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.