ESR Project Build - Part 5 - Test Readings

With the opamp section soldered up and tested, I found that the range was a bit wider than I wanted. The designed range was good if you want to test down to 1 uF. However, to see more meter movement down near the 1 ohm range, I found that I could put a 47 ohm resistor in parallel with the 10 ohm resistor at the DUT terminal. This expands the scale near 1 ohms slightly, so that the readings vary between about 1 and 4 ohms. I plan to make this a "fine" switch setting on the finished meter assembly.

With the setting on "fine" you can measure about 100 uF and higher. Any caps below that, will read off scale (to the left). Turning the switch off (coarse), the unit does measure 1 uF and up.

Figure 1 below shows the Sencore transistor testor 100 uA meter that I used in the zeroed position (right).

Figure 1. ESR meter in zeroed position.

The remaining figures are readings while the switch is on "fine" at various resistances.

Figure 2. 1 ohm

Figure 3. 2 ohms

Figure 4. 3 ohms

Figure 5. 4 ohms

From these readings, you can see that on "fine" that the resistances spread out rapidly. With the switch set to coarse, 10 ohms reads about where figure 5's 4 ohm reading is. Then anything higher bunches to the left of that.

For switching power supplies where the capacitors are expected to have milliohm values of ESR, the "fine" setting should be suitable for identifying failed caps. It is still not the best arrangement for cherry picking caps because of its inability to read milliohm differences.

Later when the hardware build of the cabinet is done, I'll add some photos to the last part in this series. Thanks for reading!