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Appendix
7. A
PPLICATION
T
7.1.
YPICAL
Ultra/super capacitors undergo chemical changes when stored or used for long
periods of time, steadily losing capacitance and increasing in ESR. If wear continues
unchecked, these capacitors can fail or no longer store enough energy to perform their
intended function, potentially causing catastrophic damage. Capacitor lifetime is
heavily dependent on use and ambient conditions, and thus difficult to predict.
Periodically measuring the capacitance of a cell or module can help quantify the wear
on and remaining lifetime of the capacitor, helping avoid catastrophic failure without
periodically replacing the entire bank.
A short description of how to use the M3628UCT to test a capacitor cell or module is
given below.
1.
Ensure the capacitor is discharged.
2.
Apply power to the M3628UCT.
3.
Connect the high-current leads to the capacitor as directly as possible. Each
additional wire and interconnect will increase the resistance and prolong charging
and discharging.
4.
Connect the clip leads directly to the capacitor terminals. The clip leads are used
to measure the voltage between the two points in response to a forced current,
thus allowing ESR to be measured. Everything between these two points will be
included in the ESR calculation.
5.
Select "Test Cycle" from the main menu.
6.
Set the charge voltage to 95% of the rated voltage of the capacitor.
7.
Set the charge current to its maximum setting or the current rating of the
capacitor, whichever is lower.
8.
Set the hold time to at least 1 minute.
9.
Begin charging the capacitor, listening for abnormal sounds or other indications
in the capacitors or attached equipment. Monitor the current indicator to make
sure the commanded current is reached, and the voltage indicator to see that the
voltage is rising. Continually monitor the capacitor for abnormal signs, such as
noise, heating, or smell.
IF AT ANY TIME ABNORMAL SIGNS ARE DETECTED, OR THE LOAD
CAPACITORS ARE OVERVOLTAGED, PRESS CANCEL, THEN PROCEED TO
DISCHARGE THE CAPACITOR IF POSSIBLE.
10.
After the hold period is complete, the unit will discharge the load and calculate its
capacitance and ESR. Wait until discharging is complete before disconnecting
the load, indicated by the appearance of a test record. Record the calculated
capacitance and ESR somewhere safe, along with the designation of the
capacitor being tested. Multiple tests may be performed if desired, to ensure
repeatability.
11.
If the procedure is completed successfully, the capacitor bank or equipment can
be returned to storage or put into use, as appropriate.
N
OTES
C
T
APACITOR
ESTING
P
ROCEDURE
User's Manual
29
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