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Adding geyser control to smart home - wiring question


Jatho

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3 minutes ago, Bloubul7 said:

I have not tested it as yet, need to go and buy a spare Sonoff TH16 to run the tests with.  Will keep you posted

Thanks - was referring to changing the original sensor.  Even if the original is not a digital one, if it can be easily replaced with a digital one, it is not an issue.

From your photo, it looks like non-polarised wires on the original probe, so very likely just a thermistor.

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1 minute ago, JustinSchoeman said:

Thanks - was referring to changing the original sensor.  Even if the original is not a digital one, if it can be easily replaced with a digital one, it is not an issue.

From your photo, it looks like non-polarised wires on the original probe, so very likely just a thermistor.

Correct, was refering to the testing the DS18B20 and Mechanical cut out as well.  Would like to get the readings from the DS18B20 and see if the mechanical switch still cuts out at 90 degrees.

For testing the original sensor, I'm looking at getting a MAX31865 to convert the signal to digital.  Want to see if I can get the Sonoff & Geyserwise to work in parralel with the Sonoff being the primary driver and the Geyserwise as a backup safety net.

 

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  • 1 month later...

Fantastic thread - thanks everyone! We've put in an offer on a new place and if the bank comes to the party will be moving in early next year. The new place has three geysers (one for the bathrooms, one for kitchen and one for outside flat). I plan to retrofit all three to solar, and since three geyserwise units will be pretty pricey I'm looking at possibly DIY-ing a solution to turn on the geyser element based upon time and temp (i.e. if not warm enough by 5pm). The other nb function of the geyserwise is to turn on the circulation pump when appoaching freezing temp to prevent flat panels from bursting - I plan to only install tubes, so I won't need this function.

I'm not well versed in smart switches etc so please do let me know if you have better suggestions. My current thinking is simply to use a sonoff TH10 to power a relay that'll turn the geyser on and off based on time and temp settings. The circulation pump I'll hook up directly to a 10W panel, so if the sun shines the water will circulate.

Is the solution as simple as this, or am I missing something?

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We've got a solar geyser at our place and I made it quite simple by adding a TDDGT timer in the DB board which turns the geyser on at 5pm and off at 6pm and again from 5am until 6am, but with a low-ish temperature set on the thermostat of 55 degrees. This is simply to ensure that there is warm water in the evenings and in the mornings. If the sun was out in full force and the water temperature is higher than 55 degrees already then the thermostat simply won't switch on the element.

I think that's the most basic of basic and cheap configurations to ensure there's warm water, but you can obviously then start looking at Sonoff's with relays and temperature sensors etc. which a lot of people are doing to feed excess solar into the geyser if the batteries are fully charged etc.

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32 minutes ago, fredhen said:

We've got a solar geyser at our place and I made it quite simple by adding a TDDGT timer in the DB board which turns the geyser on at 5pm and off at 6pm and again from 5am until 6am, but with a low-ish temperature set on the thermostat of 55 degrees. This is simply to ensure that there is warm water in the evenings and in the mornings. If the sun was out in full force and the water temperature is higher than 55 degrees already then the thermostat simply won't switch on the element.

I think that's the most basic of basic and cheap configurations to ensure there's warm water, but you can obviously then start looking at Sonoff's with relays and temperature sensors etc. which a lot of people are doing to feed excess solar into the geyser if the batteries are fully charged etc.

They say simplicity is the ultimate sophistication. This is such an elegent (and easy) solution. Thanks

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  • 6 months later...

Good day.

I am very interested in what is been done here. I do home automation and I have not found a solution for the  temperature probe.

I would like to keep the standard thermostat for safety reasons but would like to control the geyser relay using a D1 Mini or TH16 connected of course with a DS18B20 sensor. All this being controlled by home assistant.

Has anyone found a solution for getting the probe in there?

 

Any assistance would be appreciated

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Hi Vassen. Thank you for your response. Question. if your ripped out the geyserwise thermostat. How is the mechanical safety still working? Apologies but I dont know much about thermostats.

 

If it still works then this would probably be the best option I have see so far

 

Many thanks 

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7 minutes ago, kobusdb said:

Hi Vassen. Thank you for your response. Question. if your ripped out the geyserwise thermostat. How is the mechanical safety still working? Apologies but I dont know much about thermostats.

