fan speed affected by relay

So, I have this circuit with two major components, a fan and a mechanical relay (controlling a heating element). The fan is powered from a 12v power supply using a mosfet.

I have connected one pin to control the relay and one pin to trigger the mosfet (connected to the gate) for the fan to start.
I dont need to start/stop the fan, I just need it to run.

But when the relay control pin is HIGH then the fan drops rpm! All grounds are common. Obviously something affects my mosfet's gate. right? how can I solve this?

First post a diagram of your circuit, with all the details of components, part numbers and
datasheets. A photo of the set-up might be useful too. What is the power supply? Where
does the heating element get its power?

this is the diagram. the heating element is powered from 230VAC (europe).

Hi, the heater and fan use the same supply?
If so measure the voltage of the supply,
Fan OFF Heater OFF

Fan ON Heater OFF
Fan OFF Heater ON
Fan ON Heater ON.

What are the specs of the heater and fan and the power supply you are using.

Can you please post a copy of your sketch, using code tags?
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png or pdf?
The fritzing diagram you have posted is not a circuit diagram.

Sounds like you are overloading the power supply.

Tom..... :slight_smile:

It seems from your diagram you've made a 1K-1K voltage divider at the gate of your FET. I doubt that IRF540 will turn on at 2.5V.

You can lose the resistor to ground and depend on the Arduino to keep it low when you want it off.

No, the resistors are 10k and 1k. But the 1k should be 150 ohms for best results.

The problem is likely current - breadboards are simply not designed to take more than
a few 100mA and the contacts have significant resistance - any more current and you'll
see voltage drops and the contacts can overheat and become oxidised or the surrounding
plastic melts.

Route high currents through screw terminals or soldered connections, not breadboards.