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ACS712 30A, zero current problem

Posted: Fri Jan 19, 2018 4:17 pm
by rork69
Hi all.
I bougth some ACS712 30A of various brand and I want to connect to my pi3 using an AD converter.

If I connect Vcc and Gnd to a 5v source, without any load, I expect to measure Output-Gnd a value of 2.5V (Vcc/2).

My problem is that with voltmeter of my tester (great impedence) I measure only 0.5v.

Where I'm wrong?

Thanks

Re: ACS712 30A, zero current problem

Posted: Fri Jan 19, 2018 4:33 pm
by mahjongg
Are you sure there are no magnetic fields around the sensor?

Re: ACS712 30A, zero current problem

Posted: Fri Jan 19, 2018 8:10 pm
by rork69
yes, I tried in different sites

Re: ACS712 30A, zero current problem

Posted: Sat Jan 20, 2018 10:43 am
by Burngate
The board in your picture has more than just the chip on it - a couple of resistors and a couple of capacitors? - but it's difficult to see the tracks clearly, so what goes where is unclear.

Have you measured the voltages on the chip itself?
And have you confirmed that the 5v & ground are 5v when reaching the chip?

Re: ACS712 30A, zero current problem

Posted: Sat Jan 20, 2018 9:18 pm
by rork69
Yes, i measured the voltage in the chip (the output is directly connected) and the 5v are correctly supplied to the chip.
This is the schema:
http://www.electroschematics.com/wp-con ... ircuit.jpg
Thanks

Re: ACS712 30A, zero current problem

Posted: Sat Jan 20, 2018 10:46 pm
by mahjongg
I don't see a fault, seems the chip is defective. what happens if you short the two current sense inputs?

Re: ACS712 30A, zero current problem

Posted: Sat Jan 20, 2018 11:32 pm
by rork69
If i short or open the input, the result is the same.
I bougth 4 differenti chip from two different suppliers but the result is same :(

Re: ACS712 30A, zero current problem

Posted: Mon Jan 22, 2018 6:20 am
by omarlim
Same problem here. 20pcs tested with the same result.
It was noted that the 0.5V reacts with the change in current, which is beneficial in my application since I can connect the sensor to a 3.3v microcontroller and have the values within the range of the uC.
Another thing to note is that (at least the units I received) is operating at 3.3v with identical output voltage as when it was connected to 5V.
Further testing leads us to believe that this specific IC is a clone of ACS712. For reference the batch number we have are all 16329

Re: ACS712 30A, zero current problem

Posted: Mon Jan 22, 2018 8:59 pm
by rork69
I can connect the sensor to my AD converter (waveshare) successfully.
But I can measure correctly only when current go in one direction (volts raise from 0.5v) not in the opposte: the output is not symmetric.

Re: ACS712 30A, zero current problem

Posted: Tue Jan 23, 2018 1:25 pm
by omarlim
It seems that I'm not yet entitled to post real time in this forum. If my previous reply does not get posted, here's the summary: This is not an ACS712 chip. Although the IC show ACS712, it is actually an ACS713. It is only unidirectional with zero current at VCC*0.1

Re: ACS712 30A, zero current problem

Posted: Tue Jan 23, 2018 5:20 pm
by rork69
Omarlim thanks!

You have reason also because I measured sensitivity and it seems 150mV/A, similar to 713. Vout at A=0 is Vcc*0.1.
I Also measured a sort of reverse sensitivity and it seems 40mV/A.

But how could it be possible?
In the IC I read: ACS712T ELC-30A 16329

Thanks!