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 transformer, shorted secondary diode and etc. But in this article i'm gone to show you another secret of electronic troubleshooting
I got frustrated as to where
is the cause of power problem. Every time 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 even though 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
resistance (ESR) and
It can check aluminum electrolytic capacitor, film capacitor, ceramic, high voltage 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.
Author By : Jestine