Dear All,

I can't seem to find a discussion where the Aux output is used to "cleverly" switch loads from Non-essential to to essential bus.

My idea is to switch my geysers over to the essential bus, but only if my battery is say between 90% and 100%. (The battery will only get that much charge if the sun shines) In addition, I am planning to switch my 3X geysers on in sequence, i.e the first go on, when hot (and thermostat switch off) the next geyser switch on, and so forth. This ensures that I can have all my geysers hot by the end of the day, never drawing more than 3kW at a time to the geysers since only one is on at any time.

This idea also do not take away the function that I can actually switch all my geysers on simultaneously (using my existing smart switches) at night and early mornings on the non essential bus (white phase) should I wish to do so (lots of people in the house, no sunshine, etc.).

Doing it like this uses the geysers as energy storage after the battery is fully charged by the sun.

Attached is a diagram I want to implement (Blue is existing), orange is to be added. ECU=Energy control unit. This monitors current, and switch if the current exceeds 6A. So the 2X ECU will ensure only one geyser draw current at a time while on the essential bus. C1 is basically a contactor (changeover switch) switching from essential to non essential load, and also isolating the geyser circuits from each other while overriding the smart switches (that currently only switch geysers on early evening and early morning).

Please let me know what you think, and if there is a better or simpler solution. One condition is that I don't want to lose my current functions on the geysers, and I also don't want the system to require manual input by looking at the app all the time and switching loads. I also don't want the geysers to heat up during the day if the sun don't shine, so just managing it by timers won't work.

I look forward hearing from you. Thanks in advance.

5 hours ago, Wlotzkas said:

I look forward hearing from you. Thanks in advance.

Good idea. But don't you want a seperate neutral for your inverter?

I assume your inverter doesn't export past the municipal meter. However, I think you will get limited benefit if water isn't used during the day. It seems to me like your control units will give each geyser only one chance to draw current. Furthermore, geysers tend to draw a lot of current for a short period. This is somewhat incompatible with solar generation.

I would install additional thermostat pockets in the geysers. On grid, the temperature would be limited to 55 degrees Celsius. The thermostat and solar power would run to 75 degrees Celsius... If there are no small kids in the house.

You could also consider some parallel and series arrangement on solar power to limit geyser power.

I have three phase supply from Eskom, my neutral is earthed. My inverter Neutral and my Eskom Neutral is the same, both earthed. Is that not good?

The ECU units will keep on cycling between geysers as they switch on and of (thermostat). It is not a one a day limit. The ECU purely check if one geyser draws current, the next won't be able to.

My plan is to have two geysers in series (the water flow) at each bathroom to ensure there is ample water for evening and next morning use, eliminating the need to heat water early mornings.

Thanks for your valuable reply!

19 hours ago, Wlotzkas said:

My inverter Neutral and my Eskom Neutral is the same, both earthed. Is that not good?

The Sunsynk manual indicates that in SA you should have the neutral of the inverter connected to that of the supply. It seems like this neutral is then used as earth for your essential loads. I had the wiring in mind suggested on the following page where the inverter neutral is seperate.

On 2025/03/06 at 3:57 PM, Wlotzkas said:

Dear All,

My idea is to switch my geysers over to the essential bus, but only if my battery is say between 90% and 100%. (The battery will only get that much charge if the sun shines) In addition, I am planning to switch my 3X geysers on in sequence, i.e the first go on, when hot (and thermostat switch off) the next geyser switch on, and so forth. This ensures that I can have all my geysers hot by the end of the day, never drawing more than 3kW at a time to the geysers since only one is on at any time.

This idea also do not take away the function that I can actually switch all my geysers on simultaneously (using my existing smart switches) at night and early mornings on the non essential bus (white phase) should I wish to do so (lots of people in the house, no sunshine, etc.).

Doing it like this uses the geysers as energy storage after the battery is fully charged by the sun.

I did something similar to this.

I have both of my own geysers on Aux. (Though their combined rating is still significantly lower than my inverter's: Aux is governed by the same maximum power that limits UPS/Load).

My installer did change-over switches to allow us to (manually) swap them over between Aux and Non-Essential. (But in all cases, they're fed by excess PV through zero-export-to-CT).
So be safe, by default I just leave the main (most frequently-used) Geyser on Aux in case of a power outage. But if it's sunny and the power is out for an extended period, we leave them both changed-over to Aux because there's no risk of them tripping the inverter if both were to turn on simultaneously.

