January 10Jan 10 Good morning all and best for 2026! As the title alludes to, how do you switch the geyser off when battery volts drops?Yes, there are expensive Home Assistant, Geyserwise and such solutions, but there surely are cheaper and simpler ways? How about an analogue adjustable DC Volt sensing switch that energizes a relay? I cannot find such a gizmo, although such should find a ready market. Surely some electronic tinkerers have built it already? Thought I would find it at instructables.com but not. Any other websites I can look? Thanks for your attention in this matter... ;-)
January 10Jan 10 Is this for a residence or rented property? How many of you? I'm always quick to say "heat pump" because it works well for my wife and I (and we run it off of batteries at least once each day). But we are two people with a fixed routine, and so can run it on a timer. That's a totally different way of heating the water, rather than controlling the element in your geyser. It's a different way of addressing the problem of heating water without flattening the battery. But it costs more than other routes you have already ruled out.Realistically if you want to react to the battery voltage, you're probably going to have go the smart home route, and with something that can speak to the batteries or the inverter. And you'll have to program it. The fun here is accounting for cases where you turn the geyser off at X volts and 10 minutes later it's X.01. Or you turn back on at X and 10 minutes later it's (X - 0.05).Home Assistant has plug ins for many inverters, and for Tuya or Ewelink for a smart device to control the geyser. The last mentioned will cost you less than R700 (CBI Astute) if you can do the installation yourself. HA itself will need a computer to run on. Most likely this will be a Raspberry Pi. A Pi 4 will cost about R2500 with the casing, memory card and etc. So HA need not cost you that much. Just check that there's an integration available.You may still have the problem I referred to above when it comes to writing the rules, but try and use a flow chart of whatever sort of plan works for you. Then once you are sure the design is right, write the rules. Edited January 10Jan 10 by Bobster.
January 10Jan 10 1 minute ago, Bobster. said:So HA need not cost you that much.HA itself is free. The inverter plug ins will usually be free. So you are in for the cost of the hardware that HA runs on, and for the cost of a device that controls your geyser. And you need to be comfortable when it comes to installing HA and doing all the setup.I think I'm right in saying that most of the smart devices on sell in SA are Tuya or Ewelink. The gap in my knowledge here is whether or not HA can directly control these devices or whether it sends instructions via the cloud. Wiser heads can fill in the blanks in my knowledge. Ewelink (Sonoff) will need a hub between it and HA.
January 10Jan 10 7 hours ago, Abe53 said:Good morning all and best for 2026! As the title alludes to, how do you switch the geyser off when battery volts drops?Yes, there are expensive Home Assistant, Geyserwise and such solutions, but there surely are cheaper and simpler ways? How about an analogue adjustable DC Volt sensing switch that energizes a relay? I cannot find such a gizmo, although such should find a ready market. Surely some electronic tinkerers have built it already? Thought I would find it at instructables.com but not. Any other websites I can look? Thanks for your attention in this matter... ;-)The solution is very simple. Just use a charger controller and inverter the output via n/c contact to switch of the geyser when voltage drops to the set level. Then the on board relay will switch off at charged voltage which will then provide power to the geyser again.Use an external relay if you don't trust the on board blue relay. Setting points for on/off as low as 0.1V apart and up to 60V. This model has an output of 230V and the input that is switched is 230V as well. Thus external relay will also be cheaper 230V than DC Relays.XH M602 Cost R145 or lower. PM me for details if in doubt. Long time no speak. Edited January 10Jan 10 by Scorp007
January 10Jan 10 8 hours ago, Abe53 said:Good morning all and best for 2026! As the title alludes to, how do you switch the geyser off when battery volts drops?That would obviously also depend on your current hardware - inverter brand and size, number of PV panels, and capacity of your batteries... As an example, I run my geyser from my inverter, via a CBI smart switch - but that only controls time on/off, and does not measure battery voltage. This has worked quite adequately for me during the past 1.3 years, but I must keep an eye on the weather forecast and from time to time adjust the time "on" and "off" as dictated by available PV power (i.e. intensity of clouds), but that's a simple switch change on my cellphone app (supplied by CBI at no extra cost over that of the smart controller). In my case, the CBI switches the geyser "on" at 04:00 each morning to "top up" the hot water for the morning, and then re-heat the now cold water in the geyser after the batteries have been fully recharged, set for 10:00 "on" and 14:00 "off" for normal sunny days, and only tweaked to not switch "on" at 04:00 if there is heavy clouds forecast the previous evening, and with the late morning heating subject to a manual "switch off" if it becomes clear that there won't be any sunlight on a specific day AND the batteries' SOC is below 70%.Obviously, if you don't have adequate PV and/or battery capacity, then things become a lot more complicated (impossible?). Perhaps you should give us more information on your system, and on your consumption of hot water, then we would be able to provide more accurate feedback.
