# A circuit’s electrolytic capacitor was blown up while the fuse remains

Joined Aug 30, 2017
85
How can a circuit Elcos be blown up while the fuse remains intact and the biggest one, 400V 110 uF is surely burst up?
What's the best explanation on this and how to determine the fuse max limit?

ltec
PET 8228D

02H1-ROHS L2-28

Last edited:

#### Papabravo

Joined Feb 24, 2006
21,225
How can a circuit it’s Elco be blown up while the fuse remains intact and the biggest one, 400V 110 uF is surely burst up?
What's the best explanation on this and how to determine the fuse max limit?
If I knew what an Elco was I might be able to help. Different components fail at different times for different reasons. There is no single answer to your question that covers all situations.

#### Alec_t

Joined Sep 17, 2013
14,312
How can a circuit it’s Elco be blown up while the fuse remains intact
It depends what the fuse was intended to protect, what the fuse type and rating are, and what caused the elco (electrolytic capacitor) to blow up. Internal pressure, rather than excessive current, can cause an elco to blow up.

Joined Aug 30, 2017
85
Why if an Elco having white silica gums stick onto it which quite likely burst out of the casing, after being separated and measured, it has correct Farad value for capacity?

Where did actually white silica come from and how to definitively ascertain the good and faulty Elcos?

#### AlbertHall

Joined Jun 4, 2014
12,346
Where did actually white silica come from and how to definitively ascertain the good and faulty Elcos?
I expect that the 'silica' is silicone rubber added during manufacture to support the capacitor against vibration.

#### Alec_t

Joined Sep 17, 2013
14,312
The ESR (equivalent series resistance) of an elco often increases with age, so the normal rated current passing through the increased resistance causes above-normal heating which can increase the internal pressure enough to cause the cap vent to open (perhaps violently) and let the goo escape.
Measure the cap's ESR and check it's according to the maker's specification.

#### rsjsouza

Joined Apr 21, 2014
383
It depends what the fuse was intended to protect, what the fuse type and rating are, and what caused the elco (electrolytic capacitor) to blow up. Internal pressure, rather than excessive current, can cause an elco to blow up.
Indeed. Fuses/breakers in a house circuit are there to protect the wiring, while the fuses inside an equipment are rated to protect the highest current element of the circuit.

It also depends on what you call a "blow up"; in general it is a high intensity event that happens at a very short time which causes catastrophic and irreparable damages to a part or subsystem (the capacitor in this case). Fuses work by increasing their temperature to the point of rupture of the metal - an event that can be exceedingly slow depending on the nature of the fault. A transient, for example, may rupture or damage a number of parts in micro- or mili-seconds before the fuse even starts to become hot. Other events caused by slow degradation (as mentioned before) may bring the fuse to a warmer state but the weakest link on the chain might fail before that.

In all cases, it is interesting to know the rupture curve of the fuses you are using - some of them take several seconds to open at the rated current, for example (check here for one example)

#### Orson_Cart

Joined Jan 1, 2020
90
cheap caps don't last - luckily, somtimes when they go bang, they go open ckt faster than the fuse can react ....

#### Martin_R

Joined Aug 28, 2019
137
Was the capacitor wired up reverse polarity? That would cause it to explode. No guesses how I know....

#### crutschow

Joined Mar 14, 2008
34,406
A bad electrolytic capacitor (Elco?) develops a high leakage current which can cause it to overheat and burst.
The current necessary to cause this can still be well below whatever the fuse rating is.

The fuse rating is typically some value above (perhaps about 25%) the maximum current the device will ever use in normal operation.

#### Deleted member 115935

Joined Dec 31, 1969
0
There is an old saying on the lines of
"the circuit blows up, and that blows the fuse so you know something has gone wrong,"

In the case of the capacitor,
its gone bang, and then open circuit, so the fuse will not blow,

Different electrolytic have different life's,

these can be down in the thousand hour region for the cheap ones running at their limits / running hot.

thats life I'm afraid,