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MPPT solar charger manual

6. Operation

In this section:

6.1. Start up

The solar charger will power up as soon as it has been connected to a battery and/or to a solar panel. As soon as the solar charger has been powered up, it can communicate via the VE.Direct port and Bluetooth. The solar charger's data can be read out and setting configurations can be made using the VictronConnect or the optional display.

The solar charger will commence battery charging as soon as the PV voltage is 5V higher than the battery voltage. For charging to continue, the PV voltage must remain at least 1V higher than the battery voltage.

6.2. Battery charging

The charge controller will start a new charge cycle every morning, when the sun starts shining and when the PV voltage is 5V higher than the battery voltage.

Default method to determine length and end of absorption for Lead-acid batteries

The charging algorithm behaviour of solar chargers differ from AC connected battery chargers. Please read this section of the manual carefully to understand the solar charging behaviour, and always follow the recommendations of your battery manufacturer.


The voltage values mentioned in this chapter are for 12V systems, for 24V systems multiply by 2 and for 48V systems multiply by 4.

By default, the absorption time is determined on idle battery voltage at the start of each day based on the following table:

Battery voltage at start up


Maximum absorption time

< 11.9V

x 1


11.9V - 12.2V

x 0.66


12.2V - 12.6V

x 0.33


> 12.6V

x 0.16


The default absorption voltage is 14.4V and the default float voltage is 13.8V.

The absorption time counter starts once switched from bulk to absorption.

The MPPT solar chargers will also end absorption and switch to float when the battery current drops below a low current threshold limit, the "tail current". The default tail current value is 2A.

The default settings (voltages, absorption time multiplier and tail current) can be modified with the VictronConnect app.

There are two exceptions to normal operation:

  • When used in an ESS system; the solar charger algorithm is disabled; and instead it follows the curve as mandated by the inverter/charger.

  • For CAN-bus Lithium batteries, like BYD, the battery tells the system, including the solar charger, what charge voltage to use. This Charge Voltage Limit (CVL) is for some batteries even dynamic; changes over time; based on for example maximum cell voltage in the pack and other parameters.

Variations to the expected charging behaviour

  • Pausing of the absorption time counter:

    The absorption time counter starts when the configured absorption voltage is reached and pauses when the output voltage is below the configured absorption voltage. An example of when this voltage drop could occur is when PV power (due to clouds, trees, buildings) is insufficient to charge the battery and to power the loads.

  • Restarting the charge process:

    The charging algorithm will reset if charging has stopped for an hour. This may occur when the PV voltage drops below the battery voltage due to bad weather, shade or similar.

  • Battery being charged or discharged before solar charging begins:

    The automatic absorption time is based on the start-up battery voltage (see table). This absorption time estimation can be incorrect if there is an additional charge source (eg alternator) or load on the batteries. This is an inherent issue in the default algorithm. However, in most cases it is still better than a fixed absorption time regardless of other charge sources or battery state. It is possible to override the default absorption time algorithm by setting a fixed absorption time when programming the solar charge controller. Be aware this can result in overcharging your batteries. Please see your battery manufacturer for recommended settings.

  • Absorption time determined by tail current:

    In some applications it may be preferable to terminate absorption time based on tail current only. This can be achieved by increasing the default absorption time multiplier (warning: the tail current of lead-acid batteries does not decrease to zero when the batteries are fully charged, and this “remaining” tail current can increase substantially when the batteries age).

Default settings for LiFePO4 batteries

The default absorption voltage is to 14.2V (28.4V, 56.8V) and the absorption time is fixed and set to 2 hours. The float voltage is set at 13.5V (27V, 54V). Equalization is disabled. The tail current is set to 0A, this so that the full absorption time is available for cell balancing. The temperature compensation is disabled and the low temperature cut off is set to 5. These settings are the recommended settings for LiFePO4 batteries, but they can be adjusted if the battery manufacturer specifications advise otherwise.

Reset of the charge algorithm:

The default setting for restarting the charge cycle is Vbat < (Vfloat – 0.4 V) for lead-acid, and Vbat (Vfloat – 0.1 V) for LiFePO4 batteries, during 1 minute. These values are for 12 V batteries, multiply by two for 24V and by four for 48V.

6.3. Automatic equalization


Do not equalize charge Gel, AGM, VRLA or lithium batteries.

Equalization can cause damage to the battery if the battery is not suitable for an equalization charge. Always check with the battery manufacturer prior to enabling equalization.

Automatic equalization is by default disabled. When enabled, it can be configured with a number between 1 (every day) and 250 (once every 250 days).

When automatic equalization is active, the absorption charge will be followed by a voltage limited constant current period. The current is by default limited to 8% of the bulk current and can be adjusted between 0% and 100%. The bulk current is set by default to the maximum charge current the solar charger is capable of, unless a lower charge current has been chosen.

The maximum equalization duration is set by default to 1 hour and can be configured between 0 minutes and 24 hours. The automatic equalization will end when the voltage limit has been reached or when the set maximum equalization duration has been reached, whichever comes first.

When automatic equalization has not finished within a day, it will not resume the next day. The next equalization session will take place as determined by the day interval.

6.4. Lithium batteries

Lithium Iron Phosphate (LiFePo4) batteries do not need to be fully charged to prevent premature failure. The default lithium (and recommended) settings are:


Absorption voltage

Absorption time

Float voltage

12V system




24V system




48V system




These settings are adjustable.

6.5. Shutdown and restart procedure

The solar charger is always active when the PV and/or the battery terminals are powered. The solar charger does not have an on/off switch.

To shut down the solar charger, perform these steps in the prescribed order:

  1. Disconnect the PV supply to the solar charger by switching the PV supply off or by removing the external fuse(s) or circuit breaker(s).

  2. Disconnect the battery supply to the solar charger by switching the battery supply off or by removing the exterenal fuse(s) or circuit breaker(s).

To restart the solar charger after it was shutdown, perform these steps in the prescribed order:

  1. Connect the battery supply to the solar charger by switching the battery supply on or by inserting the external fuse(s) or circuit breaker(s).

  2. Reconnect the PV supply to the solar charger by switching the PV supply on or by inserting the external fuse(s) or circuit breakers(s).

6.6. Maintenance procedure

The solar charger does not need regular maintenance.