capacitor rating

the power supply for a voip telephone unit has failed twice . it's rated 5v 3a.

both the original and replacement still would read 5v but would not power the base units.

today i again replaced the power supply. i then proceeded to open up the defective PS. i found a 470mf polarized cap with a bulge. as an experiment and with the only thing i had laying around at 11pm i replaced it with a much larger in physical size and rating, 1000mf cap.

well the darn thing now works, puts out 5v and powers the base unit. is it safe to use? why does the very different rating of the capacitors not seem to effect the output? thanks

by roadkillwi
4 days, 2 hours ago

The bulge is a typical sign of an electrolytic cap which has dried out. It was behaving more like a resistor than like a capacitor in its last days. Some repair guys claim that they are the source of the problem of 85% of faulty standard electronic equipment.

1 Farad cap is a big cap. It may be a "supercap" with problems of its own, be sure that it can safely handle the 5V. But the original 0.47F was big too.

Capacitors at the exit of a full bridge diode bridge can be replaced with a bigger one (at least same voltage and the right polarity) without problem, since their main job is to smooth the transition between peaks of the half sinuses waves. They are just more expensive. Try to use one from a known company, and a recent one. They age even if they stay on the shelves, but luckily for you, or not, the ones with higher volage rating are more robust.

by vanderghast
3 days, 23 hours ago

thank you, i ill keep my repaired / altered power supply as a back up. on the ooma voip blog it seems these power supplies are very problematic and the source of many complaints.

by roadkillwi
3 days, 21 hours ago
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