I have a 240v AC main (switched) and wish to control a 24v DC logic with it.

Background: I bought a cheap WiFi enabled (Broadlink chip) thermostat to control my central heating. It's a surprisingly decent unit. However, up on receiving it I realised the output is switched mains, whereas the logic board on the boiler (Ferroli) is 24v DC.

What is the easiest/cheapest way to achieve this?


[Note- I realise this is the converse of the typical switching scenario wants and clearly the "cleanest" solution would be return the controller and get a more appropriate one!]


What you want is a relay. There are many available with coils rated for 240 VAC. Now you only have to pick one that can switch 24 VDC at whatever your maximum current is. Fortunately for you, most relays with 240 VAC coils will be able to switch 24 VDC at a few 100 mA easily, but always check the datasheet carefully.

  • \$\begingroup\$ Hi Olin, thanks. I guessed a relay was the most convenient. Can you suggest (a link) for something in handy packaging (with screw terminals etc) I can wire in directly? \$\endgroup\$ – P.Windridge Nov 3 '17 at 11:39
  • \$\begingroup\$ Followup: I eventually got an Omron MY2NJ with the standard base and put it in a Schneider fire retardant box (photo: photos.app.goo.gl/mBmSa4sY4UoyMX9u2 ). It works fine but any comments about better solutions welcome. Now I am working on a homebrew ESP8266 + DS18B20 based which will take DC directly from the boiler (and have no screen, which I hardly use anyway) \$\endgroup\$ – P.Windridge Nov 26 '17 at 22:53

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