Unstable relay when using single power source

Question

I am trying to control a 5V fan using an ESP01 and a relay module from LC Technology.

The setup works when I use 2 power sources but my setup requires a single power source which is unstable. The relay turns on but turns off after a couple of seconds.

Stable setup:

Unstable setup:

I do not know all the electronic terminology, which has made it very hard to search for a possible solution. I hope someone here can help with the missing pieces.

The USB PSU supplies 2.5 amperes, which should be more than sufficient.

Can you measure any voltage drop? How much current does the fan pull? — winny, Jul 16 '20 at 10:02

score 1 · Accepted Answer · answered Jul 16 '20 at 10:08

1

Try re-wiring like this and adding a 1000 uF capacitor: -

If this doesn't work then maybe your USB supply is dropping too low when the fan is activated. This could easily cause the circuit to reset.

answered Jul 16 '20 at 10:08

Andy aka

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Thank you for the quick reply. I will try to find a 1000 uF capacitor to test with. – Martin Printzlau Jul 16 '20 at 11:18
1

That worked like a charm! – Martin Printzlau Jul 16 '20 at 12:53
@MartinPrintzlau i understand adding the capacitor. But why did you rewire the ground line like that? Why do they have to be connected directly from supply ground individually? – Ujjwal Syal Jul 18 '20 at 15:18
@UjjwalSyal to avoid volt drops down the load wires affecting the voltage presented to the MCU. – Andy aka Jul 18 '20 at 15:44

Unstable relay when using single power source

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