Since there's a discussion brewing here, it's been my experience that for original capacitors (particularly larger ones) which
do measure within spec (obviously not always the case), their ESR will often be lower (and thus ripple current rating higher) than the exact-value (capacitance and voltage) modern replacement. This makes sense to some extent, as ripple value has some proportionality to surface area / size. On top of this, many new capacitors measure below-spec in capacitance by 10-15% (a cost-cutting initiative rather than coincidence, I suspect). Obviously this doesn't apply to original capacitors which have degraded.
In my experience, the best solutions for these problems are:
- Increase the voltage rating of the replacement, with the knowledge that in many cases it's not an "upgrade", rather somewhat a necessity to maintain factory-new ripple values. My conclusion is that "new caps being smaller due to superior modern technology" is somewhat misleading, the measurements seem to agree. Fitting a capacitor with a similar physical size to the one removed is a good rule of thumb IMO - which often involves jumping up a voltage rating or two.
- If the model of capacitor chosen offers small capacitance steps, jump up a rating and measure what you're putting back in. 20% over is better than 10-15% under in my book. I've found some brands/models are worse than others on this front, but if you get into the habit of measuring everything, you get a feel for what to order next time.
I think the solution isn't to avoid recapping - but rather to be more conscious of what we're recapping with.
With these comments in mind today I started testing the some of the caps that I bought. The test quantities are admittedly low but interesting nonetheless. All caps tested are fresh out of the package from Mouser in the last week except for a few cases which I'll note as I go.
Panasonic FM, 100µF/50v, 10 pieces.
Lowest/highest µF = 103.7 / 104.9µF. Average = 104.5µF.
Lowest/highest ESR = 0.05 / 0.07 ohms. Average = 0.056 ohms.
Lowest/highest vLoss = 0.6 / 0.7%. Average = 0.62%.
Panasonic FC 100µF/50v, 10 pieces.
Lowest/highest µF = 94.2 / 95.6µF. Average = 95.1µF.
Lowest/highest ESR = 0.15 / 0.18 ohms. Average = 0.16 ohms.
Lowest/highest vLoss = 0.7 / 0.8%. Average = 0.71%.
And a couple of UCC KYB 100µF/50v (I only have 2).
110.2µF, 0.09 ohms, 0.6% vLoss.
109.8µF, 0.08 ohms, 0.6% vLoss.
I don't have any Nichicon in 100µF/50v to directly compare but have some ca 6 month old 63v, 10 pieces.
Lowest/highest µF = 101.5 / 103.3µF. Average = 102.24µF.
Lowest/highest ESR = 0.07 / 0.09 ohms. Average = 0.079 ohms.
Lowest/highest vLoss = 0.7 / 1.0%. Average = 0.79%
More later,
James
edit: I forgot to show the ripple current rating on these, and since this one is for the power supply that might apply. Best to worst in that regard...
FM: 870mA
KYB: 620mA
FC: 615mA
FG: 255mA
I guess that I'll be using the FM caps.