4.2. # Features specific On-grid and off-grid systems combined with PV
4.2.1. # External current transformer (optional)
When used in a grid-parallel topology the internal current transformer cannot measure the current to or from the
mains. In this case an external current transformer has to be used. See appendix A.
4.2.2. # Frequency shift
When solar inverters are connected to the output of a MultiPlus-II GX, excess solar energy is used to recharge the
batteries. Once the absorption voltage is reached, charge current will reduce and excess energy will be fed back into
the mains. If the mains is not available, the MultiPlus-II GX will slightly increase the AC frequency to reduce the
output of the solar inverter.
4.2.3. # Built-in Battery Monitor
The ideal solution when the MultiPlus-II GX is part of a hybrid system (diesel generator, inverter/chargers, storage
battery, and alternative energy). The built-in battery monitor can be set to start and stop the generator:
Start at a preset % discharge level, and/or
start (with a preset delay) at a preset battery voltage, and/or
start (with a preset delay) at a preset load level.
Stop at a preset battery voltage, or
stop (with a preset delay) after the bulk charge phase has been completed, and/or
stop (with a preset delay) at a preset load level.
4.2.4. # Autonomous operation when the grid fails
Houses or buildings with solar panels or a combined micro-scale heating and power plant or other sustainable
energy sources have a potential autonomous energy supply which can be used for powering essential equipment
(central heating pumps, refrigerators, deep freeze units, Internet connections, etc.) during a power failure. A problem
is however that grid connected sustainable energy sources drop out as soon as the grid fails. With a MultiPlus-II GX
and batteries, this problem can be solved: the MultiPlus-II GX can replace the grid during a power failure. When the
sustainable energy sources produce more power than needed, the MultiPlus-II GX will use the surplus to charge the
batteries; in the event of a shortfall, the MultiPlus-II GX will supply additional power from the battery.
4.3. # Battery charger
4.3.1. # Lead-acid batteries
Adaptive 4-stage charge algorithm: bulk – absorption – float – storage
The microprocessor-driven adaptive battery management system can be adjusted for various types of batteries. The
adaptive function automatically adapts the charging process to battery use.
The right amount of charge: variable absorption time
In the event of slight battery discharge, absorption is kept short to prevent overcharging and excessive gas
formation. After deep discharging, the absorption time is automatically extended in order to fully charge the battery.
Preventing damage due to excessive gassing: the BatterySafe mode
