AC Dropout switch?

[ef.berlin]

Hi I am new to this forum and find it to be an incredible wealth of information. I do have a question that i cannot seem to work out.

I am trying to create a simple system to switch 220V AC on and off using a short pulse, or absence of current.

The problem: I only have one pair of wires going from mains through a switch to outside a building, hot and zero wires. I want to split this current outside into a constantly powered source, and a switched source. Basically I want to be able to switch on and off a light and keep other electronics running.

My initial 'solution' was to change the wall switch from a SPST switch to a SPDT switch, run both poles to together and try to take advantage of the short fallout pulse to switch a latching relay outside. The other electronics are wired with enough protection for this very short break of current(up to .5 seconds is okay. The problem, however, was that the pulse is too short to reliably switch the relay. A spring loaded SPST NC switch is not acceptable for this scheme because of the possibility of it being open too long and the resulting long current break will power down the electronics.

Does anyone have any ideas?

 

[ef.berlin]

Ok it looks like I stumped you guys. Or does nobody deal much with AC? Is there a possibility of increasing the length of the 'dropout pulse' by charging a capacitor or the help of another relay? Or are there relays that anyone knows of with a fast switching time? Am I totally off-base here?

 

[KMoffett]

I'd like to think of a way...but my brain hurts this morning.

Have you considered an "X10" control? These are plug-n-play, over-the-power-line remote controls. Don't know where you are (please add your location to your profile...it helps us help you). Available at Radio Shack (US) and many, many web stores.

Ken

 

[eblc1388]

Momentarily reverse the Live and Neutral polarity of the supply going out to the far end and detect that condition from the far end to operate a relay.

This is, however, against most electrical wiring regulations and is definitely not advised. There are other simpler means to achieve the same goal, like using wireless remote control.

 

[Willbe]

Please post one or two proposed schematics or a series of logic statements for what you want to do.
It sounds solvable. . .?

 

[ef.berlin]

Hey thanks for the replies. Using a remote control has been what I kinda thought might be the only viable solution. my goal was to modify a simple switched light while not adding the complications of having to change batteries and whatnot. I would rather not go against any codes to avoid any possible liability later.
the idea with the pole reversal is a good one, i think. but the question is, will one of those relays react so fast? is ther no switch that reliably cuts the power for about a fifth of a second?

oh, and profile updated, i'm in berlin.

 

[ef.berlin]

Willbe... I'll get back with you on that one...

 

[eblc1388]

the idea with the pole reversal is a good one, i think. but the question is, will one of those relays react so fast?

Why would speed matters in this case? The reversal can be there for a few seconds and then reverts back to normal.

 

[ef.berlin]

Oh? (rubs hands together in excitement) what would be the dangers, why not recommended?

 

[KMoffett]

Impulse stepping relay: **broken link removed** and **broken link removed**]
Just connect the coil across the light wires. Contacts are toggled on or off with each off/on of the light.

Ken

 

[Willbe]

Willbe... I'll get back with you on that one...

Ja, spater. . .

 

[ef.berlin]

na klar...
sorry it took a while for me to get this posted but here it is, its quite a simple drawing, but i hope it makes sense.
**broken link removed**

the latching relay should switch in the absense of current, and it does, but not regularly. the pause is just too short.
the solution i seek would be to have a reliable system where the light is turned on and off by a normal looking wall switch but the other stuff is not effected.

Kmoffett: this relay would work? i don#t see how it solves the problem, is it so fast switching?

eblc: the relay you mentioned sounds like a good solution, how much does something like that cost?

Remote controls are an option, but one i would rather avoid, for cost and lost remotes, battery changes..

 

[ef.berlin]

bump! bump!

 

[KMoffett]

So... you want to always maintain power to the "wlan bridge", but be able to switch the light on and off? How long can the power be removed from the "wlan bridge" before it is stops working...your brief pulse width?

Ken

 

[blueroomelectronics]

Why not just run an extension cord to the bridge?

 

[ef.berlin]

yes, and power can be removed for about 1/2 second without problems. an extension cord would get in the way, and wouldn't look very nice

 

[KMoffett]

OK, here's a shot at it. This is based on a standard relay and a bistable impulse relay. The closed switch powers the bridge and RLY1. The when the switch is opened, RLY1 is turned off, "making" the contacts that power RLY2 on. This toggles the contacts of RLY2, turning the light on or off. When the switch is closed again, RLY1 is powered, cutting of the power to RLY2. RLY2's contacts stay in the last state, holding the light on or off. The next off-on cycle of the switch will change the state of RLY2 and the light. This all depends on how long the bridge will operate with no power, and how fast the relays can switch. This is just conceptual, as I've not tried it. The Tyco impulse relay is about $25. Is that within your "experimental" budget.

Ken

 

[ef.berlin]

this sounds promising, without the problems of a rc. i'll give it a shot, and let you know.. thanks!

 

[john1]

I am going to guess that "WLAN" is a wireless lan.

Have you considered increasing the value of the smoothing capacitor in the wlan ?
Enough to ride out the brief absence of power.

Or use the earth to operate a relay independently between neutral and earth,
that may or may not require an isolating transformer, depending on your supply conditions.

If its only on the other side of a wall, you could maybe run a pull-cord through
to operate a pull-switch for the light.

Best of luck with it, John

 

[john1]

(add)

a pull switch has the advantage that you can operate it just as easily from the switch end.