3.0
Installation Instructions
ProStar MPPT Operator’s Manual
27
26
STEP 1: Check Controller Limitations
Verify that the highest temperature compensated solar array
open-circuit voltage (Voc), and load current do not exceed
the ratings of the ProStar MPPT version being installed.
Multiple controllers can be installed in parallel on the same
battery bank to achieve greater total charging current. In
this type of system, each ProStar MPPT must have its own
solar array. The load terminals of multiple controllers can
only be wired together if the total load draw does not ex-
ceed the nameplate current of the LOWEST rated controller.
STEP
2: Battery Voltage Sense Wires
Due to connection and cable resistance, voltage drops are
unavoidable in power cables that carry current, including the
ProStar MPPT battery cables. If
Battery Sense
wires are not
used, the controller must use the voltage reading at the bat-
tery power terminals for regulation. This voltage may differ
from the actual battery bank voltage due to voltage drop.
Battery Voltage Sense
is a high impedance connection that
enables the ProStar MPPT to measure the battery termi-
nal voltage precisely with small gauge wires that have no
voltage drop. When connected directly to the battery, the
sense wires will improve battery charging accuracy. Battery
voltage sense wires are recommended if the controller is
more than three meters (10 ft) from the battery.
Generally accepted wiring practice is to limit voltage drops
between the charger and the battery to 2%. Even properly
sized wiring with 2% drop can result in a 0.3 volt drop for
14.4V charging. Voltage drops will cause some undercharg-
ing of the battery. The controller will begin Absorption or
limit equalization at a lower battery voltage because the
controller measures a higher voltage at the controller’s ter-
minals than is the actual battery voltage. For example, if the
controller is programmed to start Absorption at 14.4V, when
the controller "sees" 14.4 volts at its battery terminals,
the true battery voltage would only be 14.1 volts, if there is
a 0.3 volt drop between the controller and battery.
Note that the battery sense wires will not power the
controller, and the sense wires will not compensate for
losses in the power wires between the controller and the
battery. The battery sense wires are used to improve the
accuracy of the battery charging.
The two sense wires, can range in size from 1.0 to 0.25 mm
2
(16 to 24 AWG), and should be cut to length as required
to connect the battery to the voltage sense terminals. A
2-position terminal (see figure 3.3) is used for the battery
sense connection. A twisted pair cable is recommended but
not required. Use UL rated 300 Volt conductors. The voltage
sense wires may be pulled through conduit with the power
conductors.
Observing correct polarity, connect both battery voltage
sense wires to the ProStar MPPT at the 2-position
Battery
Sense
terminal, and to battery (+) and (-) terminals. No
damage will occur if the polarity is reversed, but the control-
ler cannot read a reversed sense voltage.
Tighten the connector screws to 5 in-lb (0.56 Nm) of torque.
The maximum length allowed for each battery voltage sense
wire is 98 ft (30 m).
Connecting the voltage sense wires to the RTS terminal will
cause an alarm.
NOTE:
If the battery input voltage is greater than 5 volts
different than the
Battery Sense
, due to voltage drops or
faulty connections, the
Battery Sense
input will not be recognized
by the ProStar MPPT.
A battery voltage sense connection is not required to
operate the ProStar MPPT controller, but it is recommended
for best performance.
