Testing Capacitor-How To Test A Capacitor When Breakdown Under Load


Have you ever come across power problem where onceyou switch on the power supply and the fuse blow? Youhave checked all the components in the power (primary)and secondary section and all the components seems to beok! Where is the fault? A fuse blown are usually causedby a shorted bridge rectifier, defective posistor, powertransistor or FET, shorted primary winding of switch modepower tranformer, shorted secondary diode and etc. Butin this article i'm gone to show you another secret of electronic troubleshooting tips.

I got frustrated as to where is the cause of power problem.Everytime when i switch on the power supply the fuse blowimmediately (the fuse became dark color and this indicatethat there is a major short circuit in the power supply).I have checked all the components in the power supply and can't find the culprit! What i do is i desoldered all the suspected parts one by one and replaced with a known good component. I eventually found the caused of the power supplyproblem. Guess what? It was the main filter capacitor(220 microfarad 400 volt). After replacing the filter capthe power supply worked perfectly fine. I begin my detective work to find out why this capacitor can caused the fuse to blow eventhough i already confirmed it ok with my meters.

The meters that i used to check the filter cap were analogmeter, digital capacitance meter and esr meter. In thisarticle i will not explain about how to check capacitor ortesting capacitor and how capacitor work.I believed most of you know how to check capacitors and also generally using this type of meters. Measured with analog it showed capacitor charging and discharge, with digitalcapacitor tester it showed around 220 microfarad and withesr meter it showed low esr reading!

This proved that the bad capacitor breakdown when underfull operating voltage. Then, how do i confirm that thisfilter capacitor is faulty? By using an analog insulation tester. When i connect the faulty cap to the meter and pressthe go button-it showed a very low resistance and this is the proved of short circuit between the plate when voltage applied!There is nothing to do with bad electrolyte.A good capacitor will just showed a charge and discharge in theinsulation meter just like you are checking a capacitor usinganalog multimeter. In the market there is quite a number of ranges that you can buy. It has the range of 50v, 100v, 250v,500v, 1000v and even 5000v! If you want to test a capacitorof 100 microfarad 160v then you have to select 100v. If youselect 250v, it will blow your capacitor that is under test.

If you have the SENCORE TEST EQUIPMENT such as thesencore lc meter LC102 OR LC103, these meters have the capabilities of checking any type of capacitors with four tests:
-testing for capacitor values
-checking for leakage
-equivalent series resistance (ESR) and
-Dielectric absorption

It can check aluminum electrolytic capacitor, film capacitor,ceramic, high voltage capacitor and etc.

Conclusion-Different capacitor manufacturer produced different type of quality of a capacitor. Perhaps the bad capacitor that Iencountered are from the lowest grade one.A capacitor failure when under load is very rare.Using ESR capacitor meter alone can solvemost of the electrolytic capacitor problem.

Jestine Yong is a electronic repairer and a writer. For more electronic repair information please visit his website at http://www.noahtec.com/electronic-repair-articles.htm