5.3 Description of Function Codes 5.3.5 H codes (High performance functions)
Capacitance of DC link bus capacitor (H42)
Calculating the capacitance of DC link bus capacitor
• The discharging time of the DC link bus capacitor depends largely on the inverter’s internal load conditions, e.g.
options attached or ON/OFF of digital I/O signals. If actual load conditions are so different from the ones at which
the initial/reference capacitance is measured that the measurement result falls out of the accuracy level required,
then the inverter does not perform measuring.
The capacitance measuring conditions at shipment are extremely restricted, e.g., all input terminals being OFF
in order to stabilize the load and measure the capacitance accurately. Those conditions are, therefore, different
from the actual operating conditions in almost all cases. If the actual operating conditions are the same as those
at shipment, shutting down the inverter power automatically measures the discharging time; however, if they are
different, no automatic measurement is performed. To perform it, put those conditions back to the factory default
ones and shut down the inverter. For the reference capacitance setup procedure, see “[ 1 ] Measuring the
capacitance of DC link bus capacitor in comparison with initial one at shipment” on page 5-233.
To measure the capacitance of the DC link bus capacitor under ordinary operating conditions when the power is
turned OFF, it is necessary to set up the load conditions for ordinary operation and measure the reference
capacitance (initial setting) when the inverter is introduced. For the reference capacitance setup procedure, see
“[ 2 ] Measuring the capacitance of DC link bus capacitor under ordinary operating conditions at power
shutdown” on page 5-234.
Setting bit 3 of H98 data to 0 restores the inverter to the measurement in comparison with the initial capacitance
measured at shipment.
When the inverter uses an auxiliary control power input, the load conditions widely differ so that the
discharging time cannot be accurately measured. In this case, measuring of the discharging time can be
disabled with the function code H98 (Bit 4 = 0) for preventing unintended measuring. (For details, refer to
H98.)
ON-time counting of DC link bus capacitor
• In a machine system where the inverter main power is rarely shut down, the inverter does not measure the
discharging time. For such an inverter, the ON-time counting is provided. If the capacitance measurement is
made, the inverter corrects the ON-time according to the capacitance measured. The ON-time counting result
can be represented as “elapsed time” and “remaining time” before the end of life.
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