Hi, i am working on my senior project. I am building an AC ammeter. My design as of right now is a DC voltmeter with a .1 ohm shunt which allows it to read correct DC current. I have already proved this works correctly. My problem now is rectifying an AC signal to DC and have the correct current read on the meter. I have tried using a low resistance power resistor as a shunt on the AC side then in parallel to the shunt is a full wave bridge rectifier. As of now i have not been successful. I would like any suggestions on how to fix this problem or ways to read the AC current correctly.

 

What is the voltage developed across the 0.1Ω shunt? What is the minimum voltage required by your rectifier? If the shunt develops only a small voltage, this may be insufficient to allow the rectifier to function.

You might consider simply increasing the increasing the shunt resistance to obtain a bigger voltage to drive the rectifier, but this would considerably increase the power loss (burden) and the response would still tend to be non-linear and temperature dependent, especially at lower currents.

Alternatively, if you can get a rectifier rated for the full load current, this could be inserted before the shunt so that the shunt is passing DC.

Finally, a current transformer can be used to derive a divided down current with a relatively large driving voltage capability. This can be rectified and fed to an ammeter (or a shunt to give a voltage to drive a voltmeter). Don't ever leave the output open-circuit though, as the output voltage can get dangerously large.

 

Check out the (now vintage) AVO meter schematic which had useful AC current range - using a current transformer and bridge rectifier.

http://www.qsl.net/pe2jeb/AVO_meetapparaten_AVO_8.htm