Testing Capacitor-How to test a capacitor when breakdown under
load.
Have you ever come across power problem where once you switch on
the power supply and the fuse blow? You have checked all the
components in the power (primary) and secondary section and all
the components seems to be ok! Where is the fault? A fuse blown
are usually caused by a shorted bridge rectifier, defective
posistor, power transistor or FET, shorted primary winding of
switch mode power tranformer, shorted secondary diode and etc.
But in 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 blow
immediately (the fuse became dark color and this indicate that
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 supply problem. Guess
what? It was the main filter capacitor (220 microfarad 400
volt). After replacing the filter cap the 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 analog
meter, digital capacitance meter and esr meter. In this article
i will not explain about how to check capacitor or testing
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 digital capacitor tester it showed around 220
microfarad and with esr meter it showed low esr reading!
This proved that the bad capacitor breakdown when under full
operating voltage. Then, how do i confirm that this filter
capacitor is faulty? By using an analog insulation tester. When
i connect the faulty cap to the meter and press the 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 the insulation meter just like you are
checking a capacitor using analog 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 capacitor of 100 microfarad 160v then you have to
select 100v. If you select 250v, it will blow your capacitor
that is under test.
If you have the SENCORE TEST EQUIPMENT such as the sencore lc
meter LC102 OR LC103, these meters have the capabilities of
checking any type of capacitors with four test; -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 i
encountered are from the lowest grade one. A capacitor failure
when under load is very rare. Using ESR capacitor meter alone
can solve most of the electrolytic capacitor problem.