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Having taken apart a few guitar amplifiers now and replaced a few caps with success warrants a question that continues to bother me. Some caps when I read them read low or read high. Is there a rule regarding how much in either direction? Examples: 1000uf reads 960.5uf or 6800uf reads 6418uf. I have had some that read higher then the amount printed on the cap = what are your thoughts on those? Thanks in advance.
Capacitors - Read low Read high Rules?
- Thread starter ColoradoRobert
- Start date
All electronic components have a manufacturing tolerance. Capacitors come with various tolerance specifications in their nominal capacitance value, e.g. ±5%, ±10%, ±20%.
It is typical for large value electrolytic capacitors (greater than 1μF) to have a tolerance of 20% if not otherwise stated.
If your measured value is within ±20% then that may be considered acceptable.
It is also typical for new, unused large value electrolytic capacitors to have measured values that are +20% over the nominal value.
If you suspect that a capacitor that reads low (-10% to -20%) has aged, subjected to high temperature or high voltage abuse then you may want to consider replacing it. (Edit: If an electrolytic capacitor (greater than 100μF) reads higher I would be comfortable with that. If it reads lower than nominal value, you may want to replace it.)
Non-polar capacitors lower than 1μF should not alter that much with aging. Capacitors in frequency sensitive circuits such as filters, time delays, should have a tighter tolerance. In such circuits you would want the capacitance to match the circuit design requirements more closely.
Capacitors used as power supply filtering and decoupling will not affect the operation of the circuit so drastically. Hence a larger deviation is tolerated. In such applications, degradation of ESR (equivalent series resistance) is more of a concern.
It is typical for large value electrolytic capacitors (greater than 1μF) to have a tolerance of 20% if not otherwise stated.
If your measured value is within ±20% then that may be considered acceptable.
It is also typical for new, unused large value electrolytic capacitors to have measured values that are +20% over the nominal value.
If you suspect that a capacitor that reads low (-10% to -20%) has aged, subjected to high temperature or high voltage abuse then you may want to consider replacing it. (Edit: If an electrolytic capacitor (greater than 100μF) reads higher I would be comfortable with that. If it reads lower than nominal value, you may want to replace it.)
Non-polar capacitors lower than 1μF should not alter that much with aging. Capacitors in frequency sensitive circuits such as filters, time delays, should have a tighter tolerance. In such circuits you would want the capacitance to match the circuit design requirements more closely.
Capacitors used as power supply filtering and decoupling will not affect the operation of the circuit so drastically. Hence a larger deviation is tolerated. In such applications, degradation of ESR (equivalent series resistance) is more of a concern.
Thank you for the info Mr Chips I will need to think through that since I am not sure every cap has written on it the values. Given my actual example the 6800 now reads 6418 is that within the percentage you would use not knowing the value for sure? - #2. Hello Juneler - I have never heard the amp I am working on. Most that I buy are broken and will not turn on when I get them. But I have read articles saying that if your cap is 10 years old you might want to consider changing it. The 6800 caps I mentioned as the example have written right on their top 99 and the rest of the amp has 1999 on the PCB so I have decided to change them. Let me know your thoughts please.
