Okay, so today I messed around with shunt settings. It all started because I wanted to get a more accurate reading of the current being drawn by this motor I’m working with. I’ve got this multimeter, see, but it’s not great at measuring the low currents accurately.
First, I grabbed a shunt resistor I had lying around. It’s just a low-value resistor, really. The idea is that you put it in series with the load (the motor, in my case), and then you measure the voltage drop across the shunt.
Getting Started
I connected the shunt in series with the positive lead going to the motor. Pretty straightforward, just make sure you have good connections so you don’t get weird readings.
- Connected the shunt.
- Double-checked all the connections.
Measuring the Voltage
Next, I set my multimeter to the millivolt range. This is important because the voltage drop across the shunt is going to be small, especially at low currents. I attached the multimeter probes to either side of the shunt resistor.
Then I powered up the motor, slowly increasing the voltage. As the motor started spinning, I could see the millivolt reading on the multimeter go up.
Making Sense of it All
Now, here’s the “magic” part. It is all to use Ohm’s Law! You know, V=IR? I knew the resistance of my shunt (it was printed on the side), and I measured the voltage. So, I could easily calculate the current: I = V/R. For example if I am reading 10mV (0.01V) on multimer and the shunt resister is 0.01 ohms, then the current is 1 Amp.
So basically that is it. I played around with different motor speeds and took some notes on the current draw. I can see how the current went up when I put more load on the motor. Pretty cool, huh?
It’s not rocket science, but it’s a super useful technique to have in your toolbox.
