ESR Meter Recommendations
drlegendre at gmail.com
Wed Sep 30 19:05:37 CDT 2015
Good primer paper from Sencore (manufacturer of instruments, not
capacitors..) on the nature, causes and effects of ESR:
On Wed, Sep 30, 2015 at 5:50 PM, drlegendre . <drlegendre at 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 <chrise at 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
>> > readings is around 10,000ufd. Larger than that and the ESR is too close
>> > 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.
>> Chris Elmquist NØJCF
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