4. Operation
4.1. Charge algorithm
The Victron Phoenix Smart IP43 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 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 display the active charge state; refer to the image below:
4.2. Temperature compensation
The Victron Phoenix Smart IP43 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 for 12V chargers (-32.4mV/°C for 24V chargers) or as configured.
Notice
Note: 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. VE.Smart Networking
VE.Smart Networking enables Bluetooth connectivity and communication between multiple Victron products.
This powerful feature enables chargers to receive accurate battery voltage (Volt-sense), charge current (Current-sense) and battery temperature (Temp-sense) data from a compatible battery monitor (such as a BMV, SmartShunt, Smart Battery Sense or VE.Bus Smart Dongle) and/or multiple chargers to operate in unison with synchronised charging to further enhance the charge cycle.
4.3.1. Voltage, temperature and current sense
Voltage Sense uses battery voltage data that is accurately measured directly at the battery terminals (or very close) and provides it to the charger, the charger then uses this voltage data to dynamically increase the output voltage and precisely compensate for voltage drop in the cabling and connections between the charger and battery.
This enables the battery to be charged with the exact voltage as configured in the charger, instead of a lower voltage due to voltage drop in the cabling and connections.
Voltage drop is proportional to the charge current and cabling/connection resistance (V=IxR), so voltage drop will vary during a charge cycle and can be quite significant when charging at higher charge currents through cabling and connections with higher than optimal resistance; in this scenario voltage sense will be particularly beneficial.
Note that voltage sense does not allow inadequately rated cabling or connections to be used, for reliable and safe operation cabling and connections must always be rated to carry the maximum current (including the fault current required to blow the fuse/trip the breaker) in the particular installation conditions.
Temperature Sense uses battery temperature data that is accurately measured directly at a battery terminal or on the battery body and provides it to the charger, the charger then uses this temperature data to dynamically compensate the charge voltage (decrease or increase) according to the specified temperature coefficient (X mV/°C).
The optimal charge voltage of a lead acid based battery varies inversely with battery temperature with the nominal charge voltage specified at 25°C; automatic temperature-based charge voltage compensation avoids the need for manual charge voltage setting adjustments in hot or cold environments.
For lithium batteries the optimal charge voltage remains constant under all normal operating temperatures, however lithium batteries can be permanently damaged if charged in cold conditions; in this case the temperature sense data can be used to automatically disable charging in cold conditions (typically <5°C).
Current Sense uses battery current data that is measured by the battery monitor shunt (requires a BMV or SmartShunt) and provides it to the charger, the charger then references this current data (as opposed to the charger output current) for the tail current setting.
The tail current setting references the diminishing level of charge current (typical at the end of a full charge cycle) in relation to the trigger threshold to determine when the battery is fully charged and consequently when the absorption stage can be ended (prior to the absorption stage time limit being reached). The use of tail current to end absorption stage is a highly effective and common method used to properly charge lead acid based batteries.
In order to end the absorption phase at the correct point, it is important that the true current flow into the battery is referenced in relation to the tail current threshold, rather than the charger output current which may be significantly higher; if any loads are powered while charging a portion of the charger output current will be flowing directly to the loads, making the tail current condition more difficult or impossible to meet without current sense.
Multiple compatible chargers can be added to a common VE.Smart network and receive voltage, temperature and/or current sense data from the same battery monitor. Once multiple compatible chargers are in a common VE.Smart network their charge algorithms will also be syncronised, refer to the 'Synchronised charging' section for more information.
4.3.2. Synchronised charging
Synchronised charging capability enables multiple compatible chargers to be combined together in a common VE.Smart network, allowing the chargers to operate in unison as if they were one large charger.
The chargers will synchronise the charge algorithm between themselves with no further hardware or physical connections required, and simultaneously change charge states.
Synchronised charging works by systematically prioritising all chargers and assigning one as the 'master', this charger then controls the charge stage of all other 'slave' chargers. In case the initial 'master' is disconnected from the VE.Smart Network for any reason (out of Bluetooth range for example), another charger will be systematically reassigned as the 'master' and take over control; this can also be reversed if communication with the initial 'master' (that has a higher priority) is re-established. The 'master' charger can not be manually selected.
Synchronised charging does not regulate or equalise the current output of multiple chargers, each charger still has total control over it's own current output. Accordingly, current output variation between multiple chargers is normal (dependent on cable resistance and other factors) and a total system current output limit cannot be configured. For systems where a total system current output limit is important, consider using a GX device with DVCC instead.
Synchronised charging can be setup with different model chargers, providing they are VE.Smart Networking compatible (this includes VE.Smart Networking compatible Blue Smart chargers, Smart chargers and MPPT solar chargers). Charging from MPPT solar chargers is not prioritised over mains supply chargers, so in some installations (dependent on cable resistance and other factors) and charging conditions it is possible for solar power to be underutilised.
Synchronised charging can also be used in conjunction with a battery monitor (BMV, SmartShunt, Smart Battery Sense or VE.Bus Smart Dongle) to provide voltage, temperature and/or current sense data to the chargers in a common VE.Smart network, refer to the 'Voltage, temperature and current sense' section for more information.
In the absence of a battery monitor providing current-sense data (requires a BMV or SmartShunt), the charge current from each individual charger is combined by the 'master' and referenced against the tail current setting.
4.4. Multiple battery outputs
The 1+1 and 3 output charger models both have an integrated FET battery isolator and therefore feature seperate isolated outputs.
Multiple isolated outputs make it possible for a single charger to charge multiple batteries that are at a different voltage/SOC level, charge current will be prioritised to the battery/batteries that are at a lower voltage level.
The 1+1 output charger models can supply the full rated current from the main output, and the starter/auxiliary output is limited to a maximum of 4A; however the combined current of all outputs is limited to the full rated current.
The 3 output charger models can supply the full rated output current from all 3 outputs; however the combined current of all outputs is limited to the full rated output current.
Notice
Note: Multiple outputs are not regulated individually, one charge algorithm (charge cycle and charge voltage) is applied to all outputs.
Accordingly all batteries will typically need to be the same chemistry type, and compatible with the common charge algorithm.
4.5. 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 used to select a new charge mode.
VictronConnect is used to select a new charge mode or change the function from ‘Power Supply’ to ‘Charger’ mode
VictronConnect is used to disable and re-enable the charger (via the switch in the settings menu).
The remote terminals are used to disable and re-enable the charger (from an external switch or BMS signal)
The AC supply has been disconnected and reconnected
4.6. 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.
4.6.1. 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
4.6.2. 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