4. Operation
4.1. Charge algorithm
The 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 when configured as a 6V charger) or 2 minutes have elapsed.
If reverse polarity, short circuit or excessively high battery voltage is detected the battery will be rejected, and an error will be indicated by the LEDs; in the event of an error, disconnect the AC mains power source before attempting to diagnose and rectify the issue.
A false rejection may occur if attempting to charge a deeply discharged battery while it is simultaneously connected to a load; in this case all loads should be isolated before attempting to charge again.
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 (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:
Alternatively, a Bluetooth enabled device (mobile phone or tablet) with the VictronConnect app can be used to view the active charge state; refer to the 'Monitoring > VictronConnect' section for more information.
4.2. Temperature compensation
The Blue Smart IP65 Charger range feature temperature compensation, which will automatically optimise the nominal/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 for 12V chargers (-8.1mV/°C when in 6V mode) or as configured.
Refer to the graph below for the default temperature vs charge voltage curve for 12V chargers:
Notice
The temperature compensation coefficient is specified in mV/°C and applies to the entire battery/battery bank (not per battery cell).
If the battery manufacturer specifies a temperature compensation coefficient per cell, it will need to be multiplied by the total number of cells in series (there are typically 6 cells in series within a 12V lead-acid based battery).
4.3. Commencing a new charge cycle
A new charge cycle will commence when:
The configured Re-bulk condition is satisfied (typically due to a large load):
Re-bulk current is disabled (default configuration): The current output must be maintained at the maximum current output for four seconds.
Re-bulk current is configured with a user defined value: The current output must exceed the configured Re-bulk current for four seconds while the charger is in float or storage stage.
VictronConnect is used to select a new charge mode or change the function from Power Supply to Charger mode.
The power supply to the AC power supply has been disconnected and reconnected.
Notice
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
The time required to recharge a battery to 100% SOC (state of charge) is dependant on the battery capacity, the depth of discharge, the charge current and the battery type/chemistry, which has a significant effect on the charge characteristics.
4.4.1. Lead-acid based chemistry
A lead-acid battery is normally 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.
The absorption stage duration Tabs will vary depending on the depth of discharge; up to 8 hours of absorption may be required for a deeply discharged battery to reach 100% SOC.
For example, the time required to recharge a fully discharged Lead-acid based 100Ah battery with a 10A charger would be approximately:
Bulk stage duration, Tbulk = 100Ah x 80% / 10A = 8 hours
Absorption stage duration, Tabs = 8 hours
Total charge duration, Ttotal = Tbulk + Tabs = 8 + 8 = 16 hours
4.4.2. Li-ion based chemistry
A Li-ion based battery is normally well above 95% 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 95% SOC.
The absorption stage duration Tabs required to reach 100% SOC is typically less than 30 minutes.
For example, the charge time of a fully discharged 100Ah battery when charged with a 10A charger to approximately 95% SOC is Tbulk = 100 x 95% / 10 = 9.5 hours.
For example, the time required to recharge a fully discharged Li-ion based 100Ah battery with a 10A charger would be approximately:
Bulk stage duration, Tbulk = 100Ah x 95% / 10A = 9.5 hours
Absorption stage duration, Tabs = 0.5 hours
Total charge duration, Ttotal = Tbulk + Tabs = 9.5 + 0.5 = 10 hours