Run HWC dependent on battery SOC, and with remote switching through Cerbo

DIY
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1

System: 2x 5KVA MultiPlus II in parallel, BYD LVS 24kWh batteries, Cerbo, SmartSolar MPPTs.

I want to switch on the hot water cylinder circuit dependent on battery state of charge, e.g. HWC on at 95%, HWC off at 90%. I also want the circuit to be switchable through VRM relay switches.

Two questions:

  1. Can I use the K1 relay on the master inverter to drive a 12VDC contactor, which in turn drives a 230Vac contactor to turn the cylinder on and off?
  2. Can I run the 12VDC + from the K1 through the Cerbo NC relay and then to the 12VDC on the contactor so the circuit is switchable remotely?

If there is a better way to do it, please let me know!

TIA

Ross.

2

Have considered to switch the load via Shelly and use NodeRed to control the Shelly?

NodeRed is more easy to deploy and debug compared to some Victron assistants.

I personally have all my automation in Home Assistant integrated with the Cerbo via HACS MQTT integration.

3

I’ll look into that, thanks for the suggestion.

4

Using AC Out 2 and switching it using an Relay Assistant using SoC running the inverters is another alternative. You can get clever and hook an Aux input on the inverter to Relay 2 on the Cerbo, and then use Node-RED to control it.

But as @BjoernK suggested, doing the control logic somewhere else (Shelly + Node-RED on the Cerbo) can be easier.

Also, I believe the Shelly switching is soon to become much easier if you don’t want to play with Node-RED.

5

I prefer using Shelly‘s for non-critical control and high frequent switching, as it is easier to replace if the relais is damaged.

For critical, rare switching e.g. emergency disconnect I go for MP2 or Cerbo internal relais.
For those uses cases I do not want to rely on network working properly.