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[on:]

Hi,
    I just bought a 0.01uf capacitor: MF103-400 Metallized Film Radial Capacitor .01uf 400V  . I didn't find any datasheet on the web.

Problem: I just not sure which side is positive/negative ?

Printed side:    There is 2 dot on the ride side


Thank you

[Reply #1 on:]

There's a problem with your attachment, could you re-upload it? Perhaps it's non-polarised... polarities are normally marked pretty clearly with a bold stripe or something similar.

[Reply #2 on:]

And that bold stripe indicates the anode (+) on aluminum electrolytics in a metal can and cathode (-) on everything else.  Go figure.

http://en.wikipedia.org/wiki/File:Cap-elko-smd-polarity.jpg
http://en.wikipedia.org/wiki/File:Electrolytic_capacitors.jpg

All from the Wikipedia capacitor page.  Have a read.

http://en.wikipedia.org/wiki/Electrolytic_capacitor

Tantalums are a little bit different and it's a shame they don't show them in the images above.  But, they are the most obviously marked of all:

http://www.learningaboutelectronics.com/Articles/Tantalum-capacitor-polarity-markings

[Reply #3 on:]

Film capacitors don't have a polarity. Just electrolytic and tantalum are the ones you need to worry about.

[Reply #4 on:]

It is very unlikely for it to be polarized.

[Reply #5 on:]

This is the capacitor:



Thank

[Reply #6 on:]

As Chagrin says, if it's metallized film then it doesn't have a polarity and it doesn't matter which way round you connect it.

[Reply #7 on:]

I found a tutorial on how to control ac phase with the arduino( 110-220v) : http://wiki.dxarts.washington.edu/groups/general/wiki/4dd69/AC_Dimmer_Circuit.html


Can I use it in this schematic(created by the guy from the tutorial) :
 





Thank

[Reply #8 on:]

They're non-polarized.  So there's no positive/negative side.

HOWEVER, some manufacturers denote though which side is the OUTER FOIL of a capacitor.
This is useful in certain cases where you want to take advantage and use the outer foil connection as a shield. 

[Reply #9 on:]

Can I use it in this schematic(created by the guy from the tutorial) :

You should look up the capacitor in the supplier's catalogue and see if it has an AC voltage rating. But as it's rated for 400VDC, it's probably OK on 120VAC.

[Reply #10 on:]

But as it's rated for 400VDC, it's probably OK on 120VAC.

Don't forget the saying
"Assumption is the mother of all fuckups."

If these caps will be connected across AC lines, make sure they are "Safety Certified Capacitors" and AC rated. 
They're usually classified as either X or Y capacitors.
X for use in line-to-line applications and type Y for line to ground applications.

Capacitors designed for use across AC lines are special in that when they fail, they fail as "open" and not as "short circuits."
So you can imagine what will happen if a capacitor used in an AC line-to-line application failed as a "short." -- KA BOOM!

The caps also need to be able to withstand multiple high voltage impulses and operate under normal AC voltage conditions.
i.e. for example 250VAC (rated voltage), 1500VAC (withstanding voltage), 2500V impulse voltage

[Reply #11 on:]

Actually Historically speaking they are polarized... a polyester film capacitor is two long parallel plates (ribbons but the idea is the same) and the polarity came from old tube days and to a point even today for capacitors of similar construction. The major exception being metalized layered monolythic caps.
The standard american symbol looks like this:  This end was considered the inside foil and therefore more susceptible to noise pickup  > -----|(-----   < and this end was commonly accepted as the 'ground' end or outside foil. "From the 1949 Radio Amateur Radio Handbook" Published by the ARRL.
{Edit RKJ}
Bob

[Reply #12 on:]

And that bold stripe indicates the anode (+) on aluminum electrolytics in a metal can and cathode (-) on everything else.  Go figure.

Wrong way round - stripe is for negative on Al, positive on tantalum....  Usually.   But you read the manufacturer's datasheet anyway
so you didn't get it wrong

It's not usual to say anode or cathode for a device that accepts current flow in either direction BTW, since its rather ambiguous!