Wawa:
Are we still talking about the diagram from post#10, with the LM358.
? ? ?
I think we need an updated circuit?
Shouldn't you have a 1K in series with pin3?
Where are the resistors you are talking about?
Thanks.. Tom.. 
I think we need an updated circuit?
Shouldn't you have a 1K in series with pin3?
Post # 32
ted:
Post # 32
Okay, what OP-Amp?
Tom....
LM358
Hi,
Okay.
I think you will find if you put R6 in circuit, it may perform better.
Operational Amplifiers operate in neg feedback mode by trying to establish a Virtual Gnd at its inputs.
Have you grounded the other two inputs of the LM358?
Tom...
R6 - maybe, grounding maybe also.
OP has another problem, I think he is using not isolated power supply for load and for op amp, probably common ground, so complete circuit is limping
Hi,
Yes, not sure, will readup, but I don't think the LM358 are keen to behave when the inputs are near signal gnd.
R6 I've added may help, you will have to suck it and see..
Tom..
Hi,
Some interesting reading;
And from the LM358 TI spec/apps;
That is acting as a unity gain buffer, so then add an amplifying stage.
An instrumentation amp would probably be best, but if we don't experiment..
Tom..
Post # 65 - ground problem.
Post # 45 = post # 66 = post #47 and # 50.
Post # 66 - I cut ground connection between - Shunt lower end of resistor and C1. = Classic differential amplifier,
Hi
This is my circuit that I used from were TED posted it.
All the mods and measurements was done on this circuit.
With linear I mean when I draw 1A and get 1V output from the opamp.(not real figures just for example)
Then 2A drawn should give 2V output from the op amp.
This I dont get I will get almost 3V.
The above value only show that double the amps drawn does not give double the voltage output.
I always get a significant amount more than what was expected.
When the shunt is 0.1 ohm(1 resistor) the output is linear.
When 6 x 0.1 ohm in parallel is used for the shunt the output is far from linear.
Did anybody build this circuit with the same op amp and got it to work??
I will replace the op amp and re-test to see what happens.
You measure voltage between two points of isolated guy
Post # 59
Hi
TED..what is the multiplication value of your circuit with the 6V batt?
multiplication is not related to 6V, I put that so you can use 4 batteries 1.5V.
By theory multiplication should be 100 in practice is 10
Yes TED I know the 6V batt does not determing the gain.
I removed the shunt negative side from the op amp negative supply and used a separate batt to power the op amp.
15A gives 3.77V output , this is the max output (5V-1.2V) the opamp will give,1.2V below rail.
Seems like the gain is to high ,I replaced the 2 x 100k's with 2 x 10k.
The circuit is working as expected now.
15A = 0.21 V on shunt = 2.1V at op amp output pin.(x 10 amplified)
1A = 0.018V on shunt = 0.18V at op amp output.(x 10 amplified)
Thanks.
probably my resistors were 10k
Next time start with schematic so problem can be solved in 1 page not 6.
Hi
What software do you use to create all this nice circuits???
Thanks.
