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Current sense shunt resistor on high current pcb
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nctnico:

--- Quote from: coppice on November 12, 2018, 04:31:51 pm ---The important thing to remember when even trying to get 5% accuracy is copper has a temperature coefficient of 0.4%/C. Even small amounts of it in the measured path can seriously screw up accuracy.

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You can use that. In a design which didn't need very accurate current sensing I had a temperature sensor (cheap NTC) near the trace and measured the voltage drop across a piece of PCB trace. Together with the temperature you can get current readings and compensate for the temperature.
r0d3z1:

--- Quote from: coppice on November 13, 2018, 11:56:44 am ---The real issue you need to worry about is the CMRR of the input to the electronics. In the OP's case this is not an amp. Its a differential ADC input with a really good CMRR. Its designed for shunts around 500 micro-ohms when the maximum current is 30A.

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I confirm this, usually the problem is the CMRR, could you be more precise about the circuit, is it a low side sense ? phase sense ? high side sense ?
For a low side current sense you can use this kind of shunt with a difference amplifier. You must be careful with the resistance due to the soldering which is comparable to the shunt value. For this reason, you have to use a 4 wire sensing as already suggested.
Zero999:

--- Quote from: coppice on November 13, 2018, 11:56:44 am ---
--- Quote from: Hero999 on November 13, 2018, 11:43:10 am ---Yes, the power calculation is wrong. To dissipate <4W at 30A, you need a resistance of <4.444mOhm.

R = P/I2 = 4/302 = 4/900 = 0.004444

30A across a 4.444mOhm resistor would be a voltage drop of:
V = I*R = 0.004444*30 = 0.13333V.

Aiming for exceptionally low voltage drops, increases errors due to noise and the offset voltage of the amplifier. For example, if the amplifier has an input offset error of 100µV and you're using a 0.004mOhm shunt, the current offset error will be:
 I = V/R = 0.0001/0.004 = 0.025A = 25mA.

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Why would amplifier offsets matter when measuring AC? You estimate and remove an DC. The real issue you need to worry about is the CMRR of the input to the electronics. In the OP's case this is not an amp. Its a differential ADC input with a really good CMRR. Its designed for shunts around 500 micro-ohms when the maximum current is 30A.

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Yes, you're right, I missed it was AC, the offset voltage is no problem.
perieanuo:
Acs723?


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