How to measure capacity - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 20th February 2007, 03:03 PM   #1
diyAudio Member
 
Join Date: Dec 2006
Default How to measure capacity

Hello,

I'va got a filter from a friend, but the capacitance values are scratched out of the capacitors, is there a (cheap) way to measure them? I don't have a capacitor multimeter,just a normal multimeter.

Thanks, Henri
  Reply With Quote
Old 20th February 2007, 03:27 PM   #2
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
You would need a signal generator at the least. It would probably be easier to just buy a new meter with capacitance on, they don't cost much these days.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 20th February 2007, 06:33 PM   #3
diyAudio Member
 
Join Date: Mar 2006
Location: Cowboy capital
You probably have everything you need except a resistor. I use a 10 ohm, 2 watt, 0.1% resistor.

Set up the simple circuit and vary the signal until the voltage drop across the resistor and the voltage drop across the cap are the same. Then calculate the capacitance. You can do inductors this way too.

You can easily get better than 1% accuracy. Hand held meters usually are 5%.

An impedance bridge would probably be faster but cost an extra dollar.

Click the image to open in full size.
  Reply With Quote
Old 20th February 2007, 09:35 PM   #4
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Be wary of running in the 20Hz region this way though as most PC soundcards have roll offs around there. Also check your soundcard can drive a low load.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 26th February 2007, 01:32 PM   #5
diyAudio Member
 
Join Date: Dec 2006
So I can connect the cicuit directly to my soundcard an try different frequency's, and if the Volts across the cap and the resistor are equal, then i can measure the capacitance?

But how can I calculate the capacitance?
if the volts are the same, should i use the following:

Capacitance = ( volts across resistor / 10 (ohm) ) / ( 2 x pi x frequency in herz x volts across capacitor)

And: can i just play a sine of a value of Herz bij a program on my computer?

Grtz. Henri
  Reply With Quote
Old 3rd March 2007, 01:59 AM   #6
diyAudio Member
 
Join Date: Mar 2006
Location: Cowboy capital
Capacitance = 1 / ( 2*Pi*f*Z)

Z = 10 ohm when you use a 10 ohm resistor.

I donít drive the circuit with a sound card. I use the signal from a sound card and use that signal as the input to an amplifier. My amplifier has output meters so I can see how much power is flowing through the circuit.

I use this function generator

http://www.marchandelec.com/ftp/fg_lite.exe

It is very simple but as richie00boy has pointed out it's not perfect. You will not be able to measure a 0.1 uF capacitor with any accuracy because your sound card can't see it. You can't hear it either so I wouldn't be to concerned about it.

For audio frequencies, and the values of capacitors you will find in almost all speakers, this method will work just fine.

If you need a better explanation of what I do, email me.

Jon
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Calculating current capacity? sorenj07 Tubes / Valves 12 23rd June 2009 10:28 PM
transformer capacity krish2487 Chip Amps 5 15th January 2009 07:35 PM
Capacity of L'Art du Son cleaning fluid Sunsun22 Analogue Source 4 27th April 2008 01:12 AM
Speaker Workshop - using "Measure -> Passive Components" to measure ESR ? percy Multi-Way 0 12th March 2006 09:18 PM
Wire AWG & Amperage Capacity KevinLee Parts 12 10th December 2003 02:42 AM


New To Site? Need Help?

All times are GMT. The time now is 09:57 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2