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my new UNI-T multimeter just arrived but unfortunately i dont have a 9V battery to power it, however im having a 9V wall adaptror which im using as a power supply for my arduino (with a 5V regulator). Can i just connect the cables directly on to my multimeter's battery department or i will blow up anything?

About the adaptor

  1. Input voltage 220V (europe)
  2. Output voltage 9V
  3. Output current 0.950 Amps

It's logical to work because its exactly the voltage my multimeter wants but im not experienced with this kind on stuff.

Meletis Flevarakis
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1 Answers1

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You should NOT power the multimeter with the same power supply that you are using for your project.

One reason is that the negative lead of the meter is probably NOT tied to the battery (-) connection. That means that you may damage your meter if you do connect the black lead to the battery (-) lead.

Note that the most common voltage measurement that you are going to make is with the meter black lead connected to the Arduino ground buss. But you might also be doing a high-side measurement such as measuring the voltage across a resistor in series with your power supply.

There are several other reasons that you should NOT power your multimeter from an external power supply.

1) Safety. Does your external power supply have sufficient isolation between its' input and output? When you connect the leads of your multimeter to the circuit under test and that circuit is sitting at a high voltage (line potential, for example), that means that the power supply output is sitting at or near that same potential. Most inexpensive power supply adapters are not rated to have the output sitting at some potential high above earth ground.

2) Noise. Any noise that is present on your AC Mains will be passed into your meter. This has two consequences: you can couple that noise into the circuit that you are measuring; and that noise can corrupt your meter readings.

Dwayne Reid
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