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MultiPlus-II 120V

2. Description

In this section:

2.1. Boats, vehicles and other stand-alone applications

The basis of the MultiPlus-II is an extremely powerful sine inverter, battery charger and transfer switch in a compact casing.

Important features:

Automatic and uninterruptible switching

In the event of a supply failure or when the generating set is switched off, the MultiPlus-II will switch over to inverter operation and take over the supply of the connected devices. This is done so quickly that the operation of computers and other electronic devices is not disturbed (Uninterruptible Power Supply or UPS functionality). This makes the MultiPlus-II highly suitable as an emergency power system in industrial and telecommunication applications.

Two AC outputs

Besides the usual uninterruptable output (AC-out-1), an auxiliary output (AC-out-2) is available that disconnects its load in the event of battery operation. Example: an electric boiler that is allowed to operate only if the genset is running or shore power is available. There are several applications for AC-out-2.

Please enter “AC-out-2” in the search box on our website and find the latest information about other applications.

Three phase capability

Three units can be configured for three-phase output. Up to 6 sets of three units can be parallel connected.

PowerControl – maximum use of limited AC power

The MultiPlus-II can supply a huge charging current. This implies heavy loading of the AC mains or generator. Therefore a maximum current can be set. The MultiPlus-II then takes other power users into account, and only uses “surplus' current for charging purposes.

PowerAssist – Extended use of generator or shore current: the MultiPlus-II “co-supply” feature

This feature takes the principle of PowerControl to a further dimension allowing the MultiPlus-II to supplement the capacity of the alternative source. Where peak power is often required only for a limited period, the MultiPlus-II will make sure that insufficient AC mains or generator power is immediately compensated for by power from the battery. When the load reduces, the spare power is used to recharge the battery.

Programmable relay

The MultiPlus-II is equipped with a programmable relay. The relay can be programmed for different applications, for example as a starter relay for a generator.

External current transformer (optional)

External current transformer option to implement PowerControl and PowerAssist with external current sensing.

Programmable analog/digital input/output ports (Aux in 1 and Aux in 2, see appendix)

The MultiPlus-II is equipped with 2 analog/digital input/output ports.

These ports can be used for several purposes. One application is communication with the BMS of a lithium-ion battery.

2.2. On-grid and off-grid systems combined with PV

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.

Frequency shift

When solar inverters are connected to the output of a MultiPlus-II, 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 will slightly increase the AC frequency to reduce the output of the solar inverter.

Built-in Battery Monitor

The ideal solution when the MultiPlus-II 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.

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 and batteries, this problem can be solved: the MultiPlus-II can replace the grid during a power failure. When the sustainable energy sources produce more power than needed, the MultiPlus-II will use the surplus to charge the batteries; in the event of a shortfall, the MultiPlus-II will supply additional power from the battery.


All settings can be changed with a PC and free of charge software, downloadable from our website

2.3. Battery charger

2.3.1. 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

If, in order to quickly charge a battery, a high charge current in combination with a high absorption voltage has been chosen, damage due to excessive gassing will be prevented by automatically limiting the rate of voltage increase once the gassing voltage has been reached.

Less maintenance and aging when the battery is not in use: the Storage mode

The Storage mode kicks in whenever the battery has not been subjected to discharge during 24 hours. In the Storage mode float voltage is reduced to 2.2V/cell (13.2V for 12V battery) to minimise gassing and corrosion of the positive plates. Once a week the voltage is raised back to the absorption level to ‘equalize’ the battery. This feature prevents stratification of the electrolyte and sulphation, a major cause of early battery failure.

Battery voltage sense: the correct charge voltage

Voltage loss due to cable resistance can be compensated by using the voltage sense facility to measure voltage directly on the DC bus or on the battery terminals.

Battery voltage and temperature compensation

The temperature sensor (supplied with the product) serves to reduce charging voltage when battery temperature rises. This is particularly important for maintenance-free batteries, which could otherwise dry out by overcharging.

Two DC outputs for charging two batteries

The main DC terminal can supply the full output current. The second output, intended for charging a starter battery, is limited to 4A and has a slightly lower output voltage (12V and 24V models only).

2.3.2. Victron Lithium Battery 12.8V & 25.6V Smart

If Victron Lithium Smart batteries are used, use the VE.Bus BMS V2 or the Lynx Smart BMS.

2.3.3. Other lithium batteries

If other lithium batteries are used, follow this link for a list of compatible battery types and how to install and configure them:

2.3.4. More on batteries and battery charging

Our book "Energy Unlimited" offers further information on batteries and battery charging and is available free of charge on our website. It can be downloaded from:, or a hard copy can be ordered from:

For more information on adaptive charging, please refer to the technical paper: Adaptive charging, how it works.

2.4. ESS – Energy Storage Systems: feeding energy back into the grid

When the MultiPlus-II is used in a configuration in which it will feed back energy into the grid it is required to enable grid code compliance by selecting the appropriate grid code country setting with the VEConfigure tool.

Once set, a password will be required to disable grid code compliance or change grid code related parameters.

Depending on the grid code there are several reactive Power control modes:

  • Fixed cos φ

  • Cos φ as function of P

  • Fixed Q

  • Q as function of input voltage


Reactive Power capability

If the local grid code is not supported by the MultiPlus-II an external certified interface device should be used to connect the MultiPlus-II to the grid.

The MultiPlus-II can also be used as a bidirectional inverter operating parallel to the grid, integrated into a customer designed system (PLC or other) that takes care of the control-loop and grid measurement.