I'm searching for a relay that can both trigger and switch on either 110v or 240v. To clarify - both the coil voltage and the switched power would be the same voltage - and as low as 110v or as high as 240v.

(think of an appliance that could ship in the US, or internationally).

The relays I've found so far trigger at ~80% of max coil voltage, which isn't enough latitude to run in both scenarios. Am I likely to find a relay like this, or should I devise another solution?

Per request: here's the relay I was looking at with a datasheet for LY2F-AC220/240

  • \$\begingroup\$ has it got to accept 110/240 with no reconfiguration, like a laptop power supply does, or can you switch it between 110 v and 240 v use? \$\endgroup\$
    – Neil_UK
    Commented Aug 28, 2018 at 16:00
  • \$\begingroup\$ Do you have a data sheet link for the type you have found? \$\endgroup\$
    – Andy aka
    Commented Aug 28, 2018 at 16:46
  • \$\begingroup\$ I'd prefer to have it work like a laptop power supply - essentially zero chance of error. \$\endgroup\$
    – J. Knight
    Commented Aug 28, 2018 at 17:04
  • \$\begingroup\$ Transistor's solution is clever, but I don't think it actually does anything, more than a bit of wire that is. What do you actually want to do? Assume that by magic you have an ideal 110-240 relay, draw how you want to use it in a schematic. \$\endgroup\$
    – Neil_UK
    Commented Aug 28, 2018 at 17:16
  • \$\begingroup\$ photos.app.goo.gl/aNFQ21dzcjHo9Jtv6 Neil, here's an ideal schematic. I'd like it to work if the source is 110v (115v, 120v, etc) or up to 240v. From the other comments, it sounds like I need to use a transformer that has a more tolerant input, and use that to drive a DC-coil on a relay. \$\endgroup\$
    – J. Knight
    Commented Aug 28, 2018 at 18:00

3 Answers 3



"70%V or less of nominal voltage" means it won't be more than 70% but it also means it may be unreliable or slow or not activate at 50% Vac rating and 200% would exceed power rating of coil.

There are many alternatives, but appliances usually have a low Vdc for power relays.

  • \$\begingroup\$ To do low Vdc, I'd need a transformer - which is ok, though it adds a little cost. Can I accomplish the same goal (universal power input), by carefully selecting a transformer that will take either input and produce an identical output - then match a relay-coil to that output. Could you help me with some search terms I can use with Newark/Mouser/Digikey to find such a power supply? \$\endgroup\$
    – J. Knight
    Commented Aug 28, 2018 at 17:00
  • 1
    \$\begingroup\$ mouser.ca/ProductDetail/MEAN-WELL/… \$\endgroup\$ Commented Aug 28, 2018 at 17:05

You may need to use two relays - one 240 V and one 110 V.


simulate this circuit – Schematic created using CircuitLab

How it works:

  • On 240 V RLY1 is energised, disconnects the coil of RLY2 and feeds 240 V AC to OUT.
  • On 110 V RLY1 is de-energised, supply is connected to the coil of RLY2 which is energised and feeds 110 V to OUT.
  • When supply is low (maybe < 40 V AC) then both RLY1 and RLY2 are off and there is no connection between L and OUT.

Relay hold-on voltage is generally quite low relative to the pick-up voltage and this can cause problems in some applications. In this case, however, both relays will have dropped out by the time you get from one continent to the other so I don't think there will be a problem.

  • \$\begingroup\$ Nice use of relay logic, but I think essentially the same functionality could be got with a wire from L to OUT. I wonder what the OP actually wants to achieve? \$\endgroup\$
    – Neil_UK
    Commented Aug 28, 2018 at 17:14
  • \$\begingroup\$ Until RLY1 is energized there will be 240V on the RLY2 coil. \$\endgroup\$ Commented Sep 25, 2019 at 10:30
  • \$\begingroup\$ Correct. The over-voltage is unlikely to be a problem for a quarter second or so unless there is a varistor or similar across the coil. If RLY1 fails to pick then RLY2 would probably overheat and start to short the windings. That's what F1 is for! \$\endgroup\$
    – Transistor
    Commented Sep 25, 2019 at 10:43

It's possible but unlikely you could find something like that- the relay would have to be designed for that purpose meaning it would be larger (more expensive) and less efficient than a regular relay.

You might want to consider a universal input DC power supply (or wall wart) and a 12V relay. That would be particularly convenient if you actually needed the 12V elsewhere.


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