4. Operation
4.1. Charge algorithm
The Victron Blue Smart IP65 Charger range are intelligent multi-stage battery chargers, specifically engineered to optimise each recharge cycle and charge maintenance over extended periods.
The multi-stage charge algorithm includes the individual charge stages described below:
Test
Before the charge cycle commences the battery is tested to determine if it will accept charge, even if the battery is fully discharged (close to 0V open circuit voltage) it may successfully accept charge.
The test stage will continue until a charge pulse is able to increase the battery voltage above 12.5V (6.25V for a 6V battery) or 2 minutes have elapsed.
If there is a clear issue such as reverse polarity connection, a short circuit or if the charger is connected to a higher voltage battery, the battery will be rejected, and an error will be indicated; in this case the AC mains power source should be disconnected before checking the DC wiring/connections and rectifying the issue.
A reverse polarity connection will cause the 'reverse polarity' LED to be illuminated, all other error states are indicated by the '12V' (green) and '6V' (orange) LEDs blinking fast.
Bulk
The battery is charged at maximum charge current until the voltage increases to the configured absorption voltage.
The bulk stage duration is dependent on the battery’s level of discharge, the battery capacity and the charge current.
Once the bulk stage is complete, the battery will be approximately 80% charged (or >95% for Li-ion batteries) and may be returned into service if required.
Absorption
The battery is charged at the configured absorption voltage, with the charge current slowly decreasing as the battery approaches full charge.
The default absorption stage duration is adaptive and intelligently varied depending on the battery’s level of discharge – this is determined from the duration of the bulk charge stage.
Adaptive absorption stage duration can vary between a minimum of 30 minutes, up to a maximum limit of 8 hours (or as configured) for a deeply discharged battery.
Alternatively, fixed absorption duration can be selected; fixed absorption duration is the automatic default when Li-ion mode is selected.
Absorption stage can also be ended early based on the tail current condition (if enabled), which is when the charge current drops below the tail current threshold.
Recondition
The battery voltage is attempted to be increased to the configured recondition voltage, while the charger output current is regulated to 8% of the nominal charge current (for example - 1.2A maximum for a 15A charger).
Recondition is an optional charge stage for lead acid batteries and not recommended for regular/cyclic use - use only if required, as unnecessary or overuse will reduce battery life due to excessive gassing.
The higher charge voltage during recondition stage can partially recover/reverse battery degradation due to sulfation, typically caused by inadequate charging or if the battery is left in a deeply discharged state for an extended period (if performed in time).
The recondition stage may also be applied to flooded batteries occasionally to equalise individual cell voltages and prevent acid stratification.
Recondition stage is terminated as soon as the battery voltage increases to the configured recondition voltage or after a maximum duration of 1 hour (or as configured).
Note that in certain conditions it is possible for the recondition state to end before the configured recondition voltage is achieved, such as when the charger is simultaneously powering loads, if the battery was not fully charged before recondition stage commenced, if the recondition duration is too short (set to less than one hour) or if the charger output current is insufficient in proportion to the capacity of the battery/battery bank.
Float
The battery voltage is maintained at the configured float voltage to prevent discharge.
Once float stage is commenced the battery is fully charged and ready for use.
The float stage duration is also adaptive and varied between 4 to 8 hours depending on the duration of the absorption charge stage, at which point the charger determines the battery to be in storage stage.
Storage
The battery voltage is maintained at the configured storage voltage, which is slightly reduced compared to the float voltage to minimise gassing and extend battery life whilst the battery is unused and on continuous charge.
Repeated absorption
To refresh the battery and prevent slow self-discharge while in storage stage over an extended period, a 1 hour absorption charge will automatically occur every 7 days (or as configured).
The indicator LEDs can be used to determine the active charge state; refer to the image and table below:
4.2. Temperature compensation
The Victron Blue Smart IP65 Charger range will automatically compensate the configured charge voltage based on ambient temperature (except for Li-ion mode or if manually disabled).
The optimal charge voltage of a lead acid battery varies inversely with battery temperature; automatic temperature-based charge voltage compensation avoids the need for special charge voltage settings in hot or cold environments.
During power up the charger will measure its internal temperature and use that temperature as the reference for temperature compensation, however the initial temperature measurement is limited to 25°C as it’s unknown if the charger is still warm from earlier operation.
Since the charger generates some heat during operation, the internal temperature measurement is only used dynamically if the internal temperature measurement is considered reliable; when the charge current has decreased to a low/negligible level and adequate time has elapsed for the charger’s temperature to stabilise.
For more accurate temperature compensation, battery temperature data can be sourced from a compatible battery monitor (such as a BMV, SmartShunt, Smart Battery Sense or VE.Bus Smart Dongle) via VE.Smart Networking - refer to the 'Operation - VE.Smart Networking’ section for more information.
The configured charge voltage is related to a nominal temperature of 25°C and linear temperature compensation occurs between the limits of 6°C and 50°C based on the default temperature compensation coefficient of -16.2mV/°C (-32.4mV/°C for 24V chargers / -8.1mV/°C for 6V chargers) or as configured.
The temperature compensation coefficient is specified in mV/°C and applies to the entire battery/battery bank (not per battery cell).
4.3. Commencing a new charge cycle
A new charge cycle will commence when:
Bulk stage is complete and the current output increases to the maximum charge current for four seconds (due to a simultaneously connected load)
If re-bulk current is configured; the current output exceeds the re-bulk current in float or storage stage for four seconds (due to a simultaneously connected load)
VictronConnect is used to select a new charge mode or change the function from ‘Power Supply’ to ‘Charger’ mode
The AC supply has been disconnected and reconnected
Notice
Note: In the event that the DC cables are disconnected/isolated from the battery and/or load while the charger is powered by the AC supply, it is recommended to allow 5 seconds for the charger to reinitialise before the DC cables are reconnected and a new charge cycle is commenced.
4.4. Estimating charge time
A lead acid battery is at approximately 80% state of charge (SOC) when the bulk charge stage is completed.
The bulk stage duration Tbulk can be calculated as Tbulk = Ah / I, where I is the charge current (excluding any loads) and Ah is the depleted battery capacity below 80% SOC.
An absorption period Tabs of up to 8 hours may be required to fully recharge a deeply discharged battery.
For example, the charge time of a fully discharged 100Ah battery when charged with a 10A charger to approximately 80% SOC is Tbulk = 100 x 80% / 10 = 8 hours.
Including an absorption duration of Tabs = 8 hours, the total estimated charge time would be Ttotal = Tbulk + Tabs = 8 + 8 = 16 hours. A Li-ion battery is more than 95% charged at the end of the bulk stage and reaches 100% charge after approximately 30 minutes of absorption charge.