Measuring Capacity of Capacitors?

[voyager2]

Hi All
I've got a really dumb question:how do you measure the capacity of a capacitor?
Is it something to do with the numbers on the side?
 Please Help!

[Alfa_Zulu]

umm, well electrolytic caps which I believe are the most common ones,
they are black with numbers on the side such as 2uf, 100uf, 330uf, 470uf and so on.
then there can be some ceramic capacitors and they don't all say, but look for a
number and Google it like "34m ceramic cap" and see if you find info that way

but they electrolytic caps should always say unless their really small (physical size) and
the number accidentally didn't find on the side of the label, I have had a couple like this.

however there are also other types of caps I haven't mentioned.

if your still unsure upload a pic of the cap you have an I can tell you what type it is.

[Choco_liger]

Well the amount of farads (uF) is a measurement of the capacitance of a capacitor.

As said before you can get the readings on usually electrolytic caps but not on ceramic.

You can also get a multimeter with a special farads function.

For example this one:
http://www.bkprecision.com/products/model/2704B/tool-kit-dmm-05-w-cap.html

I wish I had one of these... 

EDIT: Whoops, I forgot to say you can get them on the datasheets too.

[billhowl]

You can make this is a simple but very useful capacitance meter kit.
http://www.seeedstudio.com/depot/capacitance-meter-kit-p-268.html?cPath=104_108
It can measure range from 1pF - 500uF  with cost USD$14.50
http://www.jyetech.com/Products/CapMeter/eCapMeter.php
Schematic

The measuring principle

A proven method of measuring capacitance is to form an RC network, which consists of the unknown capacitance and a known resistor. When a voltage is applied to the series connection of these components, the voltage accross the capacitor will slowly rise. So, by measuring the time constant the capacitance can be calculated easily.


how to read capacitance values

Like resistors, capacitors are generally manufactured with values to two significant digits. Also, small capacitors for general purposes have practical values greater than 1 pf and less than 1 µf. As a result, a useful convention has developed in reading capacitance values. If a capacitor is marked "47," its value is 47 pf. If it is marked .047, its value is .047 µf. Thus, whole numbers express capacitance values in picofarads while decimal fractions express values in microfarads. Any capacitor manufactured with a value of 1 µf or greater is physically large enough to be clearly marked with its actual value.
A newer nomenclature has developed, where three numbers are printed on the body of the capacitor. The third digit in this case works like the multiplier band on a resistor; it tells the number of zeros to tack onto the end of the two significant digits. Thus, if you see a capacitor marked "151," it is not a precision component. Rather, it is an ordinary capacitor with a capacitance of 150 pf. In this nomenclature, all values are given in picofarads. Therefore you might well see a capacitor marked 684, which would mean 680000 pf, or 0.68 µf.

[voyager2]

Big help guys!
So ceramic cap with 224 marked on it is 224pf?
And one with 103 is 10000 pf?

[billhowl]

Big help guys!
So ceramic cap with 224 marked on it is 224pf?
And one with 103 is 10000 pf?

ceramic cap with 224 marked on it is NOT 224pf is 220000pF or 0.22µf.
103 is 10000 pf or 0.01µf.

[Alfa_Zulu]

thanks billhowl lol, i wasn't aware of that

[voyager2]

Big help guys!
So ceramic cap with 224 marked on it is 224pf?
And one with 103 is 10000 pf?

ceramic cap with 224 marked on it is NOT 224pf is 220000pF or 0.22µf.
103 is 10000 pf or 0.01µf.

Slip of the keyboard(the dog ate my homework)
I understand...
But how many uf is one pf?

[billhowl]

http://en.wikipedia.org/wiki/Pico-

pf = picofarad =  10^-12farad
µf = microfarad = 10^-6farad

1µf = 1000000pf = 1000nF

some big value capacitors given in millifarads
etc. 22000µF = 22mF

[Alfa_Zulu]

i saw a 1Farad capacitor at our local electronics store the other day lol, it was over a foot long 

[cyberfish]

For a school project we used a 555 in oscillator mode to measure capacitances down to ~10pF.

It's a linear capacitance to period (1/f) converter. Probably not terribly accurate, but otherwise works pretty well.

You can use a microcontroller to measure the period.

[voyager2]

i saw a 1Farad capacitor at our local electronics store the other day lol, it was over a foot long 

They ain't that big!

[billhowl]

i saw a 1Farad capacitor at our local electronics store the other day lol, it was over a foot long 

Are you sure?

[voyager2]

Just the Sparkfun 10f super cap is only 13x33.5mm
http://www.sparkfun.com/commerce/product_info.php?products_id=746

[Alfa_Zulu]

yeah it was, but it did also have integrated circuitry that displayed a voltage and stuff, it was defiantly that big lol

[Soeren]

Hi,

That's for large car stereo powers (to get a better bass response).
The small 1F caps are made in either 2.5V or 5V - the large one you saw has to safely handle around 15V and it has to have a low impedance, hence a larger plate area.

[Gertlex]

Some multimeters can measure capacitance (mine can do it up to 200µf.  I didn't try anything greater).

Not sure how common that feature is, but I think mine's just a $20 one.

[Admin]

Typically the multimeters can measure no more than 100uF-200uF . . . so make sure it can do what you want before buying.

And that foot long cap would be an electrolytic, while the tiny 1F caps are supercapacitors. Supercaps, as Soeren pointed out, have really high ESR - making them fairly useless for frying kittens (high current applications).