cupoftea
Advanced Member level 5
Myth 1A))…Wet Electrolytic caps can be damaged by high leakage current if powered up after >2 years in storage.
..This isn’t true, the high leakage current that initially results isn’t high enough to overheat the capacitor, and reduces within a short time of having voltage applied.
Myth 1B))…Wet Electrolytic caps can be damaged by high leakage current if powered up after >2 years in storage, and they have been stored at temperature >40degC
..This is true, and its particulalry difficult to proove that any particualr batch of electrolytic capacitors has not been stored at too high temperature (>40DegC) for too long a period of time. The distributors are not likely to throw capacitors away, but will try and disguise them as being fresh from production. Capacitors may well not be stored in temperature controlled environments, because they cost so little, so the cost of temperature control would not be worthwhile. -and nobody could proove that they have been stored for too long at too high temperature...or rather, no companies bother to test the wet electrolytics for "state of health" prior to fitting to PCB.
Myth 1C))..Wet Electrolytic caps are far more sensitive to high storage temperatures, and long storage times, than any other type of capacitor. (in other words, more susceptible to damage by such conditions)
..This is true.
Myth 2))..Tantalum capacitors are particularly sensitive to high surge currents compared to all other capacitors with solid dielectrics.
..This isn’t true, all capacitors with solid dielectrics have essentially the same capability with surge currents. Its just that tantalum capacitors can have higher capacitance within a smaller volume, and so a higher surge current can flow through them when a voltage is suddenly applied to them….and being small, they don’t have the mass to be able to distribute and handle the heat from the surge…however, tantalum capacitors essentially are the same as all other solid dielectric capacitors when it comes to high surge currents.
Myth 3))..Electrolytic capacitors have generally longer lifetimes, the farther below rated voltage they are run at.
..This is only very slightly true. Its only film capacitors that have significantly longer lifetimes when run at voltages well under their rated voltage.
Myth 4))..Electrolytic capacitors can be used on voltage rails that are less than 10% of their rated voltage
…this isn’t true, electrolytic capacitors need at least 10% of their rated voltage applied to them in order for them to “form” properly, otherwise they do not present anywhere near their datasheet capacitance value.
Myth 5))..Aluminium polymer capacitors, when run at 10 degC less ambient temperature, experience a ten times increase in lifetime.
…this is not true, the lifetime increase is 2 times.
Myth 6))..Wet Electrolytic capacitors don’t vent any of their dielectric at any time.
..this is not true, wet electrolytic capacitors, at temperatures above approx. 25degC, continuously vent their dielectric into the surrounding atmosphere, since they are imperfectly sealed. Its only small amounts, but its ongoing, and even if not on load, electrolytics will eventually completely dry out.
Myth 7))..A 10uF , 0805, 16V, X7R MLCC capacitor would be more prone to stress cracking than a 4.7uF , 0805, 16V, X7R MLCC capacitor
..This one is true.
Myth 8))..Generally , MLCC capacitors can suffer stress cracks. The demarcation point, where stress fractures become significantly more prevalent, is between 0805 and 1206 size capacitors….in other words, 1206 size and above are far more prone to stress cracks.
..This is true
Myth 9))..Film capacitors can handle high ripple currents and surge currents better than wet electrolytic capacitors..
..This isn’t true, the wet electrolytic capacitor is the king of being able to handle high surge and inrush currents
Myth 10))..When not loaded, Small thin electrolytic capacitors are more prone to drying out than thicker/taller ones (higher diameter or taller ones)
This is true (i had to give the situation of "not loaded" in order to assert that there internals are at the same temperature)
..This isn’t true, the high leakage current that initially results isn’t high enough to overheat the capacitor, and reduces within a short time of having voltage applied.
Myth 1B))…Wet Electrolytic caps can be damaged by high leakage current if powered up after >2 years in storage, and they have been stored at temperature >40degC
..This is true, and its particulalry difficult to proove that any particualr batch of electrolytic capacitors has not been stored at too high temperature (>40DegC) for too long a period of time. The distributors are not likely to throw capacitors away, but will try and disguise them as being fresh from production. Capacitors may well not be stored in temperature controlled environments, because they cost so little, so the cost of temperature control would not be worthwhile. -and nobody could proove that they have been stored for too long at too high temperature...or rather, no companies bother to test the wet electrolytics for "state of health" prior to fitting to PCB.
Myth 1C))..Wet Electrolytic caps are far more sensitive to high storage temperatures, and long storage times, than any other type of capacitor. (in other words, more susceptible to damage by such conditions)
..This is true.
Myth 2))..Tantalum capacitors are particularly sensitive to high surge currents compared to all other capacitors with solid dielectrics.
..This isn’t true, all capacitors with solid dielectrics have essentially the same capability with surge currents. Its just that tantalum capacitors can have higher capacitance within a smaller volume, and so a higher surge current can flow through them when a voltage is suddenly applied to them….and being small, they don’t have the mass to be able to distribute and handle the heat from the surge…however, tantalum capacitors essentially are the same as all other solid dielectric capacitors when it comes to high surge currents.
Myth 3))..Electrolytic capacitors have generally longer lifetimes, the farther below rated voltage they are run at.
..This is only very slightly true. Its only film capacitors that have significantly longer lifetimes when run at voltages well under their rated voltage.
Myth 4))..Electrolytic capacitors can be used on voltage rails that are less than 10% of their rated voltage
…this isn’t true, electrolytic capacitors need at least 10% of their rated voltage applied to them in order for them to “form” properly, otherwise they do not present anywhere near their datasheet capacitance value.
Myth 5))..Aluminium polymer capacitors, when run at 10 degC less ambient temperature, experience a ten times increase in lifetime.
…this is not true, the lifetime increase is 2 times.
Myth 6))..Wet Electrolytic capacitors don’t vent any of their dielectric at any time.
..this is not true, wet electrolytic capacitors, at temperatures above approx. 25degC, continuously vent their dielectric into the surrounding atmosphere, since they are imperfectly sealed. Its only small amounts, but its ongoing, and even if not on load, electrolytics will eventually completely dry out.
Myth 7))..A 10uF , 0805, 16V, X7R MLCC capacitor would be more prone to stress cracking than a 4.7uF , 0805, 16V, X7R MLCC capacitor
..This one is true.
Myth 8))..Generally , MLCC capacitors can suffer stress cracks. The demarcation point, where stress fractures become significantly more prevalent, is between 0805 and 1206 size capacitors….in other words, 1206 size and above are far more prone to stress cracks.
..This is true
Myth 9))..Film capacitors can handle high ripple currents and surge currents better than wet electrolytic capacitors..
..This isn’t true, the wet electrolytic capacitor is the king of being able to handle high surge and inrush currents
Myth 10))..When not loaded, Small thin electrolytic capacitors are more prone to drying out than thicker/taller ones (higher diameter or taller ones)
This is true (i had to give the situation of "not loaded" in order to assert that there internals are at the same temperature)
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