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I'm planning a device that can switch a 240VAC 1A current - most likely 0.5A but it's nice to have the head room.

A relay seems the most obvious choice but given the low current it seems over the top and is pricey. Are there alternatives that I've missed?

UPDATE: Load is an IR heating pad so no initial rush current that I am aware of.

UPDATE 2: Load would turn on for an hour and then turn off, 5VDC or 12VDC timing circuit to control the relay to do this. Basically, push a button and the 240VAC load stays on for 1 hour and then turns off. Press again if more time needed.

UPDATE 3: Would this do the trick? https://www.mouser.co.uk/ProductDetail/Sharp-Microelectronics/PR36MF21NSZH?qs=sGAEpiMZZMve4%2fbfQkoj%252bCr9xHrLc8XaMpgkbqJI%2f1s%3d

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    \$\begingroup\$ Does give separation though - which may address a safety concern... \$\endgroup\$ – Solar Mike Jan 23 '19 at 16:23
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    \$\begingroup\$ How often are you toggling the load? \$\endgroup\$ – calcium3000 Jan 23 '19 at 16:39
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    \$\begingroup\$ AliExpress, not everybody wants to buy from there. aliexpress.com/item/… \$\endgroup\$ – Michel Keijzers Jan 23 '19 at 16:42
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    \$\begingroup\$ "A relay seems the most obvious choice but given the low current it seems over the top and is pricey." What is your life worth? Whenever you switch 240 AC, you potentially expose yourself to it. A relay will isolate your load from the power line. If you don't think this is a good thing, you might read about the Darwin Awards. \$\endgroup\$ – WhatRoughBeast Jan 23 '19 at 16:52
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    \$\begingroup\$ @SimonBarker I was thinking in series, because there might be the chance that the relay contact sticks and will not interrupt the current as expected. So using to relays will give some redundancy as both relays would have to fail. Additional information: There are relays available which are designed for higher inrush currents and are specially designed to prevent sticking of relay contacts. \$\endgroup\$ – Johannes Jan 23 '19 at 17:11
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I'm using one like this in a light stage box I built:

one 1 channel relay module 5V 12V 24V

I am not sure how many times it has opened/closed, but I'm sure it's more than 1,000 times, varying between weeks (when not in use/power switched off) until a few seconds or faster for testing.

My load is a 240V/36W (or slightly less) LED light, thus only 0.15 A, however according to the specs it can take 10A.

It has an optocoupler builtin, so the switching part is separated from the high voltage part.

The price is about 50 cents, so I would say such relay module is perfect for what you need (even if 10A is more than what you need).

Note: there are different types for 3(.3) V, 5 V or 12 V.

[enter image description here

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    \$\begingroup\$ The one you show doesn't have an optocoupler, just a transistor so that the microcontroller doesn't have to switch the full coil current. There are versions that do include an optocoupler, but it doesn't seem to serve a purpose, given that the relay provides the isolation from the switched circuit, and the supply to the relay coil is commoned to the input side of the optocoupler. \$\endgroup\$ – Phil G Jan 23 '19 at 20:41
  • \$\begingroup\$ @PhilG You are right (although it's mentioned in the description). I found another one (53 cents), which has an optocoupler (white IC partly shown). I think it's an 817 because I saw similar ones with that optocoupler too). \$\endgroup\$ – Michel Keijzers Jan 23 '19 at 21:21
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Only you can say if galvanic isolation is required in the off state. If not, there are many small solid state relays that can handle the load. I recommend using one with an output rating of 1 A or more (2 A preferred) so the part runs cool with your 0.5 A load. Here are some solid state options:

https://www.digikey.com/products/en/relays/solid-state-relays/183?k=&pkeyword=&sv=0&pv127=57&pv127=4&pv127=8&sf=0&FV=1c0003%2Ca40153%2Ca40154%2C1140050%2C20800ed%2C1f140000%2Cyr0V+%7E+230V%7C2133%2Cyr0V+%7E+250V%7C2133%2Cyr0V+%7E+280V%7C2133%2Cyr0V+%7E+300V%7C2133%2Cyr0V+%7E+350V%7C2133%2Cyr0V+%7E+400V%7C2133%2Cyr100V+%7E+240V%7C2133%2Cyr12V+%7E+280V%7C2133%2Cyr19V+%7E+264V%7C2133%2Cyr24V+%7E+230V%7C2133%2Cyr24V+%7E+240V%7C2133%2Cyr24V+%7E+250V%7C2133%2Cyr24V+%7E+253V%7C2133%2Cyr24V+%7E+280V%7C2133%2Cyr3V+%7E+264V%7C2133%2Cyr75V+%7E+250V%7C2133%2Cyr75V+%7E+264V%7C2133%2Cffe000b7%2Cmu1.2A%7C434%2Cmu1.5A%7C434%2Cmu1A%7C434%2Cmu2A%7C434&quantity=&ColumnSort=0&page=1&stock=1&pageSize=25

For long timing periods I like the CD4060. This is an oscillator and 14-bit divider in one package. With the oscillator running at approx. 2.25 Hz, the Q14 output will go from low to high 1 hour after a reset. When the Q14 output goes high it inhibits the oscillator, and the circuit sits waiting for a manual reset to restart. The output can sink about 4 mA in the low state, which is enough to turn on an Opto-MOS solid state relay.

I have a version of this circuit I whipped up for another forum. I'll try to post it here.

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I've whipped up a schematic for a 1-hour SSR circuit. On power-up the relay is on for 1 hour. At that time Q14 goes high and inhibits the oscillator through D9. The circuit is locked in the off state until the reset button is pressed. R1 and R2 are scaled to give a narrow adjustment range around 1 hour.

enter image description here

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  • \$\begingroup\$ I feel like this should have been an edit to your previous answer. \$\endgroup\$ – Hearth Feb 4 '19 at 23:26
  • \$\begingroup\$ In a scramble, I forgot that I described the circuit in detail and just threw it up there. I can edit it in if the mods say so. The rules about editing previous posts are different here compared to other fora I'm on. \$\endgroup\$ – AnalogKid Feb 5 '19 at 0:30
  • \$\begingroup\$ Edits to improve posts are strongly encouraged here. I think multiple answers from the same person, especially if one is an elaboration of the other, are frowned upon. \$\endgroup\$ – Hearth Feb 5 '19 at 0:32

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