In this guide
A barrel connector is a cylindrical coaxial power connector — with a center pin and an outer sleeve — used to connect low-voltage electronics like routers, cameras, and Arduino boards to external power supplies.
- The plug and jack inner/outer diameters match exactly
- Polarity (positive tip or negative tip) is the same on both ends
- Voltage and current ratings meet the device’s requirements
- The correct mounting type (PCB, panel, or cable) is used for the application
- The pin or sleeve diameter is mismatched — it will fit loosely or not at all
- Polarity is reversed, risking damage to sensitive components
- The insulating layer between pin and sleeve is damaged, causing a short circuit
- Used in high-vibration environments without a locking or high-retention version
How a Barrel Connector Is Built
A barrel connector has three main parts: an outer metallic cylindrical body, an inner hollow metallic cylinder (the pin), and an insulating layer separating the two. The male plug attaches to the power supply cable. The female jack mounts on the device — either on the PCB, on the device panel, or inline on a cable.
The center pin almost always carries positive voltage. The outer sleeve carries ground. Some power supplies reverse this, so always check the polarity marking (a small diagram with a plus and minus near the jack) before connecting.
Common Sizes
Barrel connectors are not universal — size matters. The two critical measurements are the inner diameter (ID) of the pin hole and the outer diameter (OD) of the sleeve. The most common sizes in consumer electronics are:
- 5.5 mm OD / 2.1 mm ID — the most widely used size, common on routers, LED drivers, and Arduino boards
- 5.5 mm OD / 2.5 mm ID — looks identical but the slightly larger pin means a 2.1 mm plug will rattle inside it
- 3.5 mm OD / 1.35 mm ID — common on smaller devices and older laptops
Even a 0.4 mm difference in pin diameter can cause an unreliable connection or no connection at all. Always check your device’s manual or measure with calipers if unsure. SparkFun’s connector guide has a useful breakdown of power connector sizing conventions.
Where Barrel Connectors Are Used
- Home routers and network switches
- CCTV cameras and security systems
- Arduino and Raspberry Pi power inputs
- LED strip power supplies
- Portable audio equipment and effects pedals
Barrel Connector vs Other Power Connectors
| Setup | Works? | Need | Note |
|---|---|---|---|
| Matching OD, ID, and polarity | Yes | Nothing extra | Standard plug-and-play |
| Wrong pin diameter | No | Correct-size plug | Even 0.4 mm mismatch causes issues |
| Reversed polarity | No | Polarity-correct supply | Can damage device instantly |
| High-vibration use | Risky | Locking barrel connector | Standard connectors disconnect easily |
If you are working with display or data cables alongside power, see our guide on whether USB-C can connect to HDMI or check why USB-C to HDMI stops working for related troubleshooting.
Bottom line: A barrel connector is a simple but size-sensitive power connector. Get the outer diameter, inner diameter, and polarity right and it works reliably for years. Get any one of those wrong and you risk a loose connection, no power, or a damaged device.