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ACS711 not outputing full voltage range.
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IDEngineer:

--- Quote from: guitchess on October 24, 2019, 12:40:31 pm ---I got to wondering if the ACS711 was being upset by the magnetic flux(I'm a rookie, not sure what this is really called) of the relay, but yesterday I  tested without the jumper that leads to the MCU and it functioned no differently.
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There are (internally) differential versions of the ACS family that eliminate sensitivity to external magnetic fields. The "standard" ones can be affected (since they are Hall devices). We encountered this phenomenon (relay coils causing a measurement offset) but switching to the (pin compatible) diff versions resolved it.
IDEngineer:

--- Quote from: guitchess on October 24, 2019, 05:02:25 pm ---With the blower motor that I tried this morning, there was no reaction from VIOUT when measuring DC but when measuring AC, the voltage was right on.
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Huh? The ACS will give you an output voltage based on current flow, no matter if that current flow is AC or DC. It is not an AC coupled device. The version you're using is biased at 1/2 the supply rail so it can report current flowing in both directions, as you'd expect with AC, but it will report DC just fine. There are other unidirectional versions for pure DC applications, and they don't have the midpoint output bias, but the midpoint versions still report DC in either direction just fine.

"no reaction from VIOUT when measuring DC" doesn't make sense. Are you certain you were flowing some current when you performed this "DC" test?

EDIT: Up to the frequency limit of the device (looks like 100KHz from this spec sheet), an AC current should give you an AC output (into a pure resistive load, anyway  :)). This device does not "convert"  AC current into a DC representation - that implies filtering which this device does not do. There are versions that have a filter pin to which you can connect a capacitor for some first-order filtering, but this device has the fault output instead. Try running a (say) 10KHz sine wave through the ACS - what do you see on the output? It should be a 10KHz sine wave.
guitchess:

--- Quote from: IDEngineer on October 24, 2019, 07:17:39 pm ---
--- Quote from: guitchess on October 24, 2019, 05:02:25 pm ---With the blower motor that I tried this morning, there was no reaction from VIOUT when measuring DC but when measuring AC, the voltage was right on.
--- End quote ---
Huh? The ACS will give you an output voltage based on current flow, no matter if that current flow is AC or DC. It is not an AC coupled device. The version you're using is biased at 1/2 the supply rail so it can report current flowing in both directions, as you'd expect with AC, but it will report DC just fine. There are other unidirectional versions for pure DC applications, and they don't have the midpoint output bias, but the midpoint versions still report DC in either direction just fine.

"no reaction from VIOUT when measuring DC" doesn't make sense. Are you certain you were flowing some current when you performed this "DC" test?

EDIT: Up to the frequency limit of the device (looks like 100KHz from this spec sheet), an AC current should give you an AC output (into a pure resistive load, anyway  :)). This device does not "convert"  AC current into a DC representation - that implies filtering which this device does not do. There are versions that have a filter pin to which you can connect a capacitor for some first-order filtering, but this device has the fault output instead. Try running a (say) 10KHz sine wave through the ACS - what do you see on the output? It should be a 10KHz sine wave.

--- End quote ---

First, thanks for replying. 

Second, I'm no longer sure of anything.  :/  After today's testing I only have more questions. 

You are correct that I should trust the device is working.  I took the time/effort/risk to change the IC only to get exactly the same results. 

I'm fairly certain that I'm passing current.  I can use the same set up with a DC motor and get perfect results.  I just haven't focused on DC current because I'm trying to switch an AC receptacle. 

I get an AC signal on my scope(small ebay kit unit).  A 60hz sine that varies in amplitude depending on amperage measured.  I has a DC offset of the 1.64v, which is Vcc/2.  Unfortunately, this shows my lack of knowledge/experience.  In V.3 I was trying to rectify that Sine wave into something usable.  I'm assuming that the DC offset is keeping the rectifier from working.  It's just voltage following the whole wave.

I'm sure by now I really showing my ignorance.  I'll keep studying.  Thanks again
IDEngineer:
Here's an idea: Switch to one of the unidirectional ACS parts. You'll magically get only one half of the AC waveform, which will effectively act as rectification with no extra parts. Then average that using a simple RC filter (if sufficient) or a higher order filter built with an opamp, and you'll have a "DC" level that indicates average AC current flow. That can be digitized by the A/D in the PIC and away you go.

In case you're wondering... yes, the ACS will still pass your normal AC current. The current sensing terminals are a direct shunt, no rectification or filtering occurs. But the unidirectional part will only "report" current in a single direction - classic single-diode rectification behavior. Follow it up with a filter and it's almost like building a small power supply.
ZaphodBeeblebrox:
Looking at your V3 schematics, I think you are overcomplicating things. I've used an ACS711 in the past as well, and the schematic was basically your V1, but without the extra capacitor on the output pin of the ACS711 (and as has been mentioned: the datasheet only allows for 1nF). The pullup on the \Fault pin should not interfere with correct functioning of this IC.

You also got me very confused when you talk about the AC versus DC thing. Could you connect a known current source to the IC and measure the output voltage with an oscilloscope and post the picture? And then the same again with a varying load (say a block wave of 1kHz or similar -- or 50 Hz sine wave if that is easier)? Note: measure this without attaching the output pin to the MCU.

Also, the LM358 you used does not have a rail-to-rail output, which is an issue if you want to use the full range of the ACS711.
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