Original poster: Ed Phillips <evp@xxxxxxxxxxx>
With voltmeters that will work OK - ideally you should use a
full-wave rectifier bridge of output voltage rating at least twice
the voltmeter full scall reading (for safetly); you'll have to play
with the "multiplying resistor" in series with the meter. In the
case of the ammeter life gets a LOT more complicated. The typical
full-scale voltage drop for an ammeter is 50 millivolts and, while
you can use a rectifiier as above, but with suitable current
reading, its voltage drop will be nearly 1.5 volts full scale so
the power lost in the ammeter (and dissipated in the rectifier)
could get pretty large. With ammeters there's usually an internal
shunt between the terminals and a calibration resistor in series
with the meter - the calibration resistor and meter are connected
to the terminals of the shunt.
Ed