Testing capacitors
 

"Don Pearce Geriatric Fool "


For a quick and dirty test, just connect a multimeter on the ohms range.
The needle should flick across to short circuit, then drop back towards
high resistance. The time it takes to drop back is proportional to the
value of the capacitor. If the needle ultimately drops back to open
circuit, the cap is probably ok.


** ROTFLMFAO !!!!!!!!!!

Hey grand-dad !!

Got any ****ing idea how long it is since " multimeters " had needles ??

Bet your pathetic old AVO has a nice BENT one - eh ?


Why don't you **** the HELL off - grand dad -

& spare the planet you dumb as dog **** WRONG advice.

IMBECILE




...... Phil

Testing capacitors
 

In article ,
Don Pearce wrote:
You don't have a multimeter with a needle? You are missing one of the
best alignment tools anyone could own - and a handy capacitor tester of
course. Go out and buy one now - it isn't a replacement for a DMM, but a
very useful complement.

Absolutely. But you can't expect bar room 'experts' like our Phil to know
such things...

--
*The only difference between a rut and a grave is the depth.

Dave Plowman London SW
To e-mail, change noise into sound.

Testing capacitors
 

Phil Allison wrote:
"Don Pearce Geriatric Fool "


For a quick and dirty test, just connect a multimeter on the ohms range.
The needle should flick across to short circuit, then drop back towards
high resistance. The time it takes to drop back is proportional to the
value of the capacitor. If the needle ultimately drops back to open
circuit, the cap is probably ok.


** ROTFLMFAO !!!!!!!!!!

Hey grand-dad !!

Got any ****ing idea how long it is since " multimeters " had needles ??

Bet your pathetic old AVO has a nice BENT one - eh ?


Why don't you **** the HELL off - grand dad -

& spare the planet you dumb as dog **** WRONG advice.

IMBECILE




..... Phil




Try
http://www.maplin.co.uk/Module.aspx?ModuleNo=25414

You really must learn to control that temper

Roger

Testing capacitors
 

"Marky P" wrote in message
...
Hi,

Is it possible to test capacitors reliably without a capacitance
meter?


Marky P.

Yes, put your tongue across the contacts a few seconds after switching off.

Testing capacitors
 

David Looser wrote:

"Marky P" wrote in message
...
Hi,

Is it possible to test capacitors reliably without a capacitance
meter?

If you want to test capacitors reliably you need an ESR (Effective series
resistance) meter, not a capacitance one.

Otherwise testing by substitution is your best bet.

David.


Its possible measure the value of capacitance using a low Rout signal
generator feeding a potentiometer in series with the capacitor with one
lead grounded. A volt meter is used to measure signal voltage across the
C. Set the signal gene at 10.0V sine wave at some chosen F. Alter the
value of the series resistance until you see 7.07Vrms appear across the
capacitor.
Disconnect the pot without altering its resistance, then measure its
resistance accurately.

C in uF then can be calculated = 159,000 / ( R in ohms x frequency ) so
say you had R = 5,000 ohms, and F = 1.0kHz, then C = .0318uF .

You could also have an air cored inductor of known inductance, and
parallel the C with the L, and feed it with a signal from a 10k
resistance from the sig gene. Using an osciloscope, tune the gene F for
the highest peak in resonance, known as Fo. Record Fo.

C in uF = 25.351 x 1,000,000 / F in Hz squared x L in milliHenrys.

Eg, if L = 100mH, F = 1kHz = 1,000 Hz, C = 0.251uF.

There are other ways using an old fashioned bridge.

ESR is measured in other ways, but it seems the OP wanted to know how to
work out the C value without a C meter.

Many cheap DVMs now sold measures C very well.

But they don't always measure L very well, espcially iron cored items
with variable L value at different F and V applied.

Patrick Turner.

Testing capacitors
 

Phil Allison wrote:

"Marky P"

Is it possible to test capacitors reliably without a capacitance
meter?

** No * ONE * test ( or cap tester) will establish that a capacitor is
perfectly OK, however, if a cap fails even one important test - is IS
faulty.

Different types of caps have different electrical characteristics, ie
electros are very different from plastic film or ceramic types - so the
tests you do must suit the type of cap.

Indeed, and I forgot these valid points in my last post.

Testing for leakage current can be done by applying dc voltage via a
100k to the cap and measuring the voltage drop across the 100k R over
some long time. But the voltage across the cap must not exceed the value
marked on the cap for all caps,
and for electros, the cap voltage should not be less than 1/4 of the
working Vdc marked on the cap.

