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jakudo avatar image
jakudo asked

Use of overflow to heat water

Hi,

I have a novice (perhaps stupid) question regarding use of overflow (not sure whether that is the correct therm) to heat water.

I have a Cerbo GX + 3x Multiplus II 48V/3000 + pylontech batteries. The system is ESS.

I also have a water tank and electric heater (2 kW) in it.

How should I manage the electricity when the battery is full and the overflow is going back to grid, so in that case the electric heater will turn on and store the energy to the water instead of going to grid?

I guess that I can use the relay 1 (or 2) on the Cerbo GX to turn the heater on/off or something like that. Is that correct? Or am I wrong?


Thanks,

Jakub

cerbo gxwiring
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4 Answers
mondeoman avatar image
mondeoman answered ·

For me, the easiest would be to use the Node-RED installation from the Venus OS Large and drive one of the relays from a Node-RED flow.

Read the power from the Grid Meter for L1, L2, L3, calculate the sum and feed it into a hysteresis node (ON when grid power lower than -2kW, OFF when grid power above 100W, no action if grid net power is between these limits) and a node to forward the state to the Cerbo relay.

PS: The relay must be connected to a heavy-duty contactor that can handle the 2kW load for a long time.

And the 2kW heater must have a thermostat that will cut off at a high enough temperature...Do you have an anti-scalding thermostatic mixing valve on the tank DHW output?

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jakudo avatar image jakudo commented ·
Thanks for the reply. I'm thinking about using NodeRED in my house. Just to try it and test what it can do.

However, this installation is in my parents house, so I'm looking for more simple solution there. Is there any?

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mondeoman avatar image mondeoman jakudo commented ·

Then maybe an off-the-shelf solution like AC-THOR?

https://www.my-pv.com/en/products/ac-thor-9s-en


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jakudo avatar image jakudo commented ·
Hi, so after few days of researching, I've decided to try the Node-Red. I was already thinking of it before due to some smart home automations, however, haven't needed it yet.

I just would like to ask you one thing to clarify - I have a home server running some apps (Scrypted, HomeBridge etc), so I would like to install NodeRed there. However, I saw some videos on youtube that when I activate the option in Cerbo, it installs the Node-Red inside the Cerbo, so at that time I would have 2 Node-Red installations? Or is it enough to install the Node-Red on the server and then install some plugin inside it for Victron and then I wouldn't need to install it on Cerbo? Or did I misunderstood it completely?

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h8mecz avatar image h8mecz jakudo commented ·
Hi Kuba,

have you figured it out somehow? :) I am looking for exactely the same solution. I want to use Node-RED for it with AC2 out controling of power outlet via contactor in technical room where I have connected 2kW heater for heating of water. It is my bivalent (not used) backup source of heat in case heat pump will be broken somehow. So I want to use this to save lifetime of compressor of heat pump.


Thanks for reply in advance. Martin, Czech rep.

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mvas avatar image
mvas answered ·

All posts in Hot Water Diversion ...
Hot Water Diversion

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Alexandra avatar image
Alexandra answered ·

@jakudo

Is AC 2 out already in use? If not that is the simplest option

The second one is using a contactor and a relay from either in the inverter (k1 or other) and switch it based on SOC or something like that). You can explore options in demo mode in ve config.

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jakudo avatar image jakudo commented ·

Thanks for the help. I will check that. Currently, I'm playing with Node-Red, which also seems to be a good thing.

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matt1309 avatar image
matt1309 answered ·

Hi @jakudo

I have a similar setup to what @MondeoMan describes however I have a larger buffer than 100w for the turn off criteria just in case, but you can tweak that over time.


In regards to a relay that MondeoMan described I've used a shelly smart switch. They're rated for 16amps and relatively cheap.

They also have a built in time out feature, so you can get it to auto turn off after x minutes for example. (plus can add to any home automation software or use their built in app to manually turn on/off if you ever need to)

I use this connected to a standard immersion heater in a water tank. (This has a thermostat built in for safety so I don't need to worry about wiring that in either).


I activate the shelly via http node in node red, rather than the cerbo relay. This also allows me to have multiple loads ie if ones already on or if the water heat thermostat has turn it off then i can turn on another load, as I'm not limited to cerbo relays. It also means i can have the smart switch far away from cerbo as long as the smart switch and GX device are on the same LAN/network.

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jakudo avatar image jakudo commented ·
I know Shelly. I use many Shelly and Sonoff switches at my house. That is the reason I'm playing with Cerbo with NodeRED installed on it. That seems the easiest way for me know.
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