Based on the assumption that I can determine the ESR of a capacitor with a voltage divider circuit, I first wanted to try out if this is the case and I use LT-SPICE for that. What I need is a ground connection and signal generator that I set up here. Of course the capacitor, which is a device under test and for a voltage divider I also need a resistor. There we go, wire it all up. Yeah, I forgot a ground connection there. That is all there is to the circuit. Of course all the components need their values. For this capacitor I go for 10 microverts and I simply assume ESR of 1.7 ohms and if all works out as I think it should, that is what we will measure. I will go for 100 ohms resistor and I need to change the signal source to a sine wave generator. The actual signal level doesn't really matter because it is all being a voltage divider circuit. It is all the matter of relations between the two voltages and frequency should be 100 kilohertz. Here we go, I can start the simulation. I have to find the right start and stop times for it. It is a bit of an experimentation. Yeah, that is obviously too long a time. I need to go for a short period. Even shorter than that. What we are looking at now is just a 2.2 millisecond time period. If I hold down the control button and click on the voltages, I get the measured values of the simulation. We make note of this. Put that into a little Java script I made. Here again is the circuit. You get a watch out because it is a bit different than measuring voltages in a voltage divider with a multimeter. Put in the values there. If all works out correctly, we will end up with 1.7 ohms. In theory, my circuit does work. So onto the workbench. The first thing I do is 0 out my meter to make sure I have it 0 properly. I measure the value. It is just a carbon film resistor. These are never quite precise. It is 98 ohms. By the capacitor I am testing with the cheap tester has 0.9 ohms ESR. Let's see how that compares to what we get with the method described before. I hook up my signal generator and my scope. I set the scope to heavy, ever-riching to smooth out the noise that I always get. You see it reacting a bit sluggish. The second channel should show a bit more amplitude. I increase the sensitivity to get a proper reading. That looks better. I made a proper screenshot. We will see that in a moment where we can also read the values. I set 100 kilohertz and peak-to-peak values of the two curves. Put that into the calculator. JavaScript. All in millivolts. I have to shift the decimal points around a bit. And our 98 ohms resistor. That is significantly less than the cheap ESR tester. I have another capacitor. One with the somewhat higher ESR. This reads out as 1.1 ohms. And let's see if applying the same method to that capacitor wheel and up with a higher ESR than before. At the low voltages that we are working with in this voltage divider, it doesn't really matter which way round you put in the capacitor. Won't do any harm to it. I'm just saving a few screenshots for later. Right, and here is the reading we have. Again, frequency 100 kilohertz, peak-to-peak values 3.22 volts and 29.0 something millivolts. And that results in obviously less than 1.1 ohms, but insignificant more than what we saw with the previous capacitor. So what's the verdict? Well, you tell me.