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Shunt resistor Power rating - Current Sensing

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Jeffrey Peter

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Hi, I need to measure current of 30Amps having 230V supply. I'm using a CT of 1000:1 so I will get an output of 20mA. What should be the power rating of the Shunt resistor(12m ohm) that is short circuiting the secondary of the CT. ?
Thnks in Advance.
 

Why such a low shunt resistance? That gives a signal voltage at 20mA of only 240µV which is rather difficult to detect. :?: Do you mean a 12 ohm shunt resistor?
 

I want to use ADE7763 or ADE7755... in both IC's they have used very small shunt resistor but I don't know the power rating that I should use.....

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I want to use ADE7763 or ADE7755... in both IC's they have used very small shunt resistor but I don't know the power rating that I should use.....
 

Jeffrey Peter said:
I want to use ADE7763 or ADE7755... in both IC's they have used very small shunt resistor but I don't know the power rating that I should use.....

- - - Updated - - -

I want to use ADE7763 or ADE7755... in both IC's they have used very small shunt resistor but I don't know the power rating that I should use.....
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I don't see anywhere that they use one as small as 12 milliohm. :?:
 

Sorry its ADE7768 or ADE7755
ADE7755.PNGADE7768.PNG
 
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    gondo

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ADE7768 has a fixed current channel sensitivity of 21 mVrms, ADE7755 has selectable gain. Preferably the input signal should be scaled to span at least half the range.

Apparently the dataheet is presuming that a designer is aware of basic electrical equations, e.g. ohms law, so it doesn't verbosely explain the calculation details.
 

Those diagrams show the IC sensing the current of interest directly. If you are using a CT to step the current down, then you should adjust the sense resistor up by a similar amount in order to maintain the same overall sensitivity. So your sense resistor should be more in the range of 1-10 ohms, not milliohms. Consult the device datasheets for more info.
 

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