rork69
Posts: 6
Joined: Fri Jan 19, 2018 3:21 pm

ACS712 30A, zero current problem

Fri Jan 19, 2018 4:17 pm

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
Attachments
acs712.jpg
acs712.jpg (57.08 KiB) Viewed 1859 times

User avatar
mahjongg
Forum Moderator
Forum Moderator
Posts: 12338
Joined: Sun Mar 11, 2012 12:19 am
Location: South Holland, The Netherlands

Re: ACS712 30A, zero current problem

Fri Jan 19, 2018 4:33 pm

Are you sure there are no magnetic fields around the sensor?

rork69
Posts: 6
Joined: Fri Jan 19, 2018 3:21 pm

Re: ACS712 30A, zero current problem

Fri Jan 19, 2018 8:10 pm

yes, I tried in different sites

User avatar
Burngate
Posts: 6048
Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK Tralfamadore
Contact: Website

Re: ACS712 30A, zero current problem

Sat Jan 20, 2018 10:43 am

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?

rork69
Posts: 6
Joined: Fri Jan 19, 2018 3:21 pm

Re: ACS712 30A, zero current problem

Sat Jan 20, 2018 9:18 pm

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
Last edited by rork69 on Sat Jan 20, 2018 11:29 pm, edited 1 time in total.

User avatar
mahjongg
Forum Moderator
Forum Moderator
Posts: 12338
Joined: Sun Mar 11, 2012 12:19 am
Location: South Holland, The Netherlands

Re: ACS712 30A, zero current problem

Sat Jan 20, 2018 10:46 pm

I don't see a fault, seems the chip is defective. what happens if you short the two current sense inputs?

rork69
Posts: 6
Joined: Fri Jan 19, 2018 3:21 pm

Re: ACS712 30A, zero current problem

Sat Jan 20, 2018 11:32 pm

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 :(

omarlim
Posts: 2
Joined: Mon Jan 22, 2018 5:52 am

Re: ACS712 30A, zero current problem

Mon Jan 22, 2018 6:20 am

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

rork69
Posts: 6
Joined: Fri Jan 19, 2018 3:21 pm

Re: ACS712 30A, zero current problem

Mon Jan 22, 2018 8:59 pm

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.

omarlim
Posts: 2
Joined: Mon Jan 22, 2018 5:52 am

Re: ACS712 30A, zero current problem

Tue Jan 23, 2018 1:25 pm

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

rork69
Posts: 6
Joined: Fri Jan 19, 2018 3:21 pm

Re: ACS712 30A, zero current problem

Tue Jan 23, 2018 5:20 pm

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!

Return to “General discussion”