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The module OCV can be measured at the terminals, by turning the unit ON. While under load, an approximation of the OCV can be
measured if the current, either charge or discharge, is less than 4.9 Amps (at 25 ºC and higher).
The internal resistance of the Evolion module varies with temperature and age due to the change in the cells’ electrochemical
impedance. About ½ of the total Evolion resistance is associated to the cells at 25 ºC. The internal resistance increases approximately
20 % when at 10 ºC and decreases by approximately 20 % when at 55 ºC. It is independent of the SoC.
Additionally, the internal resistance increases in normal aging during its useful life. The typical end of life resistance is approximately
double when 20 % of its beginning of life capacity is lost over its useful life.
Module T (°C / °F)
Internal resistance (Ri) at beginning of life (± 15
%)
25 / 77
0.045 Ω
When the network voltage is lower than the Evolion’s terminal voltage, the module begins discharging. The available discharge
capacity is utilized to a low voltage cut-off at 42 Vdc.
The available capacity is a function of discharge current. See Figure 6 for the typical discharge characteristics representing runtimes
of approximately 2 hours (1750 W), 4 hours (925 W), 8 hours (485 W) and 16 hours (240 W).
6. Internal resistance
7. Discharging
Figure 6. The typical discharge characteristics of the Evolion at 25ºC.
% of Nominal Capacity
Unit Voltage
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110%
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41
40
Nominal Capacity = C
8
= 77Ah
1750 W
925 W
485 W
240 W
The discharge characteristics at different temperature are show in Figure 7. The factor affecting these characteristics is the internal
impedance of the cells.
Note: The internal heater maintains the Evolion’s internal temperature higher than 10
ºC. Discharge curves at less than 10
ºC are for
information and not representative of normal operation mode.
The discharge starts and continues until one of the following conditions is met.
•
The network voltage becomes equal to or higher than the module voltage
•
The battery voltage reaches 42 Vdc or a cell voltage reaches 2.5 Vdc
•
The ON/OFF button is pressed for at least 4 seconds
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