I'm measuring the current through a 100W motor with a 50A current sensor and I'm getting reasonably good data but there's also a fair amount of noise:

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This is the current sensor I'm using. It measures current on the high side of the motor coming from a 3s1p lithium ion battery pack. To collect the data, I'm using the 10-bit ADC on an Arduino nano and saving it to an SD card the sampling rate is about 30ms.

There is no PWM controlling the motor, only a switch.

Is this normal for motor current data? If I used the 30A current sensor (instead of 50A) would the data be less noisy? Where is this noise coming from?

Thanks in advance.

  • 2
    \$\begingroup\$ What is the sample rate? The scale of the x-axis is too large to say anything about the noise. Could you post a screen with 100ms across the x-axis? My first guess is that you're measuring a 50Hz hum imposed on the signal. It could also be commutator noise, but first post some better graphs! \$\endgroup\$ Jul 24, 2019 at 7:09
  • \$\begingroup\$ Sampling rate is about 30ms - added graphs with smaller scale. \$\endgroup\$
    – Sean Dever
    Jul 24, 2019 at 7:35
  • 6
    \$\begingroup\$ It's a brushed permanent magnet DC motor. That's commutator noise. A large capacitor across the motor will quiet it somewhat. Alternatively or additionally, put a lowpass filter between the current sensor and your ADC. \$\endgroup\$
    – Neil_UK
    Jul 24, 2019 at 7:38
  • 1
    \$\begingroup\$ Scope the signal directly and adjust the time scale until you can see the frequency content of the signal. Have you added the jumper for the low-pass filter option? \$\endgroup\$
    – Mattman944
    Jul 24, 2019 at 7:50

1 Answer 1


It's the noise from the commutation. Put capacitors on the power feed, and low pass the ADC


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