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3 posts

Wannabe Geek

# 249177 29-Apr-2019 15:23
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Does anyone know of a NZ compatible smart switch for controlling and monitoring a hot water imersion heater ? (its to be added to a solar + wetback system, so requires a bit of optimization in winter and summer hence wifi and temp monitoring makes much easier), ideally the switch should have a thermocouple feedback and logging and wifi control, the "sonoff-th" (google it if interested)  from china  looks perfect and cheap, but not sure if is wise for NZ install....any advice would be appreciated. Thanks in advance





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Ultimate Geek
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  # 2227817 30-Apr-2019 10:39
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Regarding the Sonoff:


Legally you can't install a Sonoff yourself - it doesn't come under the exemptions for domestic work.


If a sparky installs it for you then he/she needs to certify it as electrically safe, and in the absence of any SDOC this will be problematic.


The off-the-shelf functionality of the Sonoff (using the eWeLink app) is very basic and it needs an internet connection. Most people re-flash it to run as an MQTT client (usually Tasmota), and then control it using home automation software through an MQTT server (using something like Home Assistant). So then it becomes not quite so simple.


On top of all that, personally I would be very uneasy using the on-board relay to switch a hot water heater element, even the 15A one. I'd use a separate contactor.


3 posts

Wannabe Geek

  # 2227838 30-Apr-2019 10:55
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Thanks McLean, some good advice there


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Uber Geek
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  # 2227860 30-Apr-2019 11:04
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I wouldn't want to put a Sonoff on a hot water cylinder... and I have 20+ of them on lighting circuits around the house. They are awesome, after being flashed with Tasmota and controlled by home automation.


The relays are only 10A, and as above, even if you went for the larger 15A models, there isn't much room for movement when it comes to heating water where potentially big current draws could happen.

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Uber Geek
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  # 2227881 30-Apr-2019 11:34
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Worth seeing what your water heater is rated at - probably 2.4 or 3kw?


The Sonoff TH only comes in 16A IIRC - which is probably fine for a 2.4kw (10A) element but no way for a 3kw element.


Interested in the assertion above that the Sonoff doesn't come under exemptions for home owner work - wouldn't it just be considered a 'water heater switch' or 'thermostat' under 47(1)(a) of ECP51?

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Wannabe Geek

  # 2227888 30-Apr-2019 11:42
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Sounds like the Sonoff might be a bit risky, Is there any other system anyone could recommend that is more robust for NZ ? Temp mononitoring , switching and wifi control ? I came across the system below from a company in Serbia that looks perfect , but again not sure on applicability to NZ

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Uber Geek
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  # 2227897 30-Apr-2019 12:00
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The sonoff ticks all of your boxes, it's just the switching high currents that you need to be cautious of. Just grab something like this to put between the Sonoff and your hot water cylinder, so the Sonoff isn't switching the full load

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Uber Geek
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  # 2227900 30-Apr-2019 12:02
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How / what kind of solar controller are you using on your cylinder? As you might be able to use its element controller.

Otherwise just get an electrician to install a contactor with a 12V coil, to control the element. Then you can use whatever controller you like. Assuming that your controller uses a relay for its output.

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