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I have a heating coil (actually an e-cigarette vaporizer) that I soldered two 10cm wires to. If I hook it up to a regulated 5V power source and measure the voltage over the coil, it measures about 4.07V. I find this puzzling because I can't figure out where the remaining 0.93 volts went. I'm measuring straight on the point where the wires connect to the power source leads. If I take away the coil, the leads measure exactly 5V.

I also have a 9V battery that, when measured, still has about 7.47V. If I connect the coil to that and, again, measure on the point where the wires connect to the battery leads, I measure only 2.39V over the coil, meaning 5,08V has somehow disappeared.

How is this happening? Is a heating element like this some sort of non-ohmic resistor? What exactly is going on here?

Bas
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    What is the actual part number of your "regulated 5 V power source"? Please provide a link to its datasheet if possible. How much current does your vaporizer draw? – The Photon Oct 30 '19 at 18:26
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    Bas, a 9V battery has a series resistance of something like 2 Ohms. That internal battery resistance will definitely lower the apparent voltage you see on the outside. – jonk Oct 30 '19 at 18:28
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    I'm with Jonk here. Your battery is losing steam because it's being pushed too hard. Internal series resistance of the battery. – DKNguyen Oct 30 '19 at 18:29
  • Related: Why does the battery voltage drop for custom PCB? – The Photon Oct 30 '19 at 18:32
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    Possible duplicate of Why does measuring the voltage drop across a thing not simply measure the battery voltage? – Huisman Oct 30 '19 at 18:50
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    Odds are that you connected your wires in parallel, which halves the resistance and doubles the current, which quadruples the power required. – StainlessSteelRat Oct 30 '19 at 18:50
  • @jonk Thanks for that, I guess I have some reading up to do. – Bas Oct 30 '19 at 18:59
  • @StainlessSteelRat The vaporizer and multimeter are definitely parallel, because I'm measuring the vaporizer's voltage, which wouldn't work if I connected it in series. – Bas Oct 30 '19 at 19:00
  • With the coil connected to the 5V supply, measure the voltage on the coil again, then measure the voltage at the 5V supply. Then measure the voltage drop of each one of those 100mm wires you're using to connect them up. If the drop is in the wires, let us know what gauge or diameter they are. – TimWescott Oct 30 '19 at 19:02
  • @Bas Usually, when you see a voltage drop it is because of current flowing through some resistance (obvious or hidden) that is causing a voltage drop. Sometimes, a hidden resistance is inside a battery. Sometimes, it is inside a voltage regulator system. Sometimes, it is hidden inside the secondary winding resistance of a transformer. Sometimes it is your wiring or solder joints. But sometimes it is due to poor transformer regulation behavior. Those cover many situations you'll find. – jonk Oct 30 '19 at 19:03

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