Thank you! This is exactly the info I was looking for!
This is so useful, This particular info should be a sticky post in the Beginners or Repair section (its probably a very common problem that destroys a lot of equipment before its time.)
Neat to see the internal structure of whats going on too.
This is an example of where I am really glad I still have my old Radio Shack (Well, Micronta) analog multimeter
Monitoring the voltage drop (proportional to current) as I apply the voltage I see this voltage drop (the current leakage level) going up fast and then settling down with each increase in the voltage, (but the curve isnt perfectly linear there is a tiny bit of noise in there.Popcorn noise's DC equivalent )and it is a very reassuring thing to see it going down.
But I want to make sure I am doing it right.
Thank you!
Dave, have you done a video on reforming capacitors? I bet you have, somewhere.. You should do one if you havnt already.
I have a large stash of top quality but older capacitors, Properly de-rated (by a lot) after doing this, I can still use them.
Floobydust, There is one sentence in what you said - the one about the
half-cell, that I want to ask you what you mean.
Ive noticed that even after being discharged with a resistor, immediately after removing the resistor, the capacitor starts behaving like a battery, as its not fully discharged yet, its still storing some of the previous energy.So I may have to do it several times.
I assume thats kind of an interaction between its charge holding ability and its internal resistance..
I have a DE-5000 which will happily measure all sorts of parameters that I still don't understand but of course unfortunately it cant do that under high voltages.. So even after shorting a capacditor (through a hefty resistor) I double check its all gone and often have to do it twice or even more.
This situation is a great demonstrator for my SO as to how useful it is to have all this "junk" as she sometimes calls it around. If your power supply is not under full load (low ripple current) then I would use a low voltage soak and then a nominal voltage (idle) before loading it up.
I find electrolytic capacitors have a half-cell potential, you can measure some in your parts bins.
If the device has resistive loading (bleeder) that ensures the capacitors are completely discharged right to 0V, the oxide layer seems to degrade faster. Measure the DCV on the filter caps and if they are flat zero, then I would fully reform them.
"attention must be paid to the fact that after storage the leakage current may be up to 100 times higher than normal during the first few minutes following the application of power."
In VFD's where the capacitors will pop if ESR is high, they (ABB) have guidelines:
Under 1 year storage, no reforming necessary.
After 1-2 years storage, 1 hour idle at nominal bus voltage.
Beyond 2 years storage, reforming is necessary.
Variac with 25% for 30 mins, 50% for 30 mins, 75% for 30 mins, 100% for 30 mins to 1 hour per year of storage.
Cornell Dubilier reforms:
1. With full rated DCV but 100R (<100VDC) or 1k (>100V) series-resistor for 2-4 hrs.
2. Discharge with that resistor for 1hr.
3. With full rated DCV+extra and series-resistor for 5 minutes+5RC tau.
4. Check leakage current
Note electrolytic new capacitors are "formed" at up to 200% of their rated DCV.
"When the forming voltage VF is exceeded, the forming process restarts and large amounts of gas and heat are generated."
ref.
https://www.cde.com/resources/catalogs/AEappGUIDE.pdf
https://library.e.abb.com/public/9f1befcd62ce445ec1257466003c02e2/3BFE64050629.pdf