Relay board doesnt work with external power?

Hi,

When i supply my 4ch relay board with external 5v it doesnt switch..
Do i need to connect ground to the arduino or something else?

Greets

What relay board do you have, show us a good image of your wiring along with schematic.

.

LarryD:
What relay board do you have, show us a good image of your wiring along with schematic.

.

This is an 8 relay board and wiring for such.
Wire your board in a similar way, make sure your external relay power supply matches your relay voltage.
( looks like 5v )

edit:
looks like your header with the jumper has no GND, use the other GND with the external supply.
No jumper is used.
.

LarryD:
This is an 8 relay board and wiring for such.
Wire your board in a similar way, make sure your external relay power supply matches your relay voltage.
( looks like 5v )

edit:
looks like your header with the jumper has no GND, use the other GND with the external supply.
No jumper is used.
.

Sorry but I don't understand you, what do I have to connect?

PS, the external power supply also gives power to the arduino.
But because the relay doesnt switch sometimes due to (i think) unsufficient power i wanted to connect it to the power supply direct without the arduino board.

Use an external power supply so the opto-isolators are properly connected to provide isolation.
Here would be your board wiring:

2016-06-30_13-04-42.png
.

Thnx it works, but i still have the problem that the relay wont switch, the led goes on and off but the relay doesnt work ( sometimes it does )

If you are using the 5V pin on the Arduino to power the relay PCB, don't.
You may over heat the Arduino voltage regulator and damage your Arduino!

Use two power supplies, one for the Arduino, one for the relay PCB.

.

Yes but if i try that the relay won't switch.. That is the problem..

You risk damaging the Arduino's power regulator (or other circuitry) if attempting to power the relay board with Arduino's 5V.

Try testing the relay board on its own, without the Arduino connected and without any load connected to any of the NO/COM/NC terminals.

Just have an external 5V power source connected (rated at least 0.5A) as shown by LarryD, then test with a 100 - 470 ohm resistor from any INx pin to the GND pin on the relay board. The appropriate LED and relay should turn on. Note that he resistor will prevent a power supply short if VCC is accidentally touched.

dlloyd:
You risk damaging the Arduino's power regulator (or other circuitry) if attempting to power the relay board with Arduino's 5V.

Try testing the relay board on its own, without the Arduino connected and without any load connected to any of the NO/COM/NC terminals.

Just have an external 5V power source connected (rated at least 0.5A) as shown by LarryD, then test with a 100 - 470 ohm resistor from any INx pin to the GND pin on the relay board. The appropriate LED and relay should turn on. Note that he resistor will prevent a power supply short if VCC is accidentally touched.

Okay thanks but now i have a weird problem.. if i feed the arduino from an external power source it is tripping.. als pins on and then off.. But with usb not

Show us a good image of your wiring.

.