sKiZo
Hates received: 92644 43.20°N 85.50°W
Plan "c"
Found this. Another example of careful what you ask for.
Application Guide, Aluminum Electrolytic Capacitors (CDE)
Seems to be THE definitive white paper on the subject. A couple interesting quotes ...
RATED DC VOLTAGE
Rated DC voltage is the voltage marked on the capacitor,
and it is the maximum peak voltage including ripple voltage
that may be applied continuously between the terminals
and over the rated temperature range. Higher rated
voltage capacitors may be substituted for lower rated voltage
capacitors as long as case size, DF, and ESR ratings
are also compatible.
FORMING
The anode foil carries the capacitor’s dielectric. The
dielectric is a thin layer of aluminum oxide, Al2O3, that is
chemically grown on the anode foil during a process called
“formation.” Formation is accomplished by pulling the
anode foil on rollers through an electrolyte bath and continuously
applying a DC voltage between the bath and the
foil. The voltage is 135% to 200% of the final capacitor’s
rated voltage. The thickness of the aluminum oxide is
about 1.4 to 1.5 nm for each volt of the formation voltage,
e.g., the anode foil in a 450 V capacitor may get a formation
voltage in excess of 600 V and have an oxide thickness
of about 900 nm. That’s less than a hundredth the thickness
of a human hair.
Formation reduces the effective foil surface area because
the microscopic tunnels are partially occluded by the oxide.
The tunnel etch pattern is adjusted by choice of foil and
etching process so that low-voltage anodes have dense tunnel
patterns compatible with thin oxide and high-voltage
anodes have coarse tunnel patterns compatible with thick
oxide. The cathode foil is not formed and it retains its high
surface area and dense etch pattern.
Granted - a quick read by me, but here's my take on it. Voltage isn't all that important - maybe once, but the forming process that was once a big bugaboo is no longer an issue. The caps are formed in the factory at much higher voltages than the real world will ever throw at them and should stay stable over a broad range.
With that - common sense would dictate one uses as close to the original rated voltage as is available. With that in mind, sticking with "audio grade" capacitors designed for signal path applications <should> be better than substitution of general purpose caps of the rated voltage value.
So there. I think. <G>
That doesn't cover the point that the manufacturers can play voltages close to the vest to keep costs down. It does address the fact that out of spec voltages can cause oscillations and other not so good nastiness depending on the application.
PLAN C
- Elna Silmic II where available (any voltage)
- WIMA poly where they'll fit OR Nichicon KW when all else fails
Bypass caps strictly Polypropylene, either .047 or .1 depending on availability. The Panasonic ECQ come highly recommended for bypass caps, but come to find out those are polyester? Still a bit confuzed there.
So ... any closer to right?
Baby steps ... baby steps.
Found this. Another example of careful what you ask for.
Application Guide, Aluminum Electrolytic Capacitors (CDE)
Seems to be THE definitive white paper on the subject. A couple interesting quotes ...
RATED DC VOLTAGE
Rated DC voltage is the voltage marked on the capacitor,
and it is the maximum peak voltage including ripple voltage
that may be applied continuously between the terminals
and over the rated temperature range. Higher rated
voltage capacitors may be substituted for lower rated voltage
capacitors as long as case size, DF, and ESR ratings
are also compatible.
FORMING
The anode foil carries the capacitor’s dielectric. The
dielectric is a thin layer of aluminum oxide, Al2O3, that is
chemically grown on the anode foil during a process called
“formation.” Formation is accomplished by pulling the
anode foil on rollers through an electrolyte bath and continuously
applying a DC voltage between the bath and the
foil. The voltage is 135% to 200% of the final capacitor’s
rated voltage. The thickness of the aluminum oxide is
about 1.4 to 1.5 nm for each volt of the formation voltage,
e.g., the anode foil in a 450 V capacitor may get a formation
voltage in excess of 600 V and have an oxide thickness
of about 900 nm. That’s less than a hundredth the thickness
of a human hair.
Formation reduces the effective foil surface area because
the microscopic tunnels are partially occluded by the oxide.
The tunnel etch pattern is adjusted by choice of foil and
etching process so that low-voltage anodes have dense tunnel
patterns compatible with thin oxide and high-voltage
anodes have coarse tunnel patterns compatible with thick
oxide. The cathode foil is not formed and it retains its high
surface area and dense etch pattern.
Granted - a quick read by me, but here's my take on it. Voltage isn't all that important - maybe once, but the forming process that was once a big bugaboo is no longer an issue. The caps are formed in the factory at much higher voltages than the real world will ever throw at them and should stay stable over a broad range.
With that - common sense would dictate one uses as close to the original rated voltage as is available. With that in mind, sticking with "audio grade" capacitors designed for signal path applications <should> be better than substitution of general purpose caps of the rated voltage value.
So there. I think. <G>
That doesn't cover the point that the manufacturers can play voltages close to the vest to keep costs down. It does address the fact that out of spec voltages can cause oscillations and other not so good nastiness depending on the application.
PLAN C
- Elna Silmic II where available (any voltage)
- WIMA poly where they'll fit OR Nichicon KW when all else fails
Bypass caps strictly Polypropylene, either .047 or .1 depending on availability. The Panasonic ECQ come highly recommended for bypass caps, but come to find out those are polyester? Still a bit confuzed there.
So ... any closer to right?
Baby steps ... baby steps.
Last edited:
