I have a capacitor labeled 1 μF (micro Farad) and when I measure capacitance I get 1 μF but when I measure resistance the meter shows out of range on any dial setting except on 200 MΩ (mega Ohm) where it shows a constant value.

Is the capacitor good or bad?

  • 1
    \$\begingroup\$ Just fine. Why would you expect it to show resistance? (Well big polarized caps can take a while to charge up from the DMM current source used to measure resistance.) \$\endgroup\$ – George Herold Jan 19 '15 at 23:52

A real-life capacitor can be modelled as an ideal capacitor of nominal value parallel with a resistor (\$R_p\$), and this all is in series with another resistor (\$R_s\$). \$R_s\$ is the equivalent series resistance (several ohms), something that comes from the fact that the pins of the capacitor have some resistivity.


simulate this circuit – Schematic created using CircuitLab

The parallel resistance, \$R_p\$, is ideally infinite, because in an ideal insulator has zero conductivity. As no real insulator is ideal, the parallel resistance that depicts leakage has some finite, but usually quite large value. When you measure the resistance of a capacitor, you will get a value of \$R_s+R_p\$, which is likely to be pretty large as well.

That said, and knowing you only got a value when measuring in the 200 M\$\Omega\$ limit, your capacitor seems alright.

  • \$\begingroup\$ all right but shouldn't there be a transient charging period for the capacitor when its hooked up to the meter, and in that period it would show a growing resistance witch goes out of range eventually? \$\endgroup\$ – adoion Jan 19 '15 at 23:54
  • 1
    \$\begingroup\$ The time constant is likely to be too small for you to notice. \$\endgroup\$ – hryghr Jan 19 '15 at 23:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.