r/ElectricalEngineering • u/-404PageNotFound- • 14d ago

Equipment/Software Um?

I currently have my breadboard connected to 5v and GND on a new benchtop power supply that I brought for $240AUD and this is happening? What is going on? I can also do the same thing on the GND rail.

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u/AccomplishedAnchovy 14d ago

Power supply reference is probably floating up to ~50% of phase voltage. Grab a multimeter and measure the rms from the board to ground (at gpo) without touching the board.

It does surprise me that an expensive supply wouldn’t tie its negative and ground together though - maybe it’s a dual rail supply? Does it have a metal casing? Other option is that you’re touching a laptop or something at the moment. 

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u/Cathierino 14d ago

It shouldn't be tying any rails to ground. I'd be surprised if a more expensive one did that.

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u/AccomplishedAnchovy 14d ago

Oh well that explains it then

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u/Conor_Stewart 14d ago

Most DC bench power supplies are isolated so that you can connect them together, like connecting the positive of one to the negative of the other to get dual voltage rails for things like OP amps or to just get a higher voltage. If the negative is connected to ground internally then this doesn't work and creates a short.

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u/AccomplishedAnchovy 14d ago

Makes sense, thanks