I think the OP mainly wanted the C value.

Patrick Turner.

..... Phil

Testing capacitors
 

"Patrick Turner" wrote in message
...



ESR is measured in other ways, but it seems the OP wanted to know how to
work out the C value without a C meter.

Does it? the OP talked about "testing" a capacitor, not "measuring" it; that
sounds to me more like someone who wanted to know whether a capacitor was
faulty.

Since the OP has remained silent since his first post what he actually
wanted remains a mystery.

David.

Testing capacitors
 

Phil Allison wrote:

"Don Pearce the Geriatric Fool "

For a quick and dirty test, just connect a multimeter on the ohms range.
The needle should flick across to short circuit, then drop back towards
high resistance. The time it takes to drop back is proportional to the
value of the capacitor. If the needle ultimately drops back to open
circuit, the cap is probably ok.

** ROTFLMFAO !!!!!!!!!!

Hey grand-dad !!

Got any ****ing idea how long it is since " multimeters " had needles ??

Bet your pathetic old AVO has a nice BENT one - eh ?

Why don't you **** the HELL off - grand dad -

& spare the planet you dumb as dog **** WRONG advice.

...... Phil

Calm down Phil. You'll give grandad a heart attack.

The ohm test across a C does give some indication of the status of the
C.
If the cap is shorted, a DMM just shows a very low R number immediately.

If its not shorted, and doesn't have a stored charge (that well might
bend a meter needle in granpa's work shed), then the DMM will eventually
read OL for most plastic caps at least after some time as the cap
charges up with applied Vdc from the meter via the meter's series high
output resistance.

Most ohm meters produce a very low Vdc to test ohm values and a cap's
integrity needs to be tested at a Vdc across the cap for quite some time
and near the V rating of the cap, and when the temp is raised to near
operational if need be and with a CRO connected across the cap to detect
Vdc movements or intermittent noise/arcing in the cap.

Patrick Turner.

Testing capacitors
 

Don Pearce wrote:

Phil Allison wrote:
"Don Pearce the Geriatric Fool "


For a quick and dirty test, just connect a multimeter on the ohms range.
The needle should flick across to short circuit, then drop back towards
high resistance. The time it takes to drop back is proportional to the
value of the capacitor. If the needle ultimately drops back to open
circuit, the cap is probably ok.


** ROTFLMFAO !!!!!!!!!!

Hey grand-dad !!

Got any ****ing idea how long it is since " multimeters " had needles ??

Bet your pathetic old AVO has a nice BENT one - eh ?


Why don't you **** the HELL off - grand dad -

& spare the planet you dumb as dog **** WRONG advice.




...... Phil




You don't have a multimeter with a needle? You are missing one of the
best alignment tools anyone could own - and a handy capacitor tester of
course. Go out and buy one now - it isn't a replacement for a DMM, but a
very useful complement.

I have several analog and digital meters in my shed. But 99% of what i
measure is done with a Fluke DMM.

I got the analog meters for almost free at ham fests and dumpster bins.
Some I have calibrated for voltage measurement using an opamp drive with
diode in the shunt FB path so the meter reads logarithmically. These are
then calibrated in up to 30dB each side of a centre idle point, making
readings of speaker responses quite easy and accurate enough over 33
chosen filter Fo of the audio band. The signals measured are those
recovered from a pink noise source fed to the speaker, and a mic signal
amplified and filtered by a bandpass filter with Q = 12 at all F.

Its an old fashioned thing I made before I got a PC. I have not got
around to buying a Spectral analyser program to display speaker response
immediately on a PC screen, and variably as you change the mic position,
or alter a cross over component.

But it tells me 90% of what I need to know about loudspeakers. And if
the C values in crossovers were correct, or labelled correctly at the
factory; sometimes you get old "100uF" caps but they measure say 52uF,
but look perfect, and have not obviously dried out, and sometimes much
more C is there than the amount on the can. But its never an accurate
way to measure the C in crossovers, so see my other posts.

Patrick Turner.





d

Testing capacitors
 

"Patrick Turner"


Indeed, and I forgot these valid points in my last post.


I think the OP mainly wanted the C value.


** Then it would indeed profit the good fellow - most greatly -

to learn how to ****ING READ !!!!!!!!!!!!




........ Phil