Help! Regarding AC voltage amplification(mV to V)

Willbe said:

https://en.wikipedia.org/wiki/Arc_Flash

And, don't you want to sense the high side current?

Click to expand...

mananshah93 said:

It's 15 ohms, but I am trying with other combination so I can improve the mV drop, and for current range, it is generally limited to 70-100 amps max, but accidently due to short circuit (between phase or neutral) it can carry more than 1000amps, so it should detect it.

By the way which op-amp I should prefer......LM series or traditional 741..


Heartly Thanks for your support.

Click to expand...

ya I want to sense high side current also..

Click to expand...

ericgibbs said:

hi,
If you have a 15R series current sense resistor and you pass 100A thru it,
using Ohms Law you get Vsense = 15 * 100 = 1500 Volts.!!!!!

I think this would exceed the input voltage range of the 741 opa.



Does this mean you plan to put a sense resistor in the LINE/PHASE wire of the mains supply.?

Click to expand...

mananshah93 said:

look, I have put 15 ohm resistor parallel to the line phase, and I am getting 11mV across resistor when I give 100Amps current in line.

Click to expand...

Nigel Goodwin said:

I suggest you consult ohms law, although what you say makes little sense anyway - but this may be due to the language problem? - try posting a diagram of EXACTLY how you have it connected.

Click to expand...

Willbe said:

With a few turns of wire wrapped around the conductor you can make your own low-output & isolated current transformer and then use an opamp to amplify. You will need to calibrate it, though.

Click to expand...

Nigel Goodwin said:

What's the 15 ohm resistor for?.

It's doing nothing, you're measuring the voltage drop across a piece of the cable, essentially a very low resistor.

Click to expand...

mananshah93 said:

Now, to all,
regarding my project, can you help me how I can sense current (AC) flowing in the line. How I can get D.C voltage according to the value of AC current.

Click to expand...

ericgibbs said:

I have already posted a working circuit diagram of a two stage amplifier and precision rectifier, what else do you want.?

How you detect the low mV levels is up to you, using a tapped series section of the mains wire itself or as Willbe suggests a few turns of wire around the mains lead.

Remember, the resistor method is not mains isolated so could be harzardous also the problem of power supply and PIC isolation will need to be considered.

What is the 'load' current passing thru.? motors, lights, solenoids etc.

Click to expand...

mananshah93 said:

This is for general purpose that means it can be any load, not necessary that it is motor or lights.....

Click to expand...

mananshah93 said:

hi,
Do you mean 15 milli ohms.??? and a maximum of 100A not 1000A.?

Look at this circuit, it could be modified to give what you are asking.

Click to expand...

Hey! Eric , I understand your idea of the circuit which, shows 2-stage amplification of gain-10 and rectifier after it, but at this stage I want to know the specification of SOT.Can you help me out with it?

Click to expand...

ericgibbs said:

hi,
I dont see any circiuit.?

When you say SOT, is that Select On Test value for the resistor.?

Click to expand...

mananshah93 said:

o.k , you have written it beside the capacitor, so it's value should be selected after testing..right?
but, the value of C3 is written as 0-1.....??????//
Another thing , can i replace dual supply opam with single supply......

Click to expand...