4 Operating From a Personal Computer
Operation Guide Flatpack MCU,
351300.013, v8-2006-07
63
Ensure you have a stable load current of approx. 40-60 % of the rated shunt current
Measure the load current with a current probe, or directly by measuring the voltage over the rectifier shunt and then
calculating the current:
I
shunt
=
V
shunt
/
R
shunt
R
shunt
=
60mV/I
rated
*
* Note that the shunt voltage drop is dependant on specific shunt type. 60mV shunts are typically used, although 50mV
shunts may be used in some cases. If in doubt, inspect the shunt body for the actual rating markings.
Enter the calculated or
measured
current for the
Low CalibrationPoint
in
Amps
Select
Accept
Ensure that you have a stable load current of approx. 30-60 % of the rated shunt current
Measure the voltage over the rectifier shunt and calculate the current
Enter the calculated or
measured
current for the
High CalibrationPoint
in
Amps
Select
Accept
Click
OK
to exit the calibration menu, if done.
4.11.2.3 Internal System Current and Shunt Calibration Considerations
Perceived calibration errors may exist when no system load is connected, where the Flatpack MCU display indicates
some battery discharge current due to the internal power system load current. Awareness of the reasons for this
condition should alleviate concerns regarding the perceived discrepancy, and the intent of these paragraphs is to avoid
confusion over the issue.
In LVD contactor-equipped DC power systems where the contactor coils are fed from the battery side of the system
distribution bus, it is necessary to consider the effects of the resultant internal power system current drain on the battery.
This current consists primarily of the LVD contactor coil power requirements. This current must be considered as part
of the battery discharge current when calibrating the current shunts. Typical contactor coil currents are on the order of
500mA per contactor (Example: in a three LVD system, a “phantom” current of approximately 1.5 amperes exists).
Note that attempts to calibrate the battery current shunt to read zero with the internal load current present will result in
an offset error in the Total and/or Rectifier current readings due to the mathematical summation of Rectifier and Battery
current readings by the Flatpack MCU to arrive at a Total load value.
4.11.2.4 Calibrating the output voltage
Calibration of the output voltage needs only one calibration point (at working voltage). The output voltage should be
measured at the load terminals.
•
Enter the
Output Voltage
in
Volts
, a figure between 10.00 and 75.00.
•
Select
Accep