4. Operation
4.1. Charge algorithm
The Victron Blue Smart 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:
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 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.
The 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.
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.
Refresh
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 POWER and STATUS LEDs can be used to determine if the Blue Smart Charger is powered up or not, and the active charge stage; refer to the table below:
LED | State | Power / Charge Stage |
|---|---|---|
Power (green) | Illuminated | Power On |
Off | Power Off | |
Status (orange) | Fast blinking | Bulk |
Slow blinking | Absorption / Recondition / Refresh | |
Illuminated | Float / Power supply mode | |
Off | Storage |
4.2. Temperature compensation
The Victron Blue Smart 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.
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 24v chargers multiply the coefficient by 2) 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)
The MODE button is pressed or a new charge mode is selected
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
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 = 100/10 = 10 hours.
Including an absorption duration of Tabs = 8 hours, the total estimated charge time would be Ttotal = Tbulk + Tabs = 10 + 8 = 18 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.