Digital Volt and Ammeters

[bigbigjimb]

Hi,
I have purchased a digital voltmeter and ammeter for to use in my control box for my cnc mill.
First problem is the wiring of the ammeter to show the full load of all the motors on the X,Y,Z and A axis.
The other part of this problem is how to wire in the shunt, it is a 30 digital ammeter panel mounted.
The second problem is the digital voltmeter The DC regulated output from the capacitor is 36VDC with my multimeter (this is the correct Voltage) when I hook up the digital voltmeter across the 2 connectors of the capacitor I get a reading of 78Volts.
The voltmeter range is 0-200 VDC
Can anybody help with both problems and explain why the voltage problem.

Jim

[Al_The_Man]

First it depends on what type of ammeter it is, if it requires a resistive shunt then it is probabally a mill-volt meter and you need to know if it is possible to scale it, then you will have to place a suitable very low ohm resistor (using ohms law) at a suitable wattage in the DC supply line to wire the meter accross.
The best types are ones that use a current transformer as there is no insertion into the supply line. There are DC type now available.
For the DC voltmeter, try it on another stable source, car battery etc. and see if it reads OK, if it does, read the voltage on the meter terminals with your multi-meter and see if there is the same discrepancy when hooked into the power supply.
Al.

[bigbigjimb]

The Ammeter was advertised as a 0-30 Amp it is one of the digital oblong panel meters and comes with the shunt, the problem i have is how to wire it up with the shunt and also where to place it in the circuit so that I get the amp reading for the total of all the motors all the motors.
The power circuit is 220VAC in to tyrodial with an output of 25 VAC.
Then throught the rectifier and the capacitor giving 36VDC at thisd point it divids of to supply 4 motors on the XYZ and A axis

[Al_The_Man]

I would think that if you wire the shunt as close as you possibley can to the DC out at the capacitor, and then connect the separate feeds to the motors at the outgoing side of the shunt. Hopefully the shunt is a fraction of an ohm.
Have a large gauge wire from cap to shunt.
Al.

[bigbigjimb]

So the ammeter is wired in Series, I have seen somewhere that it goes in series and the ammeter is bridged across the shunt.
But i want to be sure before I do it.

[Al_The_Man]

Originally Posted by bigbigjimb So the ammeter is wired in Series, I have seen somewhere that it goes in series and the ammeter is bridged across the shunt. But i want to be sure before I do it.

That it usually, the shunt is in series with the load and the meter reads the mill-volt drop across it.
Al.