Sunday, March 31, 2013

How To: Read Capacitor Values

Capacitors are categorised in terms of their capacitance, voltage and construction - so it is often necessary to tell different similar-looking capacitors apart based on their value markings.

Electrolytic capacitors are marked in terms of micro Farads (uF) - these are easy to interpret.
For example, the capacitor below is a 100uF capacitor, because it is marked as 100uF.

If a ceramic capacitor only has two digits (XY), then this value is XY pico Farads (pF). For example, the ceramic capacitor shown below has a value of 20 pF.

If a ceramic capacitor has three digits (XYZ), then the value of the capacitor is equal to:

XY * 10 ^ Z pico Farads

In the case below, XY is 22 and Z is 3. Thus, the value is:

22 * 10 ^ 3 pico Fards = 22,000 pF.

We can see from this example that, effectively, Z is the number of zeroes after XY.

In the example below the value of the capacitor is give as: 104J100V. This indicates that:

104 is the capacitance code
J is the tolerance code
100V is the voltage rating

Let's concentrate on the capacitance code.

Capacitor values are given in micro (u), nano (n) and pico (p) Farads. To convert between these magnitude prefixes, consider that:

1 Farad is the same as
1 000 000 micro Farads is the same as
1 000 000 000 nano Farads
1 000 000 000 000 pico Farads

1,000 pF = 1 nF
1,000 nF = 1 uF

Therefore, a capacitance code of 104 = 100,000 pF = 100 nF = 0.1 uF.