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22nd August 2016, 06:19 #1
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100A AC current measurement
100A AC current measurement. Yes its a easy job to do with CT and Shunt resistor.
But if I use ACS sensor (hall effect current sensor) instead of Shunt resistor will it be a wise decision?
Will it be precious enough to measure up to 100A AC current?
I'm using 100A:5A CT and shunt resistor to ADC of microcontroller.I love my profession, I love my M's Lab. __MKDas

22nd August 2016, 06:58 #2
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Re: 100A AC current measurement
Hi,
Will it be precious enough to measure up to 100A AC current?
We don't know your application data nor the used sensor, therefore we can't answer your question.
Klaus

22nd August 2016, 07:04 #3
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Re: 100A AC current measurement
One advantage of a CT is that you can put a bridge rectifier before the burden resistor and then your adc only has to measure unipolar (all +ve ) half cycles with respect to ground.
A Hall sensor will need positive and negative power supplies and produce an ac output which can be inconvenient for an adc, unless it too can handle both ve and +ve input.
Probably not too much difference in accuracy or linearity, but I suppose it depends on which has the most useful type of output.Cheers, Tony.

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22nd August 2016, 07:04 #4
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22nd August 2016, 07:07 #5
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Re: 100A AC current measurement
Hall effect current sensor for 100A is available
http://www.allegromicro.com/en/Produ...Cs/ACS756.aspx

22nd August 2016, 07:08 #6
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Re: 100A AC current measurement
The output of the hall sensor ASC7125A can be processed to measure the signal. But will it be wise to use instead using a burden resistor with CT secondary?
I love my profession, I love my M's Lab. __MKDas

22nd August 2016, 07:35 #7
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Re: 100A AC current measurement
Hall sensor output will be in DC voltage but CT with burden resistor output will be AC
Ans also voltage level may be vary

22nd August 2016, 07:39 #8
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Re: 100A AC current measurement
I have never used one of those, so I cannot offer an opinion.
Cheers, Tony.

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22nd August 2016, 07:48 #9
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Re: 100A AC current measurement
I don't see an advantage in using a hall current sensor at the CT secondary. It adds noise, gain drift, a DC offset (to be compensated in software) and magnetic crosstalk to the measurement.

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22nd August 2016, 07:50 #10
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Re: 100A AC current measurement
Actually ACS712 can measure both AC and DC current. Output is ac or dc as input. So no problem should be here with AC.
Actually I want to measure up to 1000A using different rated CTs. Such as 800A:5A, or 600A:5A etc.
So if I replace the burden resistor in the secondary of CT then it will be easy to measure the current. Also required space will be less than with resistor.
Here I attached an image of ASC712 datasheet.
But as I never used ACS712 with CT secondary before so I'm asking will it be wise to use hall sensor or I should use burden resistor of high watt?
Note: using a burden resistor will create power loss but hall sensor will not loss that much.I love my profession, I love my M's Lab. __MKDas

23rd August 2016, 09:06 #11
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Re: 100A AC current measurement
Normally your define what error you can allow then choose the best method.
Hall sensors are convenient and can be low cost but high cost for selfcalibrated liner type
I prefer a 50~100mV shunt and have used this method up to 10kAA best design is easily achieved with good test specs™
A better question deserves a better answer. ™
... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.
... Tony Stewart EE since 1975
 slightly north of Toronto

23rd August 2016, 10:26 #12
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Re: 100A AC current measurement
Hi,
before it was 100A , now it is 1000A.
You ask if it is precise enough, but you don´t say what precision you need.
If you use a low ohmic burden, then the dissipated power is also low.
Your posts lack a lot of informations and specifications. So it´s impossible to give good answers.
Klaus

23rd August 2016, 13:29 #13
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Re: 100A AC current measurement
What voltage isolation , peak current and accuracy is required.?
Core saturation and Remanence may occur if over driven.
A good design question lists your overall requirements™ These are "SPECS"A best design is easily achieved with good test specs™
A better question deserves a better answer. ™
... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.
... Tony Stewart EE since 1975
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23rd August 2016, 14:01 #14
Re: 100A AC current measurement
You beat me to it, Tony. You have +16 hr timezone advantage...
And with the properly sized burden resistor, they are indestructible.
I like to use current transformers for those reasons, when the measurement involves AC only. Of course, if there is a DC component, a hall cell must be used instead.My batteries are recharged by "Helpful Post" ratings.
If you feel that I've helped you, please indicate it as a Helpful Post
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24th August 2016, 09:29 #15
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Re: 100A AC current measurement
Yes it was 100A before. Whatever, if I can measure 100A then I can measure 1000A too. All the CT s are rated x:5A where x = 100 to 1000A. So CT secondary is always 5A max.
I've designed one controller with keeping 3 resistors in parallel rated 5Ohm/50Watt each. So total resistance = 5/3 Ohms. I'm testing it today. Hope I post the result soon.I love my profession, I love my M's Lab. __MKDas

24th August 2016, 09:57 #16
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Re: 100A AC current measurement
Hi,
A 100A:5A CT (or an 1000A:5A) is rated for RMS usually. So the output current is +/ 5A x sqrt(2) = +/7.1A .. a total range of 14.2A.
If you have a 5/3 Ohms shunt then the output voltage is +/11.8V a total of 23.6V but you talk about an ADC.
With 5A RMS this gives a power of 41.7W. Huge!
I assume your ADC has 0..5V input range: Then:
Why don´t you use an appropriate shunt to give +/2.5V? = 0.35 Ohms (use 0.33 Ohms) then the dissipated power is only 8.25W and you don´t need extra circuitry to adjust to ADC input range?
You additionally could use a lower ADC_VRef. Maybe one to get 0...2.50V ADC_input_range.
Then a 0.15 Ohms resistor produces max. 3.75W of heat (use a 5W rated).
I see no benefit in using 3 pieces of 5 ohms...
Klaus
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24th August 2016, 10:33 #17
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Re: 100A AC current measurement
If all the "big fella" current transformers normally have a ratio to provide a standard 5 amps in the secondary, it should be possible to feed that five amps through a second much smaller current transformer mounted on the circuit board, to generate 5mA or 50 mA.
The power loss would then be negligible, and the small CT could be mounted up close to your ADC for minimal noise pickup. Its a win/win situation.Cheers, Tony.
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24th August 2016, 13:36 #18
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24th August 2016, 15:42 #19
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Re: 100A AC current measurement
Hi,
before you worried about precision... now you consider to use two CTs in series. This won´t improve precision...
Klaus

24th August 2016, 21:33 #20
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Re: 100A AC current measurement
Consider a CWT Mini 1
http://www.gmw.com/electric_current/...9;14%20web.pdfA best design is easily achieved with good test specs™
A better question deserves a better answer. ™
... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.
... Tony Stewart EE since 1975
 slightly north of Toronto

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