heating element drawing too much power away from arduino

I have a project with a small heating element, temperature controller, LCD readout, and input buttons. When I breadboarded it it worked fine, I upgraded it to a more permanent enclosure with the heating element and arduino powered by the same 9v 2A DC adapter. I’ve debugged everything else and it works fine, but whenever the heating element comes on, the LCD flickers badly, starts displaying gibberish, the temperature readout is fixed at 85 C, and the heating element just keeps heating up (a little strange since the relay is normally off). When I connect it with USB it works perfectly.

I think the heating element is drawing too much power from the power supply away from the arduino, when it is heating it draws 2.7A and the arduino supply voltage drops from 9V to 5.2V. (on a side note the power supply reads out 4.2A instead of the printed 2A, is that normal or is it mislabeled?)

I am pretty new to electronics, any suggestions how to keep the voltage from dropping so much for the arduino? A resistor for the heating element?

If you're powering it with a 9V 2A adapter and the heater requires 2.7A I'd say your answer is right there. Get an adapter that can supply more current. Probably 3.5A at least.

the power supply reads out 4.2A instead of the printed 2A, is that normal or is it mislabeled?

You must have measured that when the voltage had dropped to 5.4V. The 2A rating is the maximum you can draw from the supply before it starts to sag.


The heating element is just coiled nichrome wire, I've driven it with a weaker power supply to get hot enough for what I need, from what I have read you can keep increasing the current and it will just increase the max temperature. Any way to limit the current to it from this power supply to keep it at 6V for the arduino?

I measured the amps on the supply without it hooked up to anything, just the multimeter on the inner and outer leads.

Your heater draws too much current for the supply. Either use a different supply or put a resistor inline with the heater. The weaker supply did the same thing this supply is doing. The supply voltage dropped and that limited the current through the heater.

This is why the most common recomendation is to run 2 supplies. 1 for the Arduino and one for your load.

To repeat. Even though it has sort of worked in the past, the power supply is too small and what you see happening is that as you draw too much current the voltage output drops which in turn limits the current through the nichrome wire.