Arduino Uno 5 V pin current limit: what it can and cannot power

Small sensors and a display can use the Uno 5 V pin, but motors, servos and LED strips need their own supply.

What the message means

Over USB the current comes from the computer port, which has a limit. From the barrel jack the on-board regulator limits the current and heats up.

Fix it in this order

Add up the current of everything you power from the 5 V pin and compare it with the supply limit.
Power servos, motors and LED strips from a separate supply, and join the grounds.
Feed the barrel jack with a voltage in the range the board recommends.
If the board gets hot or resets, reduce the load on the regulator.
Check the voltage on the 5 V pin with a multimeter while the load runs.

Why it happens

The 5 V pin gives only what the USB port or the on-board regulator can supply, and the Uno regulator gets hot when it feeds several parts from a higher input voltage. Servos and motors can draw far more than the pin should supply.

Power servos, motors and LED strips from a separate regulator or battery and join the grounds. Keep only low-current sensors on the board 5 V pin, and check each datasheet.

If you see this, do this

You see	Do this
Board resets when a servo moves	Separate servo supply.
Regulator very hot	Input voltage too high or load too large.

Arduino Uno pinout, common ground, reset on motor start.

Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.

Why this happens

The 5 V pin gives only what the source above it can deliver. Over USB, that is whatever the computer port allows, nominally 500 mA, and the board has a resettable fuse near that figure. From the barrel jack or the Vin pin, an on-board linear regulator makes 5 V. A linear regulator wastes the voltage difference as heat: power lost is (Vin – 5 V) times the load current.

That is why a 12 V supply into the barrel jack with a few hundred milliamps of load runs the regulator hot, while a 7 to 9 V supply does not. Motors, servos and LED strips draw far more current than the pin can supply, and they also generate electrical noise and sudden current steps that make the Arduino reset when they share a rail with it.

How to confirm the cause

Write down the current of each part from its datasheet and add them. Include the board itself, which is roughly tens of milliamps. Compare the total with the source limit.
Measure the voltage on the 5 V pin with a multimeter, first idle and then with the load running. A fall to 4.5 V or lower is a sign of overload.
Watch for resets when a servo or motor starts. A reset exactly at that moment points to supply sag.
Check the regulator temperature carefully with a fingertip for a second or with an infrared thermometer. A very hot regulator means too much input voltage or too much load.
Plug in USB only and then a separate supply only, and see whether the problem changes.

Worked example

Heat in the regulator and a simple current budget, using example figures that you should replace with your own datasheet values:

Regulator heat = (Vin - 5 V) x load current
12 V in, 300 mA load: 7 x 0.3 = 2.1 W (very hot for a small regulator)
 9 V in, 300 mA load: 4 x 0.3 = 1.2 W

Budget example from the 5 V pin (all figures illustrative):
 board 50 mA + OLED 20 mA + sensor 15 mA = 85 mA  -> acceptable over USB
 add one servo that can draw several hundred mA -> use a separate supply

Common mistakes

Powering a servo from the Arduino 5 V pin because it seems to work with no load.
Forgetting to join the grounds of the Arduino and the separate supply.
Using a 12 V adapter and then powering many 5 V parts from the board.
Feeding 5 V into the 5 V pin from a second source while USB is connected, without checking that the sources will not fight each other.
Judging the supply by a no-load voltage reading.

If this did not fix it

Supply wiring: thin wires or a long USB cable drop voltage before the board sees it.
A separate buck converter may be too small for the load; check its rating and its heat.
Missing capacitors near the servo or motor supply allow current spikes to disturb the logic.