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CAUTION: NEVER ‘ROCK’ OR ‘WALK’ THESE TERMINALS TO GET THEM ON OR
OFF OF RELAYS. USE AS ‘DIRECT’ IN/OUT MOTION WHEN INSTALLING AND
REMOVING THESE TERMINALS.
Your goal is to minimize widening or spreading of the ‘curl’ of the female terminal that reduces
the clamping strength and area of surface contact with the blade in the capacitor. Position the
terminals of the transformer wire leads so that they are distant from any electrically conductive
objects near them as shown in Figure 10A. Do not attach your meter test leads at this time.
A failed capacitor will measure either shorted or open
when tested for resistance. To test the
capacitor adjust your meter to measure resistance at the highest scale (3000) available as
shown in Figure 10A. Attach the test leads to the fully discharged capacitor, allow 5 seconds
for the meter to stabilize, then note the value displayed on the meter.
A capacitor
that has failed shorted will display “000”, “000.1” or a similar very low resistance
value. This is exactly what you would see if you were to touch and hold the test leads of your
meter together. A capacitor that has failed open will display a
flashing
“3.000”, “0L” or a similar
very high resistance value. This is exactly what you would see if you were to keep the test
leads of your meter separated.
A good capacitor will cause the value in the display to increase incrementally. The display in
this meter flashes on and off about three times a second. The value increased with each cycle
as follows; “079”, “175”, “264”, and so on until the meter reached its limit. This is why this
capacitor measured ‘”3.000”. If you thought it had failed open you would have guessed wrong,
because the meter exceeded its limit just before the picture for Figure 10A was taken.
The reason why the resistance value increases is that the battery of the test meter charges the
capacitor, and the meter indicates this increased charge. Unlike an instrument quality meter
this consumer grade meter did not indicate polarity.
If we allowed this meter to charge the capacitor until it reached its limit and then reversed the
polarity of the leads, it would take as long as six seconds before the display value began to
increase from “000”. Do not make the mistake of assuming the
flashing
reading you just measured is accurate. Unlike the transformer and
diode tests where a
flashing
reading may be valid, if not excusable, a
capacitor test is unforgiving if you are unfamiliar with your meter or how
a capacitor behaves in response to it.
An old-fashioned analog meter (sweep-needle) works very well for
capacitor tests. A good capacitor will cause the needle to move
smoothly clockwise from zero to about 2/3 to the right on the scale, at
which point it will stop and bump back clockwise. This indicates the
capacitor has accepted a charge from the battery in the meter.
To accurately measure the actual capacitance of a capacitor requires a
meter closer to instrument quality as shown in Figure 10B. The
practical need for this investment will be rewarded when you find that
someone has replaced the 4 micro-farad capacitor required with a
generic, unmarked 3 micro-farad capacitor that is identical to the one
required. Could this be why the charger outputs 5 amperes instead of
20? Access to a quality test instrument may be your only option.
Figure 10B
