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User Manual – R2485 & System
Alarm Condition
Earth Leak Alarm
Possible Cause
Excessive Earth current due to either
failure of load supply isolation or faulty
load equipment.
Action Suggested
Locate source of earth leakage current and
correct accordingly.
7.2. MCSU Fault Finding and Repair Procedures
In addition to performing a supervisory function by monitoring output voltage and current and the various system
alarms, the MCSU also performs a voltage control function in order to achieve battery charging current control,
battery temperature compensation, battery equalization and active current sharing.
To control current to the lowest battery voltage, the MCSU has the ability to suppress the SMR output voltage to a
value lower than the minimum battery voltage.
It therefore follows that it is possible for a MCSU fault to occur which can suppress the SMR voltage to that low
level and thus cause a battery discharge despite the precautions that have been taken to ensure that this does not
happen.
In such a situation disconnecting the 4-way cable which connects the SMRs to the MCSU will remove
the voltage suppressing PWM control signal and thus avoid the batteries discharging. Without the
MCSU connected, the SMRs will revert to their pre-set Float voltage and passive current sharing.
The MCSU can then be changed to resolve the problem.
There are virtually no electronic components on the MUIB except for the Remote alarm relays, and some fuse links,
but there are many connectors. It is worth checking for poor connections when a MCSU system problem is being
investigated.
7.2.1. Replacing MCSU
To replace a MCSU the following procedure should be followed, Mini CSU connector Diagram Shown in Figure 7.1:
1. Remove the knurled screws holding the MCSU front panel to the rack and remove it;
2. Gently pull the MCSU unit forward, and hold it in a horizontal position until the back is just clear of the rack.
3. Unplug the 34-way cable first (removes all power) and then the other cables. The SMRs will now be working in
passive current sharing mode and current sharing may not be as good as previously. The output voltage will
also rise to the value pre-set in the SMRs. Please refer to the paragraph 7.2.2. as per steps for removing MCSU
from the magazine.
4. Bring the replacement MCSU to its position in the rack and plug in all the cables making sure that the
34-way cable is connected last. Please refer to the paragraph 7.2.3. as per steps for inserting the MCSU
into the magazine;
5. Gently push unit into rack and secure the MCSU front panel with screws supplied;
6. Check operating parameters.
Figure 7.1
Allis Electric Co.,Ltd.
MCSU connector Diagram
page 47 of total 82
2002.02