Need to isolate my ammeter (measuering and powering the unit from same power source)

Question

I have a problem and Im not sure what the best way is to address this. I converted an ATX PC power supply to use as a lab power supply I installed a digital volt meter and a digital ammeter. To power my meters I am routing a 12v wire and ground to my meters. I am also measuring my voltage and amps ( on the same power) with these meters. it works fine for the volt meter however my ammeter will not function properly this way. if I hook up my ammeter to a 12v battery then measure the current from my power supply it works but I dont want to hook up my ammeter to a separate power supply to use it. how can I isolate the 12v power to my ammeter to run the meter? I was thinking a 1:1 transformer but this is DC to DC so that may not work. maybe an optocoupler?

Answer 1

You need a "floating" power supply:

• Could be a mains powered wall-wart or similar. Cheap and easy and connect and go.

• Could use an isolated switching power supply powered from any of the AT supplies. This could be an inductor based design or a switched capacitor design as was discussed here recently. Be sure that the isolation provided meets your safety needs for both equipment and people.