Project files: Mains controller with offboard relay

What is it?
A version of my Standby-PSU & controller for applications that need to switch very high (or very low) currents, switch multiple relays or simply prefers to use an offboard relay, be it mechanical or SSR. A couple of matching PCBs for relays and a soft start will follow very shortly, I just need to process the pictures and finish the write-up. This is basically the same circuit as the “v1.5” of the standbyPSU (found here) without the onboard SSR.

How big are the boards?
This version measures 3.2″ x 1.875″ (app. 81 x 48mm) – so just a little smaller than the v1.5.

What is the status of the boards?
This board is v1.0 and it works as expected – not entirely surprising given that it is mostly identical to the v1.5 circuit which also worked well.

Does it use any special/expensive/hard-to-find parts?

Anything else I need to know?
Note that big mechanical relays tend to draw a lot of power, so there might not be that much power left over to power anything else. As an example, the relay board that I will post later draws app. 1.2W. Throw in a couple of LEDs and the losses in the transformer, and there isn’t actually that much left over from the 2.5-3VA transformers that are the maximum that will fit on the board. You can of course use the controller to control a separate standby-PSU as well.
If you want to use an SSR, then be aware that they can be a bit tricky to work with and some attention must be paid to minimum load etc. I can recommend reading this document from Omron that explains a lot.

Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.

You can also read the other posts on this controller design for information.


4 Responses to Project files: Mains controller with offboard relay

  1. Walker says:

    I think this is what another group of students in my class need for their senior design project. Pretty sure they’re shelling out way too much money for something prebuilt that comes with an enclosure, etc. They’re trying to get two generators to power one load (and other slightly more complicated variants on that problem) without the generators flipping.

    To be honest, my group could use this too–if it was driving IGBTs instead of relays.

  2. theslowdiyer says:

    Not sure exactly what it takes to drive a large IGBT, but this circuit is pretty much as simple as it gets – it’s just a transistor driving either a relay or an LED (in an SSR). There is of course an onboard power supply and a couple of extra things, but overall it is very simple.


  3. Pingback: Project files: Little helpers – Powerhelpers | theslowdiyer

  4. Pingback: Another mains controller… | theslowdiyer

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