 

If it still works then this would probably be the best option I have see so far

 

Many thanks 

He only replaced the sensor (inside the brass tube), not the whole thermostat.

If you are using a D1, you can probably use the existing sensor (10k NTC) as-is. My hardware + code for interfacing is here:

https://github.com/justinschoeman/ModbusThermostat/blob/master/temp_geyserwise.h
 

If you use that code, you will need to adjust the 'to voltage' calculation according to the power supply voltage and ADC resolution.

 

/*
 * Geyserwise input/conditioning:
 * 
 *    ------- 5V (PIN 5 MCU)
 *       |
 *       /
 *       \ 10k NTC
 *       /
 *       \
 *       |      1k 5%
 *       + ----/\/\/\-----+ ---------> PIN 32 (MCU)
 *       |                |
 *       /              -----
 *       \              -----
 *       / 3k 1%          |   10uF ?
 *       \                |
 *       |                |
 *    --------------------------- 0V (PIN 1 MCU)
 */

 

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Hi Vassen,

I have a geyserwise control and my frustration is that I always have to go to the panel to see the temperature.

Does the geyserwise continue to function as per the schedules set when you replace the sensor with the Sonoff one?

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On 2021/05/16 at 7:33 AM, Vassen said:

No, it will not work. I just bought a geyser wize thermostat separately and used it for the mechanical cutoff. 

Thanks, it's a pitty, as I am not much of a DIY fan.

 

20 hours ago, JustinSchoeman said:

If you tee the temperature sensor on the Geyserwize, you can connect it to any HA device with 5V analog input.  You can then use the calculations from my code above to convert this voltage to a temperature.

Thanks, what HA device would you recommend that is not too much DIY?

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On 2021/05/14 at 1:48 PM, JustinSchoeman said:

He only replaced the sensor (inside the brass tube), not the whole thermostat.

If you are using a D1, you can probably use the existing sensor (10k NTC) as-is. My hardware + code for interfacing is here:

https://github.com/justinschoeman/ModbusThermostat/blob/master/temp_geyserwise.h
 

If you use that code, you will need to adjust the 'to voltage' calculation according to the power supply voltage and ADC resolution.

 


/*
 * Geyserwise input/conditioning:
 * 
 *    ------- 5V (PIN 5 MCU)
 *       |
 *       /
 *       \ 10k NTC
 *       /
 *       \
 *       |      1k 5%
 *       + ----/\/\/\-----+ ---------> PIN 32 (MCU)
 *       |                |
 *       /              -----
 *       \              -----
 *       / 3k 1%          |   10uF ?
 *       \                |
 *       |                |
 *    --------------------------- 0V (PIN 1 MCU)
 */

 

Thank you Justin for the info. I am assuming that code is for arduino? Anything for Tasmota?

 

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On 2021/05/14 at 2:04 PM, Vassen said:

As Justin mentioned, the geyserwise thermostat is still there. I just replaced the sensor, which is independent of the thermostat. 
 

I use sonoffs so I used what I know. Justin’s solution works with the geyserwise thermostat as is but needs some additional Diy skills 

Thank you Vassen. I get it now

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4 minutes ago, kobusdb said:

Thank you Justin for the info. I am assuming that code is for arduino? Anything for Tasmota?

For arduino, yes, but you only need the calculation to go from voltage to temperature, and you should easily be able to do that in any language/reporting platform of your choice.

The calculation is:

// Thermistor R@25C
#define TEMP_R 10000.0
// Thermistor B val
#define TEMP_B 4200.0
// Kelvin offset
#define TEMP_K 273.15
// 25C in Kelvin
#define TEMP_REF (TEMP_K + 25.0)

  // to current through 3k resistor
  double i = (5.0 - v) / 3000.0;
  // resistance
  double r = v/i;
  // calculate temp from r
  double c = (TEMP_B * TEMP_REF);
  c /= TEMP_B + (TEMP_REF * log(r / TEMP_R));
  c -= TEMP_K;
  if(c <= 0) {
    mb_temp = 0;
  } else if(c >= 999.0) {
    mb_temp = 999;
  } else {
    mb_temp = c;
  }

Thermistor constants are defined above, then the basic calculations to go from the voltage across the sensor (v) to the temperature (mb_temp).

NOTE: This calculation is slightly different from that in my code. My code is based on the voltage between the sensor and ground, so I have swapped it around in the above sample to work with the voltage across the sensor.

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