SunSynk Hybrid Inverter/Charger Integration

Introduction / Important Note

This article explains how to interface SunSynk 48V Hybrid Inverter/Chargers with Redflow BMS+ZBM clusters.

This documentation is limited to explaining the differences and requirements to interface Redflow ZBMs rather than Lead-Acid or Lithium batteries into an otherwise standard SunSynk based energy system.

If you plan to integrate SunSynk products into energy systems, you need to obtain appropriate training to do so.

Redflow does not offer SunSynk system integration training generally, nor does it offer SunSynk operational support.

Redflow's ambit here is limited to ensuring that the Redflow BMS+ZBM combination are successfully interfaced and able to transfer energy to and from the SunSynk products.

Once integrated, the combination is operated by the SunSynk system just as it if was running a Lithium battery array - the BMS-to-Inverter communication protocol is the same. 

Firmware Requirements

For successful operation:

• The Redflow BMS must be running BMS version 1.13 or later
• The BMS must be supplying CANBus data to the inverter/charger at all times

CANBus Cable

The Redflow BMS must be cabled to the SunSynk device using a CANBus cable.

There is an RJ45 CANBus input socket on the SunSynk device.

The simplest way to make a cable is to cut one end from a standard RJ45 cable and wire the appropriate wires into the Redflow BMS screw terminals.

As per the diagram below, the relevant pins on the inverter-side RJ45 plug are pins 4, 5 and 6.

Simply connect these to the labelled screw terminals on the Redflow BMS.

(The ground pin is actually optional - CANBus cables will work without it)

Redflow BMS Configuration

Beyond normal BMS and CANBus configuration, one checkbox needs to be turned on, in order for the SunSynk unit to successfully 'activate' a totally discharged battery.

This checkbox is available in Redflow BMS version 1.13 onward and is located in the menu system at 'Config->EMS Integration', on the 'CANbus' tab. It is called "Send Override Values to Support Black Start".

Simply turn this on and hit 'Submit' - see screen shot below:

This flag causes the BMS to send appropriate synthetic voltage reading values to the SunSynk inverter whenever the ZBM battery array is totally discharged. This functionality is required for successful use of the SunSynk the "Battery Activation" function.

SunSynk Unit Configuration

Review all configuration pages and consider appropriate settings for your Redflow battery array.

Review especially all tabs under the 'Batt Setting' pages.

On the Battery Setup tab shown below, configure as follows:

• Batt Capacity in Ah set to "Number of ZBM's x 200"
• Charge Amps set appropriately (it acts as a global constraint that overrides CANBus-sent values)
• Discharge Amps set appropriately as well
• "Batt Type" set to "Lithium'
• 'Activate' is checked (enables the 'Battery Activation' function to start up ZBMs from empty)

On the Battery Setup tab shown below, the shutdown/restart percentages set to values reasonable for Redflow batteries, for instance:

Make sure to set the grid settings page parameters appropriately to your AC grid standard and situation (e.g. AS4777 for Australia):

Verifying CANBus Communication

You can verify that the Redflow BMS is sending CANBus data and that the SunSynk is properly 'hearing' it by bringing up the battery status page (see example below).

A page display that is showing a different output format to the below (and a lack of useful data) indicates that the CANBus communication process is not yet operating correctly.

Battery "Activation" (black-start of a fully a discharged Redflow array)

The SunSynk product has a 'Battery Activation' function, designed to recover batteries that have run flat. This function operates to successfully bring up a Redflow battery array from empty (zero volts).

The battery 'Activation' function does not commence operation until the unit has been powered up for ten minutes.

At the ten minute mark and providing the unit has a reason to charge generally (see next point), the system starts to slowly ramp up the DC battery bus voltage.

The process of ramping this voltage can take a few minutes, before the voltage rises to the point where the Redflow system is able to complete its normal 'bubble purge' and 'pre-charge' functions and then commence normal battery functionality.

Two examples of conditions that will lead to the system Activating and then charging the battery (after ten minutes) are:

• DC solar is present at a power level exceeding local site energy demands (i.e. 'surplus solar' exists); OR
• There is an AC grid connected and the system has been programmed to undertake grid-based charging of the battery

Battery Activation Limitations

SunSynk products have limitations (as at mid 2023) that can stop the 'Battery Activation' function from working properly.

In particular these hardware limitations mean these products will not activate a battery from AC power, and that the AC grid input needs to be disconnected in order for battery activation to succeed from DC Solar energy.

A work-around for the battery black-start limitation

It is possible to attach a suitable current-limited DC power supply to the DC battery bus, to overcome the limitation noted above and to achieve automatic, unattended black-start in the field from AC grid energy.

Please see  this article for details of a suitable power supply unit that can be used for this purpose. This article explains how to connect and configure this support power supply to ensure that the system can self-recover after total site energy discharge.

Notes on Fault/Warning indications

• An "F31 AC SlaveConductor_Fault", should it be shown on the "Device Info" (alarms/warnings) page of a SunSynk unit, just means that there was an unsuccessful attempt at a Battery Activation cycle. These cycles re-try automagically, and no action is required in response to this fault indication as such.
• If activation repeatedly fails, review the activation limitations notes (above) - you may need to manually intervene to achieve initial battery activation.
• A 'W31 Battery_Comm_warn" warning, should it be shown on the Device Info page, indicates that the battery activation process was interrupted due to an unexpected value being sent by the Redflow BMS to the unit. This usually means that the Black Start support flag (see above) has not been enabled in the Redflow BMS. Turn that flag on and try again, and this warning should disappear.

Caveats

• If the battery electrolyte temperature is below 15C the system won't be able to complete the initial activation from empty until that temperature rises above 15C. Once the battery starts to charge, it can keep itself warm 'on its own' from then on (even if the ambient temperature falls far below 15C).