Project Logs

Collapse

• Switched from mechanical relay to SSR for hot water tank

  nodemcu12ecanada • 10/20/2024 at 14:55 • 0 comments

  I used to use a 30 amp 240VAC mechanical relay to switch the hot water tank but the relays would only last a year or two.

  I have now switched to an inexpensive, ($7.32 Cdn with free shipping over $10 so I bought two), DC-AC Solid State Relay instead which should last forever.

  I bought one capable of switching 60 amps even though I measured only 15 amps used by the water heater.

  Bigger because, why not? 

  Difference in cost is insignificant. Same size.

  The 3.3V NodeMCU is only 12 mA per output so it can't directly turn on the SSR from an output.
  

  The previous 30 amp mechanical relay needed 5 VDC to turn on so I used a small 4 channel relay for switching the 5V which is what I now use for the SSR. The small 10A 4 channel relay is only switching mA so no issue with durability.

  I mounted the SSR to a flat aluminum plate with heat sink grease because I read SSRs can get hot while on.

  But it doesn't even get warm.

  The datasheet says it has a 1.6 volt drop x 15 amps which should mean 24 watts of heat needs to be dissipated.

  I could have bought a heat sink for it which costs $5.25 Cdn.

  But I only measured a 0.9 volt drop x 15 amps which means only 13.5 watts of heat, but it doesn't even get warm.

  In Ontario there is a 2.8 cent per kWh optional overnight rate.

  We switched to the new rate and save another $150/year on top of the fact we have always had timers on the hot water tank and hot tub. We save even though the new low rate comes with a 28.4 cents per kWh 4-9 pm weekdays cost.

  2.8 cents per kWh is cheaper energy than natural gas. More expensive to buy and now more expensive to operate natural gas water heaters are obsolete with the new rate.

  Also it's only $100/year to "fuel" an EV at the ultra low cost overnight rate. 

• Switching from DHT22s to BME280s

  nodemcu12ecanada • 12/07/2023 at 16:59 • 0 comments

  I was having issues with my DHT22 humidity sensors which also include a temp sensor. Random very high values. Apparently the sensors don't last forever. The humidity sensors are used to determine when to open the windows in the basement in the summer to greatly reduce the humidity. Without a noisy, kWh guzzling dehumidifier. It's not obvious when it's a good time to open or close the windows.

  I have two of them on one controller for upstairs and downstairs. There is a separate one of a different type, SHTC3, outside on a separate microcontroller. I only use DS18B20s for critical temp sensing used for control.

  The sensors each take up one input with some dedicated DHT22 protocol.
  With the new I2C sensors I free up those two inputs. It's better to use the limited NodeMCU I/O for a bus to talk to various devices instead of each device taking up dedicated I/O.  Two inputs with I2C talk to many devices. 

  One input using the OneWire protocol talks to many DS18B20 temperature sensors. With multiple temp sensors it's much more reliable to use the unique 64 bit sensor address method. Otherwise I found temps can be mixed up occasionally. https://lastminuteengineers.com/multiple-ds18b20-arduino-tutorial/

  I looked around for some I2C humidity sensors. There are quite a few different ones.
  If you use I2C sensors they don't take up any new I/O if you put the data lines in parallel with the ones used for the clock. Many different sensors as well as digital and analog I/O expanders can go on the same two I2C inputs.

  Different types of sensors have different I2C addresses so there is no conflict.
  The issue I had was I want to use two of the same I2C sensors on the same I2C inputs.
  One way is to get an I2C multiplexer chip that selects which device to talk to if they have the same address.
  Another way is to get a sensor where you can change the I2C address. This is what I did.
  Putting 3V or Gnd on one of the pins changes the address.
  This sensor not only does humidity but also temp, pressure and altitude which is interesting. 

  It can tell if you lift it up a couple of feet based on the slight change in air pressure. 

  Altitude, instead of pressure, is used to determine if the trend is high pressure (lower than actual altitude reading) or low pressure (higher than actual altitude reading). High pressure can indicate good weather and low not so good.

  I got 3 of them for $12. I always buy more than I need for stuff worth next to nothing in case I smoke a few. Or there is a defect. 

  I followed this website to work with multiple BME280s. Not waterproof like DS18B20s.
  Tiny little board. The actual sensor is a teeny tiny 2.5mm cube.
  New sensors usually need you to load a new library if it isn't already included with Arduino IDE.
  https://bluedot.space/tutorials/how-to-connect-two-bme280-sensors-on-i2c-bus/

View all 2 project logs