Our 'Aux On When Grid Up' setting is ticked - so Aux stays running regardless of battery SOC when the grid is up, and when the grid goes down, Aux is set to be only on above 90% to protect the SOC in case it's an extended outage. If it's load shedding we might drop this to 50% to allow us to to use the stove (also on Aux).

Further to your diagram, we adopted a software approach to do this (using the standard CBI Astute timers that my electrician installed onto the geysers), to achieve round-robin' ing like you're suggesting, where if a geyser is idle (Powered On = Yes and Power Consumption = 0), then we power it off and try the next one. We only do this when the battery is close-to-full (if it's under 80%, we fail over to regular timers).

Regarding Aux, think of it as an extension to UPS separated by a relay/switch. So if you want to allow the geysers to turn on only when the battery is above 80% (regardless of Grid), you'd need to set Aux On to 80%; but if you want to be able to fail over to grid, you'd need to combine this with your System Mode Timer to force the battery (from grid) to 80% if PV is insufficient; that way you can still get some geyser heating on cloudy days.

So in our case, we just:

• Have the Aux set to be on whenever grid is up (and on at above 90% SOC when grid is down)

• Use timers for all our basic heating. We know that our one geyser needs 3 hours to get to full temp and the other needs 2 hours, so they're governed by CBI Astute times to switch them on and off accordingly.

  • To boost their stored-energy capacity, we've cranked the thermostat of the one up to maximum. This means we can heat it beyond our regular requirements (essentially treating it like a battery).

• Then, in the event that the day is sunny and the battery hits 80%, in between these geyser timeslots, we do additional load-searching ( IF (Powered On = Yes and Power Consumption = 0) THEN Turn-Off-And-Try-Next-Geyser).

  • Because the timers will already give us the hot water we need daily, this load-searching essentially dumps spare PV energy into the geyser which might be useful the next day if it's cloudy; or if hot-water demand is higher than expected that evening.

Since we always need hot water (more important than full battery!), we leave Aux on whenever the grid is up, and the battery instead charges from whatever is left over.

On a day when we can't heat our water from PV (and need to dip into grid), we usually can't get the batteries charged anyway, which is why (for us at least) waiting for a full battery before heating water didn't make sense.

I feel like the most important take-away, in my experience, is that doing a Geyser round-robin only makes sense if you have spare sunshine - so like you suggest (with Aux), Battery SOC % does need to be brought into this equation.
If you don't have spare sun, it's more efficient to do the 'minimum' heating your house requires via timers. Or you could perhaps measure kWh consumed by each geyser (against your average daily requirements) and use that as a cut-off when it's not sunny. (If the hardware/wiring route doesn't work out, Home Assistant might be a good software solution for both of these requirements, since it can integrate with both the inverter and your geyser timers.)

Edited March 11, 20251 yr by JayMardern

16 minutes ago, JayMardern said:

I did something similar to this.

I have both of my own geysers on Aux. (Though their combined rating is still significantly lower than my inverter's: Aux is governed by the same maximum power that limits UPS/Load).

My installer did change-over switches to allow us to (manually) swap them over between Aux and Non-Essential. (But in all cases, they're fed by excess PV through zero-export-to-CT).
So be safe, by default I just leave the main (most frequently-used) Geyser on Aux in case of a power outage. But if it's sunny and the power is out for an extended period, we leave them both changed-over to Aux because there's no risk of them tripping the inverter if both were to turn on simultaneously.

Our 'Aux On When Grid Up' setting is ticked - so Aux stays running regardless of battery SOC when the grid is up, and when the grid goes down, Aux is set to be only on above 90% to protect the SOC in case it's an extended outage. If it's load shedding we might drop this to 50% to allow us to to use the stove (also on Aux).

Further to your diagram, we adopted a software approach to do this (using the standard CBI Astute timers that my electrician installed onto the geysers), to achieve round-robin' ing like you're suggesting, where if a geyser is idle (Powered On = Yes and Power Consumption = 0), then we power it off and try the next one. We only do this when the battery is close-to-full (if it's under 80%, we fail over to regular timers).

Regarding Aux, think of it as an extension to UPS separated by a relay/switch. So if you want to allow the geysers to turn on only when the battery is above 80% (regardless of Grid), you'd need to set Aux On to 80%; but if you want to be able to fail over to grid, you'd need to combine this with your System Mode Timer to force the battery (from grid) to 80% if PV is insufficient; that way you can still get some geyser heating on cloudy days.

