Blue Sky SC30 - Manual (Page 7)

Installation and Operation Manual
6
MAXIMUM SETPOINT VOLTAGE LIMIT
The maximum setpoint voltage limit is not a charge voltage setting but rather places a maximum limit or ceiling on the charge voltage setpoint actually
used by the SC30 in all charge modes. Regardless of setpoint values entered by the user or how setpoints may adjust due to temperature compensation the
SC30 will not use a charge voltage setpoint greater than the maximum setpoint voltage limit factory set to 15.5V. The purpose of the maximum setpoint voltage
limit is to prevent charge voltage from getting so high that Inverters or other equipment shut down due to excess voltage. Note that actual battery voltage
may briefly exceed this value by perhaps 0.1 – 0.2V as the voltage control system responds to sudden changes in loads or available PV current.
PULSE WIDTH MODULATION
The SC30 uses Pulse Width Modulation (PWM) charge voltage control. When battery voltage is below the present charge voltage setpoint the PV module is
continuously connected to the battery to deliver maximum charge current. Once the battery recovers sufficient charge for voltage to rise to the charge voltage
setpoint, charge current must be reduced to regulate battery voltage or voltage would continue to climb. When a reduction in charge current is necessary the PWM
control system reduces average current delivery by rapidly connecting and disconnecting the PV module at a fixed frequency of 50Hz. The rapid on/off switching of
PV charge current may produce a slight 50Hz buzzing sound which may come from the SC30 or user installed wiring.
If only 80% of the available PV current is required to hold battery voltage at setpoint the PV is connected (or turned on) for 80% of the time and remains off
for 20% of the time. The control system varies or “modulates” the ON time “pulse width” percentage as necessary to control battery voltage, hence the term Pulse
Width Modulation. Because charge current is either full on or full off during PWM control the battery provides a very important voltage filtering function in a PWM
control system due to its very stiff resistance to changing voltage quickly. Therefore a battery must always be connected to provide proper voltage control.
PANEL TEMPERATURE AND THERMAL PROTECTION
Internal power control devices use the front panel as a heatsink. It is normal for the front panel to become quite warm to the touch when the SC30 is
operating at high power. When mounted to a vertical surface with good ventilation, the SC30 can deliver full output in an ambient temperature of up to 45 °C
(113 °F). If an over temperature condition exists, the SC30 will simply cycle on and off to keep internal temperature within acceptable limits.
INSTALLATION
¾ WARNING: The SC30 is designed for use with 12 volt DC electrical systems only. Read, understand and follow the Important
Safety Instructions in the beginning of this manual before proceeding. This unit must be installed and wired in accordance with
National Electrical Code, ANSI/NFPA 70. Over current protection must be provided externally. To reduce the risk of fire, connect to
a circuit provided with 40 amp maximum branch-circuit over current protection in accordance with National Electrical Code,
ANSI/NFPA 70. Do not connect a PV array capable of delivering greater than 27 amps short circuit current (I
SC
) or 24 volts open
circuit voltage (V
OC
) at STC. Do not connect BAT– & PV– together external to the unit. To reduce risk of electric shock or product
damage, remove all power before installing or servicing. Figure 3 shows generalized connections only is not intended to show all
wiring, circuit protection and safety requirements for a photovoltaic electrical system.
¾ CAUTION: The SC30 is protected against reverse battery polarity, short duration reverse PV polarity, and swapped PV and
battery connections. The SC30 will be damaged by long duration reverse PV, reverse battery to the PV terminals, and voltage in
excess of 30 volts on the battery or PV terminals.. Damage resulting from these user induced faults voids the limited warranty.
SELECTING PV MODULES
The SC30 is designed to work with 12V PV modules only. Higher voltage modules or input power sources other than PV modules will damage the SC30 in
a manner which voids the limited warranty. Voltage, current and power produced by PV modules vary widely with operating conditions. As a result a set of test
conditions referred to as Standard Test Conditions or STC are used to rate modules in a meaningful manner and the manufacturer’s published STC ratings
that must be used when selecting PV modules. STC ratings are not maximum or optimal ratings. Operating conditions can be present where PV voltage and
current may exceed published STC ratings which is why PV module voltage and current must be limited to the values shown below. While conditions may be
present where V
OC
, I
SC
& I
MP
exceed STC ratings, in real world conditions actual charge current typically seen may only be about 75 – 80% of I
MP
at STC.
Key PV module specifications;
P
MAX
Maximum power in watts (P
MAX
= V
MP
x I
MP
)
V
OC
Voltage with module open circuit (typically ≈20 – 23V for 12V nominal modules)
V
MP
Voltage where module produces Maximum Power (typically ≈17 – 18V for 12V nominal modules)
I
MP
Current where module produces Maximum Power
I
SC
Current with module Short Circuit
Select PV modules that DO NOT exceed the maximum ratings below and preferably deliver at least 3 amps I
MP
per 100 amp-hours of battery capacity.
Maximum PV Power @
STC
Maximum PV
Isc @ STC
Maximum PV
V
OC
@ STC
Recommended range of V
MP
at STC
Nominal 12V PV
450W 27.0A 24.0V 16.0 – 19.0V
ELECTROSTATIC HANDLING PRECAUTIONS
All electronic circuits may be damaged by static electricity. To minimize the likelihood of electrostatic damage, discharge yourself by touching a water faucet
or other electrical ground prior to handling the SC30. The risk of electrostatic damage is highest when relative humidity is below 40%.