On Thursday 17 September 2015 05:09:07 Erik Christiansen wrote: > On an old thread; 08.05.15 05:29, Mark Wendt wrote: > > I bought a little transistor/cap tester kit from Banggood a while > > back, > > Having followed suit, I was disappointed today to find a new/old-stock > great fat 10,000 uF electrolytic giving an ESR reading of 0.8 ohm. > Being, at least philosophically, Scottish, I thought I'd give > reforming the dielectric a go. (My method is just to put the > multimeter on ohms range, to apply a low voltage at low current. Mine > emits + on the negative terminal in ohms mode, so reverse connection > of the leads is needed.) > > When I came back later, the needle had crept up to full scale on ohms > x 1, and after briefly shorting with a screwdriver, just in case, > retesting gave an ESR of 0.03 ohms. > > I don't know how typical that improvement might be, but it does show > that a capacitor oughtn't be ruled out at first glance. > > Erik > And as a CET, and an old hand at that, thats a capacitor that would go in the bin Erik. And its not open for discussion around my workbench.
The fact that you shorted it while charged with only the meters volt or so charge, and "fixed" it, which punches thru the foil oxides and restores a good but temporary connection, making that cap look good again, also says it will be bad again quick enough to eat your warranty budget. Making a good, very low resistance connection between the external terminal metal, normally made out of something solderable like copper, and the alu foils that make up the capacitors "plates" is a high art form because the alu is so reactive with the oxygen in the air we breath. Throw in that it is etched chemically to increase its surface area 10 to 50 fold over plain alu, which increases its capacitance by the same factor, and you can begin to imagine the difficulty in actually getting a "gas tight" joint between the terminal and the alu foils. The lack of that says the ESR will rise to the failure point in a relatively short time. In low power stuff, the circuit will just mis-behave. In higher powered situations, the heating from the ESR will eventually blow the caps case top open, or causing bulging of it before. When inspecting any circuit that uses electrolytic capacitors, seeing any of them with bulged tops, is grounds to warm up the iron & replace them. They have already failed in terms of their ESR. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Monitor Your Dynamic Infrastructure at Any Scale With Datadog! Get real-time metrics from all of your servers, apps and tools in one place. SourceForge users - Click here to start your Free Trial of Datadog now! http://pubads.g.doubleclick.net/gampad/clk?id=241902991&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
