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Topic: ACS712 500mV at 0Amps (Read 545 times) previous topic - next topic


Good morning,

last week I startet to use a ACS712 sensor for current measuring up to 30A with my Arduino UNO (and later Nano). After reading the datasheet, tutorials, etc. I excpected to get something like:

~102 ~0.5V <--> -30A,
~512 ~2.5V <--> 0A,
~920 ~4.5V <--> 30A.

However I recieved 102 when absolutely no current was flowing. First I thought the sensor was damaged, so I used a new one, but got the same values. So I took out my voltmeter and measured the following (0A):

VCC <--> GND = 5V
VO <--> GND = 0.48V - 0.53V

When AC current was flowing the voltage raised.

What's my mistake?




Well, your measurement of 0.48V - 0.53V agrees with the ADC value of 102, so that seems to make sense.

You don't have any big magnets or chunks of metal next to it do you ?

Is the sensor on a module you bought ?
Can you post your wiring diagram and/or a picture of your setup ?



Not a fake one perhaps?  So long as its properly decoupled and not near any magnets it should output approx
midrail with no current.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]


Jan 30, 2018, 07:09 pm Last Edit: Jan 30, 2018, 07:31 pm by Fabian94
Sry was a long day in the office...

Today I recieved some new sensors. I connected one of them (green wire) and one of the old ones (white wire) as well. I attached a picture, my sketch and the serial monitor.

I'll send them back tomorrow.

Thanks anyway :)


I'll send them back tomorrow.
Hmm, interesting.

From the picture it looks like the GND/5V are on different pins ? So are the new ones a different type to the old ones?

From what I can make out, it almost looks like the boards are a mirror of each other ?

Might be worth posting where you got good and bad from for anyone else to see.



Hello Everyone!

Last month I've received 10 modules and yesterday found out that they are fake ones...
I contacted the Alliexpress seller Store name: FAR EAST ELECTRONICS...but no reply yet.  I am over the grace period to open dispute so i've lost about $17....

I am pretty sure they have probably ripped of many people.

I was getting the same results as Fabian94....



A 10% output value when idle is normal for the uni-directional version of ACS sensors.
But the ACS712 comes AFAIK only in bi-directional.

Did you try if there is an output change when a DC current flows through the sensor (direction sensitive).

Can you post the printing that's on the sensor.
Maybe it's an ACS722 or ACS723. They come in both bi- and uni- versions (xxAB or xxAU in the serial nr.) 



Not much change when current applied through. Here is the picture of the ones I've received...


here i the one with meter...


How about some pics with a tad less zoom, so we can see the whole module, front and back of new AND old.
And don't you love those auto ranging meters with 20mm high numbers you can read across the room, but microscopic range indicators so you have to hold it 20cm from your nose to see V, mV or uV.  >:(


ACS712 modules are simple. Just three pins. VCC, OUT and GND.

If 'out' isn't half the voltage of VCC, with nothing connected to the current terminals, then it's a dud.

Time to hassle the ebay seller.


I've opened a case with AliExpress even I was over a grace period for opening a dispute...

I told them that the seller is selling counterfeit parts and AliExpress is responsible for allowing illegal activities... and last,  " IF I DON'T GET MY REFUND, I WILL NOT BUY ANYTHING AGAIN FROM ALIEXPRESS/ALIBABA OR IT'S SUBSIDIARIES.

Let's see what happens...

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