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Electtrolytic Capacitor Becomes Hot

I

Indu Prakash

Jan 1, 1970
0
I repaired a networking router whose power filtering capacitor was sorted
and appeared buldged. The original capacitor was rated 1000mF 15V but since
the power adadpter was itself 12V so I used a capacitor rated 25V.

The router is continuosly on (has been so for the last week) and the
replaced capacitor again feels slightly warm to hand (as warm as the
external power adapter); although there are no problems with the operations
of the router. The only other parts before the capacitor are a filter and 4
rectifier pair; the external power adapter supplies 9V AC.

The capacitor is rated to be used upto 40 C and so I don't think there
should be a problem or should replace it wth a higher rated capacitor ?

Thanks
 
S

Sam Goldwasser

Jan 1, 1970
0
I always use 105C capacitors. It's well worth it.

There may be some other fault in the power supply resulting in the
capacitor heating. And capacitors with a higher temperature rating
may have a higher ESR, which would result in more heating if there
is excessive ripple current or something like that.

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R

RonKZ650

Jan 1, 1970
0
It's probably a high ripple current filter capacitor. Get a good high
frequency, high ripple current 105 degree cap. Panasonic FC, Nichicon
PW or HE series are 3 good choices.
 
G

Gerard Bok

Jan 1, 1970
0
And capacitors with a higher temperature rating
may have a higher ESR,

Are you sure of this or is this a typo ?

I understand that 105 Centegrade types are higher quality / SMPS
rated capacitors. If anything affects the ESR, I would expect
those capacitors to have a lower ESR value, not higher.
 
R

Rick

Jan 1, 1970
0
I suspect the full wave bridge is not anymore - a diode in it is
shorted and the poor capicitor is dealing with a half wave rectified,
rather than full wave... put a scope on it and see !

Rick - Atlanta
 
J

JANA

Jan 1, 1970
0
You should be using a 105C rated cap.

--

JANA
_____


I repaired a networking router whose power filtering capacitor was sorted
and appeared buldged. The original capacitor was rated 1000mF 15V but since
the power adadpter was itself 12V so I used a capacitor rated 25V.

The router is continuosly on (has been so for the last week) and the
replaced capacitor again feels slightly warm to hand (as warm as the
external power adapter); although there are no problems with the operations
of the router. The only other parts before the capacitor are a filter and 4
rectifier pair; the external power adapter supplies 9V AC.

The capacitor is rated to be used upto 40 C and so I don't think there
should be a problem or should replace it wth a higher rated capacitor ?

Thanks
 
F

Franc Zabkar

Jan 1, 1970
0
The capacitor is rated to be used upto 40 C ...

I may be demonstrating my ignorance, but I don't recall ever seeing a
40 deg C electrolytic capacitor, only 85C and 105C.

- Franc Zabkar
 
R

RonKZ650

Jan 1, 1970
0
I'd have to see a 40 deg C rated cap to believe it. 40 deg C=104 deg F.
No way. Back in the 60s there really was no electrolytics other than
the multisection filters and they were rated at 85 deg C, then in the
70s when electrolytics began appearing as small capacitors they really
never even showed a degree rating on the majority of them, the ones
that did was 85 deg C. Then in about 1985 the first 105 deg C caps
began to show up. This is the way I remember it anyway. Of course all
caps are different, a 85 degree may have a higher ripple current rating
from one manufacturer than a 105 degree rated one from another. The
high ripple current will cause the cap to run hot, as well as being
placed next to high heat resistors ect. so on top of the temp rating,
keep in mind the ripple current rating too. I always use the best
qualty highest rated ripple current caps @105 degree C rating. No use
using scum capacitors as the best still only cost about $0.20 to a
couple dollars depending on the size. Don't use scum and save $0.05 or
you'll be replacing them every 6 months.
 
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