← Wiki · Component

Electrolytic capacitor

A big, polarised capacitor (hundreds of µF) that buffers the supply where a lot of current is switched, such as LED strips and motors.

What it does#

An aluminium electrolytic capacitor stores far more charge than a ceramic of the same size, at the price of polarity, leakage and a limited life. It sits where the power enters a board that switches large currents: an LED strip that jumps from 0 to 3 A, a motor driver, a long power cable. It covers the current step until the supply catches up and damps the ringing of the cable’s inductance.

Key parameters#

  • Capacitance: 100 µF – 1000 µF for hobby loads. Adafruit’s NeoPixel guide suggests 500–1000 µF, 6.3 V or higher, across a strip’s supply.
  • Voltage: above the rail with margin: 16 V for 5 V, 25–35 V for 12 V.
  • Polarity: the stripe on the can marks minus. In the symbol the plus side is marked with +.

Example#

Example circuit: 5 V arrives on a screw terminal. C1 (1000 µF) buffers the strip's current steps, C2 (100 nF) the fast edges.
5 V arrives on a screw terminal. C1 (1000 µF) buffers the strip's current steps, C2 (100 nF) the fast edges. Open the electrolytic_bulk example from this page in PCB Canvas: “Insert into my schematic”.

Pitfalls#

  • Reversed = destroyed. A backwards electrolytic heats up and can vent. Check the + mark on the footprint against the part before soldering.
  • Not a decoupling capacitor. It is slow at high frequencies; keep the 100 nF ceramics at the chips too.
  • Inrush. A big capacitor charges with a current spike when you plug in; hot-plugging LED strip supplies can spark the connector.

Footprint#

  • Hand soldering and JLCPCB alike: the radial through-hole can (10 mm, 5 mm pitch, C88751) in the catalog. JLCPCB solders it by hand or wave, at extra cost; SMD electrolytics exist for tighter boards.