I was just ordering some big capacitors and read the notes from the manufacturer (Panasonic) about storage, I thought of sharing :
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Leakage current will increase with long storage
times.
Storage times in ambient temperatures of 40°C
or less can be four years or more before
leakage current should be checked for
conformance to the specified limit.
Longer storage times may require reforming of
the capacitor to reduce leakage current below
the specified limit. This can be accomplished by
applying rated voltage in series with a 1000R
resistor for a time period of 30 ~ 60 minutes.
Under normal conditions, shelf life can exceed
10 years, providing that leakage current is
checked before use.
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***************
***************
Leakage current will increase with long storage
times.
Storage times in ambient temperatures of 40°C
or less can be four years or more before
leakage current should be checked for
conformance to the specified limit.
Longer storage times may require reforming of
the capacitor to reduce leakage current below
the specified limit. This can be accomplished by
applying rated voltage in series with a 1000R
resistor for a time period of 30 ~ 60 minutes.
Under normal conditions, shelf life can exceed
10 years, providing that leakage current is
checked before use.
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And, if you don't want to tear a device apart, remove all the caps, put a resistor in series with each one at the correct voltage on a DC power supply, etc. A compromise that will work for many things is to slowly power up the device on an AC variac. Start with just a few volts of AC line voltage and nudge it up every so often until you finally get to regular line voltage.
This does much the same thing without all the hassle. It's generally bad to take something that's been in storage for many years and just plug it in and flip the switch--especially an audio power amp with big, relatively high voltage, caps in the power supply.
And leakage currents are typically much more of a problem in high voltage tube gear as the voltages are even higher and the higher impedance circuits are often less tolerant of leakage. So all of the above is even more applicable for anything with high voltage power supplies.
This does much the same thing without all the hassle. It's generally bad to take something that's been in storage for many years and just plug it in and flip the switch--especially an audio power amp with big, relatively high voltage, caps in the power supply.
And leakage currents are typically much more of a problem in high voltage tube gear as the voltages are even higher and the higher impedance circuits are often less tolerant of leakage. So all of the above is even more applicable for anything with high voltage power supplies.
How do you measure leakage current on a capacitor (new or old) ? Do you wait for it to self-discharge ?
Here's what they say about it:
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Leakage Current
I = 3 CV (ìA) maximum after 5 minutes of
applying rated voltage. Capacitance is the
nominal value in ìF, voltage in VDC.
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Here's what they say about it:
*******************
Leakage Current
I = 3 CV (ìA) maximum after 5 minutes of
applying rated voltage. Capacitance is the
nominal value in ìF, voltage in VDC.
*******************
Inductor said:
Do you mean non-polarized electrolytics like used in speaker crossovers? Because they're non-polarized they don't have issues with DC leakage current (nor, hopefully, should they ever see any significant DC in a speaker).
All electrolytics, however, degrade over time. And most consider their useful life around 10 - 20 years depending on temps, how they're used, etc.
akis said:
Actually you wait for it to *charge* don't you? You apply the rated voltage for 5 minutes (or whatever they specify) and monitor how much DC current flows after 5 minutes.
tinitus said:
My point is, in a speaker crossover, they should not have any DC across the caps. So DC leakage is a non-issue. They're not being used to block (or filter) DC.
And as I said, all electrolytics degrade with time including non-polars. So if you have some really old caps, don't use them. And if you have some really old speakers replacing the caps might be a good idea. These days most think a film capacitor in series with the tweeter sounds better too. And they last a lot longer.
If you can reform old caps, get the leakage current within spec, and verify the capacitance value, they might be OK for some applications--for a while. But other parameters are likely to still be degraded like ESR, dissipation factor, etc. And they may not last much longer--especially if used near their rated voltage, at high temperatures, or with high values of ripple current.
For example, the electrolytics used on most PC motherboards for the switching regulator near the CPU, are famous for failing after only 3 or 4 years. And even before they fail, their parameters are degraded enough the PC often starts to have problems because of unstable power. But those caps live in a hot environment with high amounts of ripple current. Newer high-end motherboards are using polymer caps to avoid the early failures with electrolytics.
For example, the electrolytics used on most PC motherboards for the switching regulator near the CPU, are famous for failing after only 3 or 4 years. And even before they fail, their parameters are degraded enough the PC often starts to have problems because of unstable power. But those caps live in a hot environment with high amounts of ripple current. Newer high-end motherboards are using polymer caps to avoid the early failures with electrolytics.
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