Happily using Eurotherm 425A as a thyristor power controller

My "summer" solar power diverter was an all or nothing system; enough power available for immersion heater?, yes, then turn her on. Otherwise, don't.

Looking for a more progressive thyristor based winter system to mop up all the available solar power, I came upon a cheap, (£20-ish) pre-used Eurotherm 425A on Ebay and have it now going nicely. I'm controlling it with a 0-5volt signal from a DAC controlled by a bash script in the raspberry pi. I'm using the SPI interface to talk to a MCP4921 DAC on a small interface board that I built. There's a piece of software called "spincl" that gives command line access to the SPI interface. There's still some fun software to write for the actual decision logic of the diverter, but the basic power up/down control mechanism is working great.

My solar installation doesn't have any tails on the solar side for a CT sensor, so my emonbase is counting pulses from the solar meter, sending an update every 10 seconds, and my immersion heater's power source is in the airing cupboard upstairs, hence the slightly quirky software approach to controlling the diversion. I get the information about my power usage from the emonhub.log file which I've set to logging level INFO.

The 425A did need some soldering configuration on it's pcb to make it work in phase angle mode, which was interesting because the pcb layout wasn't the same as that found in the pdf manual - which is easily found on a Google search. But the link numbers were exactly the same and conformed to the existing configuration of the pcb, so I tried it, checked, re-checked, re-checked, .... And it works great.

Not the easiest thing to box or mount as it's designed to be mounted on din rails, just a bit of ingenuity required.

It feels like a solid piece of kit, with a large heat sink. Still some available on uk Ebay.

Hope this is of some interest.