AC current measurement

[igoboon]

ac current measurement

Hi everyone,

I am trying to build a circuit that will involve current measurement for a range of appliances including PC, TV and mobile chargers. And i have measured the current to be in the range of 20mA to 1.5A


Please can you help me with a simple and cost effecitve means to measure the 20mA to 1.5A current at 230V AC.

thanks for your assistance

 

[dipnirvana]

simple ac current sensing circuit

use current transformer . That will provide isolation, too

 

[igoboon]

ac current measure

Thanks,
But the current transformers i have come across are quite bulky and expensive (about $12 - 34).

I have also checked hall effect IC (Allergo 712) which is compact and cost effective (about $3), but it seems to be more suitable for current of 5A and above. As such i am considering ot amplify the output to increase it's sensitivity for small currents, but i dont know if the 20mA will be below the resolution of the IC. Also the nominal voltage seems to be 185V AC

Hence i am now considering to use high side current sensing (using resistor and difference amplifyer IC), but most of the IC i've come across seems to suited for up to 80V DC.

Hence i need a suitable and cost effective IC for the 240V AC

Thanks

 

[pranam77]

icl1707

Hai igoboon
Refer the datasheet of ICL1707 which is an IC for LED display based digital pannel meter. You'll have an application circuit which can be used to measure voltages upto 200mv DC. This circuit can be easily implimented to read Amphere by using a small current transformor. To be simple on the current sensing side, a Magnetic reed relay can be used to sense the current when used in reverse. Mean you have to remove the Magnetic reed switch from the centre and just pass the Main line of the AC through the centre cavity and as per the load consumption, you'll get a proportinate voltage in the relay coil which can be rectified, and calibrated with a resistor network and fed in to the Pannel meter circuit. Good luck. A picture of Reed relay is given here for reference.

 

[FvM]

ac current measurement isolation transformer

It should be noted, that the suggested "transformer" doesn't behave like a ususal current transformer. In the frequency range of interest, the said "proportinate voltage" is actually proportional to the current differential di/dt. It must be integrated to achieve a frequency and waveform independet current measurement.

Furthermore, the coil isn't sensing the main field generated by the primary wire. You'll easily see by sketching the magnetic field. Remember the right-thumb-law of electromagnetics. It's only seeing stray fields and thus highly instable and susceptible to interferences.

A correct coreless di/dt current sensor is a rogowski coil, see https://en.wikipedia.org/wiki/Rogowski_coil. It also needs an integrator and is a precise, very linear measurement tool. It's often used in power electronics for harmonic current measurement, but rather insensitive, unfortunately.

I don't agree with the above price information. Small current transformers from Talema cost 1.5$ in small quantities.

 

[igoboon]

ac small current measure

thanks for the sugestions, i will check them out, and get back to you

 

[mikersia]

measure ac current circuit

From my viewpoint the easiest way is to use shunt as current sensor (1...2$) and one of IC for power measuring,- e.g. from AD (2...5$).