# Capacitor value

Discussion in 'General Electronics Chat' started by Gdrumm, Apr 25, 2009.

1. ### Gdrumm Thread Starter Distinguished Member

Aug 29, 2008
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Is it possible to discover a capacitor's value without clear markings?

Is there some type of measurement I can do with a voltmeter?

I have a small blue cap, with the numbers 104 on the side, and I want use it to set up a parallel RC circuit, to re-create a lab we have done at school.

Thanks,
Gary

2. ### Wendy Moderator

Mar 24, 2008
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A LOT of newer DVMs have capacitance meters as a feature, but I don't think that is what you're talking about, is it?

104 is 10000pf, or .01µF.

3. ### steveb Senior Member

Jul 3, 2008
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Yes, it can be measured.

Yes, some methods can use a voltmeter, but not a voltmeter alone. You can use an AC sinusoidal voltage source with an RC circuit. O-scopes are better to use however.

OK, good luck! By the way, the 104 is a clear marking of the capacitor value. - Just in case you didn't realize that.

4. ### studiot AAC Fanatic!

Nov 9, 2007
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513
Well yes if you had a sufficiently large value resistor, in relation to the capacitor, you could measure the charge and/or discharge with your voltmeter and your wristwatch.

5. ### Gdrumm Thread Starter Distinguished Member

Aug 29, 2008
684
36
Thanks Bill,
I suppose that is what I'm talking about, but I don't have a meter with that ability.

I have an Oscilliscope, a benchtop Fluke meter, and an old Function Generator.

Might I be able to apply a voltage, get a reading, and do some math to help me identify it?

Thanks,
Gary

6. ### Gdrumm Thread Starter Distinguished Member

Aug 29, 2008
684
36
By clear, I meant discernable. I have others that specify their unit of measure, such as 10 micro farad, 50 v, etc.

Do you think that would work with a low voltage?
I'm looking at a 8.78 V ac power supply, with a 4.7K resistor, and a capacitor (I thought the smaller the better?).

Gary

7. ### Gdrumm Thread Starter Distinguished Member

Aug 29, 2008
684
36
Forgive me for not reading Bill's reply completely.

Thanks Bill (and everyone).

I will read and print this off later.

The answer of 1 micro farad is what I needed.

Gary

8. ### studiot AAC Fanatic!

Nov 9, 2007
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People often forget that a scope can also be pressed into service as a voltmeter, currentmeter, chargemeter, AC or DC...the list is nearly endless.

9. ### Gdrumm Thread Starter Distinguished Member

Aug 29, 2008
684
36
Is there a way to guestimate what components would be necessary to make up a reasonable test circuit?
For example:
My AC Power supply is only 8.78 V AC
The Frequency if 60 HZ
The capacitor is .01 micro farads
The resistor is 4.637K Ohms

In solving, I'm getting some weird answers
XC = 265 K
IR = 1.91 mA
IC = 33.1 micro A
IT = 1.91 mA
Z = 4.59 K
PC = 263 K
PR = 4.59 K
PT = 4.59 K
Phase = 992???
P.F. = 1

What component would work best?
I have a wide range of resistor sizes to choose from, a few capacitors, and not many choices on voltage / frequency?

Thanks, Gary

10. ### leftyretro Active Member

Nov 25, 2008
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You better read it again, the answer given was .01 not 1 microfarad

Lefty

11. ### Audioguru New Member

Dec 20, 2007
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No.
104 is 0.1uF not 0.01uF. 103 is 0.01uf.

10 followed by four zeros is 100,000pF. 100,000pF is 0.1uf.

Why can't the Orientals label it 0.1uF or 100nF instead of 104??

12. ### thingmaker3 Retired Moderator

May 16, 2005
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Why do you credit Orientals for this convention?