Installation and Operation Manual
12
The advantage the external shunt provides could be illustrated in the following manner. Suppose a battery is at
a fairly high state of charge in the acceptance mode, and is drawing 5 amps of charge current which is being
provided by Solar Boost 3048. If a 10 amp load is then placed on the battery, Solar Boost 3048 increases output
current to hold the battery at the desired acceptance voltage. Solar Boost 3048 is now delivering 15 amps, 5 amps
to the battery as before, plus 10 amps to the load. Using the internal shunt, it appears that the battery is now
consuming 15 amps of charge current. But, the external shunt still senses 5 amps of charge current since it is
measuring net battery charge current. With the external shunt connected to the Solar Boost 3048 charge control
system, the charge control system properly measures charge current at 5 amps, producing optimal control of the
charge process despite changes in battery load during charge.
Float Transition Current Setpoint
The Float Transition Current setting controls when the system switches between acceptance and float. If
charge current is less than the Float Transition Current setpoint, the system will switch to float. If charge current
greater, the system will switch to acceptance. Set the Float Current potentiometer for a voltage on the “I Float”
relative to “Com” test point for 0.1 or 0.01V per amp of desired Float Transition Current as shown below. For
example, if battery capacity is 500 amp-hours requiring a Float Transition Current of 5.0 amps, and a 100mV/100A
shunt is used, set the “I Float” test point voltage to 0.50V. When using an external shunt, actual net battery current
can be measured on the “I Bat” test point relative to “Com” at the same scaling.
RVPP CURRENT SHUNT
PART NUMBER
CURRENT SHUNT
RATING
“I FLOAT” & “I BAT”
TEST POINT SCALING
MAX CURRENT
MEASUREMENT AT
“I BAT” TEST POINT
INTERNAL SHUNT
50A / 50mV
0.10V PER AMP
±
40 AMP
CS-100
100A / 100mV
0.10V PER AMP
±
40 AMP
CS-200
200A / 200mV
0.10V PER AMP
±
40 AMP
CS-500
500A / 50mV
0.01V PER AMP
±
400 AMP
When using the internal shunt measuring Output Charge Current, the Float Current potentiometer is also set
for a voltage on the “I Float” relative to “Com” test point of 0.1V per amp of desired Float Transition Current.
However, if battery load is a constant 10 amps, add 10 amps to the setting. For example, if the battery capacity is
500 amp-hours requiring a Float Transition Current of 5.0 amps (plus 10 amps of load), set the “I Float” test point
voltage to 1.50V for a setting of 15 amps. If load current is highly variable and the internal shunt is used, select a
Float Transition Current that allows the system to switch to float during light load and full charge conditions.
Maximum Power Voltage
The nominal setting for this adjustment is the difference between the PV module’s
open circuit voltage
(V
OC
)
and
maximum power voltage
(V
MP
). These voltage values are typically listed on both the PV module datasheet and
on the rating label affixed to each PV module. This value needs to be set correctly for the MPPT system to deliver
maximum current boost. The factory setting is 4.4 volts which is the appropriate value for popular modules. These
modules typically list V
OC
at
≈
21.4 volts and V
MP
at
≈
17.0 volts, which yields; 21.4V - 17.0V = 4.4V.
Solar Boost 3048 updates the maximum power operating point approximately every 10 seconds by briefly
turning off the output to sample PV open circuit voltage. It then operates the PV array at a voltage approximately
equal to the sampled open circuit voltage minus the MPPT voltage setting. Factors other PV open circuit voltage
fine tune the actual operating point, but PV open circuit voltage is the primary factor. Note that the values above and
the scaling shown on the MPPT adjust potentiometer in Figure 3 relate to a single 36 cell module. When two or four
modules are connected in series for a 24 or 48 volt input system, Solar Boost 3048 automatically multiplies the
voltage difference setting between V
OC
and V
MP
by two or four based on the position of dip switch 5.
SWITCH
5
ACTUAL MPPT
V
OC
- V
MP
OPERATING
RANGE
DEFAULT MPPT
V
OC
- V
MP
SETTING
NUMBER OF PV
MODULES IN
SERIES
NOMINAL PV
INPUT VOLTAGE
OFF
6V – 14V
8.8V
2
24V
ON
12V – 28V
17.6V
4
48V
