Capicitor
- Thread starter JdoubleU
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I have some that are bulging, and some that look like new. Depends on the reason it is bad. the capacitor should read +-10% of rating.
ptonsparky
Tom
- Occupation
- EC - retired
One of the few formulas I can remember from school. (2650*I)/E=MFD +-10%
Used it for years to check small capacitors before I got a meter that would read the MFD directly. I had a 40va 24v transformer and would use an amp clamp and voltmeter to take the readings at the same time. Worked pretty well.
During grain harvest I would carry the setup with me.
Yes, they do seem to degrade but mostly it is a pretty obvious failure. Blown or bulged. Shorted or open.
Used it for years to check small capacitors before I got a meter that would read the MFD directly. I had a 40va 24v transformer and would use an amp clamp and voltmeter to take the readings at the same time. Worked pretty well.
During grain harvest I would carry the setup with me.
Yes, they do seem to degrade but mostly it is a pretty obvious failure. Blown or bulged. Shorted or open.
An old timer told me that I was stupid to check the micro farads on a cap. He said that they either work or they don't work. My thought was that if they are reading to low will that mean the motor will not work and if it will does it mean that it could cause damage to the motor.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
111202-0924 EST
There are many kinds of capacitors.
A paper, Mylar, Polypropylene, or oil filled and run conservatively will not likely fail in 50 years, and have very little change in capacitance. An electrolytic capacitor may dry out over time and loose capacitance. In recent years there have been some major failure problems in computers because of bad far-east electrolytic capacitors.
A mica capacitor could probably last 100s or 1000s of years and maintain stable capacitance. The durability of the package would be the major problem here.
I have some electronic (meaning 25 V to 450 V DC electrolytic) capacitors that are 50 years old that are still good, and many others that are not.
Many small motor starting or running capacitors are electrolytic.
See http://electrochem.cwru.edu/encycl/art-c04-electr-cap.htm for a discussion on electrolytic capacitors.
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There are many kinds of capacitors.
A paper, Mylar, Polypropylene, or oil filled and run conservatively will not likely fail in 50 years, and have very little change in capacitance. An electrolytic capacitor may dry out over time and loose capacitance. In recent years there have been some major failure problems in computers because of bad far-east electrolytic capacitors.
A mica capacitor could probably last 100s or 1000s of years and maintain stable capacitance. The durability of the package would be the major problem here.
I have some electronic (meaning 25 V to 450 V DC electrolytic) capacitors that are 50 years old that are still good, and many others that are not.
Many small motor starting or running capacitors are electrolytic.
See http://electrochem.cwru.edu/encycl/art-c04-electr-cap.htm for a discussion on electrolytic capacitors.
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Last edited:
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
111202-0948 EST
If you have a motor that requires a starting capacitor, and the capacitor looses sufficient capacitance such that the motor won't start, then if the motor is left powered, then the motor will burn up.
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If you have a motor that requires a starting capacitor, and the capacitor looses sufficient capacitance such that the motor won't start, then if the motor is left powered, then the motor will burn up.
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