Remote geyser switching

Hi. While this is not really a “home automation” issue it is related, and I think you members would probably be best positioned for an answer. As a PV installer, our general approach is to split the main DB so that geysers, stoves and the like are treated as “non-essential” loads and fed directly from the grid. Lights, plugs and various other “essential” loads are fed from the inverter, in order to keep costs in check. I am pretty sure that most installers do it this way.

A problem I have come across numerous times is when you install a system in a house with out-buildings which have a single-phase supply fed from the Main DB in the house, but they also have a geyser (or stove). If you treat the outbuilding as non-essential, it has no backup power. If you treat it as essential, your risk overloading the inverter because of the geyser. The obvious alternative is to run another feed to the outbuilding, but this can be often be expensive and difficult.

I hoped there would be a way whereby a relay / geyser timer switch or the like, could be installed in the out-building geyser circuit to act as a switch, and could be controlled via wifi (or something else) from the main house so that it would switch off during outages. Thus the geyser no longer overloads the inverter, but the outbuilding has backup power. Does anybody know of a way to do this ?

A CBI Astute wifi breaker installed in the sub db in the outbuilding will do just that. There are other brands as well but I use the CBI and it has been working very well for a couple of years now.

It does however require manual intervention through an app on your phone and it must be in reach of the main house’s wifi coverage. Then you could switch it off from anywhere you have internet reception after your inverter notifies you of the grid being lost.

If this could be automated (which is first prize) I suspect it would need to be done with those fancy things like Home Assistant, Alexa etc which I still know nothing about, but I’m sure the clued up members will be here soon enough to explain how this works.

If you want an additiopnal feature the “Sonoff th20” is another option. However it would require the tempreture probe to be installed within the geyser. The gain here is that the geyser temp setting can be used to control the geyser temp remotely. So in summer and winter you can adjust temp accordingly. Alternatively a geyser timer like “CBI” or normal “Sonoff” geyser timer with wifi will do the job. I am not sure of the longevity of the relay contacts used on these devices. In my case I opted to install a seprate contactor.

Sounds like you need a ripple relay on the outbuilding geyser, which can be controlled over the same wire that feeds the outbuilding. That said, I have only seen municipalities install and control these. But essentially something in the main db that then send the signal to the out-db ripple relay to turn off when grid power is out

You jostled my brain cells for a second there. I started wondering: Is there perhaps a consumer-level ripple switch one could use?

Then I thought: Well, ripple control is essentially a crude kind of PLC (power line communication), and you already get IP-over-powerline adapters, so that might be an option to get a network connection to the outbuilding if Wi-Fi won’t reach. Then you can use perfectly standard IoT switches to get the job done, which will probably be more readily available and cheaper.

Integrating it is the harder part, because that means also building and installing the controlling part. Us tinkerers probably already run something like HomeAssistant, which makes this easy, but is this necessarily the best product for a hands-off device that a non-technical person can use in a home?

Personally I would prefer something with an hard-wired ethernet connection, which sort of sends you towards the higher end Shelly devices, which are quite costly, or to some kind of PLC (programmable logic controller).

But if you are okay with the occasional mishap because of a WiFi outage, then you could probably do something with two cheap WiFi devices.

With a Victron Multi/Quattro, you can get the signalling out of the inverter. For example, something like this switches a relay when the grid goes out/returns:

I know that with some of these ESP8266 or ESP32 devices, you can have a button on one end, which sends an MQTT or similar message, which can then activate a device elsewhere in the home. So you could have one such device connected to the relay on the inverter, and the other on the other end to switch off the geyser.

You can get rid of the MQTT requirement by using something like KNX. Supported by Tasmota and maybe others as well.

Could even use a completely different remote switching system, as long as it is a switch type (open close) and not a button (toggle) kind that can get out of sync.

So it can definitely be done, but finding the right no-nonsense hands-off hardware is the trick.

this might do what you want (no endorsement of product or supplier). Obviously decent relays/contactors on a geyser type load should be self-evident.

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@Plonkster says you could get a contact from the inverter when you lose the grid. This could be used to make a sophisticated version of what I am about to describe.

Essentially, I want to pulse the supply to the outbuildings to activate a timer on the geyser circuit.

The outbuilding’s geyser supply will be through a contactor powered by a “delay in pickup” timer, say with a 2.5 hr delay.
In other words, the geyser timer will drop out instantly when the grid is lost and can only come on 2.5 hours after the grid is returned.
So a two-second loss of supply will put the geyser out of action for a specified time.
( 2.5 hrs could be adjusted to suit your typical load-shedding duration).
These timers are cheap and are DIN rail suitable as is the contactor required.

So the absolute simplest way to achieve the desired effect is to let the inverter overload, and then it will restart sans the outbuilding geysers, and life will continue. The downside of this is that all circuits will lose supply momentarily. (Which is still an improvement on the present situation).

Or alternatively, you could get fancy and only pulse the outbuilding’s supply using a circuit incorporating @Plonkster 's contact.

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This is what I would look at. The disadvantage is the WiFi coverage to the outbuilding might not be ok.
In that case use a powerline network extender that uses the mains cable as a network cable…

I’m looking for a similar solution, but for the out-buildings as a whole (nobody lives in them).

Ideally it would I would like to be able to toggle the sub-DB between the essential and non-essential loads. This could be done in the main DB which is easily in wi-fi range. Better still would be a time driven default so that it would always switch back to non-essential at, say, 2 in the morning.

I get frustrated when there’s load-shedding but it’s a nice sunny day and my pool pump could be running.


There is already a great solution for you on this forum.

See: Geyser Power Source Selector

While that is for a geyser, should work for your use-case.

Thank you! That looks exactly like what I’m looking for, but also above my safety level. I will change a wall socket. If push comes to shove I will also do a like-for-like replacement of a breaker in the DB, but more than that and there’s a chance of something going bang or - much worse! - slowly getting too hot.

Build it away from the DB, test it like that poster with a light. Get an electrician to hook it up to your DB.

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Here is another idea, untested. Should work because when you stack multiple relay assistants, the last matching one will win.

This turns the relay off one second after the grid fails, and back on 10 seconds after the grid failed. The third assistant is there to ensure the relay comes back when the grid returns (otherwise a short outage of less than 10 seconds could leave it in the off state).

This will generate a 9-second outage when the grid fails, which can be used by a timer circuit like @Phil.g00 described to lock out loads in the outbuildings.

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Many thanks to all who responded generously with your ideas and experience. There are plenty of options for me to check out. Much appreciated.

If you are able to have a cable between the buildings (does not need to be very thick) you can use a normal contactor in your outbuilding DB triggered by a line that is not on the essentials main board.

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