question

I had a similar requirement as export to grid is not yet supported in my country (Zambia) so I had to get thinking. The Victron relays unfortunately did not give me the flexibility I was looking for but I found this in an unlikely place: My lithium battery logger! I have a SolarMD 7.4kWh lithium battery which comes with an intelligent data logger which has two relays which can be activated according to expressions.

I have set NO on Relay1 to control Contactor 2 (Multi output to water heaters) and NC controls Contactor 1 (grid to water heater).So ordinarily C1 is closed and the supply source is grid.

I had need to control two heaters independently so I came up with two additional contactors C3 and C4. C3 is controlled by Relay 2 and has an auxiliary control attached which opens or closes Relay1 NO signal to C4.

C1 & C2 are Load shift circuits so they move power source between Grid and Inverter.

The shifted power source is routed to C3 and C4 which now power Heater 1 and Heater 2.

The Battery Logger allows me to work out this logic:

Relay1:

1. 
   
   • Target: Switch ON
   • Schedule: Time: 10:0 - 15:0 Week: [Disabled]
   • Delay Expire
   • 
     
   • First Expresion Result: [true]
     • 
       
     • Combined Storage -> bank1 -> Capacity [99.58%] Greater Than 98.00
   • Evaluation: true
2. 
   
   • Target: Switch OFF
   • Schedule: Time: 12:0 - 17:0 Week: [Disabled]
   • Remaining time: 30sec
   • 
     
   • First Expresion Result: [true]
     • 
       
     • Combined Storage -> bank1 -> Capacity [0.00%] Less Than 90.00
   • Evaluation: false
3. 
   
   • Target: Switch OFF
   • Schedule: Time: 15:30 - 17:59 Week: [Disabled]
   • Delay: No Delay
   • 
     
   • First Expresion Result: [true]
     • 
       
     • [N/A ]
   • Evaluation: false

Relay2:

1. 
   
   • Target: Switch ON
   • Schedule: Time: 10:0 - 13:0 Week: [Disabled]
   • Delay: No Delay
   • 
     
   • First Expresion Result: [true]
     • 
       
     • Single Storage -> SMDBEM10303860 -> Capacity [100.00%] Greater Than 98.00
   • Evaluation: true
2. 
   
   • Target: Switch OFF
   • Schedule: Time: 13:0 - 17:0 Week: [Disabled]
   • Delay: No Delay
   • 
     
   • First Expresion Result: [false]
     • 
       
     • Single Storage -> SMDBEM10303860 -> Capacity [98.00%] Less Than 90.00
   • Evaluation: false
3. 
   
   • Target: Switch OFF
   • Schedule: Time: 13:30 - 18:0 Week: [Disabled]
   • Delay Expire
   • 
     
   • First Expresion Result: [true]
     • 
       
     • [N/A ]
   • Evaluation: false

Is it 10am? Is the battery SOC >98%? If so then activate Relay1 NO and in so doing open NC and the effect of this is that the Inverter supply is connected via C2 as C1 opens. There is also a settable delay in effecting this if so wished.

C3 activates and breaks through its auxiliary control signal to C4 which remains open. C3 closes the C2 supply to Heater1. At 1pm thereabouts C3 opens and H1 is switched off but signal continues through auxiliary to C4 which closes and power goes to Heater2. At 3.30pm or so Heater2 is switched off as C1 closes as the Relay1 opens NO and closes NC.

If anytime during this period battery SOC drops below 90% the circuit takes the load back to grid. After 3pm any battery used is replenished by remaining PV.

There are two Timers through which the C3 and C4 outputs are routed on the NC legs (passthrough) to the heaters as I time when and how long the water heaters are on in the morning on grid.

If Victron had such programmable Relay i.e Time of day, day of week, SOC or PV yield based then I wouldn't need to use the battery smart relay.

I have a 2kW and 1.5kW water heater. My typical daytime load is about 400-500W before adding the heaters. I have a 5KVA Multi so I do not run the heaters at the same time. This application helps me utilise the PV which would otherwise be wasted once the battery is charged.

You can see this in operation until 3pm (Central African Time) on VRM: https://vrm.victronenergy.com/installation/87104/share/80d299b4

Unfortunately I was getting errors trying to attach images!