I noticed that more and more radial electrolytic capacitors have a kind of cross (3 or 4 sided) scratched on the top of the case, is there a reason for why this is done?
regards, nukey
I noticed that more and more radial electrolytic capacitors have a kind of cross (3 or 4 sided) scratched on the top of the case, is there a reason for why this is done?
regards, nukey
AFAIK its' for pressure relief. When over voltage / reverse polarity, the internal pressure causes the top to deform and release the pressure, otherwise they go nukey bang.
They are safety valves in case the capacitor vents gases or liquid chemicals. Under certain circumstances such as over-voltage, aging, etc., a capacitor can literally explode violently unless it's provided with some means of controlled release.
& DLJs eevblog on exploding caps:
See
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
They also often say "VENT" somewhere on the side. An all-too-familiar sight is dried up caps with the top split open, guts leaking out.
If you abuse them heavily, they release the whole thing without drying up, hence the vent.
Tim
-- Deep Friar: a very philosophical monk. Website:
"nukeymusic"
** Despite all the good answers here - no one has addressed why such indentations are only found on the tops of RADIAL style electros.Most electros rely on the rubber end seal ( or a rubber plug in the case of large chassis mount types) to blow out and vent high internal pressures.
However, the rubber seal of a radial style electro is trapped between the cap body and the PCB it is mounted on - so cannot be relied upon to vent such pressure build ups inside the cap.
Hence makers deliberately weaken the aluminium can at the top so it will rupture more easily.
..... Phil
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