can electrolytic capacitor withstand 1 V AC?

V

val

Guest
Hi all,
I've read that capacitors manufactured under IEC 384-4 standard should
be able to withstand a reverse DC voltage of 15% of their nominal max
voltage for at least 125 hours. I wonder what could happen if you use
an electrolytic aluminium capacitor at 1V AC without polarizing it. I
found that it was OK for a couple of minutes but does anyone know if
it can work without altering it's lifetime.
thanks,
Valéry
 
"val" <vlepage@aol.com> wrote in message
news:264beacf.0309230705.6db0cbb@posting.google.com...
Hi all,
I've read that capacitors manufactured under IEC 384-4 standard should
be able to withstand a reverse DC voltage of 15% of their nominal max
voltage for at least 125 hours. I wonder what could happen if you use
an electrolytic aluminium capacitor at 1V AC without polarizing it. I
found that it was OK for a couple of minutes but does anyone know if
it can work without altering it's lifetime.
thanks,
Valéry
Click to expand...
Electrolytic caps should be used with a continuous DC bias near their
rating. However, if you use two caps, you can do this:

|
AC Voltage |
------+
| | +
- ###
^ ---
| |
------+
|
---
###
| +
|

Use Electrolytic caps with a DC voltage rating
of at least the Peak to Peak AC voltage. That is,
for line voltage in US, 2 * 120 * sqrt(2) = 340V.

The node between the caps gets charged to -PP AC,
so when the line swings to +PP AC, the difference
is PP - -PP = 2PP.

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
 
Robert Monsen wrote:
"val" <vlepage@aol.com> wrote in message
news:264beacf.0309230705.6db0cbb@posting.google.com...

Hi all,
I've read that capacitors manufactured under IEC 384-4 standard should
be able to withstand a reverse DC voltage of 15% of their nominal max
voltage for at least 125 hours. I wonder what could happen if you use
an electrolytic aluminium capacitor at 1V AC without polarizing it. I
found that it was OK for a couple of minutes but does anyone know if
it can work without altering it's lifetime.
thanks,
Valéry


Electrolytic caps should be used with a continuous DC bias near their
rating. However, if you use two caps, you can do this:

|
AC Voltage |
------+
| | +
- ###
^ ---
| |
------+
|
---
###
| +
|

Use Electrolytic caps with a DC voltage rating
of at least the Peak to Peak AC voltage. That is,
for line voltage in US, 2 * 120 * sqrt(2) = 340V.

The node between the caps gets charged to -PP AC,
so when the line swings to +PP AC, the difference
is PP - -PP = 2PP.

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
Click to expand...
I gots a question.
Start with both caps at zero volts.
Apply positive voltage to the top.
Bottom cap gets reverse biased by V/2, assuming equal C.
Aren't we already in trouble??? Especially at 140V pk.
And we're not even thru the first half cycle yet...

This is another example where vague questions without application
framework leads to...well, we all know where it leads...it leads to me
making a statement like:

You should NEVER reverse bias an electolytic, no matter what clever
means you use to minimize the effect. It's just BAD, BAD, BAD design
practice. You'll have plenty of reliability issues. No need to put
them in on purpose.
mike

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In article <264beacf.0309230705.6db0cbb@posting.google.com>,
vlepage@aol.com mentioned...
Hi all,
I've read that capacitors manufactured under IEC 384-4 standard should
be able to withstand a reverse DC voltage of 15% of their nominal max
voltage for at least 125 hours. I wonder what could happen if you use
an electrolytic aluminium capacitor at 1V AC without polarizing it. I
found that it was OK for a couple of minutes but does anyone know if
it can work without altering it's lifetime.
thanks,
Valéry
Click to expand...
Non-polarized electrolytics are just two polarized caps back-to-back
in the same can. They only have AC across them, so one would think
that it would be okay to put several volts of AC aross any
electrolytic as long as the average current is zero or with the normal
polarization, and not against it.


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