and bits of parts fly everywhere. I've occasionally wondered why tantalums aren't vented like electrolytics, at least to minimize the explosion. Tantalums have one "funny" characteristic that electrolytics don't have, which is electrolytics always mark the negative side clearly, black paint, minus symbols all over, they make it really hard to hook up backwards unless you try really hard. However, with tantalums, I have held in my paws two different mfgrs tantalums with printed out from the internet data sheets documenting that one mfgr marks his positive with a black bar and one mfgr marks his negative with a similar black bar. Legacy thru-hole component stuffing machines can be programmed not to mess it up, but with hand assembly tantalums are an absolute nightmare which I'll redesign a board/circuit to avoid using them. Oh and just like electrolytics, tantalums hooked up backwards explode, but unlike electrolytics, not immediately. So even if it took years to go "kaboom" the problem may have been reverse polarity but you'll never find enough pieces of the cap to prove it was installed backwards anyway. A final area of hilarity with ESR is everyone knows about RC oscillator networks where R times C is the frequency, well as caps ESR "R" drifts, sometimes the R times the C under certain conditions is very oscillatory and exciting. You think you're dampening out 60 Hz hum but the cap has drifted into be great oscillator network. Or even worse its synced up with some TTL clock on the board. You hope its a low pass filter but its actually a band pass filter now, whoops. -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to n8vem-s100+...@googlegroups.com. For more options, visit https://groups.google.com/d/optout. |