120VAC Time Delay Raley

[KnotYet]

Hi KnotYet,

Absolutely I could. A current sense relay can do it directly, if I can find one that also does the time delay right. But, I was having trouble doing the second part of that in isolation, so I figured I'd just do it with a coil.

OK, I think I know how to do this simply with 3 relays:

Relay1 is wired so that it is NC unless current is present at the kitchen appliances.
You can use any method to trigger it; I would just use a common hot or neutral from
those two appliances to activate the relay's coil.

The output of relay1 feeds relay2 and relay3 in parallel.

Relay2 is a time delay relay wired to provide the desired delay to the load, the A/C.

Relay3 is wired as a latching relay that gets power from relay1 and uses
a momentary contact switch to activate it and power the load, the A/C.
This avoids having to wait the duration of the delay to turn on the A/C but
does necessitate adding a momentary switch somewhere convenient.

The added switch also gives you the option to override the delay if desired.

 

[Ka_sea_ta]

Being more or less stuck inside and bored I gave this a little thought. If you interrupt the cool control line from the thermostat you get away from all the expensive high current relays... All you need is the two current sensing switches to a dtsp relay that interrupts the cool control line from the thermostat .. You can then get the delay you want with a triple nickle timer... this is all ttl level stuff with a low current relays..

 

[KnotYet]

$16 retail for a 1.5 HP (30 amp) UL rated relay is not what I'd call expensive.
Just saying.
If I was doing it I'd rather work with the 120 AC side of the appliances and A/C unit.
It just seems simpler and less of a learning curve to me.

The time delay relays I've used have their own version of the good old 555 inside them.

 

[STB]

Hey TwistedTree,
Really roughly, a MOSFET is probably 40-50MOhms vs 150-200MOhms an inch for the wire.

Just realized I wrote MOhms for the resistance of wire....dont think I'd call that wire! 10^6 vs 10^-6.

Sigh. Some days I should multitask less...any rate, hopefully you knew what I meant.

 

[STB]

Hey KnotYet,

I could absolutely use a rotary switch, but my goal is to generate less "rules" for non boater friends and family. I want them to be able to make coffee or tea or popcorn or reheat lunch just like at home. So, I'm looking to avoidbthe switch.

 

[STB]

Hey Ka Sea Ta,

When I did home automation a couple of houses ago, I did exactly that to avoid buying new thermostats and to get it to work with an incompatible garage door opener.

I'm trying to avoid that here for posterity. Eventually someone else will own this boat and I dont want to put something that isnt servicible by an everyday electrician into the system.

I replaced the thermostats when I sold my house, but the new owners have my hacked garage door controller. If it breaks, well, I hope the home automation system is obsolete by then, because the garage door tech wont be able to fix that magic box or replicate my work inside the controller.

In the boat I guess they could just replace the thermostat and pull the relay and be without. But, if I do it with a couple of Grainger's parts in a box or something, maybe just in my head, I feel it is more isolated and servicable by other folks.

 

[Ka_sea_ta]

I don't have a lot of experience with AC... but I would think that an orderly shut down of the system like what happens when the set temperature requirements are meant would be preferable to just turning off the power. Interrupting the cooling control signal might even negate the need for a delay... I would imagine that the controller built into the AC would prevent any of your compressor cycling concerns.

 

[STB]

Hey Ka sea ta,

You are entirely correct. But, I'd have to look at how the wall control and unit interact.

The on-off button isnt single function. A momentary press is variously used to turn on or off, momentarily display room temp, and maybe used in combination with other buttons for programming.

Between the wall control and unit there might be an on-off line I can bounce or pull one way or another.

Or, there could be digital commands going to a controller. If I go past the controller, then I, not it, could be managing the coordination.

If the unit allows a 2nd controller, I could act like one and send digital commands. If not, I coukld switch control wire buses.

And, Ive done this type of stuff before for home automation. But, my experience was 50-50. Sometimes it was as easy as splicing into a wire or two and sometimes I ended up building simple protocol transcoders.

Maybe I should look at the low voltage side of things first, but 2 relays in a bix seems more isolated and easier on those who follow me, e.g. when the controller or HVAC unit need to be replaced, etc.

 

[jwilsail]

You could do that with a transfer switch.