Alpha Technologies AlphaCell SMU-F - Manual (Page 10)

SMU-F-BATTERY 10
Fig. 1-2, Capacity Related toTemperature and Discharge Rate
1.2 Specifications and General Information, continued
Gassing
SMU-F batteries have a high recombination efficiency (>98%) and for cells operated at 68ºF
(20ºC) under normal operating conditions venting is virtually negligible. The following gassing
rates can be expected:
2 ml/Ah/cell/month at a float voltage of 2.27Vpc.
10 ml/Ah/cell/month at a recharge voltage of 2.40Vpc.
As hydrogen should never exceed 2% by volume in any enclosed space, all rooms or
cabinets where batteries are installed should have natural ventilation and not be fully sealed.
Customers should also be aware that hydrogen is very light and can “pocket” in portions of
the room or cabinet. Designers should take this into account when designing the battery
operating space.
Each cell has a one-way valve to permit the release of gases from the cell whenever the
internal pressure exceeds the fixed safety value. The valve is rated at approximately 0.1
atmospheres (1.5 PSIG or 10 kPa).
Operation of batteries in parallel
When the required capacity is greater than the maximum available from our range, it is
possible to connect batteries in parallel to obtain the desired capacity.
Use only blocks of the same model
Make all electrical connections of parallel circuits between the batteries as equal and
symmetrical as possible (e.g., length and type of connector) to minimize possible
impedance variations
Capacity
The battery capacity is rated in ampere hours (Ah) and indicates the quantity of electricity
which can be supplied during discharge. The capacity depends on the quantity of the active
materials contained in the battery (thus on dimensions and weight) as well as the discharge
rate and temperature. The higher the discharge rate, the lower the available capacity. As
batteries get colder, the available capacity is reduced. This is related to the kinetics of the
electrochemical reactions and the resistivity of the electrolyte (see Fig. 1-2).
•
•
•
•
20%
30%
0%
50%
60%
70%
80%
90%
100%
110%
Temperature ºF (ºC)
A
va
ila
bl
e C
ap
ac
ity
1 -10 hour discharge
5 -59 minute discharge
-4 (-20) 14 (-10) 32 (0) 50 (10) 68 (20) 86 (30) 104 (40) 122 (50) 10 (60)