[QUOTE=Zenith6S321;3058457]
Quote:
Originally Posted by DaveWM
Also if you reran the test on the old caps does the graph change (reformed) so the low current target at rated voltage is reach sooner.
QUOTE]
I ran the reform process again on the two old RCA caps and attached are the plots. Yes, they got a better result from a second reforming. They both still show a lot of dielectric absorption, as seen by the LC75.
|
I see from your graph that full rated voltage is applied after only a minute or so. I believe this is too fast. 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 have reformed quite a few capacitors with a simple variable DC supply. (I first used an old variac, rectifiers and series resitance but now use my Sprague T06 capacitor checker).
I assume by diectric absorption you are referring to leakage? Certainly the older capacitors leak more than newer capacitors. But that was normal. What is important is the leakage is kept under control and that it remains low. I find gently reforming and lengthened testing results in a higher percentage of saved capacitors.
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 inn order to determine whether the capacitor is good or bad.
The resistance indication on the graph is interesting. Perhaps the fluctuation is the dielectric rebuilding process?