DIY Capacitor Leak Tester 2

After much debate when I was over at the bench I found a popper Transformer that can output 50 volts after rectification. Even with a load on it the 1000uF cap I used as a filter was able to hold on. However the analog meter I wanted to use that I pulled from a battery charger will not work. Even with 1 amp passing through it only deflected slightly. However the analog meter that I pulled from a old multi-meter works well but it has no enclosure. If anything I could just get a new/used meter.

When I was hunting down parts I got another idea. Instead of having two momentary switches I could use one switch, a small cap for delay with and couple transistors to invert. This way when I hook up a cap to the tester and it will automatically discharge the cap and when the button is pushed it will disconnect the discharge circuit while the main circuit adds the DC charge to the cap. Since we only need to pump the cap with DC current enough to fill the cap and see how well it blocks the DC (IE Leak test). At the same time I attend to over think things and should keep it simple.

The Transformer I have here has multiple taps. One set I can test 25V rated caps and the other set I can test 50V rated caps. So I would need a DPDT switch to switch between the taps. Or I could just add another circuit and a rotary switch to switch between voltage values.

In the future I can always swap out the transformer to test higher voltage rated capacitors.

Now you don’t need to build a device like I am. You can use a Bench PSU and a Multi-meter to test a Capacitor. Just put the Multi-meter in the Amps setting and put it in series with the PSU’s positive side. Connect the negative Probe from the Multi-meter to the positive side of the Capacitor under test. Connect negative side of the Capacitor to the Power Supply’s ground. Crank up the voltage to the Capacitor’s rated voltage and you’ll get the result. However this will leave the Capacitor fully charged and you’ll need to discharge it after the test. A high wattage low ohm Resistor will work fine or if you’re daring you could just short it out with a screw driver. When you’re testing Ceramic and Film Capacitors they don’t have to be discharged. You just have to worry about electrolytic Capacitors that hold a charge. The only time you need to worry about non-electrolytic type of Capacitors is if they’re older then you. Such as Vacuum Tube equipment or early solid state equipment. Typically today you can go about the ESR value of most Ceramic and Film Capacitors. Most of the time Electrolytic Capacitors will wear out over time. All depends on how they’re used and how cool they’re kept under load.

Sparkfun has a huge article about Capacitors. Also a YouTuber Mr Carlson’s Lab has much to offer on Capacitors for vintage equipment and testing.


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