Motors stop when I switch to battery power

My robot works just fine when tethered by its USB to my PC. I can issue commands from my cell phone (terminal mode) to the robot and they are transmitted and received via HC-05 bluetooth. The robot has two 9V batteries wired in parallel that currently have 7.65 volts (in line voltmeter) and power the L298N H-Bridge. The VCC output from the H-Bridge provides power to the Nano.

When connected VIA USB, diagnostic output is transmitted over the Serial port back to the PC which displays this information. When I disconnect the USB, the robot, LED 13 on the Nano and the power LED on the H-Bridge are still lit; however, the Bluetooth connection is lost and the HC-05 starts its rapid blink.

My goal is to be able to run the robot autonomously, but I am a bit stuck here. I have two questions: 1) How do I diagnose what is happening here? 2) As a general rule, when running the Nano off battery power, what might be causing it to fail?

9V batteries aren’t able to provide large currents (as needed by motors). They are at least an order of magnitude too feeble.

Hi, What does the 5V pin on the Arduino measure, with the USB plugged in and with it unplugged?

What model Arduino are you using?

Thanks.. Tom.. :)

What if I have 2-4 9V batteries wired in series? Will that be strong enough?

rhj4: What if I have 2-4 9V batteries wired in series? Will that be strong enough?

You need them in parallel.

And if you mean those weedy little rectangular 9V batteries they STILL won't work. Maybe a dozen of them in parallel might.

But rechargeable AA batteries are best for high power requirements like motors and servos.

Steve

rhj4: What if I have 2-4 9V batteries wired in series? Will that be strong enough?

I gave my advice, you can ignore it if you want.

Hi,
Do you have a DMM to measure some circuit parameter?

Tom… :slight_smile: