3
vacon • 14
SPECIAL CHARACTERISTICS AFFECTING THE
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Figure 13. LCL ground capacitor must be disconnected
3.3
Balance or maintenance charge
The maximum voltage of the battery is needed only when charging the battery at the fullest level.
Current in that voltage is small. However, the time during which this voltage prevails can be
theoretically infinite if the battery is continuously kept 100% full (which is not advisable because of
the aging of the battery). When the charging is finished and even only little load is given to the
battery, the voltage decreases rapidly.
It is necessary (after a certain time or a number of battery charge/discharge cycles) to "reset the
trip meter" of the Battery Management System. Otherwise the state of charge calculations can
become misleading and result in poor behavior or even in exceeding the safe operation limits. The
only good way to "reset the trip meter" is to charge the battery to the full state where the Battery
Management System can safely tune its SOC value back to 100%.
Every cell must be charged extremely slowly so that the current of each cell goes as low as possible
(the cell reaches its full voltage). For a big battery system that has many cells in parallel and in
serial this is done from the same DC+ and DC- connections with the same Udc control. Do not start
to dismantle batteries to charge them individually. Because of the differences in cell level (for
example SOC, impedance) this means that some of the cells fill up sooner than others.
To avoid overcharging, the natural passive balancing of the battery system is needed. However, this
is a slow process and that is why the balancing charge needs to be slow with an accurately
controlled small current. It is difficult to say how accurate and small the current needs to be, but
the rule of thumb is that 0.01C is needed. If the device is not able to provide accurately such a
current, it is necessary to add a balance charger to the system. The battery manufacturer can also
be consulted about balance chargers.
-L1
-L2.1
-L2.2
-L2.3
-C1
-C2
HF
HF
-C3
U2
U1
V2
W2
V1
W1
-R1
-C1.1 -C1.2 -C4.1-C4.2
-C5.2
-R4
-R2
-C2.1 -C2.2 -C5.1
-R5
-C6.2
-R3
-C3.1 -C3.2 -C6.1
-R6
no HF
Summary of Contents for NX6
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