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14 | SAMLEX AMERICA INC. SAMLEX AMERICA INC. | 15
SECTION 3 | BATTERY THEORY
In case temperature compensation is not provided, the warmer battery at 40ºC will
begin to heat and outgas at 13.95V and will continue to overcharge until the non-
compensated Absorption Voltage set point is reached (14.4V). In cooler temperatures,
the 10ºC battery will experience severe undercharging, resulting in sulfation.
It is recommended that a battery charger / charge controller with a provision for
temperature sensing and compensation should be used if the battery electrolyte
temperature varies more than 5ºC to 10ºC (9ºF to 18ºF).
Loss of Battery Capacity at Low Temperatures
Batteries lose capacity in low temperatures. At 32ºF (0ºC), a battery will deliver about 70 to
80% of its rated capacity at 80ºF (26.7ºC). If the electrolyte temperature of the battery bank
is lower than 80ºF (26.7ºC), additional batteries will be needed to provide the same usable
capacity. For very cold climates, an insulated / heated battery compartment is recommended.
Freezing of Electrolyte
For applications with low ambient temperature, the lead-acid battery must also be protected
against freezing of the electrolyte. The risk of freezing depends on the state of charge. The
chart given below illustrates the freezing limit as a function of the state of charge.
- 80 °
- 60 °
- 40 °
- 20 °
0 °
0 20 40 60 80 100
State of charge [%]
Temp
erat
ure
[
°
C
]
slushy until hard
- 80 °
- 60 °
- 40 °
- 20 °
0 °
0 20 40 60 80 100
State of charge [%]
Temp
erat
ure
[
°
C
]
slushy until hard
STATE OF CHARGE (%)
TEMPERA
TURE (ºC)
Fig 3.4. Temperature vs State of Charge
3.4 Lithium Batteries
Lead Acid Drop In replacements:
There are a number of different chemistries for Lithium Batteries. The most commonly
used as a Lead Acid battery Drop In Replacement is the LiFePO4 battery chemistry.
These batteries must come with a built in Battery Management System (BMS). This
will employ safe guards on the battery for safety and operation.
Other Lithium Chemistries:
As Lithium evolves into a battery source, there may be other chemistries that come to
market. Review the battery manual and charging specifications. Then compare with
the operation of the charge controller. It may be possible for the charger to be setup
for the battery of your selection. The battery must still include a BMS that protects the
battery and for safety as the charge controller will only supply power.