So in our case, we just:

• Have the Aux set to be on whenever grid is up (and on at above 90% SOC when grid is down)

• Use timers for all our basic heating. We know that our one geyser needs 3 hours to get to full temp and the other needs 2 hours, so they're governed by CBI Astute times to switch them on and off accordingly.

  • To boost their stored-energy capacity, we've cranked the thermostat of the one up to maximum. This means we can heat it beyond our regular requirements (essentially treating it like a battery).

• Then, in the event that the day is sunny and the battery hits 80%, in between these geyser timeslots, we do additional load-searching ( IF (Powered On = Yes and Power Consumption = 0) THEN Turn-Off-And-Try-Next-Geyser).

  • Because the timers will already give us the hot water we need daily, this load-searching essentially dumps spare PV energy into the geyser which might be useful the next day if it's cloudy; or if hot-water demand is higher than expected that evening.

Since we always need hot water (more important than full battery!), we leave Aux on whenever the grid is up, and the battery instead charges from whatever is left over.

On a day when we can't heat our water from PV (and need to dip into grid), we usually can't get the batteries charged anyway, which is why (for us at least) waiting for a full battery before heating water didn't make sense.

I feel like the most important take-away, in my experience, is that doing a Geyser round-robin only makes sense if you have spare sunshine - so you should bring your Battery SOC % into this equation.
If you don't have spare sun, it's more efficient to do the 'minimum' heating your house requires via timers. Or you could perhaps measure kWh consumed by each geyser (against your average daily requirements) and use that as a cut-off when it's not sunny. Home Assistant might be the way to go here for both of these requirements, since it can integrate with both the inverter and your geyser timers.

Thanks, that is interesting.

I have limited supply, but on three phases, so I need to switch my geyser loads with a contactor between my essential load, and another phase. I can't put my geysers upstream of the inverter on the same phase.

Using the aux out to switch the changeover switch automates the changeover if there is sunshine, otherwise the battery will never get to a full stage (it does not grid charge).

I will look into the Home assistant option to control the CBI smart switches, thanks for that idea.

I am in the business of hydro power generation, my oldest turbine is a 1925 model, so I like hard wire solutions where possible :-). I understand it better.

Groete,

Dear All,

Just an update on my idea above. Although looking good on paper, once I built the panel, it did not work. For 2 reasons:

First, the switching of the contactor (C1) is too slow, so during the switch it causes the two phases to short, tripping my breakers. This can be resolved by adding timers, but it also complicates the system.

Secondly, the Energy Control units take about 2 seconds to switch once it detects a current. The result is that during the 2 seconds, all the geysers are on, resulting in overload trip.

So I changed the system completely to get the same result, but programming scenarios on the CBI smart switches:

I installed a contactor that connects each geyser to its smart switch separately (using 4X NO contacts). The contactor is energized by either:

-A relay closing when the Aux output on the inverter energizes (battery between 95% and 100%).

-A 24h timer closes forcing the geysers to be on.

With the settings of my timer and smart switches as follows:

-24h timer energizes the contactor from 05:00 to 07:00, and 16:00 to 19:00

Main Bedroom Geyser Smart switch:

-05:00 On (we shower in the morning)

-07:00 Off

-15:55 Off (Make sure it is off before the kids geyser switch on)

-17:05 On

-18:30 Off

Kids Geyser:

-10:10 On (to be on when the contactor energizes once the battery is full)

-16:00 On

-17:00 Off

Then I created 2X scenes on the smart switches, to enable the two geysers to toggle on once the other is hot during the day when the only way the geysers can be on is if the battery is full and the Aux out energized:

Scene 1:

-10:03 - 16:00: every day

-If Kids Geyser Amps goes less than 5A, then switch on main bedroom geyser, and switch off Kids Geyser.

Scene 2:

-10:00 - 16:00 every day

-If Main bedroom Geyser Amps goes less than 5A, then switch on kids geyser, and switch off main bedroom Geyser.

This is working well, and the geysers toggle between each other when the one is hot. This only happens during the day (10:00-16:00), and they only use electricity when the battery is full (Aux out on). So my inverter first fills up the battery, then heats up each geyser, one after the other.

I will add the electrical diagram later, it still needs to be made neat!

Groete!

11 hours ago, Wlotzkas said:

-24h timer energizes the contactor from 05:00 to 07:00, and 16:00 to 19:00

Is the timer the same for all your switches? Or does each switch have its own clock/timer? and if they are separate, do they synchronize with some clock source to ensure they are at the same time within 60 seconds from each other? Else you could have drift and not by the same amount and on times clashing eventually...