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AC Current Measurement (ACS-712 30A)

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Faranoid

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Hey

I am using ACS712 IC to just detect the flow of current so I can feedback it back to the microcontroller so it would know if any current is being drawn or not. But I am having troubles using this IC.

I am connecting appliances such as an electric iron, laptop charger etc to the switch board.

----[Power Supply]----[terminal1-ACS712] [Terminal2-ACS712]----[Load]----[Power Supply]

this is how I have connected the circuit but across Vout it constantly shows 2.5 volts. No matter what appliance I connect.

I have read the data sheet over n over again, still can't find why is this happening. 2.5 volts basically indicate that it detects no current.
Am I missing something? Please help a little!

P.S: Current transformer is not an option
 

chuckey said:
Its output is 66mV per amp, so with a an electric iron (P = 800W), output should be 800/230 X 66 mV ~ 250mV. Have you wired it as per :- https://www.allegromicro.com/Produc.../media/Files/Datasheets/ACS712-Datasheet.ashx
Frank
Click to expand...

Output can't be 250mV, since at no current, voltage is 2.5 volts. It would be either above or below that mark.

I actually have this: **broken link removed**
so the biasing is all catered for.

I simulated my circuit and it indicated that while detecting AC current, the output voltage would be AC as well. Makes sense actually, considering that it would correspond to the change in input signal.

But I don't get any AC signal at the output, just constant DC (2.5 volt), no matter what I connect.

You're right that I should observe a deviation of 250mV but its not showing anything and I don't know why.
 

Hi Faranoid,
have you solved your problem about the ACS712 ?
I am planning to use it, and I want to know your opinion.

thanks a lot.
Gabriel
 
gabryponte said:
Hi Faranoid,
have you solved your problem about the ACS712 ?
I am planning to use it, and I want to know your opinion.

thanks a lot.
Gabriel
Click to expand...

Could you please give a little more detail on how you plan to use it before I recommend you anything.

AC712 is a wonderful little chip though. Very accurate when it comes to DC detection. AC is another story.
 
the current measuring chip gives an a.c output that is centered at 2.5v. this is why it keeps showing 2.5v when you use a voltmeter to read its output. use a peak detector circuit at the output of the current sensor to be able to have different voltage values for different loads. i hope this helps you. the other option is to use a micro controller to measure the maximum deviation from 2.5v. this should solve the problem.
 

israel7732 said:
the current measuring chip gives an a.c output that is centered at 2.5v. this is why it keeps showing 2.5v when you use a voltmeter to read its output. use a peak detector circuit at the output of the current sensor to be able to have different voltage values for different loads. i hope this helps you. the other option is to use a micro controller to measure the maximum deviation from 2.5v. this should solve the problem.
Click to expand...

Yea. I figured that out. Like I mentioned in my 2nd comment. I hadn't read the datasheet carefully enough and when I revisited it, all concepts fell into place.

The problem in my case was the resolution. I had a 30A chip, but the current I was trying to measure hardly exceeded 1A. So that is why I was asking Gabriel if he could share some details on what he intends to do. I can help him better knowing that.
 
An AC measurement with hall sensor would preferably eliminate the DC offset (presumed there's no DC current involved), then resolution will be mainly limited by sensors noise, which should be about 100 mA peak-peak for the 30 A sensor according to the datasheet.
 
I have a motor contro board with a fault tolerant control, and we have used current sense on each one of the three phase of the brushless motor.
The sensor are LEM LTSR series, and they works perfectly, as they are closed loop hall-effect sensors.

Now we want to reduce sizes (and costs) of the PCB, and one option is a cheaper current sensor.
My choice fall under the allegro sensor, and I am investigating in the ACS712 and the ACS710.
I am more interested in the ACS710 because its higher bandwidth:
LEM LTSR->200KHz;
ACS710 ->120KHz;
ACS712 -> 80KHz;
For sensing a 20KHz PWM a BW of 120K is pretty enough (also 80K is enough, but is too far from the LEM series and we don't want to jump too much in changhing characteristics)

The measure will be an AC measure, and we already use a microprocessor analog input for acquisition.
I am evaluating the current size, which should be 6Amp, 12.5 or 25Amp, depending on the motor size of course.
For example if the motor will be a 15Amp max, I will use the 25Amps chip size.

