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Questions about using relay to trigger water heater

I'm planning to enable the water heater when charge is 90% and disable it at 80%. Since the draw is higher then what the solar panels charge this will prevent the batteries from ever getting fully charged. Is there any way to use the charge cycle management to ignore a the enable heater rule once every month when it is set to charge the batteries to 100%?

The water heater is 230V AC and is run from the inverter, would it be possible to control from a relay with this:
between the inverter and the heater element or would you recommend something else?



The charge cycle management feature cannot interfere or override a command sent by a trigger (in your case the trigger you create for the enable heater rule).  This is for your safety!

Triggers are a key component in the way the BMS implements safety measures and always have priority over the commands that could be sent by the Charge Cycle Management feature.   Therefore a trigger command cannot be overridden by the charge cycle management instructions.

In your scenario the water heater will stop automatically once the water is hot, therefore allowing for further charging of the battery.  

The 230V AC relay you suggest is a reputable brand and can be directly commanded by a BMS output.  Each contact can handle up to 150A, so one contact should be enough to power the water heater  (there are 3 contacts on the proposed model!).  As you suggest this relay is to be placed between the inverter and the water heater (inverter 230V output -- fuse or circuit breaker -- relay ---------------------------------------------------- water heater)