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Case

On a simple 220 V home appliance equipped with a manual timer switch ( a knob that you can turn clockwise up to the desired position -time- and will then automatically turn counterclockwise for the chosen time period ), I would like to either bridge the switch with an additional on/off switch, or replace the timer by an on/off switch.

Goal

The goal is to bypass the 1 hour limitation imposed by the manual timer itself by adding an "always-on / always-off" capability.

  • Q Can I do it "just like that" and if not, how could I easily do it at home with basic electronic tools ?

  • Alternative :

What if I intend to replace the manual timer by a digital timer ? I guess it might itself have to be powered somehow.

Thank you for your help.

  • I think you have a few typos in your post. – Transistor Oct 12 '19 at 19:15
  • does the appliance manual say anything about sustained continuous operation, I wouldn't want it to melt after running for 1.5 hours. – Jasen Oct 12 '19 at 20:39
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Get a slightly different timer

You are correct; a programmed electronic timer is a bad plan because it will need to power itself, and that will require additional wires (e.g. Neutral) that may not be present.

What I recommend, instead, is a different mechanical timer with a stay-on zone. This looks exactly like the timer you have, but for an additional zone past the maximum duration, which says "Hold" or "Remain on". Wound to this position, it will not unwind.

I generally don't use that type, my users are idiots, so I use the type that makes it impossible to stick the thing on continuously. That is why they market both types.

For instance, in the States, the standard brand is Intermatic and is available in both types in a variety of durations. If you're unhappy with the choice of duration range, this is also a good time to solve it.

Abuse the one you've got

One thing about those mechanical timers: you can't put "just a tiny amount" of time on them. If you have a 1 hour timer, it's clearly labeled that you need to wind it past 12 minutes (and then you can wind it back to 3 minutes). If you only wind it to 3 minutes, haven't put enough preload force into it for the snap-off mechanism to work, and it will stick there and never shut off.

Feature :)

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Yes.

Identify the live in and out on your timer switch and wire a switch rated for the supply voltage and load current across the timer terminals.

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You can add a DPST switch wired in parallel to your existing timer and you'll have an "always on/always off" and the timer. If you do this you'll need a 2 gang box, for the two switches.

You can also replace the timer switch with just a DPST toggle switch. Then you'll just have an "always on/ always off".

You can also just replace the manual timer with a programmable one that will get it's power from the 220v line side but you might need a neutral.

Just remember to turn off all power before doing any work and take pictures before you disconnect any wires.

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