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I have a computer power supply I am planning to use for electronics work. I was planning to make a box with voltmeter/ammeter panel meters on each output voltage (3.3V, 5V, 12V, -12V). I have read that the panel meter 9V supply needs to be isolated from the circuit which it is measuring. I was planning on using one of these DC-DC isolated converters to supply the panel meters from the 12V output.

The panel meter specs are:

  • Power supply scope: DC4.5-30V +

  • Measurement range: 50A, 30V

  • Operating current:<20mA

Can I use one isolator for all four panel meter supplies or should they each be isolated independently?

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  • \$\begingroup\$ Please don't use links to eBay auctions as a sole reference for a component. The eBay auction will inevitably expire, and the link will die. Your question will lose context, and it will stop being useful for future readers. \$\endgroup\$ – Nick Alexeev Nov 6 '14 at 3:59
  • \$\begingroup\$ Good point @Nick, I have removed the link and pasted the specs instead. \$\endgroup\$ – Eidelon Nov 12 '14 at 3:16
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The 9V supply is only used to power the meter itself. If your 9V supply can power all the four meters, that's OK. From the specification of the panel meter, it need 20mA to work, then all your four meter will need 80mA or so. Your DC-DC isolated converter can output 111mA max. So it should be OK.


Update:

The meter may measure voltage higher than it's own supply voltage, so it recommends you to isolate its' own supply from the circuit will be measured. So the key point now is you need a safe 9V power supply isolated from the circuit with higher voltage. Once you get such a supply, many meters can share it, given your supply can source enough current. Now, every meter is isolated from the high voltage, so it's safe, and safe to each other. You needn't isolate their power supply from each other.

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  • \$\begingroup\$ Thanks! Just to be clear, are you saying that the common ground effect that can damage ammeters just occurs when ammeter supply is wired to measured circuit but not when the ammeters share supplies with each other? \$\endgroup\$ – Eidelon Nov 12 '14 at 4:16
  • \$\begingroup\$ @nyarlathotep: I've add some more explanation. \$\endgroup\$ – diverger Nov 12 '14 at 5:06

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