Geyser Power Source Selector

This is a project ive been wanting to tackle for a while.
My geyser happily runs on my inverter, but with the lack of blending its not always ideal.
The SCR does help a lot to keep the load within limits when there are intermittent clouds.
But I have found the need to look at powering the geyser from either the Grid or Solar, specifically on very cloudy days. I can generate enough power to run the house, but not heat my geyser.

This project has gone from overly complicated to overly simplified and everything in between.

It started sometime ago when looking at the below project.

And then reading this post from @Gh3kko

Finally I decided as much as I can solder pins to an ESP8266, I am a novice and im not sure how much soldering I would like to do. Gh3kko’s post made me realize contactors could be a very simple solution and wouldnt require any soldering.

The plan was made to “build” this using products of the shelf.
Now pricing on contqactors has become really silly, and picking some that support a mechanical interlock was just crazy.

I somehow stumbled across this

I found a post on another forum where someone was using them sucessfully. I went looking for some local stock and found a unit that got delivered the next day.

So today I assembled this.

The very distinct green color of the control hardware was very much coincidence and ?I only realised once assembled.

A description of how it works.
Source A (primary) is fed from my inverter, source B(secondary) si fed from Grid (very coincidental that it says “City Power” for anyone in JHB)

I have a sonoff mini fitted inside the DB box that controls the “sense” wire for the primary load side.
So when the sonoff is turned off it switches to Grid and when I turn it on it switches to my Inverter.

Quite practical I think, and all off the shelf components.
I tested it earlier with a light bulb and the response and functionality is quite impressive.


This is brilliant. Think I also need a set of this.

Where did you buy all the components? From ACDC?

So you are replacing the SCR with this equipment? How did you do the control of the SCR and will this be the same with the new system?

The DB and the isolators are from ACDC.
ACDC have the same ATS units just rebranded as ACDC units, but none of their stores have stock.

I bought the ATS from a company that had local stock.
I liitle pricier than ordering from AliExpress, but I wanted it “NOW”

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Nope, SCR is still in place and is situated on the output side of this device. They have very different “jobs” within my system.

This is my first winter with my panels on the roof, and I can confirm that my production is vastly different to summer, mostly due to the angle of my roof, and a little added shade from a neighbors tree.

The SCR still reduces the geysers load when there is PV available to run on PV.
Its all controlled by home assistant.

The current automations in place im testing for this setup are as follows.

Geyser is set to turn on at 9AM every Morning.and run on PV.
If im draining my batteries It will reduce load by 10% every 2 mins untill it reaches 50% and then turn off. Once turned off, it will let the batteries recover for 15/20 mins and then turn on again. If im draining the batteries, it will just turn off, if not, it will try and increase the laod by 5% every 5mins, if I start draining the batteries again, it reduces load. If they geyser has turned iff 5 times, I assume theres not enough pv and switch it to Grid. /It will heat to a preset minimum temperature and then switch back to PV to try and gain any additional benefit from PV that might be available.

These control algorithms will keep you busy, that’s for sure!
I’m still thinking there’s a way to immediately determine available PV power but I haven’t come across this being done.
They always check the power availability by measuring battery voltage or power being fed back into the grid. (This, to my mind is the indirect way of doing this type of control :slight_smile: )

Waiting then for your solution. :slight_smile:

… that does not cost a kidney.

I have some lux sensors outside, and use those for part of my automation, however I find that i max out lux without maxing out generation, im thinking of trying something similar soon, by mounting one directly onto my panels to compare the data.

With load shed as is it is now , I ran into a similar issue last night.
If I need to top up the geyser temp at night I switch on the grid for that time. Now , last night , the grid went off and I missed it , @#*!! …
I added a rule in the system that if the Geyser is on and the battery is discharging more than -1500 w for more than 60s then switch off the geyser. That should account for the cloudy day’s when I have the geyser on and the production drops for a moment.

If you have access to the Solar and Battery Watts.
If the battery watts is at -x then it is safe to assume that your panels is at their maximum output.

Suggestion: rather use a small PV panel for the signal since this will have a closer response to your PV array as opposed to a LDR.

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Agree. All commercial insolation sensors actually use a small PV cell. For example, the IMT sensor.

Yes, but you need to load the small panel with a burden resistor that is sized to use the full peak power of the panel, then you can use the voltage across this burden resistor as an indication of available PV otherwise, you get the full open circuit voltage at almost all light levels.

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Yup. It will just saturate and give you the same signal always :slight_smile:

You get small panels for salt pool chlorinators. A bit expensive as a source, but maybe you can find a cheap one from eBay or something :slight_smile:



Those small garden LED lights have small PV panels in. 1.5v-1.8V if I remember.

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Then there’s the Consol jar lamps.
Plenty of those on the back shelf waiting to be re-purposed…

This is my next plan … once my other drama is resolved.

Got the Relay, thanks to Paul.

When like i.e. 3500w goes into the batteries:
Between 10-12 switch on a Geyser.1
Between 12-2 switch on a Geyser.2
And if 1000w is drawn from batteries, switch off the geyser - to be tuned.

Geyserwise stays in place, it is the manual overide.
Can fit 2 temp sensors per Geyser, 1 inlet, and 1 outlet.
Geyserwise thermostat is the final protection, it has a mechanical disconnect if the temp gets too high.

This is not an elegant solution.
Too much room for inefficiency with straight timers.
For example what if:
Geyser 1 only takes an hour to replenish and the sun is only out between 10 & 12.

This is a better solution:
Set them both to heat between 10 & 2 (or add some other supervising criteria as well) and use 1 of these:
Then first come first serve, as soon as 1 is hot the other takes over.



Is this the thermal switch version? (They also have an electronic one…)

I don’t know the innards.