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do those values look reasonable? Also, it says that "ESR generally decreases with increasing temperature." This strikes me as odd, because resistance in most materials increases when you heat it up.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Yanom wrote ... Do those values look reasonable?
Have you tried looking up some real OEM data sheets for electrolytic capacitors, and compared their specs against the chart you cited? Here's a challenge. Go here: and give us a report.
Yanom wrote ... Also, it says that "ESR generally decreases with increasing temperature." This strikes me as odd, because resistance in most materials increases when you heat it up.
But the resistance generally decreases in aqueous electrolytes as they get hotter.
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Joined: Sun Apr 29 2012, 06:14PM
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klugesmith wrote ...
Have you tried looking up some real OEM data sheets for electrolytic capacitors, and compared their specs against the chart you cited? Here's a challenge. Go here: and give us a report.
those ESR values are for a 120Hz AC current, and they're significantly higher than the (presumably DC) values on my chart(s). However, the general theme seems to be that:
-larger caps have lower ESR -ESR is greater at higher voltages aaand...
klugesmith wrote ...
the resistance generally decreases in aqueous electrolytes as they get hotter.
did not expect any of those things. How does resistance go down when they get hotter anyway?
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Joined: Sun Feb 12 2006, 04:21AM
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those ESR values are for a 120Hz AC current, and they're significantly higher than the (presumably DC) values on my chart(s).
Umm... DC current for capacitors? If the voltage isnt changing (DC) then the current into the capacitor is??? Most cap manufacturers spec both a 120/100hz mains ripple current and 10khz for a general idea of how it performs in a switching supply.
did not expect any of those things. How does resistance go down when they get hotter anyway?
Id guess that its greater mobility of the ions that carry the charges. The cold just slows them down.
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ESR for electrolytic capacitors rises with age and also rises with decreasing operating temperature. That is one of the main reasons why aged switch-mode power supplies seem to always fail during power-up.
As the electrolytics in the supply age they dry up and ESR gradually to creeps up. However, as long as the supply is kept running the ripple-current through the capacitors ESR keeps the capacitors warm and the ESR doesn't get too high. But, if you switch off the supply, the capacitors cool to ambient temperature and the ESR jumps up noticeably. Particularly if the ambient temperature is down near freezing temperatures. In this case the re-application of power usually results in unstable operation and failure to start as the ESR is now outside of operational limits for the supply.
If you are really desperate to get an old SMPSU that has failed in this manner to start, you can often *GENTLY* heat the caps with a hair-dryer (NOT a hot hair gun!!!). This can often lower the ESR of old electrolytic capacitors enough that the supply will then start up when power is applied. Once the natural ripple current from the supply is running through the caps it may then continue to work for many more hours or even days. But eventually, ultimate death of the PSU is imminent so the caps or supply entire should be replaced ASAP.
The high ESR of electrolytics at low temperatures is another reason for the use of tantalum caps in SMPSUs for harsh environments where low temperatures are expected.
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Does this capacitor ESR chart look accurate?
