Good primer paper from Sencore (manufacturer of instruments, not capacitors..) on the nature, causes and effects of ESR:
http://patriotgaming.com/manuals/gaming_monitors/sencore_instruments/LC103/TT104-4416.pdf On Wed, Sep 30, 2015 at 5:50 PM, drlegendre . <drlegen...@gmail.com> wrote: > "How are > folks testing the very large electrolytics in the 25,000, 80,000 or even > 100,000 uF range that are encountered in the power supplies of some of > these old machines?" > > The method I use is pretty close to what you mention, though I lack an > electronic load. Here are some thoughts... > > For measuring capacity - on these rather large-value caps, it's quite > acceptable to time their discharge rate through a known, stable resistance > of some reasonable value based on the marked capacitance. Make several runs > and average them out. Calculating value is then simple arithmetic - C=T/R. > > For leakage, I use a variable voltage-regulated PSU with current-viewing > resistor in series. At what percent of marked voltage does leakage clear > the noise? At what voltage does it become significant and at what point > does it exceed allowable? All electrolytics leak, and the larger value the > part, the more expected leakage. Check a datasheet, or just use your > experience and make educated guesses - hint: how much power (as in heat > rejection) is the cap dissipating at working voltages vs. its marked value > and physical size? > > And as you suggest, watching supply ripple on the scope, with the cap > under some nominal load, is a tried & true method. It's usually my first > step, if I think a cap might be in trouble. > > (I was certain that I'd have to replace the 30 yr-old 95,000uF part in my > Altair.. but the dang thing proofed out just fine. Ran it for a day at 10% > over working voltage, and leakage sat right where it was when I began the > test. ) > > On Wed, Sep 30, 2015 at 1:35 PM, Chris Elmquist <chr...@pobox.com> wrote: > >> On Wednesday (09/30/2015 at 10:54AM -0700), John Robertson wrote: >> > >> > As for testing large capacitors, about the highest value that gives >> useful >> > readings is around 10,000ufd. Larger than that and the ESR is too close >> to >> > zero ohms unless the cap is really bad... >> >> And that seems to be the usual situation for most ESR meters. How are >> folks testing the very large electrolytics in the 25,000, 80,000 or even >> 100,000 uF range that are encountered in the power supplies of some of >> these old machines? >> >> One approach I use has been to isolate the supply and then fire it up >> with an electronic load while looking at voltage sag and ripple on a >> scope while that load is swept from min to max capability of the supply. >> >> There is also the Sencore LC53 "Z Meter" which can test large caps up >> to 200,000 uF out of circuit but these are typically a $400+ instrument >> on the used market. >> >> http://bama.edebris.com/download/sencore/lc53/LC53%20OPS.pdf >> >> Chris >> -- >> Chris Elmquist NØJCF >> >> >