Motor current simulation

To answer the original question: where to get a 3A source?

I would connect a mains transformer to a variac with a power resistor across its terminals.

I would measure the voltage across the resistor as the primary voltage is adjusted and work out the current using Ohm's law. Of course this isn't an ideal solution because the current will vary as the mains voltage fluctuates but it should be good enough to test a current transformer.

fubuaks said:

but wat abt lm324, on its datasheet its written that it works on single power supply

Click to expand...

The reason is that the input voltage is going below ground. The LM324's inputs are only good down to it's negative supply rail. You could also solve this by this by using a virtual ground but this would most likely cause a problem for you when you try to use it's output and want to reference it to the negative supply lead again.

It simulated this ckt in multisim and got a correct DC output...but ven i implemented it on breadboard i dint get the correct DC output.....ny reasons for this.....?

Yes. You have connected your virtual ground incorrectly. The virtual ground needs to go to the + input of the LM324. You could try something like this, but the signal ground must be isolated from the 12v power supply ground:

ok....thnx mate....i'l try this ckt out....