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Re: AMP meter solutions



Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <ghub005-at-xtra.co.nz>

James

The reason the shunts don't have meters is because shunts are principally
used for DC monitoring. 

To measure AC current, you need to rectify the output voltage of the shunt
and feed it into a DC meter. 

The local surplus shop here has new/unused 30 and 60 amp shunts + the
correct DC meters. In my power control circuitry, I feed the ouput voltage
from the shunt into a precision rectifier circuit. A precision rectifier is
just a OP-AMP voltage follower with a signal diode between the ouput and
the feedback loop. You need a precision rectifier since the shunt only
drops 60mV for 60A, i.e. you can't use a normal silicon signal diode (0.7V
forward voltage drop etc). The half-wave rectified DC then goes into a
small smoothing cap and is read by an analog DC meter (Tareo brand).

IMO this circuit is better the a current transformer because I can switch
the input voltages across several different shunts in the control box to
get current readings at different points (I use a three phase power
system). The downside is that the output of the shunts floats at up to 240V
above the system ground as I have to power the OP-AMP in the precision
rectifier circuit from a battery.

Best regards,

Gavin Hubbard


<<
A local surplus house has 50 amp shunts for 12 bucks, but not meters. What
are you guys doing? Any suggestions? 
>>