The
ESR meter that everyone seems to believe is required piece of
test gear in the service kit was never heard of until mid
'90s when electrolytic caps of high values and low voltages
became the norm. I have never used an ESR meter and my
normal capacitors were 80 - 120 MFD at 350 - 450 volts.
Deane
Deane is quite right. Think about it this way - when the bridge diode turns
on, the capacitor charges up through the secondary resistance of the power
transformer and the reflected primary resistance, plus the series resistance
of the bridge diode. For high voltages that is generally many tens of ohms.
Even then, the effect of an ESR even equal to the charging resistance is
pretty minimal - the charging time simply doubles. The effect on discharge
when the diode is turned off and the capacitor is supplying current to the
circuit is even less dependent on ESR, since the current is less than during
the charging cycle (by roughly the charge/discharge duty cycle).
The main significance of ESR, or an ESR that is rising as the years pass, is
that the capacitor runs hotter - since the ESR is a real dissipative
component. Look at a modern cap's spec sheet - say a good power
electrolytic from RIFA - and you will see the main consideration for
reducing ESR to the milliohm level in high value low voltage electrolytics
is entirely to do with power dissipation and maximum operating temperature.
The effect on ripple is mininmal.
The main failure mode for Tek electrolytics, as we have discussed many times
on the forum, is the Sprague twist-lock caps. The failure mode is that the
internal negative tab connection corrodes through inside the can just where
it goes into the can crimp - so the capacitance falls to zero, more or less
instantly. Then you can see the ripple for sure!
Craig
