[Zenith6S321]

Originally Posted by Penthode

I generally reform much more slowly and I use a limit the initial current to no more than 3mA. I will then leave the capacitor and return, say 15 minutes later, up the current again to 3mA step-by-step until the rated voltage is reached and the current reduces below 0.1mA.

I searched the internet for capacitor reforming current limits and found a wide range of values. The highest value I saw was from my Sencore LC75 manual that describes your supply setup and says to limit the current to 50 mA! I thought that value was way too high so I used 5 mA. To make it visible on the graph I multiplied the current value by 100, so 500 for the current on the graph is actually 5 mA (sorry for that confusion factor). I will try using your 3 mA value on the next caps I reform.

Originally Posted by Penthode

I assume by diectric absorption you are referring to leakage?

Until I bought and started using the LC75 I had not heard of dielectric absorption. Here is a good description that echoes what is said in the Sencore manual:
http://en.wikipedia.org/wiki/Dielectric_absorption
It goes on to say that all capacitors have some amount of this and its generally not a problem for capacitors used in power supply circuits.

Originally Posted by Penthode

The leakage current scale on the graph is too high which does not allow you to see the resultant leakage current accurately. You must be able to ascertain that the leakage is below 0.2mA in order to determine whether the capacitor is good or bad.

I was not able to find a way to show multiple scales on the graph to make it more readable. I started out using a value of .2 mA for the target final leakage value. I have since found formulas in the LC75 manual that they got from EIA RS-395. The manual provides a table of acceptable/expected leakage values calculated from those formulas. I ended up using those formulas in my program so that it calculates the target leakage value and terminates the reforming when it is reached. During the reforming process the program prints out, on the Arduino serial monitor, the voltage and current applied to the capacitor. That data is what I cut and paste into a spreadsheet to make the plots. The Arduino analog inputs have a 10 bit (0-1023) resolution so the voltage sensing resolution is 1 volt (0-1023 volts) and the current sensing resolution is .01 mA (0-10.23 mA).

Originally Posted by Penthode

The resistance indication on the graph is interesting. Perhaps the fluctuation is the dielectric rebuilding process?

The resistance shown is calculated by taking the sensed voltage and dividing by the sensed current. So it is an equivalent DC resistance due to the leakage current (not ESR). Some of the fluctuantion probably is the rebuilding process, but I suspect a good bit of it is from the limited resolution on control of the pulse width modulation used to drive the two step-up transformers shown on the schematic this thread: http://www.videokarma.org/showthread.php?t=256919
The pulse width has a range of 0 to 255 with a value of 127 producing a 50% duty cycle waveform that I use as the upper driving limit. When the leakage current gets low a single increment in the transformer drive can make a sizeable change in the quadrupled output voltage.