The proportional SSR (also called phase angle controller) is something that not many are familiar with.

This unit can control the current to a resistive load by varying the input. The input can be either 0-10VDC, 0-5VDC or 4-20mA.

This is a wonderful device since it can switch on at any time during the sine wave. See the picture of the wave forms. This effectively limits the amps to the load.

I have tested this successfully on my geyser and old incandescent light bulbs.

I know of 2 brands, Celduc and Crydom. I have a Celduc one at home. They are expensive though. I think R2000 for the Crydom one via RS components.

With my Sunsynk inverter I would like to utilize this device to heat my geyser when there are excess PV available.

Here is what I want to do:

Using a Arduino board with a DAC I can set the reference on the SSR. I want to monitor my power from grid usage using Home Assistant and use that to control the reference on my SSR. That way on cloudy days I can send as little as 100w to the geyser element.

The problem is that I do not know of any micro controller that has a 0-5V,0-10V or 4-20mA output. I have played a bit with the Nodemcu on HA.

Does the community have any ideas on how to reference a 0-5V or 0-10V while monitoring the inverter power?

 

 

I used an Arduino (esp32 or nodemcu should work) with a 4-20ma converter and PWM to drive my SSR. I added this to theArduino and added some PWM conditioning or integration to the PWM output before feeding this module. There are PWM libraries online. All 5V microcontrollers can output 0-5V but only as PWM. Then you smooth that for 0-5V.

I used a Time proportional SSR in my geyser and you can see there (my thread on here) what I did.

This here is a pressure controller (based on a software PID in the Arduino) with a 4-20mA module I referred to above. Its the little daughter board standing vertical. If the SSR can use 0-5V input, you can save that cost for the module. Just do PWM on a 5V micro and you can go from 0% tp 11 on the dial

Edited September 8, 20214 yr by Sarel
spelling and added

Which 5v micro controller can be configured with Tasmota? Would be great if I can still use a small board like the NodeMCU or Wemos.

What do you use for smoothing?

Espressif ESP8255, ESP32, ESP32-S or ESP32-C3 chipset based device can be flashed with Tasmota. All of these as fas as I know are 3V devices. 
Smoothing is done by means of a rC circuit. Look up voltage smoothing or pwm smoothing circuits or integrators. 3.3V will get you to 66% on time or 66% of power delivery on a 0-5V SCR. Even some SSR devices can be switched on from 3V.

Solid State Relay (SSR) 40A AC, Control 3-32V DC. These are available locally. Search for the text at the start of this paragraph.

Went down this road recently. Worth keeping in mind that most SSRs sold locally are fakes, specifically fotek fakes. See: https://protosupplies.com/inferior-counterfeit-fotek-ssr-25-solid-state-relays-on-the-market/

I recently purchased from a local supplier (I don't blame them, I expect they weren't aware - I'm just trying to point out that we are likely not buying real/properly rated SSRs here), and it was sold as a "SSR-60 DA", implying 60A rated switching current. After realising this is likely not a real fotek (no datasheet available for this alleged model from fotek, which is a reputable brand), turns out its got a 40A BTA41 1000B triac inside, which in all fairness is way better than what I expected given that its absolutely not a legitimate fotek SSR. Just know what you're getting. Given these tend to fail closed, I'd never trust a locally sourced SSR after this.