Originally published at: DC Power Monitor: A Golioth Reference Design
How full is your battery? How much current is your USB device drawing? What is your energy usage of your bank of devices? Gaining granular feedback on your electricity usage is a valuable tool. We have previously discussed this as part of our AC Power Monitor. We took that concept and extended it for DC Power Monitoring. The changes were surprisingly simple, but open up a whole world of new applications. DC Power Monitor vs AC Power Monitor Because there are so many similarities between these reference designs, we thought it would be useful to compare and contrast. We’ll talk about some of the differences implemented below, but first off, a quick discussion about differences in how we measure power. In AC Power Monitoring, it’s “non-contact”. The power passing through AC wires can get up to considerable amounts, and often we don’t want to measure this “in line”. Also, it’s often not a requirement to have precise measurement levels. In both of these scenarios, we can get away with using a current clamp, which uses the magnetic fields around a wire to induce a reference current, and then couples that reference into a secondary measurement circuit. DC Power doesn’t have the same characteristics. Though there is a magnetic field that develops around a wire, the non-alternating nature of DC current means it is not possible to stimulate a current in the secondary of a measurement circuit using an inductive element. Instead, we need to measure current “in-line”, which means the current we’re measuring passes through a resistive element and we measure the voltage that develops across that resistor. The benefit is we can measure much lower current and get better…