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I have a 6V motor attached to a HiLetgo Module L298N Dual H Bridge and controlled via two Raspberry Pi 3B GPIO pins (current just using HIGH & LOW).

If I use a 5V power supply from my Raspberry USB port it works perfectly.

If I attempt to power the L298N from 4 x AA batteries it doesn't (the batteries are new duracell AAs).

The power L298N LED is on but the motor does not move when I set the GPIO pins (one HIGH, one LOW).

If I connect the 4 x AA batteries directly to the motor it works.

The voltage from the batteries are reading about 5.87V and a constant current of 55mA. The USB is showing about 4.8V and a current of 44mA when idle and about 65mA when the mottor is running.

The L298N bridge has 5V terminal and a 12V terminal (same results with both)

Will the L298N ONLY work with these voltages? (the description on Amazon says it works up to 46V so I assume not).

I was hoping to eventually run 4 motors via 2 L298N bridges using PWM via a PCA9685, ideally all motors powered from 4 AA batteries, but so far I can't get 1 motor to work.

Can anyone suggest a reason why the 4 x AA batteries don't work via a L298N bridge or another way to power my motors?

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    Check the battery output under load. Also make sure the battery/L298N ground (or "-") and the Raspberry ground are connected. – BobT Jul 28 '18 at 15:36
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    The likely problem is you haven't connected the battery ground to a Pi ground. – joan Jul 28 '18 at 15:59
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    AHA! Thank you BobT, I didn't have a shared ground! Which is obvious, now you point it out, the GPIO pins need a ground back to the Raspberry Pi! It's working now! – John HaxSyn Jul 28 '18 at 16:04
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    Can you please make an answer to finish this question? – Ingo Jul 28 '18 at 16:17
  • Note for future reference (if I read the question correctly...) - please don't try to power motors through the Pi itself, always use some form of external power!! (fine for test LEDs sort of though :-) – Wilf Jul 28 '18 at 22:28
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The problem was that there was no ground between the L298N and the Raspberry Pi. By wiring the Ground (-'ve) terminal on the L298N to a ground pin on the Raspberry (as well as the batteries) it then worked.

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On another (related) note - I see from the spec sheet that the module's power supply (not the motor supply) should be 6.5-12v... and you're powering it with 4xAA batteries, which is fine when they are fresh, since new, quality batteries output closer to 1.7v (around 6.8v total); but in THEORY, you're running a 6.5v device with a 6v battery pack...

Your module may start working erratically (or not at all) once those batteries wear down just a bit and the voltage drops. You should consider beefing up your battery pack, for more reliable performance.

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