I was wondering how you can get caps that wont fail.
Capacitors seem to be the main component to fail in any electronics that I fix.
What causes this?
Current that's too high?
Temperature effects?
The hubbel telescope has caps im sure and it works for many years, how do I avoid buying caps that fail?
Hi,
It's both the current and the temperature that have major effects on the life of the capacitor.
Electrolytic caps have lifetimes in thousands of hours at a given temperature, such as 1000hr at 85 degrees C. There are about 9000 hours in one year.
The saving grace is that capacitor life approximately doubles for every 10 degree C decrease in temperature, so that same cap is good for 2000hr at 75 deg C, 4000hr at 65 deg C, 8000hr at 55 deg C, etc. However, a cap rated at 1000hr at 105 deg C will live for 2000hr at 95 C, 4000hr at 85 C, 8000hr at 75 deg C, 16000hr at 65 deg C, 32000 hr at 55 deg C (about three or four years).
It's plain to see that the higher the initial life rating in hours and the higher the initial temperature rating the longer the cap will last.
Ripple current plays a role here too though because high ripple makes the electrolyte dry out faster. Polymer caps are supposed to be better for this though, although the proof is in the life vs temperature rating again.
You can find some caps rated for 2000 hours at 85 deg C and some rated at 10000 hours. Obviously choose the higher rating. Of course the price will reflect the better quality too in most cases.
I had a computer power supply that would shut the computer down every so often without warning. Took it apart, found several electrolytic caps that leaked. Their capacitance went way down and their ESR went up quite a bit. Replaced all of them. Cost about 10 dollars or so to get the better grade caps in there. Will probably last at least another 5 years.
Actual cost to buy the caps was a little higher than that though because i couldnt buy just 1 of each cap i needed, and i wanted a few extra anyway. Also, one cap size could not be matched perfectly so i ended up with a slightly larger diameter cap which is better for life (same voltage rating) so the other caps had to be mounted more carefully because it took up slightly more room.