Ralph Mowery wrote:

In ESR cap, what does ESR mean?

Look up equivilent series resistance. In short it is a number that tells of
the quality of the capacitor especially when used in switching and high
frequency circuits.

Most any old capacitor will be ok for filtering out 60 hz in the old power
supplies. When the switchers came out , the capacitors begain to fail .
Checking on a simple capacitor meter will show the value ok, but they fail
under the high speed/frequency high current usage.

** The ESR of an electro cap is mostly due to the conductivity of the liquid electrolyte used inside.

Modern, water based electrolytes have much better conductivity and hence lower ESR values compared to the same size caps made in the past and so can handle higher operating currents without excessive self heating.

Heat is the main killer of electros, whether from the local ambient temp or current flow in the cap or both. Luckily, the conductance of electrolytes improves with increasing temp which helps extend their life in SMPS.


.... Phil