If you couldn't guess, I'm new to electronics.
So, I've just received my 3V air pump, it didn't come with any specs, so I'm trying to figure everything out. I hooked it up to a DC variable power supply (at 3V) and a multimeter.
I switched the multimeter to 10A non-fused and placed the lead there as well, pinned a wire from the power supply ground to the pump, and used the multimeter as the bridge between the positive terminal of the supply and the other side of the pump.
I got a reading of 0.17 under normal conditions and 0.21 under full load.
Now, here's the question, 0.17-0.21, is that amps? Does that mean I am pulling 170-210 milliamps? When I toss these numbers into Ohm's law, I get 17.64706 Ohms resistance. Does this seem reasonable?
Since I'm just learning this, I just want to make sure this is all correct. If I am wrong, I would love to understand more!
Best Answer
On the 10A range, your multimeter probably won't have great accuracy with low current, but your measurement sounds reasonable. 0.17 to 0.21 A, or 170 to 210 mA.
Presumably your air pump is a small DC motor, which will have different current measurements at startup, and during running conditions with different loads.
To calculate resistance, you use Ohm's law:
$$R = E / I$$
If the voltage (E) is 3, and the current (I) is 0.17 A, then:
$$\frac{3}{0.17} = 17.6\Omega$$
Therefore, your resistance calculation seems correct. Just keep in mind that a DC motor will measure different resistances (currents) depending on what it is doing, due to induction/reactance.