I'm trying to use my 30A ACS712 on my OSD (it has ATMEGA16L).

But it is very unstable, 0 amps goes from 450 to 445, but that isn't that bad, but when I put 10A of current through it jumps from 440 to 380.

I already searched on google and tried to add filter cap between acc and gnd, but it didn't help and acs712 and osd have different power supply than the load.

Any help is welcome.

  • Are you trying to sense AC or DC current? (yes, I know that's RAS Syndrome) – Majenko Sep 18 '15 at 16:31
  • DC and I connected acs712 directly to atmega16l – Jollyfreak Sep 18 '15 at 16:39

This is not a simple chip to use. These parts of the data sheet may help you understand what is happening. It is internally an analog device and needs clean power. I would highly recommend you download the Allegro data sheet, it has a lot of information that will help you. Below is a short section of the data sheet, The first paragraph should give you a hint that the output voltage will be about 2.5V with a 5V unipolar power supply.

"Quiescent output voltage (VIOUT(Q)). The output of the device when the primary current is zero. For a unipolar supply voltage, it nominally remains at VCC⁄ 2. Thus, VCC = 5 V translates into VIOUT(Q) = 2.5 V. Variation in VIOUT(Q) can be attributed to the resolution of the Allegro linear IC quiescent voltage trim and thermal drift.

Electrical offset voltage (VOE). The deviation of the device output from its ideal quiescent value of VCC / 2 due to nonmagnetic causes. To convert this voltage to amperes, divide by the device sensitivity, Sens.

Accuracy (ETOT). The accuracy represents the maximum deviation of the actual output from its ideal value. This is also known as the total output error. The accuracy is illustrated graphically in the output voltage versus current chart at right."

I realize this does not answer your question but it does give you a good starting point to resolve your problem. Hopefully you or a buddy has some analog experience, that will help a lot. Oh Yes clean power supplies are imperative for this to work.

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