Arduino Nano Not Behaving as Expected on Independent Power Supply

Hi All,

I am really scratching my head on this one and I would like some advice on how to proceed. For my current project, I created an Electric Fan controller for my project car using an Arduino Nano clone (Elegoo Nano with ATmega 328P and CH340, not sure if that is relevant) and Im using the Arduino programmer to flash the chip. The chip controls a BJT with a Digital Pin which when activated by the Nano will essentially drive a relay and control my fans, the Nano is the brain with an analog voltage (temperature) sensor input, 4.8V input voltage from a Buck Converter and Ground from the Buck.

I am using my car’s 12V Ignition Voltage stepped down to 5V using a Buck Converter that I bought from Amazon; I desoldered the USB port to use the 5V Voltage and GND pins directly with the chip.

With my laptop plugged in, everything works as expected and no hiccups. However, as soon as I let the whole setup run on its own, the Nano randomly drives the relay. (This is independent of engine bay heat because I was reproducing the issue with some dummy temperatures at room temperature.)

I thought I may have had a grounding issue and made sure all my Grounds for logic and Power Inputs were the same on the board and circuit; likewise, Ignition Voltage and Ground for the entire circuit are from the same source. Another observation was when everything was powered from the laptop, the Digital Pin voltage when ON was near 4.8V, but when powered by the Buck the voltage on the pin was roughly 3.8V when ON.

By the process of elimination I think the Buck Converter, which is powering up my Nano, is giving me issues but I cant tell for sure. I included the link on it in case someone can spot something about the specs that I missed because from what I understand this Buck is overkill for the project so Im not expecting issues from it.

Hope that you have not cut vital lines when removing the USB port.

I wonder how then anything will work with the laptop without USB?

As a test I'd power the Arduino from its on-board regulator and the car battery. Buck converters can be of inferior quality, I'd prefer one for about 7V and let the on-board regulator do the rest.

Just to clarify, I removed the USB off of the Buck not the chip. I left the chip as is and just soldered the necessary pins. As far as I understand, the nano should not be able to handle voltage inputs up to 12V, perhaps Im mistaken.

Thanks for chiming in

Buck converters can be very noisy, could cause misfiring of signal pins. Try building an LC filter or at least sticking a big cap across the output pins.

After reading another thread, should the 5V from my Buck be going into Vin or the 5V pin of the chip?

Just forget that “Vin” exists! :cold_sweat: Blot out the marking on the board with a black marker!

I think that was you I saw post in another thread giving a good explanation between Vin and 5V, I also checked out the schematic you posted for the nano as well and it really helped.

Many thanks for your suggestion, because after I jumped Vin to 5V the Fan Controller started working on it own. I warmed the car up and monitored my gauge for the temperature and voila the Fans kicked on and off around where I had calibrated; repeated the test for several more cycles..

Last question would be concerning heat management for the unit. I have the nano chip soldered onto a protoboard inside a 3D printed enclosure, its just a rectangular black box with no air holes or anything, just wires coming in and out. Im thinking of wrapping the entire box with some reflective gold tape to help reduce the radiant heat since the entire unit is sitting inside the engine bay on the slightly cooler, intake side. Any other suggestions or things to keep in mind temperature related?

Unfortunately, the Nano itself generates heat, so insulating its enclosure will not allow it to cool down. :cold_sweat:

A heat shield between it and the engine on one side only will allow it to be cooler if there is cooler ventilation on the other side.