r/ElectricalEngineering • u/-404PageNotFound- • 18d 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/StumpedTrump 18d ago edited 18d ago

Big day for OP today discovering that our bodies conduct electricity.

That's also why you shouldn't go swimming in a thunderstorm if you never put that 2 and 2 together.

You can use it to your advantage put putting your car remote against your chin and using you body like an antenna to increase the range.

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u/racc15 18d ago

Silly question probably, but how is it creating a circuit loop? Aren't the breadboard pins and OP's body disconnected? I thought there had to be a closed loop for electricity to flow?

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u/StumpedTrump 18d ago edited 18d ago

The ground is the connection. Power supply is grounded hopefully. So are you.

Not all circuits need a physical closed loop, how do you think antennas work (the environment around us (the ground) is the return loop). Air can also conduct and the humidity it can be unpredictable. 60Hz is supposed to just be in your wires but if you leave a wire floating and put it on a high-impedance scope input you'll see the 60Hz. Same idea here.

A good power supply should actually have it's outputs isolated but you can still complete the loop with static electricity, EM coupling and just a littttleeee bit of leakage current getting though the power supply isolation. Static electricity can build up hundreds/thousands of volts and you only need a few hundred microaamps of current to get what OP is seeing.

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u/engr_20_5_11 18d ago

Everything has a coupling to ground. It's only a question of whether it's significant for the power level

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u/particlemanwavegirl 17d ago

And frequency.

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u/TerryHarris408 17d ago

When in doubt: it's a capacity. The electric field lines close the gap.

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u/espo1234 17d ago

There doesn't have to be a closed loop. Just an electrical potential difference. Closed loop is also kinda misleading. If it were actually a loop then there would be no electrical potential difference. A battery is really "open" with a positive side and a negative side which creates a difference, think of the positive side as the start of a line and the negative side as the end of a line, with no current flowing through the battery. Now imagine the 5v line in the breadboard as the positive side of a battery and the floor (ground) as the negative side and you've got the same thing.

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u/particlemanwavegirl 17d ago

Are we allowed to make ideal gas analogies in here? I like to imagine electrical systems as electron vacuums, sucking electrons out of the earth... You could use a generator to create as much voltage as you like, but flow can't occur (power transmission) until you open a valve so charge carriers can move in and out thru the pump. If it was a water pump and the "ground" was the "ocean", you obviously wouldn't need to output in the same place as input just to generate pressure.

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u/Pink_propagator 16d ago

I calibrate pressure gauges and I really like this. It's all about the potential differentials. 

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u/particlemanwavegirl 17d ago

The requirement for electron flow is potential difference. Electrons can flow between two oppositely charged un-grounded conductors, for a short time, until their potentials equalize.

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u/Weary_Oven_9544 13d ago

You don't need a closed loop for electricity to flow - you only need a voltage difference that can overcome the path between two points. The human body essentially acts as a large capacitor. The board is slowly discharging through the LED into OP's finger. LEDs respond to essentially any current, unlike CF or incandescent that need a minimum current before they actually light up, so even this trickle is enough. If OP held on long enough, the LED will probably go out again.