5 Volt relay gets warm

Thread Starter


Joined Mar 27, 2018
Hello everyone. I am new to this forum since I have a question.

I am designing a system where I use my phone to control a LED strip and the lights in my bedroom. The lights are controlled by a 5v relay which is switched with a BJT. Since I use a NodeMCU as a micro controller and the NodeMCU only has max output of 3.3V.
I attached the schematic I used to control the relays (This is only one set of 2 relays in total I have 8 relays).

Now I was testing the endurance of this circuit since I want to use it for a long time and noticed that the relays got warm. Even when there was no load attached to it. It is not that warm that I can't touch the relays, but it is noticeable a bit above room temperature. It is more like it is lukewarm. Is this normal behaviour for this type of relay?

They function as intended I only don't want that the relays brake after a while or burn my house down on accident.



Joined Jul 18, 2013
The coil is responsible for increase in temp, and is common, just ensure the relays are operated at normal voltage.
DC are much more reliable and predictable that the AC variety.

Thread Starter


Joined Mar 27, 2018
Thanks for the quick reply!

The relays are switched at 5 volts. I want to control mains voltage (230VAC) with them attached to some normal LED and fluorescent lamps. The datasheet says it can be done. So I will test that soon.


Joined Jan 23, 2018
Almost ALL relays get warm after a while, because of the current flowing through the coils. But if it never get HOT to the touch, then you have no problem. Consider that after a small amount of movement all of the rest of the power fed in is converted to heat. And that is normal operation for relays.