Control A/C Power

[k-maub]

Is there a safe/good way to turn on/off power to an A/C device?  I'm not interested in wireless X10 technology or anything.  My guess would be some sort of transistor (NPN? PNP?), but I'd like to know if there's a "right" way to do this so as to avoid electrocution/eviction.

My only fallback would be to use a servo to operate a switch, but I'd prefer something a little more elegant and less mechanical (says the mechanical engineer).

Okay, thanks for the help!

[texasclodhopper]

The truly safe way is to use a double-pole double-throw (DPDT) relay with your device wired to the normally open (N.O.) contacts; hot wire (black) on one pole, neutral (white) on the other pole.

Enclose the whole thing in an electrical junction box that is double-wide so there is room for the relay on one side. I would include a duplex receptacle (normal house receptacle) on the other side, but break the metal 'links' between the upper and lower receptacle. Wire the always-on incoming AC to the upper receptacle and wire the relay-switched AC to the lower receptacle. (I would paint the upper receptacle red to distinguish the functions.) Close the box so no one can touch any AC connections.

You can choose a relay with the coil voltage of your choice depending on how you are going to control it. How you bring the relay coil wiring to the outside world would depend on your application.

[k-maub]

I think I understand what you're saying.  It sounds like a nice and tidy solution to me.  Do they make "double-male" electric cords to connect my new junction box to the wall?

And I take it that the DPDT switch that ioBridge sells is inadequate for "wall power" (though 5 A is a decent current, no?)

[texasclodhopper]

NEVER build or use a "double-male" electric cord.

Make all of your electrical connections inside of the junction box. I have taken the "female" end of an extension cord off and used that end to wire into the junction box.

You could very well use the ioBridge relay module to switch your relay junction box.

[k-maub]

Upon reflection, I can see why a "double male" electric cord would be a terrible idea.  I'll file that one away under the "Ways to kill yourself" header.

Is there any reason why a SPDT is not perfectly adequate for the device you described? I don't mean to split hairs; I just want to make sure I absolutely understand the "why's" as well as the "what's" of the circuitry. Presumably you propose running always-on AC to a receptacle for convenience of having another outlet available (as long as you've got a duplex)?

Thanks for the mentoring!

[texasclodhopper]

SPST would be adequate, but you asked for "safe" and I always err on the safe side when using 100's of volts AC. 

Using a 2-pole relay removes all possible current carrying connection to your portable device. Leaving only the safety ground connection.

If you put your imagination hat on, you could easily build a multichannel version (up to 4 channels with the current ioBridge.)

(This kind of junction box could also be built right into a wall or ceiling just like any other receptacle.)

[walou12]

This is what I did,

purchased a remote controlled mains switch,  I used http://www.jaycar.com.au/productView.asp?ID=MS6140&keywords=240v+remote&form=KEYWORD

and Interfaced the remote to the IO Bridge by using a few cheap solid state DIL relays.

channel 1 DO pulse turns mains on,
channel 2 DO pulse turns mains off

no messing with AC and plenty of isolation with my design !

I use it to control a heater in my holiday cabin so that its nice and warm prior to arrival.  Temp probe placed near heater outlet provides me with feedback as to if the heater is on or off.

WM

[SMyers]

Check this out:

http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=119

This tutorial should help you out.

[irkgreen]

I'm sure you've already found your solution, but I did want to point out that i think X10 may have been a great solution for you too.  X10 isn't wireless.  The signals travel through your power lines.

All you'd need to power any 120 V device with a standard plug is:

A lamp module: http://www.elights.com/x10lampmodule3.html (3-15 bucks)
ioBridge's x10 module ($17)
and http://www.thehomeautomationstore.com/psc04.html ($11)

It is an investment, but then you can also control lights throughout out your house with the purchase of x10 switches.  Sky's the limit with x10 too.

This is an all solder-less solutions too.  Which is a good idea if you've never dealt with 120 volts.

2 cents

[k-maub]

Thanks.  I actually hadn't done anything yet; was waiting for some extra time on my hands around the Christmas holidays.

About X10, is that pretty robust.  I think it was Wikipedia that pointed out some of its shortcomings, but it's not clear that they are major drawbacks.

Also, do I need to worry about being on the upstairs of a two-story house?  As long as the downstairs people don't have X10, it shouldn't be a problem, right?

Okay, thanks again!

[irkgreen]

I'm not sure what you mean about drawbacks.  There is potential for interference with neighbors but you can usually adjust your house code to fix that.  There are amplifiers of sorts that help with larger houses.  It is a very stable system really.

[fillibar]

Plus there is already a good portion on the X10 side of things listed in the forums and projects. It is probably the simplest way to go although arguably not the cheapest (although many deals can be found on X10 equipment even from stores, let alone eBay or such).

[solarguy]

I think the simplest possible solution is to use a solid state relay.  The "brick" type units can switch up to 25Amps of AC and more and all they need for an input is 3-32V at about 2mA.  So put the relay in an electrical box and run a digital output from the ioBridge to the input terminals of the relay.  Keep your AC wiring safely inside a protected box and the low voltage wire can be simple speaker wire.  Simple right?