External Current Transformer (Optional); Frequency Shift; Built-In Battery Monitor; Autonomous Operation When The Grid Fails - Victron energy MultiPlus-II GX Manual

MultiPlus-II GX

5.2.1. 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. Contact your Victron Distributor for further information
about this installation type

5.2.2. Frequency shift

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

5.2.3. Built-in Battery Monitor

The ideal solution when the product 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.

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

5.3. Battery charger

5.3.1. 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.

5.3.2. Li-ion batteries

Victron LiFePO4 Smart batteries
Use the VE.Bus BMS
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