JLG X20JP - X600AJ Service Manual - Manual (Page 317)

SECTION 6 - JLG CONTROL SYSTEM
3121623 – JLG Lift – 6-101
Second Group (Cell Voltage "mV")
Figure 6-100.
Delta (mV): It is the difference from highest cell and low-
est cell (mV).
During the discharge: The cells supply the same level of
current, because they are connected as series. For this
reason, the cells should have about the same voltage
drop and the voltage drop should be less than 100 mV. If
Delta (mV) value during the discharge is increasing more
than 100 mV, it is necessary to discharge and recharge
completely the battery pack, then check the value again.
During the charge: Delta (mV) value during the charge
operation is one of the most important data for the diagno-
sis.
During the charge, this value can grow a lot, even to 300
mV or more, however at the end of the balancing opera-
tion it should be 50 mV or less.
The smaller is this value at the end of the balancing opera-
tion, the better the cells are balanced with consequent
higher performances.
To be sure that the system is well balanced, we recom-
mend periodically to leave the machine under charge for
at least one night.
If the Delta (mV) value is not decreasing under 50 mV
even after a night, it is necessary to check which cell is the
highest one, discharge and recharge completely the sys-
tem and check again.
Lowest – at : It is the voltage at the lowest cell. The num-
ber of the corresponding cell is indicated on side.
During the charge: The lithium cells have not exactly the
same characteristics at 100%, so even if they are charged
with the same current level, it is possible that one cell
reaches the max charge level quicker than the others
This characteristic is normal, and it doesn’t means that
there is a failure.
However, at the end of the charging process, even if the
lowest cell is always the same one, his value should be
about 3600 mV.
If the Delta (mV) value is less than 50 mV, the pack is well
balanced.
During the discharge: During the discharge, the cells volt-
age should drop more or less in the same way, so the
Delta (mV) value should reduce.
If one cell voltage decrease too fast compared to the oth-
ers, probably the cell has a problem.
For example if the highest cell is at 3334 mV, and the low-
est is 2,8 mV, probably there is a problem.
In this case, it is very important to analyze the value “aver-
age”, because it indicates if the other cells are more close
to the higher or to the low cell pointing out where is the
problem.
If only a cell I a battery pack is replaced after many years,
surely this new cell will drop slowly than all the other ones,
but the BMs can easily manage that aspect.
Highest – at: It is the voltage at the highest cell. The num-
ber of the highest cell is indicated on side.
During the discharge: During the discharge this value is
not so important, in fact it is normal that cells voltage
decrease differently.
During the charge: This is a very important data.
During the charge, the highest cell can change time by
time, but when one cell reach 3630 mV the BMS connect it
with an electrical resistance (see paragraph 7.2 “charging
process”) in order to allow also the other cells to reach
3600 mV without any overcharge.
As soon as another cell reaches 3630 mV, BMS connect it
to a resistance too. At the end of the balancing operation,
the highest cell changes every 5-15 seconds, because
when the BMS connect a cell to the resistance its voltage
decrease.
That’s why the Delta (mV) value should be less than 50
mV at the end of the charging process.