Troubleshooting Power Issues

Hi, this is my first post, so I apologize in advance if I don't get it right.

I have an Arduino Mega connected to an L298N motor controller controlling 4 motors, two on one side and two on the other. When I hook it up to the bench power supply, everything works as expected. When I hook it up to a battery case with 2 18650 Li-ion batteries, it does nothing.

Things I have verified:
I don't think it is a coding issue because it works fine with the bench power supply.
I tested the voltage of the battery pack and it is 7.9. I set the voltage in the bench power supply to 7.9.
When I connect the battery pack, the motor controller light turns on, so I know it is supplying power.
The total amps it pulls when the bench power supply is connected (and it is working) is 0.26 when one side of wheels is running and 0.41 when all 4 wheels are running.
The total amps it pulls when the battery pack is connected is
I bought another battery case and new 18650 batteries and tested that they were fully charged and it gave the same results.

Here is a photo in case it is useful.

Please advise on where to go from here with trouble shooting. I am at a loss as to what to do next. Thanks.

I hate power connections using multiple alligator clips. They're about the least reliable connector in the world. Try some more solid connection to the battery. Your picture shows battery +ve waving about in mid air so that's not much use.

Where are you measuring your 7.9V? It should be at the input on the L298 board. Is the USB still connected when you're using the battery?


Show us a good schematic of your circuit.

In the Arduino IDE, use Ctrl T or CMD T to format your code then copy the complete sketch.

Use the </> icon from the ‘reply menu’ to attach the copied sketch.

@casualtinkerer, your topic has been moved to a more suitable location on the forum.

This photo is of the motor controller being powered by the bench power supply, which is the alligator clips you see connected to the L298N.

I am measuring the 7.9V from just connecting the wires from the battery pack to the multimeter.

The USB is still connected when I am using the battery.

Thanks LarryD and slipstick for your suggestions and questions. I started to draw out a diagram, but got frustrated trying to draw it. My drawing skills are not that great. You are correct that the problem was the way I had wired it up. I did not realize I had to wire the ground from the motor controller back to the arduino even though I was not powering it from the arduino. The high and low signal pins coming from the arduino had no way to complete their circuits. When I ran a wire from the ground of the L298N to the arduino, everything worked.

I cannot explain how it worked when I had the motor controller wired into the bench power supply instead of the battery.

The wires from your battery case are very thin - I suspect its not designed for any significant current.

You have to watch out with pre-made hook-up wires, some are incredibly thin wire inside and will not work with motors. I use 0.6mm diameter solid-core wire for making my own hookup wires and it will, if soldered or used with screw-terms handle upto 5A at a pinch. Typical pre-made hook-up wires are often unable to handle even 0.5A reliably.

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