User manual

Figure 4-1: CYCLON
®
Battery Medium Rate Discharge
Voltage Profile
Figure 4-2: CYCLON
®
Battery High Rate Voltage Profile
4.3 Discharge Level
The voltage point at which 100% of the usable capacity
has been depleted is a function of the discharge rate. For
optimum cell life, it is recommended that the battery be
disconnected from the load at this end voltage point. The
recommended end of discharge voltage (EODV) is a function
of the rate of discharge, and these numbers are given in Table
4-1 below:
Table 4-1
Discharge rate in amps Suggested minimum
EODV per cell
0.05C
10 (C10/20) 1.75V
0.10C
10 (C10/10) 1.70V
0.20C
10 (C10/5) 1.67V
0.40C
10 (C10/2.5) 1.65V
1.00C
10 1.60V
2.00C
10 1.55V
>5.00C
10 1.50V
NOTE: Discharging a CYCLON
®
battery cell below these voltage levels
or leaving the cell connected to a load in a discharged state
may impair the ability of the cell to accept a charge.
In "overdischarge" conditions, the sulphuric acid electrolyte
can be depleted of the sulphate ion and essentially become
water, which can create several problems. A lack of sulphate
ions as charge conductors will cause the cell impedance to
appear high and little charge current to flow. Longer charge
time or alteration of charge voltage may be required before
normal charging can resume.
Disconnecting the battery from the load will totally eliminate
the possibility of an overdischarge, provided that it is put
back on recharge immediately after the discharge. Doing so
will allow each cell to provide its full cycle life and charge
capabilities.
It is important to note that when the load is removed
from the battery, its terminal voltage will increase - up to
approximately 2 volts per cell. Because of this phenomenon,
some hysteresis must be designed into the battery disconnect
circuit so that the load is not continuously reapplied to the
battery as the battery voltage recovers.
4.4 Overdischarge Recovery
Although overdischarging the battery is not recommended,
CYCLON
®
batteries have an excellent tolerance for this type
of abuse. The following protocol may be used to recover cells
that have been overdischarged. This procedure should not be
attempted if the OCV of the battery pack is 1.0 volt per cell
(VPC) or less.
1. Bring the battery to room temperature (77ºF or 25ºC).
2. Measure the OCV. Continue to step 3 if it is at least 1.00
VPC; otherwise terminate the procedure and reject the
battery.
3. Charge the battery using a 0.05C constant current
for 24 hours. The charger should be able to provide a
driving voltage as high as 3.0 VPC. Monitor the battery
temperature; discontinue charging if the battery
temperature rises by more than 20ºC.
4. Allow the charged battery to stand on open circuit
for 18 hours.
5. Perform a capacity test on the battery and record the amp-
hours delivered. The longer the discharge the more reliable
the result. This is Cycle 1.
6. Repeat steps (3) to (5). The capacity returned in step 5 is
now Cycle 2. If Cycle 2 capacity is greater than Cycle 1
capacity proceed to step 7; otherwise reject the battery.
7. Repeat steps (3) to (5) to get Cycle 3 capacity. Proceed to
step 8 if Cycle 3 capacity is equal to or more than Cycle 2
capacity. Reject the battery if Cycle 3 capacity
is less than Cycle 2 capacity.
8. If Cycle 3 capacity equals or exceeds Cycle 2 capacity
recharge the battery and put it back in service.
1.6
1.7
1.8
1.9
2
2.1
2.2
2.3
01
Time in hours at 25°C (77°F)
2 3 4 5 6 7 8 9 10 11 12
C/5 C/10
Cell Voltage (V)
Time in minutes at 25°C (77°F)
1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
2.2
2.3
0 5 10 15 20 25 30 35 40 45 50 55
1C 2.2C
Cell Voltage (V)
10
Publication No: EN-CYC-AM-007 - December 2008
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