"Ampere meter" for 50H.p.

hi friends,
I need to make a digital LCD based ampere meter, which can measure current of a 3-Phase, 440 volts, 50H.P, A.C Motor. I think the starting current of the motor would be very high, so the circuit should be able to measure that also. Please help me, along with the basic (i think I-toV convertor will be required).

Thanks in advance.....

Your best course would be to purchase a commercial current probe. They come as clamp on (expensive) and hard wired (also called current transformers). These are basically transformers put in series with the mains. You then take the AC output and put it through a small resistor. The voltage obtained is related by the scale factor to the mains current.

For economy, you need only measure one mains conductor because if the motor is functioning properly it draws almost equal current from all conductors.

One safety advantage is that there is no direct connection to the mains so the transformer output is not at a dangerous voltage level.

The construction of both of these is a ferrous core with the mains making one turn (it passes through the hole in the middle) and the other winding multiple turns.

The power factor of big motors can be significanlty away from 1. Do you need just the magnitude of the current or are you interested in the phase?

Thanks for replying. actually i need to measure the total power the motor is consuming when put under load. can you please tell me some more details of the transformer, i.e. how to make one...
thanks..

To do the power you need to measure the current, voltage, and phase angel between them. There are special instruments to do this. If you have the calibration curve for the motor ( current magnitude, real power) vs load you can make a good guess from the current magnitude.