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mike
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 Posted:
Tue Feb 08, 2005 8:24 am Post subject:
novice: why do electrolytic capacitors... |
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Why do electrolytic capacitors have to be connected the correct way around? Why
does a circuit not work correctly if an electrolytic capacitor is reversed? Is
it like a battery - only sinks rather than sources a charge?
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Spehro Pefhany
Guest
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| Posted:
Tue Feb 08, 2005 8:34 am Post subject:
Re: novice: why do electrolytic capacitors... |
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On Tue, 08 Feb 2005 02:24:51 GMT, the renowned mike
<mike@noname.nothere> wrote:
| Quote: | Why do electrolytic capacitors have to be connected the correct way around?
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Because they can only withstand the rated voltage the correct way
around. They leak more with small voltages in the reverse direction as
well.
| Quote: | Why
does a circuit not work correctly if an electrolytic capacitor is reversed?
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Sorry, it can't be guaranteed that it won't work correctly.
| Quote: | Is
it like a battery - only sinks rather than sources a charge?
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Stupid metaphor of the day- consider a compressor storage tank- it can
withstand internal pressure of 150psi but will crumple up on a vacuum
(external pressure of 15psi).
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com |
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Kryten
Guest
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| Posted:
Tue Feb 08, 2005 8:40 am Post subject:
Re: novice: why do electrolytic capacitors... |
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"mike" <mike@noname.nothere> wrote in message
news:ol8g01dgtsr1uad4b94kc8svsai4qmndcs@4ax.com...
| Quote: | Why do electrolytic capacitors have to be connected the correct way
around? Why
does a circuit not work correctly if an electrolytic capacitor is
reversed? Is
it like a battery - only sinks rather than sources a charge?
|
Initially, current builds a very thin insulating layer on one electrode
(just like anodisation of aluminium). Reversing the polarity reverses the
process and so destroys the layer.
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John Fields
Guest
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| Posted:
Tue Feb 08, 2005 8:40 am Post subject:
Re: novice: why do electrolytic capacitors... |
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On Tue, 08 Feb 2005 02:24:51 GMT, mike <mike@noname.nothere> wrote:
| Quote: | Why do electrolytic capacitors have to be connected the correct way around? Why
does a circuit not work correctly if an electrolytic capacitor is reversed? Is
it like a battery - only sinks rather than sources a charge?
|
---
The dielectric in an aluminum electrolytic capacitor is a
microscopically thin layer of aluminum oxide which is maintained on
one of its aluminum plates when the polarity of the voltage across the
two plates, and the electrolyte between them is applied in the correct
direction. If the voltage is appled in the wrong direction, the
electrolyte will deplete the oxygen in the coating, reducing the oxide
coating to elemental aluminum and the two plates will short-circuit
through the electrolyte, destroying the capacitor.
--
John Fields |
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keith
Guest
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| Posted:
Tue Feb 08, 2005 8:40 am Post subject:
Re: novice: why do electrolytic capacitors... |
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On Tue, 08 Feb 2005 02:24:51 +0000, mike wrote:
| Quote: | Why do electrolytic capacitors have to be connected the correct way around? Why
does a circuit not work correctly if an electrolytic capacitor is reversed? Is
it like a battery - only sinks rather than sources a charge?
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They make more noise one way than the other.
--
Keith |
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Pooh Bear
Guest
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| Posted:
Tue Feb 08, 2005 8:41 am Post subject:
Re: novice: why do electrolytic capacitors... |
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mike wrote:
| Quote: | Why do electrolytic capacitors have to be connected the correct way around? Why
does a circuit not work correctly if an electrolytic capacitor is reversed? Is
it like a battery - only sinks rather than sources a charge?
|
To answer this - I rather like the Japanese name for an electrolytic cap. They call
it a 'chemicon' - i.e a chemical capacitor ( condensor ) .
It relies on electro-chemical processes to work correctly.
As such, it effectively has an anode and cathode. This is why it has to be used the
right way round.
If you want more info - google is your friend !
Graham |
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Paul Burke
Guest
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| Posted:
Tue Feb 08, 2005 8:41 am Post subject:
Re: novice: why do electrolytic capacitors... |
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mike wrote:
| Quote: | Why do electrolytic capacitors have to be connected the correct way around? Why
does a circuit not work correctly if an electrolytic capacitor is reversed? Is
it like a battery - only sinks rather than sources a charge?
|
I saw a guy test a power supply once, 20A at 50V unregulated, and the
bloke building it had put all 4 filter capacitors in the wrong way
round. Like a wedding!
Paul Burke |
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Anders F
Guest
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| Posted:
Tue Feb 08, 2005 2:51 pm Post subject:
Re: novice: why do electrolytic capacitors... |
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"Paul Burke" <paul@scazon.com> wrote in message
news:36rb6jF54iei8U1@individual.net...
| Quote: | mike wrote:
Why do electrolytic capacitors have to be connected the correct way
around? Why
does a circuit not work correctly if an electrolytic capacitor is
reversed? Is
it like a battery - only sinks rather than sources a charge?
I saw a guy test a power supply once, 20A at 50V unregulated, and the
bloke building it had put all 4 filter capacitors in the wrong way
round. Like a wedding!
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But probably a bit more messy... ;-)
Btw. there's a "basic" group where all the "novice:" posings might be better
off....
/Anders
> Paul Burke |
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Tim Wescott
Guest
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| Posted:
Tue Feb 08, 2005 9:28 pm Post subject:
Re: novice: why do electrolytic capacitors... |
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mike wrote:
| Quote: | Why do electrolytic capacitors have to be connected the correct way around? Why
does a circuit not work correctly if an electrolytic capacitor is reversed? Is
it like a battery - only sinks rather than sources a charge?
Search on "borax" and "rectifier" for the full story. You can think of |
an electrolytic capacitor as a really crappy diode that happens to have
a lot of junction capacitance.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com |
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Rob Gaddi
Guest
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| Posted:
Tue Feb 08, 2005 11:07 pm Post subject:
Re: novice: why do electrolytic capacitors... |
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mike wrote:
| Quote: | Why do electrolytic capacitors have to be connected the correct way around? Why
does a circuit not work correctly if an electrolytic capacitor is reversed? Is
it like a battery - only sinks rather than sources a charge?
Basically, yes. When reversed it acts as a very effictive current sink, |
but only for a fairly short time. |
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Michael A. Terrell
Guest
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| Posted:
Wed Feb 09, 2005 10:29 pm Post subject:
Re: novice: why do electrolytic capacitors... |
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Paul Burke wrote:
| Quote: |
mike wrote:
Why do electrolytic capacitors have to be connected the correct way around? Why
does a circuit not work correctly if an electrolytic capacitor is reversed? Is
it like a battery - only sinks rather than sources a charge?
I saw a guy test a power supply once, 20A at 50V unregulated, and the
bloke building it had put all 4 filter capacitors in the wrong way
round. Like a wedding!
Paul Burke
|
This is where you need to bring a supply up with a variac that has an
AC current meter to monitor the current. The test procedures I wrote
for linear power supplies with a bank of "Computer grade" capacitors
explained the reason, and the danger of not doing it right.
--
Beware of those who suffer from delusions of adequacy!
Michael A. Terrell
Central Florida |
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