=====MY QUESTION IS=====
If you have you already used the ACS710 or ACS712 (i suppose their internal circuitry similar)
It is usable for measuring the current generated from a PWM at 20KHz ??
I can read the datasheet, but sometimes there are things which aren't written on it ! 8-O
Such things comes out only when using the product ;-)
Do you think it works fine?

thanks a lot
 

gabryponte said:
I have a motor contro board with a fault tolerant control, and we have used current sense on each one of the three phase of the brushless motor.
The sensor are LEM LTSR series, and they works perfectly, as they are closed loop hall-effect sensors.

Now we want to reduce sizes (and costs) of the PCB, and one option is a cheaper current sensor.
My choice fall under the allegro sensor, and I am investigating in the ACS712 and the ACS710.
I am more interested in the ACS710 because its higher bandwidth:
LEM LTSR->200KHz;
ACS710 ->120KHz;
ACS712 -> 80KHz;
For sensing a 20KHz PWM a BW of 120K is pretty enough (also 80K is enough, but is too far from the LEM series and we don't want to jump too much in changhing characteristics)

The measure will be an AC measure, and we already use a microprocessor analog input for acquisition.
I am evaluating the current size, which should be 6Amp, 12.5 or 25Amp, depending on the motor size of course.
For example if the motor will be a 15Amp max, I will use the 25Amps chip size.

=====MY QUESTION IS=====
If you have you already used the ACS710 or ACS712 (i suppose their internal circuitry similar)
It is usable for measuring the current generated from a PWM at 20KHz ??
I can read the datasheet, but sometimes there are things which aren't written on it ! 8-O
Such things comes out only when using the product ;-)
Do you think it works fine?

thanks a lot
Click to expand...

Okay. Thanks for the explanation. I don't see any reason why you can't use them in your scenario but I am unsure about a couple of things.

1) The extent of similarity between ACS710 and ACS712. I do not know if they are similar or not
2) My frequency was about 60Hz, not more than that. So I am not sure how it would behave at 20k.

If I were you, I would use Proteus ISIS for simulation. That will help you a lot in understanding & choosing a chip. You can generate a 20k AC waveform, feed it to the IC and see how it behaves.
The ACS chips are good. I used the one with 30Amps resolution. A friend of mine had used the 5Amps one. They both worked great.

Since you are trying to sense AC current, your output would be AC too. Do refer to page 12 of the datasheet of ACS712 (https://www.google.com/url?sa=t&rct...foM3ZNSpXLpyj7gZg&sig2=d1b27DZ97JnQo-T7mVr3ug). It lists down typical applications while using AC. That may also give you some ideas on how you can use ACS710/712 better.
 

Sorry for reviving this post again but currently am thinking of using a hall effect sensor to measure the current in each leg of a 20Khz three phase inverter. A friend suggested using an LTS 25-NP but they are way too much expensive. Instead I wanted to see if I could get away with using a ACS710 which has a bandwidth of 120Khz. Do you think it would be a good product to measure the current in each leg and does anyone have any other suggestion?

Thanks a lot for your help.
 

AC7xx sensors are working fine for inverters. They are suitable for all applications where it's insulation strength is sufficient.
 

Thanks FvM will try to do some tests see how it goes. Since I will be placing them in the inverter leg I will try to use one of the application circuits in the datasheet. Basically since current in the inverter legs passes only in one direction there is a circuit to set the output at 0V when there is no current using an opamp and setting some gain to the voltage. That way you have 0-5V as if the sensor was uni-direction which is better for ADC full scale deflection.

Once again thanks for your help.
 
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