Voltage changes across things in circuit

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Old 02-12-19, 10:15 PM
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Voltage changes across things in circuit

I have a 12 volt circuit which reads about 12.5 volts at the battery (not too important in question). Once I connect a wire from the battery to the voltage tester, usb socket, and 12 volt socket, the voltage reads differently at the tester once something is plugged in. My question is, why is the voltage tester (which is accurate, also multi meter I have reads the same) reading a different voltage in the circuit, than the voltage directly at the battery. The wires are about 1 ft. long so that is not the issue, just very confused.
 
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Old 02-12-19, 10:31 PM
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Welcome to the forums.

The wires are about 1 ft. long so that is not the issue
Based on connected load..... wiring is always an issue. The higher the load the more the voltage drop.
There is also loss in plugs and connectors..... and that is also based on load.

The larger the gauge of the wire...... the less loss.
 
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Old 02-12-19, 10:48 PM
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No

What I meant by the wire is not the issue here, is that the wire has nothing to do with my question, the wiring is out of the question. My question is why the voltage tester is reading differently in the circuit than directly at the battery.
 
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Old 02-13-19, 05:21 AM
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Same answer as before either wire or connection. Could be on the + or - side.
 
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Old 02-13-19, 05:52 AM
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Connections can be a significant source of resistance especially with low voltage. It doesn't take much corrosion or poor contact to cause a voltage drop at low voltages. Quite often you can make the voltage shown on your meter change by how hard you press the probes into your wire or battery. You can also read higher voltage sometimes by scraping your probes back and forth so they clear away any oxidation for better contact.
 
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Old 02-13-19, 06:20 PM
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Apologize

The thing that was dropping the voltage during a load was the wires, never thought that would be it, figured a faulty meter or something. Measured resistance through the wire with my multi meter and figured out the + side has .5 loss, and the - side has a .6 loss. All makes sense now, thank you.
 
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Old 02-14-19, 05:51 AM
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Do you know the characteristics of the load? Is it simple resistance and steady state? Your meter can't measure phase shifts between current and voltage.
 
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Old 02-14-19, 05:14 PM
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Google "voltage drop" in a circuit. Electricity 101.
 
 

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