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I am using a L298P motor driver on a custom circuit board to drive a DC motor. Since I am only using one motor I connected it in parallel like shown in the datasheet (IN1 and IN4 together, etc.).

My problem is that the output voltage is way too low, about 2-3 V with an input voltage of 7.4 V (Li-po battery). I would have expected about 5-6 V.

I have tried measuring the voltage without the motor; it is about 6 V.

I am using an Arduino Nano to control all this.

Schematic Schematic of the motor Controller

  • VBATT: 7.4 V
  • VCC: 5 V (not from the Arduino)
  • SENA: Sens output connected to pin A1 on the Nano (should be tied to ground with a sens resistor, but I forgot that and just soldered pins 1, 2 and 3, 4 together)
  • IN1: Connected to pin A3 on Nano
  • IN2: Connected to pin A2 on Nano
  • PWMA: Connected to pin D9 on Nano

Board Screenshot of the eagle board editor

This is the part of the board where the motor controller is. Those vias are uncovered, to ensure the metal on the bottom does not short them. I have placed a piece of insulation tape there.

Code While I am pretty sure the code is not the issue, I am still going to include it. It simply uses two buttons to make the output voltage bigger or smaller.

// Programm um die Funktionsfähigkeit vom Motor und Treiber zu testen
// Start Button um Geschindigkeit erhöhen und Stop um zu veringern

// Motor Konnektoren
#define IN1 A3
#define IN2 A2
#define PWMA 9
#define SENA  A1


// Start und Stop Knöpfe
#define BT_STOP PD0
#define BT_START A7 // Reiner analog eingang; kein digitalRead() möglich!!!


bool richtung = true; // true => vorwärts; false => rückwärts


int motorGeschw = 0;


void setup() {
  Serial.begin(9600);
  pinMode(BT_STOP, INPUT);
  pinMode(BT_START, INPUT);


pinMode(SENA, INPUT); // WICHTIG!!! immer auf Input, weil sonst Strom über den Arduino abfliest


pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
  pinMode(PWMA, OUTPUT);
  if (richtung) {
    digitalWrite(IN1, LOW);
    digitalWrite(IN2, HIGH);
  }
  else{ 
    digitalWrite(IN1, HIGH);
    digitalWrite(IN2, LOW);
  }
}


void loop() {
  if (!analogRead(BT_START)) motorGeschw += 1; // Motorgeschwindigkeit um 1 erhöhen wenn Start Button gedrückt
  else if (!digitalRead(BT_STOP)) motorGeschw -= 1; // Motorgeschwindigkeit um 1 veringern wenn Stop Button gedrückt


motorGeschw = constrain(motorGeschw, 0, 255);
  analogWrite(PWMA, motorGeschw);
  Serial.println(motorGeschw);
}

If any of you have any idea what might be causing this issue, any help is greatly apreciated.

I have tested the motor with an Arduino Uno motor shield by Deek Robot (which uses the L298P). With that everything runs just fine and the voltages are as expected.

ocrdu
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Markus Bröll
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  • Are you measuring the voltage of a PWM output using a multimeter? If the PWM is 50%, for example, a multimeter will read the average voltage, which would be 50% of 6V, not peak voltage. – Simon Fitch Jan 27 '24 at 12:34
  • This may be your problem: Problems with L293, L298 and SN754410 H-bridge drivers on a low voltage supply – Andy aka Jan 27 '24 at 12:42
  • @SimonFitch Yes, I am using a analog multimeter. But isn't the average Voltage what I want to be looking at? Also I measured the voltages at full throttle so 100% PWM, shouldn't it just be the peak Voltage then? – Markus Bröll Jan 27 '24 at 13:15
  • @Andyaka I doubt that's my problem. I forgot to mention, but I have a arduiono Uno Shield (by Deek-Robot), with the l298p as the motor driver and with that the Motor runs great and the Voltages are as expected. I will edit my question to mention that – Markus Bröll Jan 27 '24 at 13:18
  • @MarkusBröll OK, that sounds correct. Have you measured the voltage across the L298's supply pins (right at the pins themselves) with the motors running? That will reveal whether the IC itself is causing the drop, or there's resistance further up the supply path. – Simon Fitch Jan 27 '24 at 13:27
  • @SimonFitch The Supply Voltage dirctly at the Pins is 7.4 Volts just as expected. So does that mean that the IC is the Problem? – Markus Bröll Jan 27 '24 at 13:52
  • @MarkusBröll Now measure output (motor) voltage, again, right at the L298 pins, not at the motor. If you find 3V there, and you are sure that PWM is 100%, then yes, I would suspect the IC. However, there are other potential problems like inadequate supply bypass, or motor noise coupling into signal lines. Lots of things to check. I'd recommend tying the L298 signal inputs directly to ground/Vcc, and testing voltages again, just to make sure this isn't a signal problem. – Simon Fitch Jan 27 '24 at 14:00
  • @SimonFitch Thank you, I will try those things! – Markus Bröll Jan 27 '24 at 14:07

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