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Capacitors and polarity
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joshie75


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Joined: 09 Nov 2010
Posts: 235
Location: Illinois
Posted: 16 Jan 2012 10:47:40 pm    Post subject: Capacitors and polarity
I've looked around on the internet for my answer already, as always so I don't have to bother you guys but couldn't find anything Sad

Kerm, I found the correct capacitor values for my project. The input capacitor is a .33uF, and the output is a .1uF. I picked up the .1uF at Radio shack and it is a Ceramic disk, dielectric. The .33uF that I am ordering off of amazon is a thru-hole Tantalum. I looked for the same exact capacitor, with different capacitance, but had no luck. How do I know if either of them are polarized or are non polar? I don't want to wire anything incorrectly. I checked the packaging for the .1uF, and the
amazon page for the .33uF. Neither told me if the unit was polarized. Sad
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KermMartian


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Joined: 14 Mar 2005
Posts: 55881
Location: Earth, Sol, Milky Way
Posted: 16 Jan 2012 10:53:01 pm    Post subject:
Ceramic disk capacitors have no polarity. Electrolytic capacitors, the blue or navy (usually) tubes with leads side by side coming out of the bottom, have a polarity; one side of the can is generally marked with a row of negative (-) signs.
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joshie75


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Joined: 09 Nov 2010
Posts: 235
Location: Illinois
Posted: 16 Jan 2012 10:56:17 pm    Post subject:
Ok, thanks Kerm Smile
http://www.amazon.com/gp/product/B0015A6R06/ref=oh_o00_s00_i00_details
That is the pack of .33uF I ordered. I was wondering if they were polarized because of the uneven leads.
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KermMartian


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Joined: 14 Mar 2005
Posts: 55881
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Posted: 16 Jan 2012 11:05:19 pm    Post subject:
joshie75 wrote:
Ok, thanks Kerm Smile
http://www.amazon.com/gp/product/B0015A6R06/ref=oh_o00_s00_i00_details
That is the pack of .33uF I ordered. I was wondering if they were polarized because of the uneven leads.
Ah, tantalum caps are not ceramic capacitors. The polarity of tantalum capacitors must be observed; generally, the long lead is the positive one:

http://en.wikibooks.org/wiki/Electronics/Component_Identification#Tantalum_capacitors
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joshie75


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Joined: 09 Nov 2010
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Posted: 16 Jan 2012 11:09:41 pm    Post subject:
Ahhh thought so. Thanks again Kerm, always saving me from sure failure!
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KermMartian


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Posted: 16 Jan 2012 11:13:42 pm    Post subject:
joshie75 wrote:
Ahhh thought so. Thanks again Kerm, always saving me from sure failure!
The pleasure is mine; glad to help.
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CharlieMAC


Advanced Newbie


Joined: 02 Jan 2012
Posts: 58
Posted: 16 Jan 2012 11:18:12 pm    Post subject:
Be careful of the polarity of the electrolytic capacitor. If you connect one of these capacitors with the wrong polarity, it may explode (that was something I wanted to see while I was in the electronics lab, but the teacher didn't do it).
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KermMartian


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Posted: 16 Jan 2012 11:20:37 pm    Post subject:
CharlieMAC wrote:
Be careful of the polarity of the electrolytic capacitor. If you connect one of these capacitors with the wrong polarity, it may explode (that was something I wanted to see while I was in the electronics lab, but the teacher didn't do it).
You have to drive a lot of voltage through an electrolytic capacitor backwards to trigger thermal runaway, in my experience. My worst (?) experience with capacitors was connecting an LED to a charged 10uF capacitor and causing it to abruptly and kinetically fail.
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joshie75


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Joined: 09 Nov 2010
Posts: 235
Location: Illinois
Posted: 16 Jan 2012 11:22:58 pm    Post subject:
*Hopes they label polarity on package because is now scared to mess something up* 0x5
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KermMartian


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Joined: 14 Mar 2005
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Posted: 16 Jan 2012 11:26:21 pm    Post subject:
joshie75 wrote:
*Hopes they label polarity on package because is now scared to mess something up* 0x5
Hehe, you'll be fine. Smile Just exercise proper caution, and be aware of components getting hot, smelling weird, or emitting sparks or smoke, and you should be ok.
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chronomex


Advanced Newbie


Joined: 09 Sep 2010
Posts: 74
Location: Seattle
Posted: 17 Jan 2012 04:27:13 am    Post subject:
KermMartian wrote:
My worst (?) experience with capacitors was connecting an LED to a charged 10uF capacitor and causing it to abruptly and kinetically fail.

Did that yield a Smoke Emitting Diode (soon to be a Friode) or a leaky capacitor?
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KermMartian


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Joined: 14 Mar 2005
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Posted: 17 Jan 2012 09:53:17 am    Post subject:
Haha, nice ones, chronomex. It was an explosion-emitting diode; the capacitor was fine.
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benryves


Cemetech Expert


Joined: 12 Aug 2008
Posts: 1361
Location: London, United Kingdom
Posted: 17 Jan 2012 10:02:39 am    Post subject:
Electrolytic capacitors are designed to vent safely but still spurt vile-smelling steam if you abuse them. I'm sure anyone who's replaced old leaky capacitors are well aware of the lovely rotting fish aroma of hot electrolyte...


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