34
B A T T E R Y C H A R G I N G
35
M O R N I N G S T A R C O R P O R A T I O N
4.0
34
4.0 Battery Charging
4.1 PWM Battery Charging
PWM (Pulse Width Modulation) battery charging is the most efficient and
effective method for recharging a battery in a solar system.
Refer to “Why
PWM?” on Morningstar’s website for more information
.
Selecting the best method for charging your battery together with a good
maintenance program will ensure a healthy battery and long service life.
Although the TriStar’s battery charging is fully automatic, the following
information is important to know for getting the best performance from
your TriStar controller and battery.
4.1.1 Four Stages of Solar Charging
NIGHT
NIGHT
BULK
CHARGE
ABSORPTION
FLOAT
EQUALIZE
VOL
T
AGE
TIME
Figure 4.1.1 Solar Charging Stages
1. Bulk Charging:
In this stage, the battery will accept all the current
provided by the solar system. The LEDs will display an indication of
the battery charge state as the battery is being recharged.
2. PWM Absorption:
When the battery reaches the regulation voltage, the
PWM begins to hold the voltage constant. This is to avoid over-heating and
over-gasing the battery. The current will taper down to safe levels as the
battery becomes more fully charged. The green LED will blink once per
second.
See Section 4.2.
3. Equalization:
Many batteries benefit from a periodic boost charge to
stir the electrolyte, level the cell voltages, and complete the chemical
reactions. The green LED will blink rapidly 2-3 times per second.
See
Section 4.4.
4. Float:
When the battery is fully recharged, the charging voltage is reduced
to prevent further heating or gasing of the battery. The green LED will blink
slowly once every 2 seconds.
See Section 4.5
.
4.1.2 Battery Charging Notes
The TriStar manages many different charging conditions and system configu-
rations. Some useful functions to know follow below.
Solar Overload:
Enhanced radiation or “edge of cloud effect” conditions can
generate more current than the controller’s rating. The TriStar will reduce this
overload up to 130% of rated current by regulating the current to safe levels. If
the current from the solar array exceeds 130%, the controller will interrupt
charging
(see Section 3.4)
.
Battery Voltage Sense:
Connecting a pair of voltage sense wires from the
controller to the battery is recommended. This allows a precise battery voltage
input to the controller and more accurate battery charging.
See Section 4.3 for
more information.
Temperature Compensation:
All charging set-points are based on 25˚C
(77˚F). If the battery temperature varies by 5˚C, the charging will change by
0.15 volts for a 12 volt battery. This is a substantial change in the charging of
the battery, and a remote temperature sensor is recommended to adjust
charging to the actual battery temperature.
See Section 4.3 for more
information.
Day-Night Detection:
The TriStar will automatically detect day and night
conditions. Any functions that require measuring time or starting at dawn,
for example, will be automatic.
PWM Noise:
In some installations, the PWM charging may cause audible
noise in certain equipment. If this occurs, the PWM can be changed to “On-
Off” solar charging to reduce the noise. This requires DIP switch number 8
to be turned On. However, it is strongly recommended to try to remedy the
noise problem with grounding or filtering first, because the benefits from PWM
battery charging are significant.
Battery Types:
The TriStar’s standard battery charging programs are suitable
for a wide range of lead-acid battery types. These standard programs are
reviewed in the following Section 4.2. A general review of battery types and
their charging needs is provided in Section 9.0.
4.2 Standard Battery Charging Programs
The TriStar provides 7 standard battery charging algorithms (programs) that
are selected with the DIP switches
(see Step 3 in Installation)
. These standard
algorithms are suitable for lead-acid batteries ranging from sealed (gel, AGM,
maintenance free) to flooded to L-16 cells. In addition, an 8th DIP switch
provides for custom set-points using the PC software.
The table below summarizes the major parameters of the standard charging
algorithms. Note that all the voltages are for 12V systems (24V = 2X, 48V = 4X).
All values are 25ºC (77ºF).
A.
B. C. D. E. F. G.
DIP
PWM
Time
Equalize Max Equal.
Switches
Battery
Absorp.
Float
Equal.
in Equal. Interval
Cycle
(4-5-6)
Type
Voltage Voltage Voltage (hours) (days)
(hours)
off-off-off
1 - Sealed
14.0
13.4
none
–
–
–
off-off-on
2 - Sealed
14.15
13.4
14.2
1
28
1
off-on-off
3 - Sealed
14.35
13.4
14.4
2
28
2
off-on-on
4 - Flooded
14.4
13.4
15.1
3
28
4
on-off-off
5 - Flooded
14.6
13.4
15.3
3
28
5
on-off-on
6 - Flooded
14.8
13.4
15.3
3
28
5
on-on-off
7 - L-16
15.0
13.4
15.3
3
14
5
on-on-on
8 - Custom
Custom
Custom
Table 4.2 Standard Battery Charging Programs
