My Take on a Capacitor Leakage Tester

[watchmaker]

I bought very cheaply a lot of stock room capacitors (still in sealed bags of 50); electroytics and orange drops, polyester and tantalum.  All name brands.  As I pull them out I test them with the tweezers but "needed" a way to test for leakage.

Then I found a variable 300 volt DC 30mA variable supply for $20. With a 6.3VAC tap.

I looked at the various ways people executed their enclosures for the AWA test board.  I placed the outputs in the rear and as far apart as practical.  I made my test clips short enough to avoid them shorting yet long enough to keep large electroytics above the case.  I decided on a SPDT switch with a center off.  Test/off/Discharge.  The discharge is thru a 33 5 watt resistor.  The center off allows me to confirm the cap is fully discharged, or I can time its discharge.

The voltmeter uses a simple bridge rectifier with a 220uF cap powered by the 6VAC tap off the power transformer.  I decided the voltmeter should be on the enclosure and the ammeter SHOULD be external to the system.  This means that the output is not energized unless there is an ammeter in the circuit.  Another point of safety.

While the supply is rated at 300 volts, it does hit 380 volts.  This should satisfy my needs.  It has a very nice Stancor autotransformer whose diameter is about the same as the case height.

Of course I found the supply after I ordered the AWA board.

[RoGeorge]

Nice build! 

Since you have adjustable voltage, same setup can be used to reform electrolytics.  Only last week I've measured out of curiosity the leakage of a few aluminium foil electrolytic capacitors that didn't see any use since the 80's.

When aluminium foil electrolytics are left unused for too long, the oxide layer disolves back into the electrolyte.  As a result, the leakage may increase 100..1000 times than normal, and if measured with a capacimeter they may show more capacity, sometimes up to a few times more than the nominal capacity written on the capacitor.

Many of these long unused capacitors can be recovered by re-forming them for a few hours, by slowly raising the voltage while keeping an eye on the leakage (or by adding a series resistor calculated to charge the capacitor in a few hours).  Then, once it reaches the nominal voltage, leave it under voltage for a few more hours.  This will naturally grow back the oxide layer, the capacity will lower back close to the nominal value, and the leakage current will decrease.  Sometimes it might take up to a day to regrow the oxide layer.

Unless they dried out over the years (which is not so often that one might think), most of them can be fully recovered.

Beware about very old capacitors, some may be made with PCB (Polychlorinated Biphenyls) which is a nasty chemical:
https://www.nepc.gov.au/sites/default/files/2022-09/anzecc-gl-identification-pcb-containing-capacitors-information-booklet-electricians-and-electrical.pdf

[silly sausage]

imho, without the schematic its a pretty pointless post.

[watchmaker]

Awwwww.  If you understood post no. 1 you would have figured out that providing a schematic to one who does not grasp a variable DC power supply would be a waste of time.

The AWA board may be more your speed.