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Testing Non-Polarized (Bi-Polar) Electrolytics
Non-polarized aluminum electrolytic capacitors typically
look very similar to standard aluminum electrolytics
except for the polarity marking. Non-polarized
electrolytics are typically used in circuits having no DC
voltage or established polarity. Two common circuits
that use non-polarized electrolytics are audio crossovers
and AC motor start circuits. These circuits use non-
polarized electrlytics for filtering or inducing phase
shifts.
Checking Leakage Between Sections of a Multi-Section Lytic
Multiple section aluminum electrolytic capacitors are
common, especially in many older power supplies. Such
capacitors are actually several capacitors inside one can
sharing the same negative terminal.
Leakage sometimes develops between one or two
sections of multi-section lytics. This leakage is
especially difficult to troubleshoot without the LC103
leakage test because signals from one section of the
capacitor are coupled to another section. This results in
multiple symptoms in the operation of the device in
which the capacitor is used. An ohmmeter will not show
leakage between sections of a multi-section cap because
the leakage only occurs near the capacitor's operating
voltage.
To isolate this type of leakage with the LC103 you
simply perform the standard leakage test. As you test
each section, short each of the remaining sections to
ground. Any increase in leakage when a section is
shorted to ground indicates leakage between sections.
———————— WARNING —————————
This test should only be performed by a person who
understands the shock hazard of up to 1000 volts applied
to the test leads during the capacitor leakage test. DO NOT
hold the capacitor in your hand, or touch the test leads or
capacitor leads when making this leakage test.
————————
ATTENTION
————————
Le LC103 est fait pour être utilize par une personne qui est
techniquement capable et qui comprend les chocs que peut
produire l’équipement (jusqu’à 1000 V) lorsque le test de
fuite est utilize. NE PAS tenir la capacité dans la main ou
toucher la sonde ou la patte de la capacité pendant le test
de fuite.
To check for leakage between sections of a multi-section
cap:
1.
Connect one section of the capacitor to the LC103
test leads. Be sure to observe proper polarity.
2.
Enter the working voltage of the section being tested.
NOTE: A multi-section lytic may have a different
working voltage for each section.
3.
Press the CAPACITOR LEAKAGE button and read
the amount of leakage on the display. It must be
within the maximum allowable leakage limits for its
value and voltage rating.
4.
Connect one end of a short jumper to the common
terminal of the capacitor.
5.
While pressing the CAPACITOR LEAKAGE button,
connect the other end of the jumper to each of the
capacitor terminals not already connected to the
LC103 test leads.
6.
A good multi-section electrolytic will show no
increase in the leakage as the jumper is connected to
each terminal.
Dielectric Stress
Many ceramic capacitors change value when they are
DC biased. The applied DC voltage causes physical
stress within the ceramic dielectric causing it to decrease
in value. This value change is called “dielectric stress”.
Normally a ceramic capacitor will return to its normal
value within several seconds after the voltage is
removed.
You will not normally notice dielectric stress when
checking a ceramic capacitor with the ReZolver, unless
you apply a voltage to it with the capacitor leakage test.
Then you may find that the capacitance value has
decreased by as much as 50% in ceramic capacitors
having values 10 pF or smaller. This is a normal
characteristic of small value ceramics.
Intermittent Capacitors
Occasionally an electrolytic capacitor may become
intermittent. A poor weld of the lead to the internal foil
plates or other mechanical problem can cause the
capacitor to function randomly. Often such capacitors
will also exhibit high ESR when they are working. (The
internal construction of an electrolytic capacitor is
shown in the APPENDIX).
If you suspect an intermittent capacitor, move its leads
around and pull on them as you perform a capacitor
value test. A change in capacitance indicates an
intermittent component which should be replaced.
Checking Ceramic Capacitor Temperature Characteristics
Ceramic capacitors are designed to have a wide range of
capacitance value and temperature characteristics, (More
details are given in the APPENDIX.) Replacing a
capacitor with one that has the same characteristics is
especially important in certain oscillators and other
temperature critical circuits. You can quickly determine
the basic temperature characteristics of a ceramic using
the LC103 and a heat source, such as a heat gun.
Simply connect the capacitor to the LC103 and measure
its value. Then apply heat to the capacitor while you
continue to measure its value. A COG or NPO type
capacitor will not change in value, or change very
slightly as heat is applied. An N type ceramic will
decrease in value, while a P type ceramic will increase in
capacitance.
