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B A T T E R Y C H A R G I N G
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M O R N I N G S T A R C O R P O R A T I O N
4.0
A. Battery Type
- These are generic lead-acid battery types.
See Section 9.0 for more
information about battery types and appropriate solar charging.
B. PWM Voltage
–This is the PWM Absorption stage with constant voltage
charging. The “PWM voltage” is the maximum battery voltage that will be
held constant. As the battery becomes more charged, the charging current
tapers down until the battery is fully charged.
C. Float Voltage
–When the battery is fully charged, the charging voltage will
be reduced to 13.4 volts for all battery types. The float voltage and
transition values are adjustable with the PC software.
See Section 4.5 for
more details.
D. Equalization Voltage
–During an equalization cycle, the charging voltage
will be held constant at this voltage.
E. Time in Equalization
–The charging at the selected equalization voltage
will continue for this number of hours. This may take more than one day to
complete.
See Section 4.4.
F. Equalization Interval
–Equalizations are typically done once a month. Most
of the cycles are 28 days so the equalization will begin on the same day of
the week. Each new cycle will be reset as the equalization starts so that a
28 day period will be maintained.
G. Maximum Equalization Cycle
–If the solar array output cannot reach the
equalization voltage, the equalization will terminate after this many hours
to avoid over gasing or heating the battery. If the battery requires more
time in equalization, the manual push-button can be used to continue for
one or more additional equalization cycles.
These (7) standard battery charging algorithms will perform well for the
majority of solar systems. However, for systems with specific needs beyond
these standard values, any or all of these values can be adjusted using the
PC software.
See Section 7.0
.
4.3 Temperature Effects & Battery Voltage Sense
4.3.1 Remote Temperature Sensor (RTS)
The RTS is used for temperature compensated battery charging. As the
battery gets warmer, the gasing increases. As the battery gets colder, it
becomes more resistant to charging. Depending on how much the battery
temperature varies, it may be important to adjust the charging for temperature
changes.
There are three battery charging parameters that are affected by
temperature:
PWM Absorption
This is the most important part of charging that is affected by temperature
because the charging may go into PWM absorption almost every day. If the
battery temperature is colder, the charging will begin to regulate too soon and
the battery may not be recharged with a limited solar resource. If the battery
temperature rises, the battery may heat and gas too much.
Equalization
A colder battery will lose part of the benefit of the equalization. A warmer
battery may heat and gas too much.
Float
Float is less affected by temperature changes, but it may also undercharge
or gas too much depending on how much the temperature changes.
The RTS corrects the three charging set-points noted above by the
following values:
• 12 volt battery: –0.030 volts per ˚C (–0.017 volts per ˚F)
• 24 volt battery: –0.060 volts per ˚C (–0.033 volts per ˚F)
• 48 volt battery: –0.120 volts per ˚C (–0.067 volts per ˚F)
Variations in battery temperature can affect charging, battery capacity, and
battery life. The greater the range of battery temperatures, the greater the
impact on the battery. For example, if the temperature falls to 10˚C (50˚F) this
15˚C (27˚F) change in temperature will change the PWM, equalization and
float set-points by 1.80V in a 48V system.
If a remote temperature sensor is not used and the temperatures near the
battery are stable and predictable, the PWM absorption setting can be
adjusted using the PC software per the following table:
Temperature
12 Volt
24 Volt
48 Volt
40ºC / 104ºF
– 0.45 V
– 0.90 V
– 1.80 V
35ºC / 95ºF
– 0.30 V
– 0.60 V
– 1.20 V
30ºC / 86ºF
– 0.15 V
– 0.30 V
– 0.60 V
25ºC / 77ºF
0 V
0 V
0 V
20ºC / 68ºF
+ 0.15 V
+ 0.30 V
+ 0.60 V
15ºC / 59ºF
+ 0.30 V
+ 0.60 V
+ 1.20 V
10ºC / 50ºF
+ 0.45 V
+ 0.90 V
+ 1.80 V
5ºC / 41ºF
+ 0.60 V
+ 1.20 V
+ 2.40 V
0ºC / 32ºF
+ 0.75 V
+ 1.50 V
+ 3.00 V
– 5ºC / 23ºF
+ 0.90 V
+ 1.80 V
+ 3.60 V
– 10ºC / 14ºF
+ 1.05 V
+ 2.10 V
+ 4.20 V
– 15ºC / 5ºF
+ 1.20 V
+ 2.40 V
+ 4.80 V
Table 4.3 Temperature Compensation
The need for temperature compensation depends on the temperature
variations, battery type, how the system is used, and other factors. If the
battery appears to be gasing too much or not charging enough, an RTS
can be added at any time after the system has been installed.
See Section
2.3 - Step 4 for installation instructions.
The TriStar will recognize the RTS when the controller is started (powered-
up).
4.3.2 Battery Voltage Sense
There can be voltage drops typically up to 3% in the power cables connect ing
the battery to the TriStar. If battery voltage sense wires are not used, the
controller will read a higher voltage at the controller’s terminals than the actual
battery voltage while charging the battery.
Although limited to 3% as the generally accepted wiring standard, this can
result in a 0.43 voltage drop for 14.4V charging (or 1.72V for a 48 volt nominal
system).