January 10Jan 10 Author We have several off-grid installations requiring geyser control, some with old hardware, and have unreliable wi-fi coverage which rules out Internet of Things. Scorp007 's proposal of using a XH M602 charger should work, I use buck converters with similar up-down buttons to charge DIY li-ion batteries to fine tolerances. Will tinker and revert. Thanks again for your attention in this matter... ;-)
January 11Jan 11 12 hours ago, Scorp007 said:Use an external relay if you don't trust the on board blue relay. Setting points for on/off as low as 0.1V apart and up to 60V. This model has an output of 230V and the input that is switched is 230V as well. Thus external relay will also be cheaper 230V than DC Relays.How do you cope with the situations I described above? The cut off point is X volts. And so 1) Voltage drops to X, we turn off, a minute later voltage is X.12) Voltage rises to X, we turn on, a minute later voltage is X-0.1Or does this not matter?This is not to cast shade on your solution. This sort of scenario where the geyser is cycling on or off seems possible to me, but it may not be a problem in real life. So I ask out of curiosity.
January 11Jan 11 One will never use 0.1V between on and off. When a highish load is switched on the battery can easily drop by about 0.4V.One can use it the same way all Axperts work. Geyser only on at over 52.5V and when voltage below 51V switch off. This way you can prevent the high load of a geyser even when other high loads are switched on. This will prevent shade for short periods switching it off. My example was how to use a charge controller for charging also inverted as a battery protector. The low price to even protect any battery from deep discharge is worth it over and over compared to the cost of a battery being damaged. Lots of lithium are damaged(dead cell) by a cell being discharged too deep. More a problem in camping systems than residential systems as we normally have an inverter shutdown setting.
January 19Jan 19 The simplest way is just to use a relay and connect your geyser on the N/O contact. Supply your relay coil with power from the grid and when the grid drops, supply to the geyser will be disconnected. I have this working flawlessly at my rental property
February 20Feb 20 On 2026/01/10 at 11:21 AM, Abe53 said:Good morning all and best for 2026! As the title alludes to, how do you switch the geyser off when battery volts drops?Yes, there are expensive Home Assistant, Geyserwise and such solutions, but there surely are cheaper and simpler ways? How about an analogue adjustable DC Volt sensing switch that energizes a relay? I cannot find such a gizmo, although such should find a ready market. Surely some electronic tinkerers have built it already? Thought I would find it at instructables.com but not. Any other websites I can look? Thanks for your attention in this matter... ;-)Contact Electromann SA and ask them to modify this board to accommodate 48v battery. Then use a DC relay on the output to switch the geyser off at settable threshold. I have used these curcuit boards on battery chargers for vechile starter batteries to automatically top them up if vechiles are stationary for long periods.They cost 80 bucks and work well.Electromann SAXH-M609 Battery Low Voltage Disconnect Switch with LED Di...XH-M609 Low Voltage Disconnect Switch 12.6V/13.8V/24V/36V with LED Display for Over-Discharge Protecting of 12-36V Lithium batteries Say goodbye to the stress and hassle of constantly monitoring your Edited February 20Feb 20 by TaliaB Spelling and grammar
February 20Feb 20 3 hours ago, TaliaB said:Contact Electromann SA and ask them to modify this board to accommodate 48v battery. Then use a DC relay on the output to switch the geyser off at settable threshold. I have used these curcuit boards on battery chargers for vechile starter batteries to automatically top them up if vechiles are stationary for long periods.They cost 80 bucks and work well.Electromann SAXH-M609 Battery Low Voltage Disconnect Switch with LED Di...XH-M609 Low Voltage Disconnect Switch 12.6V/13.8V/24V/36V with LED Display for Over-Discharge Protecting of 12-36V Lithium batteries Say goodbye to the stress and hassle of constantly monitoring yourCan just add a simple buck/boost converter in between without having to modify the board. The converters are super cheap also. And he just scales accordingly.
February 22Feb 22 On 2026/02/20 at 9:06 AM, TaliaB said:Contact Electromann SA and ask them to modify this board to accommodate 48v battery. Then use a DC relay on the output to switch the geyser off at settable threshold. I have used these curcuit boards on battery chargers for vechile starter batteries to automatically top them up if vechiles are stationary for long periods.They cost 80 bucks and work well.Electromann SAXH-M609 Battery Low Voltage Disconnect Switch with LED Di...XH-M609 Low Voltage Disconnect Switch 12.6V/13.8V/24V/36V with LED Display for Over-Discharge Protecting of 12-36V Lithium batteries Say goodbye to the stress and hassle of constantly monitoring yourDue to this 36V limitation I suggested the M602 model that switches 230V AC that one can then drive a beefier relay to the geyser.
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