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Topic: Error while reading Value (A0) from the ACS712 (Read 168 times) previous topic - next topic

lakshmi123

Hi,
I use ACS712 (30A) sensor to measure the AC Current connected to the Load Bulb (0.5W Bulb).
I notice that even when the Load is  connected I'm reading the 501-510 in the A0 pin.
I understand that when there's no Load Analog pin of ACS712 will be half of the supply Voltage.
My connection is like this :
ACS712             Arduino
VCC                      5V
GND                      GND
OUT                        A0.
 
As of now am just checking the A0 value and have checked this code also
https://circuits4you.com/2016/05/13/ac-current-measurement-acs712/
It's the same thing even with the Load current(A0) value doesn't vary.


pylon

A 0.5W bulb consumes about 6mA max. at 120V, about half of that if you're in Europe (230V). The smallest current detectable with an ACS712 and an Arduino is about 60mA, so ten times more than your bulb consumes. A 30A sensor is not the right choice for such small loads. You use such sensor to measure the current of heavy motors or theater light equipment.

lakshmi123

#2
Jul 17, 2019, 09:08 am Last Edit: Jul 17, 2019, 09:16 am by lakshmi123
Thanks for your reply.
- I have even tested with 15W(15W/240(India) = 65mA) Load(bulb) Even then results were same.
- Should I move to 5/10A ACS712 for measuring such small load?
- Where in the Data sheet(ACS712) is mentioned that minimum Detectable Load current is 60mA?

pylon

Quote
I have even tested with 15W(15W/240(India) = 65mA) Load(bulb) Even then results were same.
It's still within the measurement error.

Quote
Should I move to 5/10A ACS712 for measuring such small load?
That would give you at least a signal you might see but it's not enough to get an accurate reading.

Quote
Where in the Data sheet(ACS712) is mentioned that minimum Detectable Load current is 60mA?
That's not in the datasheet but a simple calculation. The idle output voltage of the ACS712 is about 2.5V, so half the Arduinos input range. As the ADC has a 10bit resolution, half the range gives you 512 steps to read over the whole input range of the sensor. 30A divided by the 512 steps results in about 60mA resolution. If you use an (external) ADC with 16bit resolution you may measure down to 1mA resolution.

lakshmi123

Okay Thanks for the information.
It is working higher Load. I tested with the 60W Bulb am able to read the current.
Thanks again.

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