The SimpleFOCShield v3.2 switched from the INA240 to the ACS712ELCTR-05B-T current sensor. As with previous boards, v3.2 features a jumper to power the current sensors with either 5V or 3.3V.
However, the datasheet for the ACS712 (https://www.allegromicro.com/~/media/Files/Datasheets/ACS712-Datasheet.ashx) mentions that the minimal supply voltage for this part is 4.5V. See image:
A circuit I recently designed and that powered this sensor with 3.3V did not work in any modes using current feedback, suggesting that the chip does not properly function with this low of a supply voltage.
If you wish to use a current sensor with 3.3V supply then the MPS MCS1802 (https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MCS1802/document_id/5066/) seems to be a valid drop-in replacement. Unfortunately, I wasn’t able to find a chip that supported both 3.3V and 5V supply voltage.
According to this post, ACS712 does run on 3.3V, even though it’s not officially supported. But if you had one that doesn’t, maybe it varies by the specific version, or even batch to batch.
ACS711 officially supports 3.3V and 5V. I think the SOIC8 variants should be pin-compatible with ACS712. It has a fault pin in place of ACS712’s filter pin, but I don’t think the filter capacitor would hurt it. ACS711’s datasheet recommends a filter capacitor on the output pin, but in my experience it’s better to leave it off and take many samples over a period of 20-30 microseconds to average out the noise. The capacitor only slows down the noise, but doesn’t significantly reduce its amplitude.
Oh, then this post is a duplicate of that post.
If the AC712 supports 3.3V then it is strange that I have been having trouble with my motor. Perhaps the problem isn’t the current sensor after all, but that wouldn’t explain why the motor spins fine when doing velocity control with a voltage controller.
We have ordered different current sensors, specifically rated for 3.3V. I’ll report whether those fixed our issues.
Could it perhaps be that running off of 3.3V changes the sensitivity of the sensor, or would that still be 185mV/A?
